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Old 8th Jul 2021, 2:07 pm   #1
DMcMahon
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Default Ferguson 3T20 Radio Cassette Player Radio Not Working

Brought this through the Forum and it arrived yesterday.

1980's so modern vintage.

As described it is overall in good condition with the battery contacts needing a bit of a clean up.

Playing a tape to my ears sounds quite reasonable, the seller said it sounds a bit warbly, I will clean the heads and check the drive belt etc later. Plenty of volume, the volume control is very crackly when turned so will give it a spray of contact cleaner, the balance and tone controls are slightly noisy when turned.

Tape aspects will be covered more in this Thread:-

https://www.vintage-radio.net/forum/...d.php?t=181743

The radio is completely dead (as the seller stated) on all 4 wave bands, no sound at all even with the volume control at max.

I do not have any AM/FM signal generators so will not be able to do any signal injections/alignment tests. Probably been at least 40 years since I did any active radio fault finding so may be a good challenge ahead.

The fact that all 4 wavebands are dead to me indicates a common area at fault, so need to study the schematic.

David
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Old 8th Jul 2021, 3:08 pm   #2
paulsherwin
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

As always, the first thing to do is to thoroughly clean all the switch contacts. If that doesn't help, measure some voltages.

Any realignment is some way down the road!
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Old 8th Jul 2021, 3:19 pm   #3
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Thank you Paul, Yes I am planning to do just that when time permits.

Even though I mentioned alignment I only would use appropriate sig generator (if I did have one) in the first instance for signal injection/signal tracing.

There is a two position switch which switches the radio on, the other position the cassette tape becomes live (reliably), I am wondering if the radio off position could be bad.

David
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Old 8th Jul 2021, 10:38 pm   #4
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Photos that I was unable to upload previously.

David
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Old 9th Jul 2021, 10:51 pm   #5
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Opened up and did various general cleaning, surprising how much greasy fluff/dust there was in some areas.

Using contact cleaner cleaned the best I could the Play/Record (S2) and the waveband selection (S1) slide switches, they are encased within metal covers so not easy to get contact cleaner inside them.

Unable to clean the rest of the switches and the rotary pots, looks like will have to strip out the large board to get access. No voltage checks done yet.

Tape is still playing well with radio still dead.
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Old 10th Jul 2021, 4:32 pm   #6
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Struggling somewhat at the moment removing the main board. The Service manual shows the board being rotated 90 degrees into a Service position. At the moment cannot get enough movement on the board to be able to rotate it upwards due to very tight wiring connections.

While removing the 5 securing screws for the board found that one is missing, maybe this indicates it has been looked at before ?

To get the board to move upwards had to disconnect the securing screw for the Drive Cord Drum (tuning) with result that have lost tension on the drive cord, may have fun getting the cord back correctly later.

If I cannot get enough movement on the board to be able to rotate it into the Service position, I will see if can get sufficient access to the remaining switches and potentiometers for cleaning.

David
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Old 12th Jul 2021, 9:56 am   #7
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Gave up trying to get the board into the Service position, to me looked impossible without unsoldering some of the short cables that appeared to be stopping the board from moving sufficiently. Presumably the Service position is supposed to be a position where the you can do live service checks ?

With the board partially lifted up, was able (could have done with longer nozzle) to get contact cleaner spray nozzle into the Volume, Balance and Tone rotary control potentiometers. After cleaning al the crackling when pots turned is now fixed. The volume control had been particularly bad, not just bad crackling but also loss of volume on one or both channels.

Cleaned the remaining switches, the only switch that would potentially affect the radio is the Radio/Tape selection switch. But still no sound when radio is selected.

Trying to get board into the Service position has resulted in the tuning cord coming unraveled, I will not try to relace it until can get the radio working.

David
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Old 12th Jul 2021, 11:28 am   #8
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

I don't have the schematic for this model, but I bet given its age that the radio is based around an IC which will have failed. Many sets of this era used an initial discreet front end, followed by an AM/FM IC.
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Old 12th Jul 2021, 1:52 pm   #9
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Yes the RF front end is an AN7213 (ICI), this feeds AM/FM IF stage a LA1201C (IC301) which feeds an FM Stereo Decoder/Multiplexor a BA1320 (IC302) and from there to two audio amps AN7115F (IC401/2).

I am extremely rusty with Radio circuits so have not yet got to grips with the radio side.

David
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Old 12th Jul 2021, 1:59 pm   #10
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

There are also some transistor stages for the non FM.

David
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Old 12th Jul 2021, 2:15 pm   #11
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

The LA1201 would be my primary suspect. The AN7213 is only for the FM front end, so if the set is dead on all bands then the combined receiver IC would be the most likely cause.

I recently had this very IC faulty in a cheap 3 band portable from the 80's; result, virtually dead radio, just a light hiss from the audio amp. Replaced the IC and the set came back to normal life.
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Old 12th Jul 2021, 6:02 pm   #12
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Thank you, I was coming to same conclusion, as that is the common point for AM & FM, once I have checked out the basic voltages hopefully can trace the root cause.

David
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Old 12th Jul 2021, 6:20 pm   #13
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Another vote for the LA1201. I've had a number of run-ins with that chip, often it goes intermittent before pegging out completely. The old SX200n scanner used one in its IF and it did its party trick in a few I had in for repair.
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Old 14th Jul 2021, 4:28 pm   #14
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

After partially re-assembling, unsuccessfully tried to measure the DC supply (+VCC) voltages to the radio ICs. Got zero volts measuring wrt the ground pin on the IC's and also measuring wrt the ground connection at the power supply board. Got good continuity of the IC ground pins back to the power supply ground.

So this would explain why no sound when switched to radio, however confusingly also measured zero volts at the +VCC pins of the 2 audio amps. The zero volts at the audio amps must be a measurement error/doing something silly because the amps are working when playing a tape.

Measured around +13V at the power supply output, according to the schematic this connects out to switch (S8) on the mains input connector (the one that opens to disconnect the batteries when mains lead plugged in) and same connection then goes out to the Radio/Tape selection switch (S3A). It looks like in tape mode the voltage has to be switched through closed switch contact S9, as of yet have not worked out what S9 is/where it is. Tried to follow the cabling to locate S9 but because the main board covers S8 cannot see the cable connections.

From S3A the 13V is connected to a transistor (TR701) regulator circuit, the 13V then being connecting out to the audio amp IC's +VCC pins.

Switch S3A is mounted on a small board that is mounted/soldered at right angles to the main board and is impossible to access its contacts for measuring.

The TR701 regulator circuit should output +6.7V which then goes via a few components and switch contacts to the radio IC +VCC pins.

So I suspect that there may a fault with the regulator circuit or something is dragging the +6.7V supply down to zero. I think the apparent zero voltage to the audio amps must be a large red herring, needs more checking.

David
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Old 14th Jul 2021, 6:06 pm   #15
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Relevant schematic section for reference.

David
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Old 14th Jul 2021, 7:31 pm   #16
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Oh my god so that guy who runs the code machine does actually scan his own schematics to sell them. I thought he only sold other peoples work he lifted of other websites.
He does not spend too much time presenting his work does he.
Mike
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Old 14th Jul 2021, 8:38 pm   #17
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

So, if you are getting zero volts at the emitter of TR701, are you getting the expected 13V at the collector? If not, then R707 the 10R safety resistor has probably expired. If you do have voltage, then check D705, C708 and of course TR701 itself.

From experience, I doubt that anything is dragging the supply rail down, but obviously anything is possible!
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Old 14th Jul 2021, 10:28 pm   #18
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

Thank you, finding it hard at the moment to see/locate these components, once found will check them out.

David
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Old 15th Jul 2021, 1:31 am   #19
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Default Re: Ferguson 3T20 Radio Cassette Player Radio Not Working

After locating relevant components measured around 11V at TR701 collector, so R707 is good (it also measured 10 Ohms). Power supply voltage now also is around 11V.

7.5V Zener diode D705 good at 7.73V but zero at TR701 base and emitter. While probing around trying to measure connections/associated components suddenly got good voltages at the base and emitter, looks like there might be some sort of bad connection in this area (probably on the solder side which I can not see).

Now get good +VCC supply voltages at the radio IC's but still no sound at all when switched to radio (tape is still working). For the LA1201 all 11 pins shown on the schematic with a DC voltage value, all read pretty close. Because of the fact that the LA1201 is common for AM and FM and the fact that it gets bad press, will probably order a new one but first will do some more monitoring in case there is another explanation.

David
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