20 Dec
2015
20 Dec
'15
3:31 p.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Paul
Koning
Sent: 20 December 2015 22:32
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: VAX 4000-500 PSU Overload?
> On Dec 19, 2015, at 4:05 PM, Robert Jarratt
<robert.jarratt at
ntlworld.com>
wrote:
find.
...
I can't tell if this is a Kelvin connected one or not, although I
suspect it probably is. You can see a picture with two here:
http://1drv.ms/1micVN7.
> These are from a second board in the PSU, but they look identical to
> the one on the problem board. It would appear to have 4 connections,
> but doesn't look anything like the only Kelvin connected one I could
It does look like a Kelvin hookup. Yes, usually they are two fat and two
skinny connections, but so long as two connections carry the current while
the other two do not, it's valid.
Thanks Paul, I have been assuming that it is Kelvin connected for the time
being.
I have no idea if the resistor is faulty or if the fault is in the detection
logic. I am not entirely sure how to test it, and if it is faulty then
finding a replacement may be hard. If it is the detection logic, then I am
really in trouble because it is all SMD stuff, the board it is on appears to
have multiple layers and I can barely make out the markings on the
components, so I can't identify their type (resistor or capacitor) or value,
and I have never desoldered/resoldered SMD before. There is an op amp and a
comparator, which are easily identifiable, but there also appear to be some
transistors, and although I can see the markings "A4H" I have been unable to
identify what type they are, what the pinout is or if they are even
transistors at all (but I think they must be). Pictures of the logic board
here: http://1drv.ms/1QT7641.
I also noticed another very low value resistor, 0.01R, which looks far more
conventional (not kelvin connected for sure, it looks just like any ordinary
resistor, only a bit chunkier), but sadly, it seems to measure fine using my
ESR/Low Ohms meter, when measured in circuit.
Regards
Rob