> -----Original Message----- > From: cctalk [mailto:cctalk-boun...@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
