Options for resurrecting VAX 4000/400 and Vaxstation 3200

[Dr. Roland Schregle]

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.

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.

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]