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Old 9th Apr 2023, 3:27 pm   #21
agardiner's Avatar
Join Date: Sep 2020
Location: Thetford, Norfolk, UK.
Posts: 1,355
Default Re: Silicon transistor failure

Hi Terry,

So I cannot comment on breakdown voltage as I haven't run any tests. At this stage though, I would not have thought that there is a high risk of complete breakdown in AF stages; yet.

The problem I am regularly coming across, is transistors that have gone low gain, or in some cases, noisy. Low gain transistors cause issues such as RF oscillators to fail, and I have also found AF low gain transistors in audio amps, causing channel mis-match. Checking with a multimeter doesn't show any issue, as the junctions still test just fine. You either need an in circuit test with say a scope, or test the transistor with a transistor tester.

Certainly in the case of radio where the oscillator is not running, my first call now is to replace the transistor and see if it solves the problem.

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Old Today, 10:28 am   #22
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 6,640
Default Re: Silicon transistor failure

Just thinking... if epoxy degradation is affecting transistors in TO92, how much more will op-amps in plastic packages be affected where there's considerable gain after the first stage?
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Old Today, 12:35 pm   #23
Join Date: Aug 2006
Location: Stoke-on-Trent, Staffordshire, UK.
Posts: 1,020
Default Re: Silicon transistor failure

Oh no I have thousands of old transistors I thought they would last for ever !
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