CBM 8032 Garbage on Screen
ard at p850ug1.demon.co.uk
Tue Feb 6 14:37:39 CST 2007
> > Now, I seem to remember that on 80 column PETs, the 2K video memory is
> > made up of 4 1K*4 chips and that alternate characters are stored in each
> > pair of chips (one pair of chips stores all the chracters in odd-numbered
> > locations on the screen the other pair the characters in even-numbered
> > locations). That would explain why you have problems with alternate
> > characters.
> Hmm... I didn't know about the even-odd interleave, but that'd be easy
> to check against the schematics.
Well, I'd not bet my life on it (it's been some years since I've been
inside a PET 8032), I am farily sure I've rememebered that correctly. It
was something a little odd that stuck in my mind.
> > And you guessed it,. Those RAMs are 2114s, a chip well-known around here
> > for failing in oadd ways.
> Exactly. In a PET, it's much more likely that a 2114 has failed than
> a bus buffer or similar IC.
In _anything_ it's more likely a 2114 has fialed than just about any
I've lost count of the number of 2114's I've replaced. But I rememeber
fixing an HP37201 HPIN extender, HP82163 video interface, TRS-809 Model 3
with video problems, CBM 8050 all by replacing 2114s.
If you don't ahve much test gear and beleive iin lucky-dip
troubleshooting, go for those chips first ;-)
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