Radio repair check list

CONVERTER STAGE

Condition of this stage can be checked by feeding modulated signals from signal generator between point (x) and chassis. Since it is here that r-f is Converted to i-f, it should be checked first to determine that' it is passing i-f satisfactorily by feeding an i-f signal as covered under i-f, amplifier. If O.K: on i-f thee feed r-f signal, tune. receiver to signal being supplied by the generator.
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A. Symptom
B. Check
C. Probable Trouble
D. Remedy

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A. No R-F Signal
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B. 1. It is usually possible to rub the metal part of a screwdriver on the oscillator stator
connection of the gang condenser and determine by the resultant noise from the loud speaker if the oscillator circuit is working or not. Very little noise is heard if it is not working. No body contact to the metal part of the screwdriver should be made. In most cases, depending on
the circuit, a negative voltage can be read on the voltmeter across the oscillator grid leak resistor of from about two to fifteen on the broadcast band when the circuit is functioning. None or positive voltage indicates trouble.

C. a. Dirty or open contacts on band switch.
D. a. Clean contacts

C. a. Shorted gang condenser.(Check with ohmmeter. Should be infinite resistance.)
D. b. Clear short in gang
condenser.

B. 2. High or infinite resistance reading on ohmmeter across oscillator coil (primary and secondary if separate).
C. Open oscillator coil.
D. Change oscillator coil.
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A. Dial calibration off.
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B. All calibration is result of oscillator circuit.
C. Dial mechanism mechanically out of line.
D. Realign per service notes.
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R. F. AMPLIFIER STAGE

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Condition of this stage can be checked by feeding an r-f modulated signal from generator to antenna and ground posts.
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A. Symptom
B. Check
C. Probable Trouble
D. Remedy
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A. Dead
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B. *No ''B '' plus voltage reading on voltmeter at screen grid of tube.
C. Shorted screen by-pass condenser.
D. Change condenser
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B. 2. a. Signal from generator O.K. when fed between grid of tube and chassis, weak from
antenna and ground.
C. Open or dirty contacts in wave switch or wiring thereto.
D. Clean or repair
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B. b. same as "a"
C. Open loop antenna circuit (check or correct reading on ohmmeter)
D. Resolder open connection.


Note: * Circuits in this stage may be totally inoperative and yet strong signals may be still reproduced due to leakage of signal into wiring, etc., to the converter tube.

End.
I hope you can put this to good use.

l-F AMPLIFIER STAGE
Condition of this stage can be checked by feeding modulated i-f signal from signal generator between grid (x) of converter tube and chassis.


A. Symptom
B. Check
C. Probable Trouble
D. Remedy


A. Dead
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B. l. No ''B '' plus voltage reading at plate of converter tube on voltmeter.
C. Open primary on i-f transformer. (Check with ohmmeter across winding for correct reading.)
D. Change i-f transformer, or regen connections.


B. 2. No ''B '' plus voltage reading at screen grid of converter tube.
C. Shorted screen grid by-pass condenser (if any). (Check with ohmmeter across condenser with one lead disconnected. Reading should be infinite.)
D. Change by-pass condenser.

A. Weak
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B. 3. Check alignment per service notes, using output meter or similar device.
D. Realign

DIODE DETECTOR STAGE AND A.V.C
This stage can be checked by feeding modulated i-f signal from signal generator between grid of i-f amplifier tube (x) and chassis. Since i-f signal and audio signal are separated here, alignment of tuned circuits is first encountered. Refer to service notes for alignment procedure.
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A. Symptom
B. Check
C. Probable Trouble
D. Remedy


A. Dead
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B. 1. No ''B '' plus voltage reading at plate of i-f tube on voltmeter.
C. Open primary i-f transformer.(Check across winding connections with ohmmeter for correct reading.)
D. Change i-f transformer, or repair connections.

b. same as "a"
C. Shorted- plate filter condenser. (Check on ohmmeter with one lead disconnected-- should read infinite.)
D. Change condenser


A. Distortion
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B. 2. Low resistance reading on ohmmeter from a-v-c connection to chassis.
C. Shorted a-v-c by-pass condenser.
D. Change condenser.


A. Oscillation
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B. 3. Oscillation stops when like condenser is substituted across a-v-c by-pass condenser.
C. Open a-v-c by-pass condenser
D. Change condenser

A= Symptom
B= Check
C= Probable Trouble
D= Remedy


FIRST AUDIO AMPLIFIER STAGE
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The condition of this stage can be checked by feeding a signal from a signal generator between point (x) connection and chassis

A. Dead
B. l. No ''B '' plus voltage reading on voltmeter at plate connection of tube.
C. Shorted plate by-pass condenser.(Check with ohmmeter across condenser with one lead disconnected Should read infinite.)
D. Change condenser.

B. 2. Normal output by feeding signal from generator on grid oftube but not on other side of
coupling condenser.
C. Open coupling condenser.(Check by substituting like condenser across.)
D. Change condenser


A. Noisy Volume Control When Turned
C. Worn control. (With no signal, no voltage. should be read across control. )
D. Change volume "control.

Power Output Stage
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Dead

POWER OUTPUT AMPLIFIER STAGE
An audio signal from a signal generator applied between point (x) of the output stage and ground will indicating the condition of this section. Some service men derive their own short cuts, such as checking the preceding tube in and out of the socket to supply a ''click '' signal to the output tube to determine if the stage is alive or dead
For accuracy. a signal generator is preferred.


A= Symptom                                        
B= Check
C= Probable Trouble                                                
D= Remedy

A.  Dead
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B.  1. No ''B '' plus voltage reading on voltmeter at tube plate connection
C.  Open output transformer.(Check resistance across primary and secondary with ohmmeter.)
D.  Change transformer

B.  2. No or low ''B '' plus voltage at tube plate on voltmeter.
C.  Shorted plate by-pass condenser. (Check resistance. across condenser,with one lead disconnected on ohmmeter---should be infinite.)
D.  Change condenser

B.  3.  Any ''B '' plus voltage on volt meter at tube grid connection.
C.  Shorted coupling condenser.( Check on ohmmeter as in (2).)
D.  Change condenser

B.  4.  Stage alive with signal applied on tube grid but dead on other side of coupling condenser.
C.  Open coupling condenser.(Check by substituting like condenser across.)
D.  Change condenser.

A.  Distortion
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B.  5. Distortion clears when like plate by-pass condenser is substituted across plate condenser.
C.  Open plate by-pass condenser.
D.  Change condenser.

B.  6. Variations of 1,2,3,4.
C.  1,2,3,4.
D.  Change indicated defective part.

B.  7. Refer to power supply and speaker

B.  No ''B '' plus voltage reading on plate of one push-pull output tube connection.
C.  Open winding on output transformer.(Check with ohmmeter.)
D.  Change output transformer

TROUBLE ANALYZING AND CORRECTIONS
By stages.

Loudspeaker stage
Note:  Field coil is taken as part of the power supply, since usually its part of the filter. This may be accepted in AC/DC models. If the radio remains silent when rectifier tube and output tube are in place then check speaker.
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PM Loudspeaker dead.
Symptom check -- 1. a. High or infinite resistance reading on ohmmeter across voice coil connections (disconnect voice coil from output transformer.)

Probable trouble -- open voice coil or open to voice coil (also check plug connections.)
Remedy--             change speaker cone or connections.
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Symptom check -- 1. b. low or low resistance across voice coil.
Probable trouble -- shorted voice coil leads or or wiring thereto (also check plug connections.)
Remedy--              remove short circuit.
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2 Distortion, Rattle, or Buzz

Symptom check --  By ear. Variable audio oscillator, if available, fed to the audio amplifier facilitates isolating the trouble.
Probable trouble -- a. Dirt in air gap around voice coil.  
Remedy --            a. Blow out with air stream.

Probable trouble -- b. Loose or excess cement around edge of cone or spider.
Remedy --            b. Clean off excess cement.  May be necessary to replace cone due to inaccessibility.

Probable trouble -- c. Loose metal parts and mounting hardware
Remedy --            c. Tighten loose parts

General:             When in doubt substitute duplicate or like rated speaker


Electro-dynamic speaker- All of the above plus the following if the speaker has a hum-bucking coil.

3 Hum

Symptom check- No change in hum by externally shorting hum-bucking coil.
Probable trouble- a. Shorted hum-bucking coil or leads thereto. (Check on ohmmeter for correct resistance reading)
Remedy- Change speaker or clear short.
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POWER SUPPLY STAGE

TROUBLE ANALYZING AND CORRECTIONS


Dead

1. Symptom Check -- No "B" plus voltage across one section of filter condenser.
Probable Trouble --    a. Open field coil or filter resistor or connections thereto
Remedy --                a.  Change resistor, speaker, or repair connection.
Probable Trouble --    b. Shorted electrolytic condenser (check with ohmmeter).
Remedy --                b.  Change filter condenser
 
2. Symptom Check -- No "B" plus voltage at filament or cathode of rectifier tube.
Probable Trouble --    b. Shorted electrolytic condenser (check with ohmmeter).
Remedy --                b.  Change filter condenser

Probable Trouble --    b. Open power transformer. (Check with ohmmeter or a-c volt­meter.)
Remedy --                b. Change Power transformer.

3. Symptom Check -- No a-c to the pilot lights, tube filaments or rectifier plates.
Probable Trouble --    Open AC power switch (Check with ohmmeter, power disconnected from power)
remedy --                 Change a-c switch.

4. Symptom check -- Rectifier tube plates get red hot.
Probable Trouble --    Shorted electrolytic (Check wiring, etc., thereto.)
Remedy --                Change electrolytic condenser.

Hum



5.  Symptom Check -- Hum stops when like electro­lytic is substituted across filter condenser.
Probable Trouble  -- Open electrolytic condenser.
Remedy --            Change electrolytic condenser.

6. Symptom Check --  A-c voltage reading on a-c voltmeter not equal within about 10% as measured from B minus or chassis to each plate connection on rectifier tube.
Probable Trouble --   Shorted or partially open section of power transformer. (Check with ohmmeter.)
Remedy --            Change transformer.



7. Symptom Check -- Low reading across filter resistor on ohmmeter.
Probable Trouble -- Resistor changed value from over heating due to other troubles such as shorted tube.
Remedy --           Change filter resistor.


General

8. Symptom Check -- Power transformer excessively hot or smoking.
Probable Trouble -- Shorted turns in Power transformer
Remedy --           Change transformer.
'

9. Symptom Check -- Hot or excessively warm electrolytic condenser.
Probable Trouble -- Partially shorted electrolytic condenser.
Remedy --           Change condenser.



Note:
Since the power supply feeds all other voltage circuits and tube filaments, pilot lights etc., any shorts or partial shorts in these sections will be reflected back to the power supply. Sometimes it may be necessary to disconnect leads feeding other parts to isolate.

I thought this would help some to stay organised including myself.
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Plan for radio repairs
1. Obtain a schematic or diagram to use for finding parts, and locations.

2. Get a note pad and record findings of defects and operational problems as this will help to trouble shoot and keep track of previous repairs.

3. Replace power cord and make sure you use one with a polarized plug and wire it correctly
.
4. Install a power-line Fuse on the hot side, as almost all antique radios don't have one! if something shorts it could damage the power transformer, or other components before you even start to turn on the radio for the first time.

5. Clean the chassis, as you work there will be less of a chance of infection from scraped knuckles and hands.

6. Inspect and replace defective and/or bad wiring,and look for bad soldering joints and connections, if possible used color matched wiring.

7. Checked All tubes and replace Bad or questionable ones and clean and repair all tube sockets and their pins.

8. Check and clean all controls, switches, moving parts and contacts they need to be deoxidized, and lubricated.

9. Check and test windings as needed for burned power transformers They will have stinky or tar or oily smell if overheated .

10. Replace all capacitors with metal film capacitors that use higher than original voltage ratings. (The old capacitors are usually leaky or intermittent and will be a cause of hum. New capacitors usually are connected to a new (small) terminal strip under the old disconnected filter capacitor, the old one(s) are left on the top of the chassis to keep the original and Authentic look.

11. Resistors are checked and if out of tolerance replaced a with higher wattage.

12. Pilot lights are replaced with correct voltage and current rating. Some rectifiers need them for filament balancing. Speakers will be replaced and if not replaced then reconed if needed and replace speaker grille cloth.

13. Radio is aligned using an accurate signal generator to the best signal sensitivity and selectivity .

14. Dial stringing is accomplished and calibrated, and dial glass is cleaned, be careful as lettering might not be water or cleaner or solvent proof

15. Voltages are checked and brought to correct levels according to service literature.

16. Cabinet is cleaned, and polished or refinished.

17. Bench test (for 24 hours just to make sure set operates and there are no problems.)

Notes:
All new parts are installed and hidden, so old parts are kept in place above the chassis in order to keep the appearance original.