Zenith Case Histories of Receiver Troubles and Their Remedies
Section 1

General Service Notes for Home Radios 1937-1941
Models 'Radiogran through 9-S-365

INDEX - SECTION 1

General Service Notes - Home Radio 1937

General Service Notes - Home Radio 1938

General Service Notes - Home Radio 1940

Zenith 'Radiogran'

Zenith 'Zenette' A, B, C, D

Zenith CH Series

Zenith LH Series

Zenith MH Series

Zenith 4-B-106, 4-B-131, 4-B-132 (chassis 5406)

Zenith 4-B-231 (chassis 5409)

Zenith 4-B-133 (chassis 5407)

Zenith 4-F-227 (chassis 5408)

Zenith 4-K-310 (chassis 5412)

Zenith 4-K-401

Zenith 4-P-26, 4-T-26 (chassis 5401)

Zenith 4-T-26 (chassis 5403)

Zenith 4-V-31, 4-V-59 (chassis 5405

Zenith 4-Z-31

Zenith 5-F-233, 5-F-251 (chassis 5522)

Zenith 5-G-500

Zenith 5-G-636

Zenith 5-R-312 (chassis 5528)

Zenith 5-S-29, 5-S-56 (chassis 5513)

Zenith 5-S-119, 5-S-126, 5-S-150, 5-S-151, 5-S-161, (chassis 5516)

Zenith 6-B-107, 6-B-129, 6-B-118 (chassis 5635)

Zenith 6-D-116, 6-D-117, 6-D-118 (chassis 5633)

Zenith 6-D-311 (chassis 5646)

Zenith 6-D-312 (chassis 5647)

Zenith 6-D-410 (chassis 5659)

Zenith 6-G-500

Zenith 6-J-230 (chassis 5642)

Zenith 6-R-481 (chassis 5675)

Zenith 6-S-27, 6-S-52 (chassis 5619)

Zenith 6-S-128, 6-S-137, 6-S-147, 6-S-152, 6-S-157, (chassis 5634)

Zenith 6-S-203, 6-S-222, 6-S-229, 6-S-239, 6-S-241 (chassis 5638)

Zenith 6-S-527 (chassis 6A02)

Zenith 6-S-580 (chassis 6A20)

Zenith 7-S-28

Zenith 7-S-204

Zenith 7-S-242, 7-S-258, 7-S-260, 7-S-261 (chassis 5709)

Zenith 7-S-323 (chassis 5714)

Zenith 7-S-432 (chassis 5719)

Zenith 7-S-432 (chassis 5724)

Zenith 7-S-487 (chassis 5725)

Zenith 7-S-529 (chassis 7A02)

Zenith 7-S-581 (chassis 7A04)

Zenith 8-S-129, 8-S-154 (chassis 5801)

Zenith 8-S-539 (chassis 5807)

Zenith 8-S-432 (chassis 5810)

Zenith 8-S-443 (chassis 5808)

Zenith 8-S-458 (chassis 5810)

Zenith 9-S-30, 9-S-54, 9-S-55 (chassis 5903)

Zenith 9-S-203 (chassis 5905)

Zenith 9-S-262 (chassis 5905)

Zenith 9-S-357 (chassis 5907)

Zenith 9-S-365 (chassis 5906)

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Zenith 1937 Home Radio (General Servicing Notes)

Weak reception, tuning eye cannot be centered.

1. replace both i-f coils if coil form is hollow paper type

Weak reception, Broad tuning (in 6 and 8 tube models).

1. increased resistance in primary windings of i-f transformers. resistance varies from the normal 6 ohms to as high as 90 or 3000 ohms. Replace all i-f transformers for permanent repair.

Difficulty in getting "peak" tracking on all bands (in 8, 10 and 12 tube models).

1. fault lies in the shifting of the inductance in the tapped first detector coil. The consequent mismatching of the inductive-capacitive design results in the shifting of the peak resonant condition of optimum alignment of the circuit. The remedy of this is to shift the small fixed 5-mmfd. mica condenser (C-1) ordinarily connected in the grid circuit of the antenna coil secondary, over to the first detector coil circuit in the identical position. When this is done, matching of the coils becomes closer, and a consequent improvement in sensitivity is obtained.

Motorboating sound, (with switch in distance position).

1. check screen and by-pass condensers (C-4). Replace faulty units.

Scratching noise heard when tuning "spinning flywheel" type models.

1. flywheel not making proper ground at end of shaft. Tighten spring at end of shaft by moving pulley toward center. Lubricate with a drop of oil.

Crackling, frying noises (which persist even after antenna and ground are disconnected).

1. noisy 1st i-f transformer. This may be checked by connecting a high-resistance voltmeter across the primary winding and observing fluctuations with set operating. When replacing this transformer, be sure that the long plate lead from the 6A8G is as short as possible, and is dressed against the chassis over its whole length. Otherwise circuit oscillation will result.

Electric tuning service adjustments.

1. make sure that nothing is obstructing the free action of either the belt, the pulley, or the drive shaft, such as wires or component parts.

2. check the band change shaft for clearance on the 9-12-15 tube models. The die-cast bracket through which the brass drive shaft for the motor travels can be centered properly by loosening the two Parker-Kalon screws which hold the bracket to the front of the dial assembly. After centering this die-cast bracket retighten the two Parker-Kalon screw

3. check the 9/16-inch nut at the rear of the chassis in this manner; loosen the nut, permit the motor to run and re-tighten the 9/16-inch nut while in operation. This will allow the front and rear bearings to align themselves properly.

4. check for ample clearance between the dial gang drive pulley and the mounting nut for the bearing through the front of the chassis approximately 1/32-inch clearance. Brass drive shaft should also have ample clearance at rear of chassis between collar mounted on motor switch.

5. the large drive pulley mounted on the rear of the brass shaft should be in line with the small pulley which will be found mounted on the motor armature. Alignment can be accomplished by loosing the two set-screws and sliding the large pulley either backward or forward on the shaft.

6. the tension of the drive belt for the motor can be adjusted by loosening the two hexagon bolts found at the rear of the chassis and holding the motor assembly. The motor assembly should be moved in the elongated holes until the drive belt has a snug tension but not too tight an action. Then re-tighten the hexagonal mounting bolts.

7. if the drive mechanism has a tendency to slip when using the large manual knob, check for a loose spring clutch. All adjustments to the clutch should be made very carefully. Adjustments are made by turning the screw mounted through the blue steel clutch spring found at the front of the brass drive shaft mechanism. By running the screw in, the action will be tightened, and by running the screw out, the action will be loosened, but in all cases only one or two complete turns should be necessary.

8. all bearings, dial mechanism and gears of the gang should be lubricated approximately once a year. If at any time it is necessary to change the electric eye tube, care should be taken not to place the tube too far forward as this will cause a strain to be placed on the dial pan (causing friction at the center hub of the gang shaft) and the motor assembly will not operate freely.

Zenith 1938 Home Radios....(General Servicing Notes)

Inoperative below 1200 kc (common in 5 tube A-C models).

1. open oscillator coil primary. Shunt this open primary with a 10,000-ohm resistor.

Inoperative, completely of band (home battery receivers) or over part.

1. if receiver employs a 1A6 or 1C6 pentagrid converter tube, reduce screen voltage (of this tube only) by connecting a 50,000-ohm resistor in series with screen. By-pass this to ground with a .01-mfd condenser.

Distortion at low volume (15 tube models).

1. connect a .0005-mfd condenser in series with a 150,000-ohm resistor and connect this combination from the first anode tube grid to ground.

Noisy tuning on short-wave bands.

1. remove condenser and switch shaft and clean with tuner cleaner. Also clean shaft bearing.

Zenith 1940 Home Radios...(General Servicing Notes)

Push-buttons inoperative.

1. if push-button does not push switch in far enough, bend switch arm so there will be more leverage.

"Noisy" operation of automatic tuning.

1. dress leads to automatic tuning assembly away from metal frame of assembly.

"Noisy" when receiver is jarred.

1. orange colored resistor on loop loading coil "grounding" against chassis.

2. broken or loose leads in 6U5 socket.

3. black wire on S.W. antenna coil not grounded properly to aeroplane terminal.

4. "noisy" Wavemagnet loop antenna due to rubber insulation of loop lead touching trimmer lug, antenna terminal, end of loop winding.

5. "poor" connection to loop shields.

Distortion (in Bakelite encased models).

1. dress leads from tone-control condenser and switch away from 6Q7 tube.

Weak radio reception in phono models.

1. check phono switch and plug contacts .

Weak phono.

1. check phono switch contacts.

Zenith 1941 Home Radios...(General Servicing Notes)

Weak reception

1. the primary winding of the Wavemagnet used on 1941 models is of the high impedance type and the natural period of this winding is within the broadcast band. When an antenna is connected to the primary winding the additional capacity tunes it below broadcast frequencies which is very desirable for energy transfer. However, this requires that the primary winding be short circuited whenever an external antenna is not attached in order to preserve the tuning characteristics of the loop winding. A shorting bar is provided for this purpose, and should always be in place when the receiver is operated on the Wavemagnet alone.

Weak reception on short-wave.

1. "open" r-f choke to 1232 tube plate circuit.

Noisy reception.

1. dial rubbing against escutcheon.

2. stator lugs on braid of gang condenser rubbing against side of opening in chassis.

3. seat all loktal type tubes firmly in their sockets.

Receiver cannot be aligned.

1. check for "open" or rosin connection on primary winding of Wavemagnet.

Overloading, distortion.

1. "open" resistor in first-detector avc circuit.

Low volume on phone.

1. check shield on lead from crystal cartridge for poor "grounding".

Distortion on phono.

1. cracked or broken crystal in pickup.

Zenith "Radiogran"

Noisy when tuning.

1. dirty condenser gang wipers, or plates.

2. flywheel touching band switch lug.

3. volume control or drive shaft not making good contact to ground.

No Control of tone.

1. insulation on 33.000-ohm resistor cut through, "shorting" to cathode lug.

Two much tone control on some buttons, none on others.

1. faulty volume control.

2. terminal of tone switch or volume control "shorted".

3. "poor" volume control contacts, or "shorted" taps.

Tone changes with each different setting of volume control.

1. faulty volume control.

2. terminal of tone switch or volume control shorted.

3. poor volume control contacts, or shorted taps.

Zenith "Zenette" A, B, C, D

Weak reception.

1. check green and red leads of coil in antenna circuit. If either one is grounded at its respective coil contact, remove this ground.

Poor reception.

1. increase in value of bleeder resistor.

2. defective 900-ohm type 45 bias resistor. Replace with a 10 watt unit.

Erratic operation, "squeals".

1. replace 25,000-ohm series plate resistor with same unit in 10 watt size.

2. check all high value resistors in detector plate circuit for 25% change in value, also 1-megohm resistor in first r-f grid-return circuit. If defective, replace.

3. connect a .00025-mfd condenser from detector choke to ground.

4. in radio-phono combinations, keep wire from phono switch as far away from receiver circuits as possible.

Intermittent hum.

1. replace filter condensers.

Zenith CH Series

Intermittent reception (tubes and voltages OK, normal operation restored when oscillator tube is tapped).

1. defective oscillator tube.

Weak reception. Whistling or squealing.

1. defective .5-mfd condenser connected from the ground to the cathode of the second detector tube (even though it may test OK). Replace with new unit.

No control of volume. Excessive regeneration.

1.defective electrolytic condenser located in square can at far end of chassis, which by-passes choke located underneath the chassis.

Loss of volume when volume control is advanced or tuning dial shifted.

1. drop in value of 1/2-megohm plate resistor in AVC tube.

Zenith LH

Weak reception.

1. 6-mfd electrolytic filter condenser open. Replace.

Weak reception. Hum.

1. 6-mfd electrolytic filter shorted. Replace.

Hum.

1. open 8-mfd electrolytic filter condenser. Replace

2. leaky .05-mfd a-f coupling condenser. Replace.

3. open .2-mfd 47 tube grid bias by-pass condenser.

Zenith MH

Intermittent reception due to intermittent oscillator.

1. resolder all coil connections.

2. check oscillator condenser for faults.

3. replace oscillator coil.

Zenith 4-B-106, 4-B-131, 4-B-132 (chassis 5406)

Inoperative on low-frequency end of dial.

1. connect a 10,000-ohm resistor across 15, oscillator tube in order to reduce bias voltage on it.

2. moisture collected on coils. Move oscillator coil and shield about 1/2 inch or more away from chassis.

Inoperative (oscillator not functioning).

1. remove oscillator coil, place 1/8 inch insulating spacing washers over mounting lugs, and reassemble.

Inoperative (pilot light burned out).

1. as pilot light is connected in series with the two type 15 tube filaments, set will not operate if pilot is burned out. Replace with 2.9 volt bayonet type bulb. Must be exact replacement, for proper receiver operation.

Noisy.

1. replace type 15 tube in first r-f stage, even if it checks OK.

Code interference. Hiss when passing through stations while dialing.

1. twist wire leading from 75 tube cathode around the condenser leading from the control grid of same tube. Both leads go to volume control.

Zenith 4-B-231 (chassis 5409)

Vibrator hash (on all but local stations).

1. replace .5-mfd 400-volt paper condenser across input filter condenser C-11.

Zenith 4-B-133 (chassis 5407)

Inoperative (pilot light burned out).

1. see ZENITH 4-B-106 above.

Zenith 4-F-227 (chassis 5408)

Short "B" battery life. Poor tone quality after battery voltage has dropped below 120 volts.

1. by-pass the plate voltage circuit with a 4-8-mfd condenser. Also, convert the circuit to use automatic bias (eliminating the "C" battery. To do this, disconnect negative "B" lead where it connects inside chassis, and connect a 300-ohm 1/4 watt carbon resistor in series to chassis. Run the bias leads from the 1H4G grid and 1K6G grid to the "B" lead (yellow). Disregard green lead, as "C" battery is omitted.

Zenith 4-K-310 (chassis 5412)

Inoperative.

1. leakage between prongs of 1H5G diode socket and chassis. Replace.

Zenith 4-K-401

Whistling or squealing. Motorboating sound.

1. replace 1A7 tube.

2. poor grounding rivet connection on electrolytic condenser. Solder connector to chassis.

Zenith 4-P-26, 4-T-26 (chassis 5401)

Squealing. Signal cuts out when volume control is advanced.

1. open 2-mfd screen by-pass condenser on the 6A7 tube.

Zenith 4-T-26 (chassis 5403)

Whistling or squealing. Hum.

1. check condenser block No. 23-407 for shorts or opens.

Zenith 4-V-31, 4-V-59 (chassis 5405)

Inoperative at low-frequencies.

1. check battery voltage. replace batteries if low.

2. if battery voltage is OK, replace the type 15 oscillator-first-detector tube.

3. check 600-kc padder C-2. Replace.

Intermittent reception.

1. faulty 200 to 550-mmfd low-frequency padding condenser C-2.

Audio oscillation (on 4-V-31 receiver).

1. unsolder blue lead from plate terminal of 38 socket and change it to the speaker socket-raising lead high above all other wiring. Unsolder lead to high side of volume control and re-run it close to chassis.

Zenith 4-Z-31

Inoperative from around 700 kc down.

1. replace type 15 tube.

2. replace also the oscillator coil assembly with type wound on impregnated wood. Oscillator coil in this receiver absorbs considerable amount of moisture in humid localities, making it impossible to make oscillator circuit track properly.

Zenith 5-F-233, 5-F-251 (chassis 5522).

Same Case Histories as listed for Zenith 4-F-227 receiver.

Zenith 5-G-500

Distortion when switched to a-c, or d-c.

1. check 140-ohm micamold resistor (No. 62-1096) and the wire-wound resistor or the 2-section cadohm (No. 62-112-), 1060 ohms on each side.

Zenith 5-G-636

Inoperative.

1. open output transformer.

2. check tube socket contacts for insufficient spring tension. Tighten contacts.

3. check tube base pins and socket contacts for dirt and corrosion. Clean.

Zenith 5-R-303 (chassis 5528)

Inoperative or weak on automatic tuning.

1. open 50-mmfd condenser C-2 (No. 22-289).

Zenith 5-R-312 (chassis 5528)

To increase bass response.

1. shunt a .02-mfd condenser across the .02-mfd audio coupling condenser already in receiver. Also connect a .01-mfd 600-volt condenser across the .002-mfd unit connected between plate and B-plus of power output tube.

Zenith 5-S29, 5-S-56 (chassis 5513)

Weak reception on "C" band.

1. check primary of 16-meter coil (No. 10) for open or poorly soldered joints.

Zenith 5-S-119, 5-S-126, 5-S-150, 5-S-151, 5-S-161, (chassis 5516)

Noisy reception.

1. faulty i-f transformer. Resolder all joints in transformers. If noise still persists, replace faulty units.

Zenith 6-B-107, 6-B-129, 6-B-118 (chassis 5635)

Distortion.

1. decreased capacity of 8-mfd filter condenser in power pack. Replace.

Zenith 6-D-116, 6-D-117, 6-D-118 (chassis 5633)

Inoperative.

1. open .02-mfd tubular condenser connected to one of the end terminals of volume control. Replace condenser and leave enough slack in leads so operation of volume control will not pull on condenser terminal.

Weak Reception.

1. replace i-f stage bias resistor with a 300-ohm unit.

Squealing at low-frequency end of dial.

1. wind about 5 widely-spaced turns of thin double-cotton-covered wire (about No. 28) around grid lead of 6K7G tube. Ground the end nearest the chassis, leaving other end free and insulated from grid clip.

Zenith 6-D-311 (chassis 5646)

Inoperative (all parts check OK and set lights up).

1. check the two 50-ohm resistors connected from switch to ground.

Whistling or squealing when tuning a station or adjusting volume.

1. ground the speaker frame.

Noisy volume control.

1. open filter condenser.

Distortion.

1. open output tube cathode bias resistor. Also see that back chassis bolts are not making contact with a filament prong on output tube.

2. replace 60-ohm and 50-ohm resistors No. 9 and No. 10.

Poor tone. Weak reception (after playing awhile).

1. check 25L6 output tube.

Hum.

1. shorted speaker field winding - usually the two leads going into the winding are shorted together where they join the winding.

Zenith 6-D-312 (chassis 5647)

Inoperative (all parts check out OK and set lights up.

1. check the two 50-ohm resistors connected from the switch to ground.

Inoperative (ballast tube blown).

1. faulty 40-mfd condenser C-9 connected to 25Z6 tube cathode. Replace this. Replace ballast tube.

Weak reception. Poor tone (after playing awhile).

1. faulty 25L6 output tube.

Distortion (tubes all light).

1. replace 60-ohm and 50-ohm resistors No. 9 and 10.

To increase bass response.

1. shunt a .01-mfd condenser across the .002-mfd unit already in the circuit. Also shunt a .02-mfd condenser across the .02-mfd unit already connected from plate to ground.

Zenith 6-D-410 (chassis 5659)

Excessive regeneration.

1. dress 12A8G grid lead away from oscillator section of gang condenser.

Zenith 6-G-500

Inoperative.

1. open .01-mfd coupling condenser connected from 1LH4 plate to 1LB4 grid.

Zenith 6-J-230 (chassis 5642)

Distortion.

1. check to see if one pilot light is out. Replace.

Zenith 6-R-481 (chassis 5675)

Hum.

1. ground the common negative circuit to chassis.

2. open the connection between the Wavemagnet shield and external ground lead, and insert a .01-mfd condenser in it.

Zenith 6-S-27, 6-S-52 (chassis 5619)

Tuning dial slips.

1. worn belt drive. to replace, remove entire dial assembly, making sure to remove back washer on the shaft.

Zenith 6-S-128, 6-S-137, 6-S-147, 6-S-152, 6-S-157, (chassis 5634)

Inoperative.

1. open voltage divider section between screen tap and B plus end of voltage divider. Replace with 10,000-ohm 10 watt unit.

Intermittent reception.

1. try new tubes.

2. poor contact in voltage divider. Try pulling firmly upon the lugs, and working lugs back and forth.

3. do same with audio coupling condenser. Check it for open.

4. poor internal contact in volume control. Weak reception. No S.W. reception.

1. open 1,100-ohm screen-grid section of voltage divider.

Weak on broadcast band.

1. check for open in short-wave antenna coil winding (is in series with broadcast winding).

Volume control ineffective at minimum end.

1. faulty 2-megohm volume control. Replace.

Squealing at high volume.

1. loss of capacity in filter condensers. Replace.

Zenith 6-S-203, 6-S-222, 6-S-229, 6-S-239, 6-S-241 (chassis 5638)

I-F oscillations.

1. antenna circuit i-f trap is directly under 2nd i-f transformer. Solder flat piece of metal in place to shield trap from the hole under this transformer.

Zenith 6-S-527 (chassis 6A02)

Noisy reception.

1. see if right hand pilot light wiring is being pinched by automatic bracket.

2. loose or poor contacts on pilot lights.

3. poor contact on manual push-button.

Whistling or squealing on short-wave.

1. dress black lead of automatic away from automatic adjustments. Dress white and green leads of automatic away from 7L7-7H7 socket.

Zenith 6-S-580 (chassis 6A20)

Troubles in automatic record changer.

1. loose lever on tone-arm vertical shaft.

2. binding in bearing of tone-arm vertical shaft.

Zenith 7-S-28

Whistling or squealing.

1. disconnect 6K7 first audio tube from common-bias system. Insert a 3,500-ohm 1/2 watt resistor by-passed with a .25-mfd condenser in cathode circuit. Connect grid-return to chassis.

Distortion.

1. realign i-f circuits carefully.

Zenith 7-S-204

Inoperative on broadcast band (OK on short-waves)

1. shorted 10-mmfd condenser C-21 in antenna transformer.

Weak, noisy reception. Tuning eye inoperative.

1. replace 1-megohm resistor connected between plate and target of 6T5 tuning eye socket.

2. leaky 25-mmfd coupling condenser connected between antenna coil and pre-selector coil. This is white unit (looks like a resistor) mounted inside of pre-selector coil. Replace with mica condenser.

Zenith 7-S-242, 7-S-258, 7-S-260, 7-S-261 (chassis 5709)

Inoperative on broadcast band (OK on short-waves)

1. shorted 10-mmfd condenser (C-21 in antenna transformer.

Zenith 7-S-323 (chassis 5714)

Inoperative or noisy on automatic tuning.

1. dirty contacts.

2. warped contact strip shorting to ground.

3. shorted compensating condenser.

4. open compensating coil No. 3 (No. 20-196).

Whistling. Noisy between stations.

1. open filter condenser.

2. open condenser or (loose condenser) across r-f choke.

3. leaky .002-mfd 600 volt condenser connected across speaker leads.

Zenith 7-S-432 (chassis 5719)

Weak reception (voltages below normal).

1. decrease in capacity of 30-mfd 250 volt electrolytic condenser C-19. Replace.

Zenith 7-S-432 (chassis 5724)

Signal cuts out on "local-distance" switch.

1. try new 6A8 tube.

Signal cuts at high-frequency end of dial.

1. loosen setting of 5 mc. trimmer slightly.

Weak audio.

1. open coupling condenser.

2. poor contact in television switch.

Whistling or squealing.

1. open screen by-pass condenser.

2. wave trap open or not properly adjusted.

3. dress 6K7 grid lead away from avc lug and 6A8 plate lead.

Noisy tuning on automatic.

1. poor contact in speaker socket.

2. washer on latch bar of push-button assembly grounding to lug.

3. automatic trimmer shorting.

4. poor contact on band switch.

No change on treble button.

1. insulation on blue tone control lead being cut by fastening lug.

To improve operation of bass Radiorgan button.

1. connect a 1-megohm resistor from high side of volume control to tap on same.

Zenith 7-S-487 (chassis 5725)

Same Case Histories as those listed for Zenith 7-S-432 (chassis 5724) receiver.

Zenith 7-S-529 (chassis 7A02)

Inoperative.

1. 480-mmfd condenser on automatic grounded against automatic frame or latch bar.

Whistling or squealing.

1. dress leads of wave trap close to chassis, keeping them away from antenna coil.

Zenith 7-S-581 (chassis 7A04)

Same Case Histories as those listed for Zenith 7-S-529 receiver.

Zenith 8-S-129, 8-S-154 (chassis 5801)

Inoperative.

1. open screen-voltage resistor section in voltage divider.

Inoperative around 6 mc on B band.

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

Fading. Weak reception (accompanied by little action on target tuning indicator).

1. try a new 6C5G tube. If target tuner now fails to work, reverse the connections to the meter.

2. resolder all connections on antenna coil.

3. check 700-ohm resistor in cathode circuit of 6C5G tube.

4. try connecting a 1,000-ohm resistor in cathode circuit of 6C5G tube.

5. shorted .05-mfd by-pass condenser on r-f input side of 6C5 shadowmeter grid.

Zenith 8-S-539 (chassis 5807)

Hum.

1. faulty 6U5/6G5 tuning eye tube.

2. faulty filter condenser.

Zenith 8-S-432 (chassis 5810)

Weak reception (voltages below normal).

1. decrease in capacity of 30-mfd 250-volt electrolytic condenser C-19.

Intermittent whistling or howling.

1. loose i-f tube shield imperfectly grounded.

Zenith 8-S-443 (chassis 5808)

Blocking of signal.

1. open resistor in avc circuit of first detector.

Tuning indicator inoperative.

1. loose lead in tuning indicator socket.

2. resistor inside tuning indicator socket shorting to socket prong.

3. cathode lug on voltage divider grounded by solder.

Automatic inoperative.

1. open winding on compensating coil.

Noisy tuning.

1. dial pulley rubbing against dial or chassis.

2. ground braid of gang rubbing against flywheel.

3. burrs on drive shaft shorting to volume control shaft.

Whistling or squealing around 500 kc.

1. adjust wave trap.

2. reduce resistance in plate circuit of 1232 tube.

Zenith 9-S-30, 9-S-54, 9-S-55 (chassis 5903)

Hum.

1. change both 6F6 power tubes.

2. check all condensers. Replace leaky or otherwise faulty units.

Zenith 9-S-262 (chassis 5905)

Inoperative (no plate voltage on 6L7G first detector and 6K7G if tube).

1. shorted .05-mfd condenser C-8.

Whistles when volume control is advanced.

1. replace 12-mfd electrolytic condenser connected across high-voltage divider tap.

Dial slips.

1. if belt is OK, tighten clutch spring screw on flywheel shaft underneath front chassis.

Zenith 9-S-357 (chassis 5907)

Distortion (similar to AVC blocking).

1. open filter condenser section.

Zenith 9-S-365 (chassis 5906)

Weak reception. Squealing.

1. open 8-mfd condenser C-21 in block No. 22-571.

Fading.

1. shorted i-f stage trimmer condenser.

Howling.

1. faulty .05-mfd condenser in AVC circuit. Replace with 400-volt unit.