I had something similar with my 7D01, except that RAMs were from even lower
layer of Pleistocene, they were 1 K capacity. Surprisingly, I was able to
find RAMs at the local junker store and price was not too unreasonable.
It is interesting that sequence of fixing resembled closely what Fred
described: first replacement did not work, but second chip did. Then, I put
back the original chip and that worked, so I concluded that problem was with
those 'low bidder' sockets that Tektronix' accountants liked to buy for
instruments that had lot of DIPs. The sockets looked like infamous TI
products, but judging from age of the plug-in, I would say, it came after TI
fixed flux wicking.
Regards
Miroslav Pokorni
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----- Original Message -----
From: "pe1fbo" <sh331182@...>
To: <TekScopes@...>
Sent: Sunday, February 29, 2004 6:07 AM
Subject: [TekScopes] 7D20 RAMS
Hi All,
Today I fixed my 7D20, it had come up with an error, (fail 531). A
closer look in the manual pointed to U710, a dynamic RAM (4116) from
the prehistoric ages.
All RAMS on the memory board where from ITT, date code 8232 and 8237
and had also a white 'TEK' marking.
I replaced the bad chip with one from a scrap TEK 9100 logic
analyser, also an ITT chip, and made me wonder, because this chip
gave me exactly the same error.... So was it perhaps something else ?
However a 9100 has 16 4116 so I took an other one, this time an NEC
one with a white TEK marking... And this seemed to be working fine.
This made me curious and I started to test them all. I found three
other ITT chips which were bad, non of the NEC or Mostek chips
failed.
Could it be that the ITT chips are of inferior quality, or is the
chip OK and is this a timing problem in the design of th 7D20 ?. I
must say, that the scrap 9100 was also failing due to a bad uP
board, the cause is still unknown.
Here are the error codes and their chips associated in case you have
a similar issue with the RAMS.
Dynamic RAMS 4114
521 U910
53 U810
531 U710
532 U610
5321 U510
54 U410
541 U310
542 U210
Static ones
321 U900
4 U800
41 EAROM
- Fred de Vries
ps look at for a similar case
