From: cd6699@notformail.com
On Sat, 29 Nov 2025 12:08:53 -0500, Phil Hobbs
wrote:
>On 2025-11-25 14:50, Cursitor Doom wrote:
>> On Tue, 25 Nov 2025 11:43:50 -0500, legg wrote:
>>
>>> On Sun, 23 Nov 2025 22:58:42 +0000, Cursitor Doom
>>> wrote:
>>>
>>>> I've been trying to trace an issue with a Uher tape deck in respect of
>>>> extremely low audio gain during recording. I was delighted when I
>>>> spotted a resistor in the AGC section with a tiny blow-hole half way
>>>> down its body. I was able to confirm this when I removed it for
>>>> examination under a stereoscope. There was even a bulge under the hole
>>>> where some pressure had clearly built-up immediately prior to the
>>>> blow.'Easy fix!' I thought; 5 minutes and it's done. However, I was
>>>> baffled when it tested spot-on its 1200 intended ohms! WTF?? Something
>>>> must have pulled excess current through that component and the obvious
>>>> culprit was the BJT it was the series resistor for. However, once
>>>> again, it tested fine! I just never have encountered an outcome like
>>>> that before. Anyone had similar?
>>>>
>>>> CD
>>>
>>> Mfring defect in the epoxy 'paint' finish.
>>>
>>
>> Unless something upstream that caused an over-current went
>> open-circuit before the resistor could totally fail?
>>
>
>The coating is cross-linked, so it chars rather than melting. If you
>ablate the resistive film with some huge overload, it just cracks off
>the coating as it goes.
>
>Cheers
>
>Phil Hobbs
Hi Phil, Not sure what you're doing on a repair group squandering that
planet-sized brain of yours, but you are of course most welcome! I
shall try to hunt down that 'suspicious' resistor tomorrow and post a
close-up image of it, as it's one of those things where - for once - a
picture really is worth a thousand words. Then everyone can chip in
their 2c worth about what the cause might be. Stay tuned!
CD
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