Bush TR 82C repair advice wanted

[ducatiguzzi]

Hi There

I have a radio here that was bought new by my parents but hasnt been working for around 25 years, it suddenly stopped working one day, new battery tried but still nothing. It has been living in the shed for all that time but I would like to give it back to my mother (87 years) as her kitchen radio is playing up.

It is a TR82C, serial number 528/04755.

I am a beginner at radio but have some electronic knowledge, I repaired a Ferranti valve set a load of years ago replacing caps, rectifier valve and one of the amplifiers so have a little experience; that was my grans bought new in 1952, drifts a bit but still working in my garage, nostalgic.

I understand that the Bush shouldn't have AF117's fitted but this has 3 off, TR 1,2 &3 and one OC71 (TR4) that I can see with the chassis still in the case.

On the test equipment front I only have a decent digital multimeter

Any advice will be greatly appreciated. I would love to give it back to my mum working.

Many Thanks

[boater sam]

You suspect the AF1**, possibly correct.
BUT rather than go off half cocked let' s see what does work first. A bit of help for you.

If the audio stages work, with a good battery, you should get some sound when you switch it on. A finger on the center tag of the volume control should cause a mains type buss.

Assuming that so far we are OK, and a good look around shows no wires snapped, and the audio works, give each AF1** a good rap with an insulated "stick"
and see were you are up to.

Like all good detective stories, another installment will follow........

[Refugee]

That is a MK2 chassis and should have 3 AF117s.
I usually use two NiMh cells with the positive connected to the chassis and probe the three electrodes but do not touch the screen terminal as this will short circuit the battery.
This usually clears the problem without removing the transistors. The other problem that can trouble these sets is the detector diode hidden inside a transformer going open circuit. Fortunately the new one can usually be added leaving the old one in place as it usually fails open circuit or to no connection.

[ducatiguzzi]

Hi Again

Is that two 1.5V NiMh in series or parallel?

I see a diode in the IF3 case, is this it?

If I need to replace the caps, transistors and diode, can you recommend a supplier for these early components?

Thanks again

[Refugee]

Series is the way to go. More than two and you start getting too close to the maximum voltage listed in the data sheet for the AF117s.
IFT-3 is the place and the pins go through to the other side of the chassis so that is where you add the new one. Almost any germanium diode will do as a replacement as it is an AM set and is not fussy about the part number. You will need to add a soldering iron to your tool kit if you have not already got one.
.

[Old Sparky]

Germanium 'point contact' diodes such as the AA119, which can be used to replace failed detector and AGC diodes in many, if not most, transistor radios, are available from most suppliers such as CPC, RS, Maplin, etc., though I haven't checked availability lately. As to AF117s, personally I replace them, until recently with AF127s, though these are now somewhat expensive. There is a Russian Transistor, type GN322, available from several eBay sellers, which can also replace AF11x transistors. Both the AF127 & GN322 are in TO-72 packages with shorter leads than the AF11x types. The pin-outs differ between the AF12x series & the GN322, the latter having the same pin-outs as the AF139, so care must be exercised when fitting them. With regard to the AA119, and other diodes, they must be fitted with the correct polarity. This can easily be checked with the 'Diode test' function on a DMM, or on a low ohms range of an analogue multimeter.

[ducatiguzzi]

Hi All

Fitted new battery and got a constant hiss at all volumes, tones, LW and MW. I tried touching the volume control centre tab but no 'mains buzz' just the constant hiss. I tried giving the AF117's a tap but still the same. I've not tried zapping the transistors yet, should I continue with this or is it obviously elsewhere?

Many thanks

[Refugee]

Try the the center tap of the volume control with it turned half way up.
If that is no good it will most likely be the electrolytic capacitors.
I am pretty sure the worst ones are on the other side of the chassis.

[ducatiguzzi]

I tried the tap tap today again starting at TR1 and it burst into life, albeit hissy. I can receive MW and LW stations with volume control and tone control.

Off station the hiss is quite loud and diminishes when on some stronger stations but always there.

Something I discovered today to my detriment is that WD40 contact cleaner melts the plastic, I still has the volume, tone and band knobs still on when I gave the chassis a good dowsing so they're looking pretty shabby now, bugger!

Anyway, progress has been made just need to sort the hiss, any ideas?

Thanks for the advice so far.

[Yorkie]

It goes without saying that on any set, you need to maker’s data sheet, which for the TR82C is comprehensive and runs to 7 pages. You can refer to the sheet when checking voltages at various points to see if they’re close to the circuit, and if not, look into why that is.

Really, you need to ascertain which part of the set the fault lies in and you can only do that by proper diagnosis – not relying on subjective speculation and folklore about AFxxx transistors, which are often assumed to be at fault but in fact may not be.

As others have said, you can check that the audio stage is working, if only after a fashion, by scratching the centre tag of the volume control, which should cause a loud scratching sound in the speaker with the volume control turned up. If you do hear that, then you can work your way to the front end of the set.

The quickest and simplest way to narrow down in which part of the set the fault lies (in any set)  is by using a simple signal injector/tracer-  a little amplifier and a tone generator. There are lots of circuits around for these, but there’s an excellent little Velleman kit ‘K7000’ which can be made in less than an hour and only needs a small speaker switch, battery lead etc to finish it. See post 38 at this link for more info:

http://golbornevintageradio.co.uk/forum/...p?tid=3881&page=4&highlight=Bush+TR82C

Basically, if you apply the injector to the volume control, if the audio stage is working, you get a loud tone from the speaker. If you then apply the tracer probe to the centre tag of the volume control and when you turn the tuning dial you can hear stations, that means that the frequency changer, oscillator, IF stages and detector are all working. If you  hear stations on one band, but not on the other waveband, the fault lies in the front end – switchery, coils, etc.

If on a Bush TR82C you hear no station with the tracer at the volume control, but you do at the collector of the third transistor (called ‘’VTR3’ in the Bush data), that points to the OA90 detector diode being suspect. As has been said, it’s inside the IFT3 can but there’s no need to disturb it. It can stay entombed in its little grave, and you can fit a new OA90 diode across pins 5 & 6 of the IFT with the stripe to pin 5.  OA90 germaniu diodes are cheap and plentiful on ebay. EG:

http://www.ebay.co.uk/itm/OA91-diodes-4-...0204.m3164&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140407115239%26meid%3D74c722843f8542b2b92352b07418433e%26pid%3D100204%26rk%3D1%26rkt%3D30%26sd%3D290569849739

If you don’t hear any signals at the collector of TR3, you can work your way to the front end of the set, applying the tracer probe to the collector of the other transistors to see if you hear signals. If you hear nothing at the collector of TR3, but do at the collector of TR2, that points to TR3 being possibly faulty. I say ‘possibly’ because there are other components that can cause faults.

Without a transistor tester (which many modern  mulitimeters have built in), where AFxxx transistors are concerned, one tip is to snip the screen lead – on in the case of the TR82C, just unsolder it – and see if that brings the set to life. I have to say that I've worked on several MK2 TR82Cs over many years, and am still waiting to find one with a duff AFxxx. Maybe I've just been lucky, but mostly, it's been the diode or other faults.

Hope that helps a bit.

Good luck with it.