16 Jan
2015
16 Jan
'15
10:44 p.m.
I am looking to test the power supply board of my VT101 before connecting it
all up and switching it on.
Reading to the Pocket Service Manual it seems to suggest that you can check
the outputs of the power supply board with the terminal controller board and
the video monitor board both disconnected. This would mean no load on the
power supply. Does this seem wise?
Regards
Rob
17 Jan
17 Jan
7:24 a.m.
In my case of vt100 powersupply test (i hope that i remember corretly) i need to load 5V
with a small load. With nothing connected, some voltages fail.
Marco
Am 16.01.2015 um 23:44 schrieb Robert Jarratt
<robert.jarratt at ntlworld.com>:
I am looking to test the power supply board of my VT101 before connecting it
all up and switching it on.
Reading to the Pocket Service Manual it seems to suggest that you can check
the outputs of the power supply board with the terminal controller board and
the video monitor board both disconnected. This would mean no load on the
power supply. Does this seem wise?
Regards
Rob
4:53 p.m.
In my case of vt100 powersupply test (i hope that i
remember corretly) i need to load 5V with a small load.
With nothing connected, some voltages fail.
From what I remember, the VT100 and VT101 PSUs are very
different. The former is a fairly conventional
SMPSU, albeit one which (as was
typical for DEC at the time) has the control circuitry on the output side of
the isolation barrier and a little linear startup PSU. The VT101 has a large mains
transformer and a regulator
board, I think some of those regulators are switchers, but they run from a lowish input
voltage (not mains) and
the isolation is provided by the big transformer.
I don't know about running them with no load, although I could well believe the VT101
PSU will work
correctly like that.
-tony
6:09 p.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
duell
Sent: 17 January 2015 16:54
To: General Discussion: On-Topic and Off-Topic Posts
Subject: RE: Testing VT101 Power Supply
> In my case of vt100 powersupply test (i hope that i remember corretly) i
need
to load 5V with a small load.
for DEC
With nothing connected, some voltages fail.
From what I remember, the VT100 and VT101 PSUs are very different. The
former is a fairly conventional SMPSU, albeit one which (as was typical at the time) has the control circuitry on the output
side of the isolation
barrier
and a little linear startup PSU. The VT101 has a large
mains transformer
and a
regulator board, I think some of those regulators are
switchers, but they
run
from a lowish input voltage (not mains) and the
isolation is provided by
the big
transformer.
Yes, that is right. There is a big transformer and the outputs are 10V and
18V (the service guide for latter shows 20V on the diagram and says 16V in
the text!).
I don't know about running them with no load, although I could well
believe
the
VT101 PSU will work correctly like that.
In the end I created a dummy load. The outputs all look fine and there is no
ripple. So I am very pleased with the state of the PSU. I am replacing a
couple of caps on the monitor control board, one because it has high ESR and
one (C439) because this page (https://trmm.net/VT100) says it is underrated.
Then I am going to have to bite the bullet and connect it up, hoping the
monitor control board is OK and isn't going to damage the flyback or
something else.
Regards
Rob
3634
days inactive
3635
days old
3 comments
3 participants
participants (3)
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ard＠p850ug1.demon.co.uk -
marco＠familie-rauhut.eu -
robert.jarratt＠ntlworld.com