15-05-2015, 09:19 AM
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/showthread.php?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-for-3-95/250826082199?_trksid=p2054897.c100204.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.
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/showthread.php?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-for-3-95/250826082199?_trksid=p2054897.c100204.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.
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
