Check the current
On 18/08/2017 18:25, Dominique Carlier via cctalk wrote:
Some news !
Following a risky way (but I did not see how to do otherwise), I
deactivated the Power Fail by hiding the contact number 23 of the two
power supplies.
The idea was to avoid automatic protection by lowering the regulated
voltages (+5V and 15V) and see first which unit was involved (G1 or
G2), and also which voltages became weak, at what level it is lowered,
and according to which board (model or number of connected boards).
Results of the observations:
- This is definitely the regulated +5V of the G2 power supply. More I
add boards more the + 5v level goes down. +5v, +4.8v, +3.6v, +2.9v. It
remains stable however with just the CPU and the three core memory
boards, it becomes difficult for the power supply when I add boards in
addition to these.
- This is definitely not a problem at the level of the Power Fail
circuit.
- The big capacitors are not in fault (I rechecked twice).
- So this maybe a problem at the level of the regulation itself, the
+5V balancing system ?
Question: a faulty voltage regulator can behave in this way? I always
thought it worked or it did not work, but not between the two states
depending on the charge.
Anyway, suggestions are always welcome ;-)
PS : I'm starting to want to put another power supply for that
regulated +5V, and bypass the +5V regulated of G2, but it would be a
shame and not in the spirit of a restoration in my opinion.
-------- Forwarded Message --------
Subject: Re: DCC-116 E / DATA GENERAL NOVA 2/10 / Nixdorf 620 -
Restoring and restarting
Date: Wed, 16 Aug 2017 23:33:31 +0200
From: Dominique Carlier <d...@skynet.be>
To: Christian Kennedy via cctalk <cctalk@classiccmp.org>
Hi !
I finally find some time to work again on my D-116, try to find the
problem(s), thus principally at the level of PSUs.
As you suggested, I inspected particularly the large capacitors of both
power supplies. I replaced those that appeared suspicious according to
the results via my ESR meter, but note that this one is not supposed to
be able to verify the capacitors of more than 22000μF. I have also some
doubt about the results (capacitor working with a real charge or not).
Anyway, unfortunately the problem is still there. I don't know where to
search now. If I understand well, the two power supplies can cause a
Power Fail if one of the regulated voltages were out of range. At this
point I do not know which of the two is in fault, because when the Power
Fail is active the + 5V is automatically dropped around 1.5V.
Following the schematics I have focused my attention on the value of
some resistors with an important role in triggering this state (eg R18).
I found nothing abnormal, I checked all the capacitors, a large package
of resistances.
At this point what I know is that I can simultaneously connect the CPU
board and the three core memory boards without problem. If I add the
controller board for the removable hard disk drive or for the tape ->
Power Fail.
Interesting thing: if I connect only the CPU board and the disk
controller: Power Fail too. Maybe the PSU in default is the one that
supply the + 5V for the boards in the upper part of the rack? (slot 1
for the CPU, solt 4, 5 and 7 for the mem, slot 10 and 12 for tape and
hdd)
I can provide pictures, schematics, ...
Regardless of this failure, I try to find information about what I could
install as an operating system on that big beast. If you have too any
ideas about that?
I would like to be able to do simple tasks such as managing files
(copying files from disk to tape and vice versa), being able to create
directories and sub directories, writing text, print on my drum printer,
programming in a simple language such as BASIC, and also, if I find a
communication board (on the CPU-board I don't found any trace of
components that evoke me an RS-232 interface), communicate with another
machine, print on a teletype ... Does this seem possible for you with
this type of machine? If yes, with which OS?
I took tons of pictures of the machine from all angles, I will post them
soon ;-)
Dominique
If I removes all the boards (printer, core memory, scanner, disk
controller, etc.), the Power Fail light eventually goes out, I get
again
the 5VDC, so the power has become "too weak" to power the computer when
it is fully populated.
It's a switcher; look at the caps in the LC filter (downstream of the
series pass transistor) that, together with the inductor, form the
energy storage mechanism of the power supply; check the source supply as
well. The fact that it eventually comes back suggests that the
reference, comparator and pass device are probably functioning.
--
Wanted one pdp-8/i rocker switch leaver to copy.
