Zenith Case Histories of Receiver Troubles and Their Remedies
Section 2

Models 10 through 756

INDEX

Zenith 10

Zenith 10-S-130, 10-S-147, 10-S-153, 10-S-155, 10-S-156, 10-S-157, 10-S-160 (chassis 1004)

Zenith 10-S-443 (chassis 1005)

Zenith 11

Zenith 11E (A-C)

Zenith 11-S-474 (chassis 1103)

Zenith 12

Zenith 12-A-57, 12-A-58 (chassis 1202)

Zenith 12-L-57, 12-L-58 (chassis 1202A)

Zenith 12-S-265, Zenith 12-S-445 (chassis 1207)

Zenith 12-S-550 (chassis 12A3)

Zenith 14

Zenith 15E, 15EP

Zenith 15-S-308 (chassis 1502)

Zenith 15-S-497 (chassis 1503)

Zenith 15-U-269 (chassis 1501)

Zenith 33, 33X, 34, 34P, 35, 35A, 35P, 35AP

Zenith 35PX

Zenith 37A

Zenith 39A

Zenith 41, 42

Zenith 50

Zenith 52, 53, 54, 55 ("50" Series)

Zenith 55-127, 55-150

Zenith 60

Zenith 61

Zenith 62

Zenith 70

Zenith 71P

Zenith 71, 73, 73, 77 ("70" Series)

Zenith 75-C

Zenith 91,92

Zenith 102, 112, 122

Zenith 134F

Zenith 230 Transformer (chassis 2036)

Zenith 240 (chassis 2036)

Zenith 244 (chassis 2036)

Zenith 245 (chassis 2036)

Zenith 342, 342P, 352, 352A, 352AP, 352P, 362, 362X

Zenith 410, 411, 420

Zenith 422

Zenith 430, 440, (chassis 2033)

Zenith 474 (chassis 2053)

Zenith 475 (chassis 2054)

Zenith 476B (chassis 2059)

Zenith 500, 501, 503, 514, 516 (chassis 2037)

Zenith 522, 532, 542

Zenith 600, 604, 606 (chassis 2037)

Zenith 608 (chassis 2035)

Zenith 705, 706, 707, 711, 712 (chassis 2052)

Zenith 715 (chassis 2053)

Zenith 730 Series

Zenith 750 (chassis 2052)

Zenith 755, 756 (chassis 2053)

---

Zenith 10

Inoperative.

1. .03-mfd audio coupling condenser shorting to chassis due to exposed foil touching chassis. Replace.

Intermittent reception. Noise.

1. faulty coupling condenser in resistance-capacity coupled stage. Replace with a .1-mfd 400-volt unit.

2. see note 1 under "inoperative" above.

3. corroded or loose contacts on 3-point antenna switch.

Whistling or squealing. Fading.

1. open circuiting .1-mfd screen by-pass condenser.

2. open circuiting .1-mfd cathode by-pass condenser.

Microphonic hum.

1. change type '24-A detector tube.

Noisy on all bands.

1. try a ground on the receiver. If it does not help, or introduces hum, try reversing the a-c line plug, or leave ground off entirely.

2. check tubes for noise.

3. check condenser bond wires to clear chassis.

4. dirty tuning condenser or wipers.

5. loose lugs on Candohm resistor.

6. shorted bus bar wires in coil circuits.

7. noisy aerial connections.

8. loose connecting wire between Z and G on aerial terminal strip.

Noisy on "C" band only in spots.

1. check dial pulley - move pulley away from dial pan.

2. condenser bonds do not clear chassis.

3. check for poor contacts on the band, tone and sensitivity switches.

4. faulty volume control.

5. faulty 16-mmfd condenser No. 22-506.

Hum.

1. check all tubes.

2. shorted elements in oscillator tube, or output tubes not matched.

3. open filter condenser.

4. open electrostatic shield in power transformer. This will give "carrier hum" and can be corrected -passing the a-c line with a .001-mfd mica condenser. Try reversing the a-c line plug also.

Fluttering on low frequency.

1. check all tubes carefully - particularly the oscillator tube.

2. rebalance i-f's to 456 kc.

Dial slips.

1. loose dial clutch. Tighten.

Zenith 10-S-130, 10-S-147, 10-S-153, 10-S-155, 10-S-156, 10-S-157, 10-S-160 (chassis 1004)

Inoperative on "B" band below 6 mc (early models).

1. replace 6A8G oscillator tube with Sylvania 6A8 metal tube.

Intermittent reception.

1. check all tubes.

2. shorting i-f trimmers.

3. dirty variable condenser.

4. loose wire link across Z and G on aerial connection strip.

5. poor contact on band switch.

7. faulty aerial.

8. faulty by-pass condenser.

Lack of sensitivity (on all bands).

1. check tubes.

2. check antenna and ground.

3. check all coils.

4. poor contact in sensitivity switch.

5. re-align entire receiver.

Lack of sensitivity (on broadcast band).

1. open r-f plate choke.

Week reception.

1. check all tubes, especially 1st and 2nd detector tubes.

2. try grounding the receiver. If it does not help, or introduces hum, try reversing the a-c line plug - or leave ground off entirely.

3. grounded .00025-mfd condenser in tone circuit (noticeable on high-fidelity position of switch, with distortion).

4. open 2nd detector cathode resistor on Candohm.

5. re-peak i-f's to 456-kc.

6. check tone switch for short to "Foreign station" lug.

Weak reception (target tuner does not function).

1. shorted .05-mfd by-pass condenser on r-f input side of 6C5 target tuner grid.

Stations "ride" in.

1. check alignment of receiver.

2. check .0012-mfd condenser in oscillator plate circuit.

Off calibration at low-frequency end of dial. Unable to adjust by regular alignment.

1. check 600-kc padder for broken wire, lug, ect.

2. check .0012-mfd condenser C-26 (No. 22-486) in oscillator plate circuit.

Poor action of target tuner.

1. target tuner is not supposed to center exactly in center of bull's eye, except on vary strong input signal.

2. check 6C5 tube, or replace target unit.

Noisy on all bands.

1. try a ground on the receiver. If it does not help, or introduces hum, try reversing the a-c line plug, or lead ground off entirely.

2. check tubes for noise.

3. check condenser bond wires to clear chassis.

4. dirty tuning condenser or wipers.

5. loose lugs on Candohm resistor.

6. shorted bus bar wires in coil circuits.

7. noisy aerial connections.

8.. loose connecting wire between Z and G on aerial terminal strip.

Zenith 10-S-443 (chassis 1005)

Same Case Histories as listed for Zenith 8-S-443.

Zenith 11

Same Case Histories as listed for Zenith 10 receiver.

Zenith 11E (A-C)

Inoperative. Intermittent reception.

1. open in the r-f grid circuit.

2. shorting compensating condenser on condenser gang. Place a small piece of gummed paper over the inside of one plate.

Zenith 11-S-474 (chassis 1103)

Same Case Histories as those listed for Zenith 8-S-443.

Zenith 12

Same Case Histories as those listed for Zenith 10 receiver.

Zenith 12-A-57, 12-A-58 (chassis 1202)

Excessive deep tone at all tone control positions.

1. remove .01-mfd condenser C-10.

Zenith 12-L-57, 12-L-58 (chassis 1202A)

Intermittent reception.

1. replace .05-mfd condenser C-29 coupling 6H6 tube to volume control R-7.

Tuning meter operation not sensitive enough.

1. try new 6C5 tube.

Zenith 12-S-265, Zenith 12-S-445 (chassis 1207)

Inoperative (no screen voltage on 6K7G and 6L7G tube).

1. open 11,000-ohm section in Candohm resistor.

Microphonic noises. Low rumbling (with volume control at minimum).

1. Microphonic 6J5G first a-f tube.

Distortion (sounding like blocking AVC action).

1. open filter condenser section.

Zenith 12-S-550 (chassis 12A3)

Hum.

1. replace first audio 6J5 tube.

Zenith 12-S-550 (chassis 12A3)

Inoperative.

1. if audio stages OK but a-f end is dead, check 5-meter coil for open circuit (broken loose from condenser gang terminal.

2. check gang and trimmer condensers for shorts.

3. check for open coils and shorted by-pass condensers.

4. check for open resistor in 1st audio plate circuit.

5. check for shorted filter condensers.

Inoperative on lowest wave band.

1. untwist grid lead wires from screw on gang condenser. Realign, using .001-mfd mica condenser from oscillator to antenna.

Weak reception.

1. check tubes

2. check r-f and i-g alignment.

3. check coils for open circuits - particularly the 2nd detector coil.

4. open r-f choke in plate circuit.

5. broken grid wires.

6. check fixed condensers grouped around volume control.

Lack of sensitivity on ultra-short wave band.

1. extreme pickup cannot be expected on this band. However, the following will affect operation on this band.

2. open oscillator coil.

3. open or shorted .0012-mfd 600-volt condenser C-7 in oscillator plate circuit.

4. shorted 50-mmfd condenser across the high-frequency coil.

5. grounded trimmer on the 1st detector section of gang condenser.

6. open 5-ohm resistor at high-frequency coil will cause "spotty" sensitivity.

7. check first-detector tube, as it has a great effect on ultra-short-wave reception.

8. do not alter the length of wires, positions of coils, ect., as this will affect the entire short-wave band operation. Leave (or replace all units) in exactly the position they were in when set was shipped from factory.

Lack of sensitivity on "D" band.

1. faulty 6H6, 6L7 tubes.

2. open coil winding.

3. poor contact at tube prongs.

4. poor contact on band switch.

5. check i-f peak (456 kc).

6. shorted .25-mmfd condenser in oscillator circuit.

7. check coupling of wires in "D" band circuit.

Stations "ride" in.

1. check alignment of receiver.

2. check .0012-mfd 600-volt condenser C-7 in oscillator circuit.

Off scale (gain is low and difficult to line up the tuning circuits).

1. check for open 20-ohm resistor (R-16) in screen circuit of 1st detector.

2. check 50-mmfd condenser (C-4) in oscillator circuit.

Broadcast band off scale.

1. check the dial pointer. The pointer should line up across the dial scale parallel to the line when the gang condenser plates are fully meshed.

2. the air trimmer for the "B" band, as shown in the earlier diagrams and listed on the service sheets, is not used on later models. The Broadcast and "D" band trimmers are in the same positions as shown on these sheets. Follow the usual alignment procedure.

Noisy on "D" band.

1. clear the gang condenser bonds away from the chassis holes.

2. check wiring of "D" band tuned circuits for shorts.

3. check coils for loose soldering on lugs.

Noisy and off-scale on "D" band.

1. replace the 50-mmfd condenser in the oscillator circuit.

Noisy.

1. where noise is definitely traced to the chassis (after tubes, antenna, and ground systems have been checked), check contacts on band switch, sensitivity switch, volume control, coil wires, air trimmers and 16-mfd screen condenser C-21 as possible noise sources.

Distortion.

1. check all tubes.

2. output tubes mismatched.

3. open 16-mfd electrolytic condenser (C-21) in screen circuit.

4. shorted 10-mfd electrolytic condenser (C-20) in output tube cathode circuit.

5. open cathode circuits.

6. faulty by-pass condensers.

7. grounded, or shorted tone circuit.

8. faulty loud speaker.

9. if distortion is accompanied by loss of output, check for shorted .005-mfd condenser (C-22) in plate circuit of one of the output tubes.

10. distortion only when tone switch is on normal may be caused by a short between the lugs on the tone switch.

Distortion at low volume.

1. replace 400-ohm 1-watt cathode resistor on 6F6 tube with a 5-watt wire-wound unit.

2. check cathode by-pass condenser for leakage.

Poor reproduction on high-frequency notes.

1. poor contact on tone switch.

2. open .00025-mfd condenser (C-15) in tone control circuit.

3. open tap on volume control (in this case, the tone control will have no effect).

Carrier or modulation hum.

1. faulty 6C5, 6H6, or power tubes.

2. open electrostatic shield in power transformer. Try reversing the a-c line plug. Try connecting a .001-mfd 400-volt mica condenser from one side of the power line to receiver chassis.

3. shorted .005-mfd condenser (C-22) in output tube plate circuit.

4. grounded tap on volume control.

5. open Candohm resistor ground.

Zenith 14

Same Case Histories as listed for Zenith 11E receiver.

Zenith 15E, 15EP

Weak reception. Distortion (no detector plate voltage).

1. poor connection or an open in 100,000-ohm detector plate resistor (mounted in a clip at audio end under chassis).

Zenith 15-S-308 (chassis 1502)

Tuning scale settings change.

1. loose Parker-Kalon screws in gang condenser gear hub.

Zenith 15-S-497 (chassis 1503)

Poor Radiorgan action.

1. faulty 6F8G audio tube.

Improper volume control action.

1. faulty 6J5G audio tube.

Zenith 15-U-269 (chassis 1501)

Weak reception (accompanied by noise).

1. open 6K7G r-f plate choke (No. 20-135).

Microphonic noises. Low rumbling (with volume control at minimum).

1. Microphonic 6J5G first a-f tube.

Trouble with split-dial mechanisms.

1. carefully lubricate all bearings and tighten all set-screws - especially the two that hold lever on waveband switch. Entire dial assembly will jam if these work loose.

Same Case Histories as those listed for Zenith 15E receiver.

Zenith 33, 33X, 34, 34P, 35, 35A, 35P, 35AP

Inoperative.

1. open section in voltage divider.

2. shorted filter condenser in power pack.

Intermittent reception. Noisy tuning.

1. variable condenser plates blistered and peeling, causing shorts. Burn with high voltage - all leads disconnected.

Intermittent reception. Fading.

1. dirty or loose socket contacts.

2. defective volume control.

3. defective audio transformer.

Weak reception (audio circuits test OK.

1. open-circuited, or omitted 2,000-ohm resistor from ground to movable antenna compensating coil under chassis. Replace with a new resistor.

Poor selectivity. Hum. Whistling or squealing when volume control is turned toward maximum.

1. open-circuited antenna primary coil located in inverted can below the first r-f tube socket under the chassis. Replace with new unit or solder a flexible lead which has a phone tip soldered to its other end to one terminal of a .01-mfd condenser. Plug the end with the phone tip into the "long antenna" tip jack and ground the other end of the condenser to the chassis. Re-align circuits for maximum response.

Tone raspy.

1. substitute a '112 tube for the '71 tube.

Noisy reception.

1. high-resistance ground in secondary of original a-f transformer (green corrosion usually found on terminal lugs.

Hum.

1. defective electrolytic filter condenser. Short-circuit the terminal of each unit momentarily to chassis and note the effect - the hum might be cured. If not, replace with new units.

2. connect 100,000-ohm resistor across type 27 first-audio tube grids.

3. defective type '27 tube.

4. defective volume control.

5. open cathode by-pass condenser in detector stage.

6. short from heater to cathode in any of the '27 tubes.

Zenith 35PX

Noisy reception. Poor tone quality.

1. noisy audio transformer. Replace.

Zenith 37A

Fading (on phono).

1. check all leads to pickup for loose connections and poorly soldered joints. Resolder all these joint.

Zenith 39A

Poor sensitivity.

1. realign tuning condensers. Remove condenser gang shield to get at the trimmer.

2. corroded wire connection on terminal strip which plugs into power pack.

Zenith 41, 42

Inoperative (no screen grid voltage).

1. check two 25,000-ohm resistors associated with screen circuit.

Inoperative (no r-f plate voltage).

1. short in the first compensator condenser. Trim and bend it so it will not short.

Fading. Noisy reception. Whistling or squealing.

1. defective contacts in "local-distance" toggle switch. This connects to a .00025-mfd condenser in antenna circuit.

2. loose or broken terminal lug on r-f plate circuit by-pass condenser.

Hum.

1. check all leads to pickup for loose center tapped resistor shorting to chassis.

2. when replacing the shield cans be sure that all wires are placed in their proper grooves.

Zenith 50

Excessive hum.

1. inductive pickup from the filter choke by the a-f transformer between the first and final a-f stages. Remove the blocking condenser between the plate of the first a-f stage and the a-f transformer primary; shunt the transformer primary with a .1 megohm resistor. Connect the low end of this resistor through a 2-mfd by-pass condenser to ground. Now connect in series with the low end of the audio transformer primary and B-plus a .1 megohm resistor. Disconnect the former connection of that part of the a-f transformer primary to ground.

2. faulty '24 detector tube

3. increase plate coupling condenser in 1st a-f stage from .05-mfd to .1-mfd. Use value giving best results.

4. connect a 100,000-ohm resistor in the detector plate return circuit. Connect a 500,000-ohm resistor in the detector screen circuit. -pass each of these resistors to ground by a .1-mfd condenser.

Poor sensitivity at one end of dial.

1. remove shield from condenser gang. Remove screens holding stators in place at each end. Place lockwashers under these and tighten.

Fading.

1. faulty volume control.

2. poor connection in grid circuit of first r-f stage.

Zenith 52, 53, 54, 55 ("50" Series)

Inoperative.

1. open 400-ohm (yellow) r-f bias resistors.

2. open 2,000-ohm (black) audio bias resistor.

Type '80 tubes burn out.

1. automatic tuner pilot light or socket shorting to metal frame.

No signals on certain wavelengths.

1. variable condenser plates blistered and peeling, causing short-circuits. Burn with high voltage -all leads disconnected.

No reception below 650 kc.

1. end rotor plates of tuning condensers shorting to stator plates.

Weak reception. Intermittent reception. Flickering of pilot light.

1. intermittent short-circuiting of the two filament supporting stems in the pilot lamp, thus also short-circuiting the filaments of the type '45 power tubes, across which it is connected. Replace lamp.

Fading. Intermittent reception.

1. cold soldered connections to variable condensers.

2. open r-f coils, leads snap at lug.

3. worn carbon resistance in volume control.

4. break in pigtail to r-f stator vernier of first r-f tuning condenser.

5. snapping of fine wire leads of r-f chokes at eyelets.

6. open between pilot lamp bracket and tuning dial.

7. defective cathode by-pass condenser.

Noisy tuning. Whistling or squealing.

1. corroded copper contact and washer at end of condenser gang rotor shaft. Add jumpers from rotor wipers to ground and from center gang shield to ground.

Hum.

1. defective electrolytic filter condenser. Short-circuit the terminal of each unit momentarily to chassis and note the effect - the hum may be cured. If not, replace with new units.

2. connect 100,000-ohm resistor across type 27 first audio tube grids.

3. defective type '27 tube.

4. defective volume control.

5. open cathode by-pass condenser in detector stage.

6. place 500,000-ohm resistor across secondary of push-pull input transformer.

7. open r-f choke in first r-f grid return circuit.

Zenith 55-127, 55-150

All signals but locals fade out completely after short period of time.

1. replace 400-ohm 1/2 watt 6A8G cathode resistor (mounted directly on tube socket near front of chassis).

Zenith 60

Same Case Histories as those listed for Zenith 50 receiver.

Zenith 61

Hum.

1. check electrolytic filter condensers.

2. cathode-to-heater short in detector tube.

Zenith 62

Weak reception.

1. warping of die-castings in tuning condenser causes set to go out of alignment. Realign while set is warmed up well.

Whistling of squealing around lower end of dial.

1. this is a normal condition in this receiver, as it can be checked by the volume control.

Hum.

1. often, after replacing the wet electrolytic condenser on these models a hum will be heard, and forming the plates of the electrolytic condenser will remove the hum only for a short time. To remedy this, disconnect the leads from the electrolytic condenser one at a time. When the correct wire is removed the hum will be lower in volume. This is the section shunting its resistance across the filter choke, allowing the hum content of the power supply to be passed through the resistance and not through the filter choke. To this wire which has been removed connect an 8-mfd electrolytic condenser and to chassis ground.

Zenith 70

Intermittent reception.

1. replace 100,000-ohm white detector plate resistor.

Intermittent reception accompanied by distortion.

1. replace .03-mfd plate blocking condenser in 1st a-f stage.

Intermittent reduction in volume, accompanied by sharp "click" and ragged tone.

1. replace first audio plate blocking condenser.

Intermittent reception and fading.

1. if signals vary from weak to normal to weak, ect., check for open or shorted .25-mfd dual plate by-pass condenser for first two r-f stages.

2. if signals fade to weak and stay weak, replace .03-mfd first audio plate blocking condenser located between plate of first audio tube and primary of first a-f condenser.

Volume dies down after set is in operation for few seconds, requiring readjustment of volume control.

1. replace 100,000-ohm white detector plate resistor.

Distortion on low volume.

1. leaky 1st audio coupling condenser.

Hum.

1. by-pass the detector cathode to ground with a 1 or 2-mfd condenser supplementing the one already in the circuit.

Zenith 71P

Inoperative.

1. shorted filter section on either side of choke coil. Cut shorted lead; connect in a 8-mfd electrolytic condenser with its negative side to the choke; positive lead goes to connector strip.

Zenith 71, 73, 73, 77 ("70" Series)

See also Case Histories listed for Zenith 52, 53, 54, 55 receivers.

Fading.

1. open or short-circuited .25-mfd dual plate by-pass condenser connected in the first and second r-f stages.

2. open or shorted .03-mfd audio coupling condenser.

Noisy reception.

1. defective a-f transformer.

Hum.

1. see Case History listed for this same trouble symptom under Zenith 62 receiver.

Zenith 75-C

Motorboating sound.

1. defective dual .01-mfd condenser.

Zenith 90

Inoperative.

1. defective 8-mfd dry electrolytic filter condenser.

Zenith 91, 92

Inoperative, until '24 AVC tube is removed.

1. open AVC voltage divider section. Connect a 15,000-ohm, 1 watt wire wound resistor across that section which is between the AVC tube cathode and the screen grid taps.

Weak reception. Poor tone.

1. check value of resistor in screen cathode audio center-tap circuit. Portion between center-tap and cathode should measure 25,000-ohms. Section between cathode and screen shield should be 10,000-ohms.

2. faulty r-f choke.

3. open .5-mfd second detector cathode bias condenser.

Fading and whistling or squealing.

1. replace '24 AVC tube.

2. check for open .5-mfd screen by-pass condensers of r-f and i-f stages.

Fading. No dip action on tuning meter. Erratic operation on "local" side of local-long distance switch.

1. change in resistance value of the 2,800-ohm and 3,600-ohm bleeder resistors connected in series across the d-c output voltage. Replace with resistors of higher wattage rating.

No AVC action.

1. defective AVC resistor.

Distortion at resonance.

1. AVC screen-cathode voltage divider changed in value.

Local-distance switch inoperative.

1. open-circuited 4.5-megohm carbon resistor.

Interference from airport radio beacon stations which transmit at 260-kc, (the i-f of the receiver).

1. readjust the i-f compensating condenser at 250 or 270-kc.

Alignment of receiver circuits impossible.

1. defective gang condenser.

Impossible to align circuits at 1400-kc.

1. open-circuited .001-mfd condenser between the oscillator coil and plate of oscillator tube. Replace with .0005-mfd condenser and set will align OK.

Zenith 102, 112, 122

Same Case Histories as those listed for Zenith 10 receiver.

Zenith 134F

Weak reception. Noisy.

1. check both i-f transformers with a low-range ohmmeter. If more than 10-ohms, replace transformer.

Zenith 230 Transformer (chassis 2036)

Distortion at low volume.

1. improperly centered voice coil of either dynamic speaker.

Hum. Distortion.

1. capacity of electrolytic filter condensers dropped below normal.

Whistling or squealing. Weak and distorted.

1. capacity of third electrolytic filter condenser dropped below normal.

Motorboating sound.

1. insufficient filter capacity. Add an additional 4-mfd condenser to the filter.

Zenith 240 (chassis 2036)

See also Case Histories listed for Zenith 230 receiver.

1. oscillator trimmer condensers out of alignment.

2. celluloid dial scale requires adjustment.

Distortion. Weak reception.

1. back left mounting bolt screwed up to far, causing it to short-circuit the bias resistor.

Zenith 244 (chassis 2036)

See also Case Histories listed for Zenith 230 receiver.

Poor tone. Distortion at low volume.

1. defective type '57 AVC tube (even though it tests OK). Replace with new tube.

Zenith 245 (chassis 2036)

Same Case Histories as those listed for Zenith 230 receiver.

Zenith 342, 342P, 352, 352A, 352AP, 352P, 362, 362X

Same Case Histories as listed for Zenith 33X receiver.

Zenith 410, 411, 420

Inoperative.

1. open-circuited shadowgraph tuning meter.

Fading after a few minutes of operation.

1. replace type '57 AVC tube.

Hum (present only when stations are tuned in).

1. partially short-circuited field coil, putting a greater load on the line and thereby lowering the plate voltage applied to the tubes. Replace the field coil.

Hum.

1. faulty electrolytic filter condensers.

Rapid motorboating sound (no radio reception).

1. open 500-mmfd condenser across plate and cathode of '56 second detector.

Zenith 422

Same Case Histories as listed for Zenith 41, 42 receivers.

Zenith 430, 440, (chassis 2033)

See also Case Histories listed for Zenith 410, 411, 420 receiver.

Weal reception.

1. partial short in .5-mfd condenser connected in second-detector plate circuit (at left side of chassis, along side of volume control).

Weak reception. Noisy.

1. poor connections at riveted ends of i-f transformer trimmer condensers. Solder the ends, and realign at 175 kc.

Zenith 474 (chassis 2053)

Same Case Histories as listed for Zenith 755 receiver.

Zenith 475 (chassis 2054)

Same Case Histories as listed for Zenith 760 receiver.

Zenith 476B (chassis 2059)

Inoperative.

1. check for open 1/4-watt 99,000-ohm diode load resistor on 56 diode second detector tube.

Zenith 500, 501, 503, 514, 516 (chassis 2037)

Intermittent reception. Whistling or squealing. Motorboating sound. Station hiss.

1. open-circuiting .5-mfd grid filter condenser for r-f, i-f, and first detector stages.

Zenith 522, 532, 542

See also Case \histories listed for Zenith 52 receiver.

Inoperative.

1. open yellow 400-ohm r-f bias resistor.

2. open black 2,000-ohm bias resistor.

Zenith 600, 604, 606 (chassis 2037)

Same Case Histories as listed for Zenith 500 receiver.

Zenith 608 (chassis 2035)

Intermittent reception. Volume cuts down to lower level.

1. open-circuiting r-f first detector, i-f secondary-return by-pass condensers.

Zenith 610, 616, 618 (chassis 2037)

Same Case Histories as listed for Zenith 500 receiver.

Zenith 701

Inoperative.

1. defective electrolytic filter condenser.

Weak reception.

1. if all parts and tubes check OK, replace filter condenser block.

Hum.

1. defective 25-5-10 mfd electrolytic filter condenser.

Zenith 705, 706, 707, 711, 712 (chassis 2052)

Inoperative, type 58 i-f tube grids get red hot.

1. shorted primary-secondary windings of i-f transformer.

Inoperative at high-frequencies.

1. intermittent oscillator plate by-pass condenser.

Intermittent reception. Whistling or squealing. Motorboating sound.

1. open-circuiting .1-mfd i-f secondary return by-pass condenser.

Change in volume.

1. leaky .01-mfd condenser in oscillator circuit.

Broad tuning.

1. remove the 5,400-ohm resistor and 5-mfd, 20-volt condenser in the cathode of the type 2A6 tube, grounding the cathode. This removes the QAVC feature of the receiver. Realign the i-f and r-f stages, before putting the set in operation.

Whistling or squealing. Motorboating sound.

1. open-circuited .05-mfd cathode by-pass condensers for first detector and i-f stages.

2. electrolytic filter condenser making poor contact with the metal chassis. Turn the condenser about 1/8 turn to tighten it.

Motorboating sound between stations.

1. defective .1-mfd by-pass condenser in AVC circuit. Replace with new unit (No. 22-190).

Distortion. Glowing type 59 tube grids.

1. can of electrolytic filter condenser grounding to shield.

2. connecting lug of electrolytic condenser grounding to chassis.

Code interference.

1. shunt a wave trap tuned to 485 kc across aerial and ground.

Hum and distortion.

1. faulty volume control. Try replacing it with a 1-megohm unit - even if it check OK.

Zenith 715 (chassis 2053)

Same Case Histories as listed for Zenith 705, 755 receivers.

Zenith 730 Series

Inoperative. Intermittent operation.

1. shorted i-f by-pass from primary to secondary.

2. shorted i-f winding.

Improving performance.

1. remove fine stranded wires of i-f coils where they pass through eyelets at base of coil form, and run externally through spaghetti, sharpening i-f resonance peak due to reduced coupling. Realign.

Zenith 750 (chassis 2052)

See also Case Histories listed for Zenith 705, 706, ect. receivers.

Inoperative (grids of i-f tube red hot).

1. shorted i-f transformer (often caused simply by leads of one winding touching leads of the other winding).

Intermittent reception.

1. defective type 59 tube (even though it may test OK). Replace with new tube.

Motorboating sound.

1. type 89 tube weak on low-frequency. Try reversing i-f primary terminal connections.

2. replace .5-mfd cathode by-pass condenser of 1st detector and i-f tubes with 400-volt non-inductive type.

Zenith 755, 756 (chassis 2053)

Inoperative (d-c output shorted).

1. type 58 r-f plate coil lead grounding to chassis.

Inoperative. Very weak.

1.open-circuited 15,000-ohm screen voltage dropping resistor.