Path: utzoo!mnetor!uunet!husc6!rutgers!mtune!codas!killer!elg
From: elg@killer.UUCP (Eric Green)
Newsgroups: comp.sys.cbm
Subject: Re: Hdwe repair help
Message-ID: <3317@killer.UUCP>
Date: 15 Feb 88 06:46:17 GMT
References: <337@dalcsug.UUCP>
Distribution: na
Organization: Bayou Telecommunications
Lines: 36

in article <337@dalcsug.UUCP>, euloth@dalcsug.UUCP (George Seto) says:
> I am posting this for a friend who has no access to the net.
> 
> In the RTC C-Link interface, there are three IC's. They have had the
> part numbers sandpapered off. HE is trying to repair it and needs to
> know what the chips are. Can anyone help? Thanks in advance.

The big chip is either a 6820 or a 6821. I bet 6821 (pinouts are identical
between the two, fanouts are different from the i/o port). It's the one that's
most probably gone. The TTL closest to the edge connector is a open-collector
high-voltage buffer that most probably is still good unless your friend really
fried things. I forget the exact number, alas, it's been awhile. I suspect
either a 7407 or its non-inverting mate.  Finally, the TTL closest to the
computer is that old standby, the 74LS30, the 8-input NAND gate used so often
in these "transparent" interface thingies. 
     A long long time ago, right after RTC declared bankruptcy and went under,
I blew up my computer with that "#$"$% stock Commodore power supply, C-LINK
included (took $40 worth of chips to rebuild everything... practically every
MOS chip in the entire computer was fried to smithereens). I had to do it the
hard way... by looking at what lines went where (stripping the board helps),
and then matching it against the TTL databook. The 74LS30 was a piece of cake,
it has a pinout that's singularly distinctive (8 inputs, 1 output?  sheesh!).
The idiots thinking that filing the number off of it was a deterrent were
either brain dead or just weren't thinking... I suspect the former,
considering that RTC went under. No wonder. As for the big chip, what the hell
could it be besides a PIA or VIA or CIA? It's easy enough to tell the
difference... a PIA has 3 chip selects, a VIA two, a CIA only 1. Sheesh.
Anyhow, pinouts matched with a PIA. Case closed, mystery solved. Those people
at RTC musta had noodles for brains, because I make no bones about being
software, not hardware, and if even I could figure it out...

--
Eric Lee Green  elg@usl.CSNET     Asimov Cocktail,n., A verbal bomb
{cbosgd,ihnp4}!killer!elg              detonated by the mention of any
Snail Mail P.O. Box 92191              subject, resulting in an explosion
Lafayette, LA 70509                    of at least 5,000 words.