Re: Electrolytic Caps in CBM equipment

From: Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de>
Date: Mon, 26 Nov 2012 19:23:05 +0100
Message-ID: <50B3B389.2020305@laosinh.s.bawue.de>
On 11/26/2012 04:26 PM, silverdr@wfmh.org.pl wrote:
>
> On 2012-09-12, at 18:37, Gerrit Heitsch wrote:
>
>>>>>> Otherwise... I had C90 got bad on a 250407. No capacity left at all, resulting in +12V for VIC and SID being only +8V. System worked, but I only got a b/w picture. That one was a light blue 407F/25V made by GRAND SONIC.
>>>>>
>>>>> I have one board that boots to B/W picture when "cold". After some time colour pops in. It also quite often hangs (after some seconds) when cold. With time it also becomes more reliable. Voltages on the regulators/stabilisers look good. Don't have scope at hand to have some more close look but maybe this rings a bell for someone?
>>>>
>>>> Can you provide some extra information about the kind of board? Assy number, which voltages were checked and where...
>>>
>>> 250425 board. Voltages checked at regulators, VIC, SID, CPU and few other points for the "second" +5.
>>
>> Still, if you have a matching one, you could replace C90 anyway. Otherwise, since it's a 250425... If you have one, try a different 8701.
>
> Got this one fixed. Crashing was unrelated to the lack of colour. Crashing was caused by broken KERNAL socket - replaced and crashes disappeared. Lack of colour was a bit more tricky though. I was hunting it for some time until I started watching the chroma waveforms on different boards recently, including the one in question. I noticed that on other boards trimming the crystal frequency leads to loss of colour and setting it back brings the colour back. But on this board no.. So I replaced the trimmer and adjusted it so that I get colour every time now. It sorts of explains also why the colour was more likely to appear after some time and less likely when cold - frequency drifting due to temperatrue difference.

Hm, never had one of those go bad... But then, it's hardware, it will 
fail sooner or later for someone.

  Gerrit



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Received on 2012-11-26 19:01:18

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