Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ames!pacbell!att!ihnp4!ihlts!acthom
From: acthom@ihlts.ATT.COM (thomas)
Newsgroups: comp.sys.cbm
Subject: 1764 expansion problems
Keywords: 1764, expansion, cbm
Message-ID: <1068@ihlts.ATT.COM>
Date: 8 Jun 88 19:57:22 GMT
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 41


OK you hackers on the net, I have a stickler of a problem.
I bought a 1764 - 256K ram expander for my c64. I read the
articles on the net about expanding it to 512K, and, after waiting 
for the warranty to expire, I popped the cartridge open.
Things looked easy. There, hunkered down in the front left was a great,
square controller chip; in the middle was a row of traces just
waiting for sockets.
So I cleaned out the holes, soldered in sockets, and plugged in
256K memory chips. Oddly, the 512K trace was already cut.
Having modified the RAMtest program according the the GEOworld
article (a couple of pokes in the basic portion to access the
upper banks), I gave the now 512K expander a try.
The test whizzed thru the lower 256K of memory and picked up an
error in the middle of the new 256K. And rerunning the test picked
up what looked like a hard error at the start of the new 256K bank.
Ah, a bad chip, I thought; plugged in a spare, and it did the same thing!
Two bad chips?
For a while it looked like the expander liked TI 256K chips and nothing
else (but I could only find 7 of the TI chips, so I'll never really know,
the 8th other chip masked any other problems).
After weeks of probing and borrowing every 150ns and 120ns chip I could
find, I brought the little bugger into my local CBM repair depot, where
the fellow in charge said "You did WHAT!" Fortunately he was impressed
with my soldering job and the sockets, so he decided to take a look
at it; to no avail.
The memory chips are good, they work in a 1750. Another 1764 controller
chip does the same thing.

So he asked me to get back on the net, and ask around if anyone
else has seen this problem:
  If you have modified your 1764, and it has the square chip
(not the old rectangular one), and you have had a problem of
the new memory working somewhat, and then going to a consistent
failure mode ... how did you fix it?

 (The current theory is that there are two versions of the controller
  chip, and the ones that they put in the 1764 are the ones that
  failed the 1750s, but could handle 256K.)

Does anyone out there have any ideas?
		Thanks, Al Thomas.