Re: R-DOS (REX DOS??) on an oceanic 1541 clone drive

From: Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de>
Date: Mon, 06 Oct 2014 17:11:21 +0200
Message-ID: <5432B119.6000204@laosinh.s.bawue.de>
On 10/06/2014 01:28 PM, Julian Perry wrote:
>
> In an unrelated query - I've been reviving a 1982  KU-14194HB
> silver-label machine. It's now working fine (RF modulator was dead) but I'd love a schematic
> for the thing, and I've been unable to locate one.  Has anyone seen
> one?

If it's really a KU-14194HB board (the 2114 color RAM on U6 is located 
between CPU and Char-ROM), you need to check C107 and C108. Theses are 2 
small electrolytic capacitors located left and right from the 74LS629 
(which is right next to VIC)

If those are black, very small and sitting directly on the board, you 
need to replace them immediatly (10F/25V will do). They don't contain 
much, but they will leak and it's enough for C107 to destroy the trace 
between Pin 15 if the 74LS629 and R26. Once that connection is gone, the 
VCO inside the 74LS629 will no longer do its job and no clock signal 
will be generated.

You can't go by looks, the leak might be limited to directly below the 
capacitor.

I had to fix this trace on more than one KU board.

  Gerrit





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