Re: Electrolytic Caps in CBM equipment

From: Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de>
Date: Sat, 08 Sep 2012 15:45:32 +0200
Message-ID: <504B4BFC.1030607@laosinh.s.bawue.de>
On 09/08/2012 03:26 PM, Rob Clarke wrote:
>
> These were all made by a company called Bellcon which I'd not come
> across before. Has anyone else had any other issues with consistently
> problematic caps in CBM equipment, either by manufacturer or in specific
> hardware?

I don't remember the maker... But not long ago I had a C64 KU-board (*) 
for repair here and the problem were 2 rather small electrolytic 
capacitors in the clock circuit, C107 and C108 (visible on the image 
below right and left of the 74LS629). Both of them had started leaking 
and the electrolyte from C107 had eaten through a trace that supplied 
pin 15 of the 74LS629, resulting in the master oscillator not working. 
After fixing the trace and replacing C107, the C64 worked again.

The capacitors were small, black and sat directly on the board. Until I 
removed them, they looked perfectly OK. The electrolyte did not appear 
outside the area covered by the capacitor.

A few weeks after that, someone else had the exact same problem with his 
KU-board. So if anyone here has such a board, check or better replace 
C107 and C108 if they look like I described.

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.

Those were the only failures I had so far. When I rework a power supply, 
I usually replace the capacitors, just to be sure, but I don't replace 
them on mainboards unless necessary.

(*) http://www.c-64.org/pics/hardware2/ku14194hb_big.jpg

  Gerrit








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