23 Sep
2014
23 Sep
'14
9:15 p.m.
On 9/22/2014 11:16 PM, Brent Hilpert wrote:
Nice! I double-checked the anode/cathode pins (1 and 14) listed for the
TID 125/126 by tracing them out with my continuity checker on IC E22 on
the H214 and they're connected to FK2 and FL1 on the edge connector as
they should be, so the 125/126 matches the DEC 2501's pinout. I found a
seller on eBay selling them for $1.79/ea, so I bought a few extra.
(see:
http://www.ebay.com/itm/TID126-TI-IC-DIODE-ARRAY-14-Pin-DIP-RARE-New-/37030…).
When they arrive, I'll let you all know how they work out...
Thanks again for the help,
Josh
On 2014-Sep-22, at 9:49 PM, Josh Dersch wrote:
:).
On 9/6/2014 1:27 PM, Josh Dersch wrote:
? right, I call it Shiny Object Syndrome - look! another
three-letter acronym. Thanks for all the info -- the core memory
overview you put together looks to be very helpful, and when I have some time (hopefully
this evening) I'll study it a bit more in-depth and see what diagnosis I can apply to
the 11.
Thanks,
Josh
A brief update (and request for further information): I finally had time tonight
to sit down and dig into this (I've been busy and easily distracted by new shiny
objects as of late). 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.
I looked into the diode packs back during the earlier discussion, the best match I found
(based on pinout) for the address-wire current-steering diode pairs (14-pin DIP) was:
TID125, TID126
http://www.datasheetarchive.com/dl/Scans-026/ScansUX10116.pdf
The DEC schematic indicates the pair-pins but doesn't seem to indicate the two
common-anode/cathode pins on the packages, the TID125/126 I think were the only type(s)
from the above page that made sense.
( DEC schematic: page 134 of 1105_RevAH_Engineering_Drawings_Jul76 from bitsavers, sheet
2 of H214-0-1 ).
There's a small chance I might have a replacement or equiv on a scrap board.
Worst case - should be able to use a couple of discrete diodes to sub for the bad ones if
you can ensure the bad ones are out-of-circuit.