Re: C128 repair advice...

From: Raymond C. Bryan (
Date: 2002-02-24 20:20:28

First check that the power to the cpus and other chips is a good 5V 
Dc (4.95 will do) then check the clock signals on the CPUs inputs and 
VIC out puts (also at the crystal) - then check for hot RAM or with a 
O'scope check the signals on all the ram chip legs - if one set looks 
strange by comparison suspect it first. --Ray

>Hello all,
>I've been tinkering with Georges prototype C128 of late.  It's a REV0
>motherboard without an FCC sticker, but with a serial number of 145, and
>REV2 and 3 EPROM ROMs.  I replaced the three broken keys from the popular
>G.P. collection photos, and made a stab at getting it to boot up.  That,
>however, has proven difficult.
>The basic symptom is a black composite start-up screen.  Using a working
>C128, I managed to confirm that all the socketed chips from the prototype
>machine are OK.  This includes the ROMs, both video chips,  and the 8722
>(MMU?).  The MMU is actually the only chip I noticed as being an unusually
>old revision, being a REV1.
>Anyways, I'm a bit at a loss.  I'm not very excited about the prospect of
>socketing memory and processor chips, just like I would ANY old C128, in
>order to fix it.  The only other clue I noticed is a particularly hot
>running Z-80, compared with the Z-80 in the working C128 I'm using for
>Any advice is appreciated, though I'm still wondering if doing anything at
>all is a good idea, since any changes would put this motherboard in the
>hands of a solderer who is merely fair at best. :)
>- Bo
>        Message was sent through the cbm-hackers mailing list

|Raymond C. Bryan  651-642-9890 vox      | The battle is sometimes |
|Raymond Computer  651-642-9891 fax      | to the small for 
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