26 Sep
2014
26 Sep
'14
11:44 p.m.
On 9/23/2014 9:15 PM, Josh Dersch wrote:
On 9/22/2014 11:16 PM, Brent Hilpert wrote:
> On 2014-Sep-22, at 9:49 PM, Josh Dersch wrote:
>> Thanks to Brent's writeup and DEC's documentation (both of which
>> are well written and relatively easy to understand) I'm pretty sure
>> I've traced down the fault to a diode on the core plane board
>> (H214), contained within a DIP package designated as a DEC 2501.
>>
>> Of course, I don't have any of these going spare (and I'm not sure
>> if there are equivalents -- I have yet to find a datasheet). Anyone
>> have any information about these, have any (good) spares, or know
>> where I might find some replacements? I suppose I could just hack in
>> a single diode (assuming I can determine the specs) but that seems
>> kind of ugly...
> Great, thank goodness it looks like a diode problem and not a
> matrix-wire.
So, it looks like I made a mistake here. I was double-checking my work
this evening (in preparation to remove the supposedly faulty chip and
install a socket) and the diodes in the 2501 at E22 all seemed to test
out fine. I don't know how this came out bad before, I must have had a
bad contact or something with my DVM's probes. (Or I was tired and it
was late and...)
Further investigation reveals that the connection between FD1 on the
card edge connector (the XS05 signal) and pin 7 of the 2501 at E22 is
broken. This, I believe, is a matrix wire (or "magnet wire" from the
engineering drawings) meaning that I've got a broken wire somewhere in
the core mat.
I'm guessing that this means game over for this particular board. I've
looked really really closely at the solder pads around the edges of the
core mat and I don't see anything obviously hanging loose, but I could
probably use a larger magnifying glass :). Even if there was something,
I'd be nervous about making it worse, my fine soldering skills are not
up to this sort of thing...
Any suggestions? Time to start looking for a replacement H214?
Thanks,
Josh