The (e,2e) spectrometer vacuum chamber (figure 1) is manufactured from 304 grade stainless steel, the construction being carried out by Vacuum Generators using a design of Jones, Read and Cvejanovic, full details of which may be found in T. 3mm thick mu-metal magnetic shielding is placed both internally and externally to decrease extraneous external magnetic fields to less than 5mG at the interaction region.
All inputs and outputs to the spectrometer pass through the vacuum chamber via feedthroughs on the top flange. The top flange of the vacuum system is a 25mm stainless steel flange with 11 conflat CF70 flanges arranged around a central 200mm flange designed for locating a hydrogen source.
Two flanges are used for the high voltage channeltron and photomultiplier tube inputs and pulse outputs. Three rotary motion feedthroughs allow the analysers and electron gun angles to be changed externally via stepper motors for both analysers and for the electron gun.
The ionisation gauge is placed at right angles to the main flange to prevent light from the thoriated iridium filament entering the vacuum system, which would increase noise on the photomultiplier tube. The ionisation gauge feedthrough is sooted, and a loose cover is placed over the entrance in the chamber flange to prevent stray light from the ion gauge entering the vacuum system. The target gas enters the system via a CF70 flange which has two 6mm stainless steel tubes welded into the flange. The other gas feed is connected to a hypodermic needle set at 90A° to the incident beam for measurements in other geometries.
The gas jet which is not currently used in the interaction region can be used to non-locally fill the chamber with gas for background counting measurements.
The final CF70 flange is used when the photomultiplier tube is cooled, usually during baking of the system following exposure to atmosphere. The tube is cooled by passing vapour from a liquid nitrogen source through expansion coils wrapped around the photomultiplier tube housing. The electron gun is a two stage non-selected gun designed by Woolf (Ph.D thesis, University of Manchester) (see figure 3). The gun consists of a filament, grid and anode source which is focussed using a triple aperture lens through two 1mm defining apertures in the centre of the gun. The apertures define the electron beam pencil and beam angles, and are focussed onto the interaction region using a second triple aperture lens located between the apertures and interaction region.
The electron gun is shielded using advance (constantin) sheet which is grounded to the body of the gun mounting. The gun is mounted onto an x-y translation table to allow placement of the electron beam as accurately as possible to the centre of rotation of the analysers and electron gun rotation axis. The gas jet is mounted from the electron gun using a narrow support of 310 stainless steel, and the Faraday cup can be attached to this support. The original unselected electron gun built by Woolf was completely rewired and a custom built PTFE 25 way inline wire-wrap plug and socket was placed between the 52 way vacuum electrical feedthrough and the electron gun. The wiring from the 52 way feedthrough to the inline plug is shielded colour coded 30 awg PTFE coated advance wire, and the inline plug and socket connectors are non-magnetic gold plated wire wrap pins.
The electron analysers are constructed from molybdenum and are mounted from two rotating gear plates controlled externally via the rotation feedthroughs on the top flange (see figure 2). The input electrostatic lenses for each analyser are three element cylindrical lenses as shown in figure 4. The interaction region is focussed onto the entrance aperture of the hemispherical energy analysers with a beam angle of around zero degrees, the image of the analyser entrance aperture being larger than the size of the interaction region. Field gradients around the input and exit apertures are corrected using standard Jost correctors.
The energy selected electrons passing through the exit apertures are finally collected by Mullard X919BL channel electron multipliers which amplify the single electron to produce a current pulse at their output.
A principle source of noise on the signal pulses arises from the turbo-molecular pump motor.
The noise from the turbo pump is reduced to ~ 5mV using these techniques, and as the average pulse height from the saturated multiplier is around 20-40 mV, this allows adequate discrimination following amplification. The pre-amplifiers located external to the vacuum system are commercial 100X preamplifiers with 400pS rise-times, manufactured by Phillips Scientific. The NIM signals produced by the discriminators drive two ORTEC 437 Time to Amplitude Converter's via appropriate delay cables and an ORTEC pulse delay unit. The main TAC output feeds an ORTEC Multichannel Analyser card located in the PC controlling the experiment, whereas the second monitor TAC drives an external MCA, allowing convenient monitoring of the coincidence signal as the experiment progresses. The high voltage supplies to the electron multipliers are two Brandenberg 5kV supplies controlled by the main PC via serial DAC's. Principally the filter is used to reduce pickup noise from entering via the HT cable onto the multiplier output.
Secondly, the filter has a slow response time for high voltage spikes, and reduces the probability of damage to the pulse electronics should the EHT supply suddenly turn on or off. Capacitor C2 decouples the 1kW load resistor to earth for high frequency pulses from the CEM's, and the voltage appearing across this load is connected via the capacitor C3 to the input of the 6954 preamplifier. Since the input impedance of the preamplifier is 50W and the CEM is effectively an ideal constant current supply, most of the current passes through to the preamplifier.
Finally, the 10M resistor prevents the output to the preamp from rising above ground when the preamp is disconnected from the circuit and is therefore a safety device for the preamplifier when initially connected. The original design placed the atomic beam nozzle and Faraday cup on the same support structure fixed to the body of the electron gun, with the atomic beam direction being in the detection plane when the perpendicular plane geometry is chosen (see figure 2).
A second configuration is adopted for exclusively perpendicular plane coincidence experiments, the atomic beam nozzle being oriented at an angle of 45A° to the detection plane so that the gas effusing from the nozzle does not fill the analysers when they oppose the nozzle (see figure 6).
In this configuration the support strut for the atomic beam nozzle is terminated lower than the detection plane, as is the nozzle itself. For non-perpendicular plane measurements the Faraday cup is once mounted from the support strut and the gas effuses perpendicular to the electron beam direction. One difficulty when aligning an (e,2e) coincidence experiment lies in the focussing the incident electron beam and analysers onto the interaction region. The throughput of electron current as detected by the Faraday cup is insensitive to both position and focusing of the electron beam, since the cup opening is usually made quite large (in this case 6 - 10mm) and the bias voltage applied to the cup to prevent electrons returning to the interaction region allows all electron trajectories within this opening to be detected. Conventionally, following maximisation of the Faraday cup current, the beam is steered and focussed onto the gas jet as detected by counts in the analysers.
This has the disadvantage that the overlap volume is maximised for both atomic and electron beam density, which tends to place the interaction volume as close as possible to the output of the atomic beam nozzle, which is almost certainly not in the centre of the detection plane. To eliminate the need for time consuming iterative techniques and the associated errors due to detection geometry, a separate method for tuning the electron gun is adopted that does not depend upon the analysers. The interaction between the target and the electron beam not only produces ionisation, but the valence states of the target also are excited with various probabilities depending upon the incident energy of the electron beam. These photons are detected by the photomultiplier tube, by placing a 450nm A± 50nm optical filter in front of the photocathode.
The interaction region is therefore defined where an aperture in front of the photocathode is focused by the lens. The plano-convex focussing glass lens is covered by a grounded fine tungsten mesh to eliminate surface charging.
The photomultiplier tube may be cooled by circulating nitrogen gas boiled off LN2 through copper coils encircling the photomultiplier tube housing.
The photomultiplier tube used in the experiment is a 9789QB EMI photomultiplier tube with a bi-alkali photocathode peaking in the blue region of the optical spectrum. As with the electron multiplier circuitry, it is important to optimise the load of the photomultiplier tube so that reflections along the feeder line to the counting electronics are minimised. The 1nF 6kV capacitors across the dynodes close to the output stage are used as charge storage pumps that quickly refurbish the surface charge on the dynodes, allowing increased counting rates.
The dynode resistors are 1% tolerance metal film resistors as these are more stable with temperature.
The EHT supply to the photomultiplier tube is a Brandenberg 2kV supply operating at 1500V for this tube. The negative going output pulses from the tube measure typically 200-500mV in height, and therefore are able to directly drive an ORTEC 473A constant fraction discriminator located in one of the NIM crates. All resistors and capacitors for the dynode chain are soldered to the photomultiplier tube base internal to the vacuum system, using standard 5-core solder.
Typical pulse heights from the electron multipliers in saturation mode are 25-40mV, whereas the typical height of the photomultiplier tube pulses is of the order of 250mV. The electron multiplier pulses are obtained from the multiplier supply circuitry as explained above. The amplified pulses from the 6954 amplifiers pass along doubly shielded RG-58 cable to the input of the ORTEC 473A discriminators. The two analyser discriminators are located in separate NIM crates to increase isolation and reduce common mode pickup. The slow rise-time positive outputs from the 473A discriminators pass to three ORTEC 441 rate-meters which allow counting and monitoring of the pulses. The fast NIM pulses from the analyser 473A CFD's pass through appropriate delay lines to two 437 TAC's.
This second multichannel analyser allows the operator to monitor the total accumulated coincidence signal during operation. The lens supplies that control the voltages impressed onto the lens elements and deflectors in the experiment were developed over a number of years, and therefore take different forms.
Three of these supplies feed the deflectors in the electron gun, the other two supply the input deflectors in the analysers.
In a second 19" crate is located the gun lens high voltage supplies together with the high voltage supplies for the Faraday cup. In a third 19" crate is located the analyser voltage supplies together with a set of serial loading supplies that control the electron multiplier EHT supplies. A further supply controls the current boost circuitry located in the filament constant current supply unit (see below). The outputs of each computer controlled supply that drives an individual lens element or deflector are connected to a 70 relay switching board. The Digital voltmeter is in turn accessed via an IEEE-488 interface which is addressed by an 8086 slave PC which converses with the central PC which controls the experiment.
The outputs from the relay board connect to the spectrometer via shielded multicore cables which take the gun voltages to the 52 way feedthrough and the analyser voltages to the two 19 way feedthroughs located on the vacuum flange. The gun supply multicore also carries the filament supply current to the 52 way feedthrough. The Faraday cup current is measured by the Keithley Digital voltmeter when under computer control but this can also be measured by an external pico-ammeter.
In addition to the analyser electrostatic lens and deflector voltage connections, the 19 way CF70 feedthroughs are used to control signals from internal sensing opto-isolators which control the stepper motor interlocks.
The stepper motors that drive the analysers and electron gun around the detection plane are five phase motors with integral 10X reduction gearboxes driving the rotary motion feedthroughs.
The intelligent stepper motor drivers are addressed via a serial port located on the controlling PC bus. An additional interference problem was traced to the RS232 serial line from the controlling PC.
The PC bus was found to be poorly earthed due to very little copper being used for the bus earth.
This was cured by decoupling the 0V RS232 line from the main 0V line for the stepper motors, as is shown in figure 10. The analyser stepper motor supplies have a facility for halting the motors using limit switches which are optically coupled to the internal 68000 logic circuits driving the supplies. The SD5443-3 phototransistor normally illuminated by the TEMT88PD photodiode during operation ensured a fail-safe mechanism should any of these components fail (this automatically prevent the motors from running). Should the analysers move into a position as defined by the four criteria (a) - (d) above, a shutter located on the analyser turntables moves between the appropriate photodiode and phototransistor, shutting off the light and thereby shutting down the stepper motor current. Only motion in the opposite direction is allowed by controlling logic, allowing the analyser to move away from the point of imminent collision but no closer. The six pairs of optocouplers that prevent the analysers moving into the Faraday cup, electron gun and gas jet support are located on the mounting struts supporting the main body of the spectrometer. Two optocouplers are located on the side of analyser 2, and two shutters are located on the sides of analyser 1 to prevent the analysers colliding with each other. Finally a ninth optocoupler is located over the electron gun counterweight which monitors when the gun is at an angle less than 65A°, where the sweep angle around the detection plane is reduced.
The current boost circuit operates from a serial driven supply card as detailed previously. The main filament drive is through six power diodes that feed the current from the constant current supply to the filament. The Darlington transistor T1 feeds additional current to the filament via three parallel 10 turn 100W trim resistors through a 1N4007 diode.
As the constant current supply acts as an infinite resistance source, the boost circuit supplies additional current only when the voltage at the anode of the feed 1N4007 exceeds the output voltage of the constant current supply.
Finally, the filament bias voltage (and hence energy of the electrons) is set to the midpoint of the filament by two 100W balancing resistors located across the terminals. In addition to the ADC buffer card, three independent isolated regulated supplies drive REF01 voltage reference sources for measurement of the positions of 10 turn potentiometers located on the analyser and electron gun rotary drive shafts.
The angular position of the electron gun and analysers is calibrated when the system is opened using visible laser diodes that define these angles to an accuracy of A±0.2A°.
Figure 13 shows an overall block diagram detailing the computer control and high speed pulse interfacing to the spectrometer.
GOFAR Services, LLC - Appliance Repair Houston, TX - Chapter 2TROUBLESHOOTING TOOLS AND SAFETYTIPS AND TRICKSLets talk aluminum foil for a minute.
The different designs are differentiated by being a different "model" or "series." Confusing the issue even more, some manufacturers "private label" their machines for large department stores.


One of these is internally connected to a gas jet which can be set at 45A° to the incident electron beam and is used in the perpendicular plane experiments. These stainless steel feeder tubes are connected to the nozzle using grounded shielded PTFE hose.
One follows the anode, another corrects the beam direction between the apertures and a third steers the beam onto the interaction region.
This shield is coated with aerodag colloidal graphite to reduce patch fields on the surface of the metal, and is made as small as possible to allow the analysers to approach the gun as close as is feasible when non-perpendicular plane geometries are selected (see figure 2). The XY translation table is mounted from the rotating yoke, to which is attached the photomultiplier tube. This allows the gun to be dismounted from the system without the need for rewiring of the feedthrough when the need arises (filament changes, cleaning etc).
The wiring between the gun and inline socket is also shielded colour coded PTFE coated advance wire facilitating spot welding to the electrostatic lens elements of the gun.
The analysers are mounted onto x-z translation tables that allow them to view the interaction region accurately over the full range of angles accessible. These lenses have a capability for energy zooming of around 10 : 1, and have a maximum entrance acceptance angle of A±3A° as defined by the entrance apertures.
This ensures that the overlap volume accepted by each analyser encompasses the interaction volume for all detection angles as the analysers move in the detection plane. These devices use an activated lead glass internal surface which has a high coefficient of secondary electron emission when a high voltage (around 3000V) is applied across the multiplier. This noise may be picked up by the channel electron multiplier and the high voltage feed to the multiplier, and is generated internally in the vacuum system. The CFD's are operated in NaI mode as this has a 2ms dead time following the initial pulse, thus reducing the possibility of false triggering due to any mismatching impedance reflections along the delay cable. These EHT supplies are connected via VERO 200 high voltage couplings to high voltage cable connecting to the pickoff circuitry located on the high voltage feedthroughs. This allowed the analysers to roam the detection plane over a complete 360A° angular range. The configuration of the target source hypodermic when perpendicular plane measurements are conducted. The common procedure is to initially maximise the current from the gun onto the Faraday cup, then onto analyser counts as the electron beam is moved through the gas jet. Maximising the Faraday cup current is therefore only a crude preliminary alignment of the incident electron gun beam. This therefore assumes that the analysers are initially focused onto the interaction region, and a slow iterative technique must be adopted where the analysers and electron gun are tuned so as to maximise the signal from both analysers.
In this case a true differential cross section is not obtained, since the scattered and ejected electron trajectories lie in a different plane than defined in the initial experimental alignment. An EMI 9789QB reduced photocathode photomultiplier tube is installed in the vacuum system together with optical focussing and defining elements (figure 2). A group of these excited states decay back to lower valence states with the emission of visible photons at wavelengths around 450nm for both helium and argon targets.
Tuning of the electron gun to PMT counts therefore guarantees that the electron gun is steered and focussed to the point at the centre of the detection plane independent of the analysers or gas beam density. This is mainly used when the vacuum system is baked at temperatures above 55A°C, since the photocathode is rapidly damaged by temperatures exceeding this. The tube is a venetian blind dynode construction, and has a reduced photocathode to decrease the noise on the output of the tube to less than 20Hz. The photomultiplier tube base was thoroughly cleaned in an ultrasound following location of these components, to displace any flux residue from the solder joints. It is therefore necessary to amplify the channeltron pulses prior to transmission to the discriminators, whereas the photomultiplier tube pulses are sufficiently large to not require further amplification.
These pulses are amplified by Phillips Scientific 6954 100X amplifiers located external to the EHT feedthroughs connected by 10cm lengths of RG-58 cable. These crates are further decoupled from the AC mains supply using filter circuitry on each supply line.
Internal to these rate-meters buffer 7400 TTL chips have been added to send to 32 bit counters located in the main PC via RG-58 cable.
These supplies are fully floating, their mid-point voltage being equal to the lens element voltage in which the deflectors are housed. All these supplies are fully computer controlled isolated units with low output impedance to reduce noise and eliminate current loops. This relay switching unit allows either the voltage or the current on each lens element to be measured by a Keithley Digital voltmeter.
This drive is further reduced internally by 10X reduction gears, resulting in a reduction ratio of 100:1.
This led to the ground line of the RS232 serial line moving around with respect to the 0V stepper motor reference as drive current to the motors returned along the ground line.
The optocoupler logic circuit circuit that controls the stepper motors and avoids collisions between the analysers, the electron gun, the Faraday cup and the hypodermic support.
Added to this filament supply is a computer controlled current boost circuit that can be used to increase the filament current during electron gun tuning.
The additional current then returns to the 12V DC regulated supply via a second 1N4007 diode.
This therefore depends upon both the current driving the filament, as well as the resistance of the filament when hot (typically 4W - 6W).
This supply feeds current to the filament without changing the characteristics of the main constant current supply used while operating the spectrometer.
These high stability reference sources ensure that the analyser and electron gun positions are accurately measured with time.
A datalogger internal to the controlling PC establishes a cubic spline relationship between the measured angles and the corresponding ADC conversion from the potentiometers. This PC also controls the selection of the relay motherboard for measurement of the required lens element either in voltage or current mode when a request is sent from the controlling computer via an RS232 serial line. Such as Sears' Kenmore and Montgomery Ward's Signature machines. Check the following list to determine if you have one of these "cross-branded" machines. The spectrometer is shown configured in the perpendicular plane, the electron gun being placed in the vertical position with respect to the analysers which span the horizontal detection plane.
The electron source is a heated tungsten hairpin filament heated by passing around 2A of DC current through the filament. The saturated gain of these devices yields around 1E8 electrons in the output current pulse for a single electron which enters the input cone.
This allows the analyser to roam over a complete 360 degrees of the detection plane when in this geometry (apart from the position where the analysers would clash wth each other). The analysers are then adjusted for maximum signal count and the procedure is iterated until a maximum is found.
The dark noise count is also reduced when cooled, however since the reduced cathode PMT only produces dark counts of less than 20Hz at room temperature, this is not necessary during routine operations. The 1.82M resistor was chosen to optimise the single photon counting efficiency of the tube. It is not found that these solder connections significantly affect the ultimate vacuum pressure in the system. Isolated DC supplies to these amplifiers is obtained from a standard +15V supply, the circuit diagram being given in figure 8.
The power supply to these TTL buffers is derived from the rate-meter supplies via 7805 5V regulators located internally. This supply boosts the current without changing the main supply, thus ensuring supply stability before and after the electron gun is tuned.
The electron gun is a two stage non-energy selected gun that produces an incident electron beam current of up to 4 microamps at an incident energy from around 30eV to 300eV. The 470k resistors bias the dynodes to achieve saturation of the current pulse at the output of the tube, hence biasing the tube for single photon counting applications. This was found to be necessary to eliminate problems associated with current loops from the 20A peak motor current feeding the common point of the logic circuitry. But even in an oven with natural convection, it can mess up airflow and cooking and even cause burners to malfunction.
The analysers are identical, and consist of a 3-element electrostatic lens focussing the interaction region onto the entrance of a hemispherical electrostatic energy analyser. The Anode deflector pair corrects for any misalignment of the filament emission point with respect to the axis of the electron gun.
If you simply must line the bottom of your oven with foil, at least poke holes in it where there are holes in the oven floor.
The Chamber is lined internally with 3mm thick mu-metal, and a mu-metal cylinder encloses the chamber externally as shown. The electrons selected in angle and energy are amplified using Mullard 919BL channel electron multipliers. The defining apertures limit the pencil and beam angles of the electron beam following focussing by lens 2 onto the interaction region. The load is set by the 50W resistor across the anode to the HT feed, the pulse being decoupled to ground via the 1nF capacitor.
They're there for a reason.2-1 BASIC REPAIR AND SAFETY PRECAUTIONS1) When working on gas cooking equipment, if you've disconnected a gas pipe to replace a valve or other component, always test the pipe joint for leaks when you reassemble it. This reduces the magnetic field at the interaction region to less than 5mG, an acceptable level for the electron energies used in this experiment. The interaction region defined by the interaction of the gas target beam and the electron beam is focussed onto the photocathode of an EMI 9789QB photomultiplier tube via a lens, 450nmA±50nm optical filter and defining aperture.
Placement of the apertures ensures that the beam angle is close to zero degrees at the interaction region over a wide range of energies, whereas the aperture opening reduces the pencil angle to around A±2 degrees over this energy range. You can do this by coating the joint with a solution of liquid soap and water and looking for bubbles. The target gas effuses from a 0.6mm ID hypodermic needle constructed from platinum iridium alloy. The 10MW safety resistor prevents the output charging up to a high voltage if the feed is disconnected. The deflectors between the apertures correct for space and surface charge beam variations inside the field free region, whereas the final deflectors allow the beam to be steered onto the interaction region defined by focussing a 1mm aperture in front of the photomultiplier tube onto the gas target beam. Apply it with a brush to make sure you coat the joint thoroughly, and use a mirror to look at the back side of the joint if necessary. The electrons passing through the interaction region which are not scattered are collected in a Faraday cup opposite the electron gun. Your appliance parts dealer has gas leak testing solution, with a brush built into the cap, made specifically for this purpose. 2) Always de-energize (pull the plug or trip the breaker on) any oven that you're disassembling. The gun, photomultiplier tube, gas hypodermic and Faraday cup all rotate on a common yoke with an axis through the centre of the horizontal detection plane, allowing all geometries from the perpendicular plane to the coplanar geometry to be accessed.
If you need to re-energize the oven to perform a test, make sure any bare wires or terminals are taped or insulated. Energize the unit only long enough to perform whatever test you're performing, then disconnect the power again. 3) If this manual advocates replacing the part, REPLACE IT!!
These machines were sold as GE, Hotpoint, and "private-labelled" as JC Penney and Penncrest brands. In 1995, GE redesigned their dryers.
There is a reason that it stopped - you can bet on it - and if you get it going and re-install it, you are running a very high risk that it will fail again. WCI's machines were sold under these original brand names, as well as Westinghouse and White-Westinghouse brands. In the '90's, WCI was bought by Swedish giant Electrolux, who changed the company name back to the Frigidaire Home Products Company. Replace the part. 4) Always replace the green (ground) leads when you remove an electrical component.
They have continued to manufacture these "Herrin" machines as Maytag "Performa" models and high-end Crosley brand machines, but they have gone through a LOT of evolution.
Wear gloves, and be careful not to cut your hands! 6) If you have diagnosed a certain part to be bad, but you cannot figure out how to remove it, sometimes it helps to get the new part and examine it for mounting holes or other clues as to how it may be mounted. 7) When testing for a 110 volt power supply from a wall outlet, you can plug in a small appliance such as a shaver or blow dryer. You can find them in the yellow pages under the following headings:APPLIANCES, HOUSEHOLD, MAJORAPPLIANCES, PARTS AND SUPPLIESREFRIGERATORS, DOMESTICAPPLIANCES, HOUSEHOLD, REPAIR AND SERVICECall a few of them and ask if they are a repair service, or if they sell parts, or both. If you're testing for 220 volt power you need to use the VOM. 8) When splicing wires in an oven, remember that you're dealing with high temperatures. Your parts dealer has high-temp connections, porcelain wire nuts and fiberglass-insulated wire for this purpose. I want to impress upon you something really important. However, you don't want to badger them with TOO many questions, so know your basics before you start asking questions. Some parts houses may offer service, too. It's unpleasant, but unless exposure is more than a second or so, the only harm it usually does is to tick you off pretty good.
They'll tell you it's too complicated, then in the same breath "guide" you to their service department.
They should contain the model number somewhere. In any case, and especially if you have absolutely NO information about your dryer anywhere, make sure you bring your old part to the parts store with you. However, you don't want to badger them with too many questions, so know your basics before you start asking questions. Some parts houses may offer service, too. If they genuinely try to help you fix it yourself, and you find that you're unable to, they may be the best place to look for service. An inexpensive one will suffice, as long as it has both "AC Voltage" and "Resistance" (i.e. On some models, you will also need the lot number to get the right part, so if there is one on the nameplate, write that down, too.2-3 TOOLS (Figure 2-A)Most of the tools that you might need are shown below. It's true that diagnosing and repairing electrical circuits requires a bit more care than most operations, due to the danger of getting shocked.


Remember the rule in section 1-5 (1); while you are working on a circuit, energize the circuit only long enough to perform whatever test you're performing, then take the power back off it to perform the repair.
You will only need to be able to set the VOM onto the right scale, touch the test leads to the right place and read the meter. In using the VOM (Volt-Ohm Meter) for our purposes, the two test leads are always plugged into the "+" and "-" holes on the VOM. When testing 220 volt circuits (usually in electric dryers) make sure you always follow the precautions in rule 1 of section 1-5!Figure B-4: Testing Voltage1-4(b) TESTING FOR CONTINUITY (Figure B-5)Don't let the word "continuity" scare you. It's derived from the word "continuous." In an electrical circuit, electricity has to flow from a power source back to that power source. It's true that diagnosing and repairing electrical circuits requires a bit more care than most operations, due to the danger of getting shocked. Remember the rule in section 2-1; while you are working on a circuit, energize the circuit only long enough to perform whatever test you're performing, then take the power back off it to perform the repair.
You will only need to be able to set the VOM onto the right scale, touch the test leads to the right place and read the meter.In using the VOM (Volt-Ohm Meter) for our purposes, the two test leads are always plugged into the "+" and "-" holes on the VOM.
It should peg the meter all the way on the right side of the scale, towards "0" on the meter's "resistance" scale. If the meter does not read zero resistance, adjust the thumbwheel on the front of the VOM until it does read zero. You can touch the ends of the wires and test leads with your hands if necessary to get better contact. It's derived from the word "continuous." In an electrical circuit, electricity has to flow from a power source back to that power source. If there is GOOD continuity, the meter will move toward the right side of the scale and steady on a reading.
This is the resistance reading and it doesn't concern us; we only care that we show good continuity.
If you do not, the switch is bad.   1-4(c) AMMETERSAmmeters are a little bit more complex to explain without going into a lot of electrical theory. It should peg the meter all the way on the right side of the scale, towards "0" on the meter's "resistance" or "ohms" scale.
If you own an ammeter, you probably already know how to use it. If you don't, don't get one. If the meter does not read zero ohms, adjust the thumbwheel on the front of the VOM until it does read zero. If the ignitor's leads are still connected to something, you may get a reading through that something. The greater the current that's flowing through a wire, the greater the density of the magnetic field, or flux, it produces aroundthe wire. The ammeter simply measures the density of this flux, and thus the amount of current, flowing through the wire. To determine continuity, for our purposes, we can simply isolate the component that we're testing (so we do not accidentally measure the cur rent going through any other components) and see if there's any current flow. To use your ammeter, first make sure that it's on an appropriate scale (0 to 10 or 20 amps will do). If you need to re-energize the dryer to perform a test, make sure any bare wires or terminals are taped or insulated. If you do not, the switch is bad. 2-4(c) AMMETERSAmmeters are a little bit more complex to explain without going into a lot of electrical theory. Energize the unit only long enough to perform whatever test you're performing, then disconnect the power again. I want to impress upon you something really important. It's unpleasant, but unless exposure is more than a second or so, the only harm it usually does is to tick you off pretty good.However, 220 VOLTS CAN KNOCK YOU OFF YOUR FEET. To determine continuity, for our purposes, we can simply isolate the component that we're testing (so we do not accidentally measure the current going through any other components) and see if there's any current flow. To use your ammeter, first make sure that it's on an appropriate scale (0 to 10 or 20 amps will do).
If the meter shows any reading at all, something in the oven is using power.2-5 WIRING DIAGRAMSometimes you need to read a wiring diagram, to make sure you are not forgetting to check something. And if you get it going and re-install it, you are running a very high risk that it will stop again.
The symbols used to represent each component are pretty universal. Wire colors are abbreviated and shown next to each wire. Replace the part. 3) If you must lay the dryer over on its side, front or back, first make sure that you are not going to break anything off, such as a gas valve.
GR or GN are green, GY is gray.A wire color with a dash or a slash means --- with a --- stripe. Lay an old blanket on the floor to protect the floor and the finish of the dryer. 4) Always replace the green (ground) leads when you remove an electrical component. And NEVER EVER remove the third (ground) prong in the main power plug! 5) When opening the dryer cabinet or console, remember that the sheet metal parts are have very sharp edges.
In some wiring diagrams, wiring and switches inside a timer or other switchblocks are drawn with lines that are thicker than the rest of the wiring. The small white circles all over the diagram are terminals. Wear gloves, and be careful not to cut your hands! 6) When testing for your power supply from a wall outlet, plug in a small appliance such as a shaver or blow dryer.
These are places where you can disconnect the wire from the component for testing purposes.
If two wires cross on the diagram without a black dot, they are not connected. Switches may be numbered or lettered. Usually the terminals on the outside of the timer or switch are stamped or printed with markings that you will see on the wiring diagram. To test a switch, mark and disconnect all the wires.
For example, in figure 2-F, if you want to test the door switch, take power off the machine, disconnect the wires from it and connect one test lead to COM and one to NC. If it does, you know that contact inside the switch is good. Remember that for something to be energized, it must make a complete electrical circuit. You must be able to trace the path that the electricity will take, FROM the wall outlet back TO the wall outlet. In this simplified circuit diagram, notice that only the heating elements operate on 220 volts. Since the locking mechanism is interlocked with the heating circuit, the oven will not reach cleaning temperature either.Let's start at the lock motor and find out which switches feed electricity to it. Tracing the other lock motor lead, we first end up at the "C" terminal of the 4-position selector switch. Looking at the switch for the chart, the "C" to "LM" contacts are closed when the "clean" button is depressed on the switch. Power then leaves the thermostat through the "5" terminal, so we need to check for continuity between terminals "5" and "6" of the thermostat. Since it is a thermostatic switch, only heat will open the switch, so we only need to test it for continuity.
They are shown in the diagram in their "normal state." So continuing with our circuit, if the locking motor is not turning, you need to check switch "B" for continuity between the "COM" and "NC" terminals.
If there is no continuity, it might mean the switch is bad. It might also mean that the switch was not returned to its "normal" state the last time it was activated!You need to examine the switch carefully to determine what the problem is. If the locking motor stopped turning before the switch unlocked, you've got other problems. You will need to trace other circuits in the diagram to figure out what. From the "COM" terminal of switch "B," the circuit goes back through the door switch to L1. The door switch feeds several other oven circuits, too, so unless there's something else not working, we can eliminate that as the problem. The door must be closed to close the switch that feeds electricity to the thermostats and heating circuit.To check for a wire break, you would pull each end of a wire off the component and test for continuity through the wire. You may need to use jumpers to extend or even bypass the wire; for example, if one end of the wire is in the control console and the other end in underneath the machine.
It will then be up to you to figure out exactly where that break is - there is no magic way. An ammeter is a safer way to test energized circuits if you have one, especially testing 220 volt circuits.
Occasionally, if the component is inexpensive enough, it's easier to just replace it and see if that solves the problem. Following is a primer on how to test each individual component you might find in any given oven.
Take all wires off the component and test continuity across it as described in section 2-4(b). Switches should show good continuity when closed and no continuity when open.
NO means "normally open" and with the switch at rest, you will see no continuity through it. SELECTOR SWITCHBLOCKS A selector switchblock, located in the control panel, is a group of switches all molded into one housing. In your oven, a switchblock might be used to allow you to choose a cooktop heat setting, for example, or a cleaning cycle instead of a baking cycle.
You must look at the wiring diagram to see which of the terminals will be connected when the internal switches are closed. Keep in mind, however, that you must also know which of the internal switches close when an external button is pressed. When you press one button on the switchblock, several of the switches inside may close at once.To test a switchblock, in addition to the wiring diagram, you must have a chart that gives you this info.
It's true that diagnosing and repairing electrical circuits requires a bit more care than most operations, due to the danger of getting shocked. Usually this is a part of the wiring diagram. Using the diagram and chart in figure 2-J, lets say we want to test contacts "T1" to "FM" for proper operation. We see that with the "clean" button pressed, these contacts inside the switchblock should be closed. Although error (fault) codes for most major brands may be found in Chapter 7, usually diagnosis consists of simply replacing circuit components until you find the bad one. Usually the problem turns out to be a bad oven sensor, stuck or defective keypad, ERC (clock) unit or a circuit board. These can be tested and rebuilt or replaced as described in this chapter.2-6 (c) THERMOSTATIC CONTROLSA thermostat is simply a switch or a gas valve that opens and closes according to the temperature it senses.
If there is an automatic oven cycle, main control thermostats must also be wired through the timer. And if there is a cleaning cycle, they must be either bypassed or adjusted for the higher temperatures of that cycle. That's where you start to get dual-control thermostats, thermostats with twelve leads, and other complexities. Some even control two levels of the same pilot. Main control thermostats are about the most expensive commonly-replaced parts in an oven.
It should be the last thing you conclude, after you have checked out everything else in the system.The liquid inside the bulb and capillary of an oven thermostat is usually a mercury or sodium compound or some other such nasty and dangerous stuff. So when you replace an oven thermostat, do not cut open the capillary or bulb, and dispose of the old thermostat properly.
The definition of "properly" varies between jurisdictions, but check with your appliance parts dealer or local fire department hazardous materials professionals.ADJUSTING THERMOSTATS The oven is adjusted by a small adjusting screw in the center of the oven thermostat valve stem. In other words, if you set the thermostat at 350 degrees, you want the heating system to cycle on if the temperature is below 340 degrees, and off when the temperature reaches about 360 degrees. With nothing else in the oven, place it in the middle of the oven, where you can see it through the oven door glass. The important thing to remember about clocks in an oven unit are that often the thermostat controls are first wired through the timer. Also, if you are troubleshooting a no heat complaint in an oven with an automatic cycle, the first step is always to check the timer controls. The greater the current that's flowing through a wire, the greater the density of the magnetic field, or flux, it produces aroundthe wire. The woman who greeted me was the ultimate Susie homemaker; everything was spotless in HER kitchen. Including the oven, which looked new, but this gal swore she'd owned it since it was new 35 years before, and by golly she knew it inside and out and didn't know why two ovens out of three suddenly didn't work. You must have a wiring diagram to determine which terminals are connected when a switch inside the timer closes. Put a resistance meter across those terminals and advance the clock to determine if the switch is opening and closing. If the clock motor doesn't run or the switches don't open and close as they are supposed to, replace the timer. If there are any special wiring changes, they will be explained in instructions that come with the new timer. Clocks and timers can usually be rebuilt.
Ask your appliance parts dealer for details.2-6 (e) ELECTRIC HEATERS AND IGNITORSElectric heater elements and ignitors are tested by measuring continuity across them as described in section 2-5(b). Replace heater elements if they show no continuity.2-6 (f) RELAYSHeating elements use a lot of electricity compared to other electrical components. The switches that control them sometimes need to be built bigger than other kinds of switches, with more capacity to carry more electricity. The switches involved in running a heater or ignitor can be too big to conveniently put inside the control console or timer. Besides that, there are safety considerations involved in having you touch a switch that carries that much electricity directly, with your finger. The way they solve that problem is to make a secondary switch.
A little switch activates an electromagnet, which closes a big switch that carries the heavier current load. Energize the unit only long enough to perform whatever test you're performing, then disconnect the power again. 3) If this manual advocates replacing the part, REPLACE IT!!
It's unpleasant, but unless exposure is more than a second or so, the only harm it usually does is to tick you off pretty good.
If they genuinely try to help you fix it yourself, and you find that you're unable to, they may be the best place to look for service. It's true that diagnosing and repairing electrical circuits requires a bit more care than most operations, due to the danger of getting shocked.
If the ignitor's leads are still connected to something, you may get a reading through that something.



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