RE: Need help fixing a C128 DCR

What if the cursor is there but the same color as the background? :) 

I am late to the conversation so wasn't sure if the question is about the 4 bit color ram on the VIC.  If so I would suspect the RAM itself, the bidirectional cmos quad buffer or the chip-select to the Ram/buffer.

If you had a scope I would say to check the /CS lines and the high order address lines that create the logic for the /CS lines, and after 25 years I have forgotten where the cursor is stored, whether it represents a high order d bit or a bit. Maybe the PLA got a case of rot and has a couple of issues (damm foot fungus) but that is why I tend to look at /CS (chip select) lines first.


Don't laugh:  Lick your finger and get it down around all of the pins on the color ram and the quad buffer and look for any change, if something changes based on your finger it probably is floating. (poor man's o-scope, I also use my finger as a hum injector)

-----Original Message-----
From: owner-cbm-hackers@musoftware.de [mailto:owner-cbm-hackers@musoftware.de] On Behalf Of Nate Lawson
Sent: Thursday, June 24, 2010 12:25 PM
To: cbm-hackers@musoftware.de
Subject: Re: Need help fixing a C128 DCR

Baltissen, GJPAA (Ruud) wrote:
> My advice: try exchanging the CIA's first. AFAIK they aren't soldered 
> do that shouldn't be much trouble. If possible, exchange them with a 
> working system. If no result, the 8502 is may be to blame.
> A brooken colour-RAM doesn't explain the missing cursor but one of the 
> CIA's also controls the video partly. So another reason to look at 
> them first.

Seconded. The CIAs connect to lots of external ports, including joystick on the C64, and are sensitive to static.

--
Nate


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