13 Dec
2015
13 Dec
'15
11:27 p.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Glen Slick
Sent: 14 December 2015 01:36
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: VAX 4000-500 PSU Overload?
I took a look at the DSSI & SCSI termination power supply board in my VAX
4000 BA440 chassis. It's the small board in the storage area of the backplane
mounted in place by a single screw. There are two identical circuits based on
the LT-1086 with the adjustable output voltage set at 5.30V [1.25V * (1 +
392/121)]. Each circuit has a 100uF 35V 105C nichicon cap between the input
and ground and the output and ground. Both circuits on my board still output
5.3V from a 12V input, but I think the caps are starting to leak electrolyte on
the PCB and I should replace them all (4 total) before things get ugly.
I just got the board out. The caps on mine look OK, but I see the ESR is at or just above
the value suggested on the table printed on my meter. So I will replace them all.
Each circuit has three diodes, an SB520 and a 1N4735A
for which I can find
datasheets, and a third one which looks like a General Instrument
MP654 for which I can't find a datasheet and I'm not sure if that is the correct
part number. I can't quite read the marking all the way around the body of
the diode. If someone else takes a look at their
BA440 DSSI & SCSI termination power supply board let me know if you can
make out what that part number is, or if MP654 is a GI part for which you can
find a datasheet.
I had a look and all I can make out on one is"P654" with "143"
underneath. On the second one I can see "MP" with "GI" underneath. So,
presumably, the full marking is MP654/ GI 143. Presumably, one of these parts is the date
code.
Regards
Rob