-----Original Message-----
From: cctech [mailto:cctech-bounces at
classiccmp.org] On Behalf Of Dr.
Roland Schregle
Sent: 10 March 2016 12:39
To: General Discussion: On-Topic Posts <cctech at classiccmp.org>
Subject: Re: Options for resurrecting VAX 4000/400 and Vaxstation 3200
On Wed, 09 Mar 2016 21:59:27 +0100, Robert Jarratt
<robert.jarratt at ntlworld.com> wrote:
I think one day I will have to equip myself and
learn how to desolder
and resolder surface mount chips. I don't know how many chips
implement the B-CACHE, but perhaps you could replace all of them,
assuming you know which ones they are. Perhaps some careful probing of
the board with a scope might show if there any chips that are perhaps
completely
dead.
You could do the same for the DSSI controller on
the other board of
course, if you can identify that.
Our lab has an EE department with some pretty fancy SM gear, I just have to
practice on it (which would come in handy anyway). The B-cache consists of
18x CY7C166-20 SRAM plus 5x CY7C170A-25 tag RAM, so they're easily
identified (the KA-675 manual infact points them out).
Replacing 18 SRAMs doesn't sound like a lot of fun, and I have no idea how to
probe the board in the cardcage without disassembling the chassis, in which
case the thing may overheat; opening the CPU bulkhead infact triggers a
prompt reaction from the fan controller.
Just powering it on for a few seconds at a time while probing for any really obvious
failures would presumably be pretty low risk. Given that the components face to the right
though, you might be able to do some probing with just the memory removed?
FWIW, here's a thermography (hope the link works) of the B-cache section of
the KA-675 after being powered up for ca. 30 mins:
https://www.dropbox.com/s/2nsx1dfngp1jfq5/TH710065.BMP?dl=0
Note that the rightmost chip just below the CPU heatsink has a pin that's ca.
2 degrees warmer than the others. I don't know if that says anything, but it
*is* reproducible. Maybe I should start with that one.
Looks like you have access to some enviable stuff, so replacing the chips might not be too
bad. I get an occasional error on my 4000-500 at test 14 (also cache related), it
doesn't appear to affect operation, but I am worried something is failing that will
need replacement.
The dead DSSI controller on the other board is easily identified, as it was
physically destroyed in transit. I'm not inclined to transplant a 160-pin PGA as
my first foray into SMT... :^\
Thanks for the feedback,
--GT
--
"END OF LINE" [MCP, 1982]
"... nowhere in the standards is it specified that 'programs that use a lot of
memory may randomly crash at any time for no apparent reason'"
[Stackoverflow forum, 2012]