28 Aug
2014
28 Aug
'14
1:15 p.m.
I'm going to have to crack one myself pretty soon; I got my VT131 out of
long term storage a few months back and tried to fire it up a few days
ago... Screen comes up, I get a flashing garbage character in place of the
block or underscore and terminal is unresponsive. The logic looks cursorily
OK and I hear that squeal that's somewhat suggestive of bad caps so I'm
going to have to take a look at the power section one of these days...
Unfortunately I can't cite mine as a working example for reference at this
point in time :|
Best,
Sean
On Thu, Aug 28, 2014 at 4:08 PM, Matt Burke <matt at 9track.net> wrote:
On 21/08/2014 23:38, Matt Burke wrote:
I'm currently restoring a couple of VT100
terminals. After checking the
power supplies over and replacing the odd capacitor on the output side
I've had both of them running on a dummy load. They seem to work OK but
I've noticed that R27, which is a large 13W power resistor, gets quite
hot after only a few minutes of being powered on. This resistor is part
of a snubber circuit on the primary side of the main transformer. After
about 5 minutes I measure a temperature of around 95C (200F) on both
power supplies.
Another component that appears to have been quite hot over time (burnt
PCB) is R55, but perhaps this is just an underrated part?
Does anyone have a VT100 and can confirm whether this is 'normal'
operation?
Many Thanks,
Matt
After a bit more searching of the archives I found a thread started by
Julian Wolfe who noted some burning on R11, R21 and R55, which is
consistent with my two power supplies (no mention of R27 though). A few
people commented that there was probably an issue somewhere but
unfortunately the thread does not run long enough to see what the
eventual outcome was.
Has anyone here ever worked on a VT100 power supply? I just want to know
if I should investigate this further or whether it's designed to run
this hot. Personally I can't see anything wrong, especially as it seems
to work just fine.
Thanks,
Matt