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Old 9th Jan 2017, 9:23 pm   #1
shadoman
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Default Possible faulty AF127?

Hi
I am in the process of repairing a Roberts RT8 which was not working when i bought it.I replaced both transistors in the I F unit with AF 127s after which the radio worked. But the radio packed up again.After checking the circuit again i removed both transistors and checked them on the diode function on my dmm the base to emitter on one of them is .149 and base to collector is .247 which indicates to me it is faulty.The other one reads b to e .306 and b to c .248. I would like someone to confirm my findings before replacing it.
Thanks Terry
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Old 10th Jan 2017, 7:18 pm   #2
Radiocruncher
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Default Re: Possible faulty AF127?

Hi Terry

Firstly it's nice to see I'm not alone up here in North Devon!

I recently had a batch of 10 AF127's in so thought I would test some and let you know the results

No. B-E. B-C. HFE (measured on peak component tester)
1. 0.31. 0.24. 193
2. 0.30. 0.26. 378
3. 0.29. 0.22. 208
4. 0.31. 0.22. 462
5. 0.30. 0.22. 97

Hope that helps. Interesting that the diode readings remained pretty much the same despite the different hfe.

Regards

Graham
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Old 10th Jan 2017, 7:24 pm   #3
Station X
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Default Re: Possible faulty AF127?

The figures mentioned in post #1 are forward volt drop?

What are the reverse resistances like?
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Old 10th Jan 2017, 7:51 pm   #4
shadoman
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Default Re: Possible faulty AF127?

Thank you both Graham's
The reverse resistance's are b to c 103.5 and b to e 0.02
I Will try another transistor in that position i need to order some anyway its also nice to hear from another forum member in North Devon.There seems to be a few of us down here now. Thanks again Terry.
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Old 10th Jan 2017, 7:54 pm   #5
paulsherwin
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Default Re: Possible faulty AF127?

That transistor does indeed appear to be faulty.
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Old 11th Jan 2017, 11:30 pm   #6
Philips210
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Default Re: Possible faulty AF127?

Hi

Agreed it is a very leaky transistor. I once had an unusual problem with an AF127 or AF124, it was suffering from a short from collector to the body (screen lead) of the transistor just like the inherent tin whisker problems of the AF11x series. I have it stored away somewhere so if I come across it will try to remove the short. Maybe the tin whisker problem will show itself in the AF12x versions, hopefully not but something to bear in mind.

Regards
Symon.
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Old 12th Jan 2017, 4:11 am   #7
Boater Sam
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Default Re: Possible faulty AF127?

No reason why they should not suffer the same whisker problem, same construction.
Try de-canning it in situ with a soldering iron.
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Old 12th Jan 2017, 9:40 am   #8
jjl
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Default Re: Possible faulty AF127?

The encapsulation "can" construction is not the same for the AF11x and AF12x series. AF11x are contained in a tin plated rather thick steel can whereas AF12x are in what appears to be a plain mild steel thinner can, so AF12x should not suffer from the tin whisker problem.
There are of course other failure mechanisms that could affect either series equally given that the semiconductor within the can is the same.

John
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