DEC Rainbow/Decmate PSU repair thread

[tradde]

I decided to start my own thread on this instead of tack onto the other one that is different than my problem. I have a dis-functional Rainbow PSU. As far as I can tell the Decmate II and Rainbow use the same supply as I took the one from the Rainbow and put it into the Decmate and it works fine. One is an -A version and one is a -D version so there are likely some minor differences. What those are I do not know. The one that is not functioning is the -A. It seems to power up fine with no load but the outputs vary around +4.5v and 11.5v. I know this means it would like a load. So I grabbed a SCSI disk that I know spins up and used that as I don't happen to have a load generator nor a car lamp to try. One connecting this disk the outputs drop to zero. I know almost nothing about power supplies so I do not know what to check. All we have for schematics are those drawn by Tony Duell. I can't read a schematic to save my life. I keep trying but it seems my brain is not wired to understand them. So any easy suggestions to try. I feel that since without a load that much of the PSU is Ok and think it may be something faulty on the smaller control board. Is that a wise thought? Thanks for any help. I'd like to get both my DEC machines to work at the same time.

 

[vrs42]

On May 26 over in the cctalk/cctech mailing list Brent Hilpert made a post that may be relevant. I think what he's saying is that you need Vstart-12 as well as Vstart+12 before you can tell what is going on. I have basically no clue about these things either.

Rainbow H7842 PSU Fault - cctalk - classiccmp.org

classiccmp.org

Vince

 

[tradde]

I believe someone else already pointed me to cctalk. Is this the post from Rob Jarrett? I plan to contact him to see what he has to offer. Thanks.