DG S/130 progress

Jay West jwest at classiccmp.org
Tue Oct 13 17:08:26 CDT 2015

Pictures of the S/130 system I'm building up are at

I think the last I posted here... the cpu was up and running, that was the
first piece I refurbished. I took everything out of the rack and cleaned
that up well, and the cpu has been remounted there.

Yesterday I mounted the 6030 dual 8" floppy drive. It was squeaky clean
inside and at power up everything does what it should. However, I can't
proceed further with it as I have no media. The docs say it uses hard sector
8" floppies, which I  believe I can find. However, it specifies 8
sectors/track hard sector floppies - and those I've never heard of. Maybe DG
made them special just for their gear, or, maybe the drive or controller or
software was smart enough to expect the more common 32 hard sector floppies
and knew to only pay attention to every 4th sector hole ;)  In any case,
before I spend "real dollar$" on media, if anyone has a single piece of 8
sector hard sectored 8" media I'd love to get one for testing :) Getting the
6030 connected to the cpu took a lot of documentation reading. It would seem
that DG didn't believe in anything plugging in to interface boards. Instead,
interface boards went in the cpu with no external connectors. Then you
wirewrap from the backplane from a given slot to one (of a stack) of paddle
boards bolted to the rear of the cpu chassis. Those paddleboards have edge
connectors, and that's where you connect the device cable. Fun stuff.

I started digging in to refurbishing a 6125 mag tape unit to go with the
above system. It has power supply issues. The schematics I have are similar
but not 100% correct so some guessing was involved. Whenever I turned on the
tape unit, any other things (shop light, oscilloscope, etc.) plugged in to
the same circuit would start randomly turning off and on. That is not a good
sign ;) Earth leakage... Checking the snubber circuit on the mains side of
the transformer led me to suspect a mylar that sat between hot and neutral.
I lifted one leg of it (just for testing) and that problem is definitely
gone. Next problem is the power supply makes a loud ringing noise. I believe
that's usually either ceramic disc capacitors or transformers, but I'm
having a really hard time locating the exact source of the sound. I'm going
to remove the power supply from the metal chassis and hook it up externally
(that's how it goes in the rack anyways) and see if I can tell for sure that
is the issue. Other than that, offline tests all work, so that will be
racked up shortly and cabled to the S/130 cpu.

Next on the list is refurbishing the DG 4084 dual cassette tape unit and
racking that. Something tells me media will be unobtainium for that.

Last step will be to refurbish and install a hard drive, most likely I'll
use a 6050.

So... some progress at least :)


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