We have a tac 50 that the ps1 power supply went out on after a power outage. One of our guys tried replaced it but now when you hook up the +12volt side the cpu won’t come up. There seems to be something dragging down the 12volt supply. Even if we pull all the pmi cards dsp and cpu the supply is still bad and we aren’t reading our -12volts on the test points in the card rack. I’m suspecting a bad card rack anyone replaced these before?

Tac50s didn’t use the +\- 12v supply. That was a TIII thing, don’t remember on a TIV but PS1 on a Tac50 should just be a 5vdc supply. There is something wrong with the part number though, when you order the correct PS1 part number from the manual you always get that big PS with the bipolar 12v but it only needs the 5v.

Dirt you might be right It might be a very early Tac50 or late TIV
It’s in a grey Tac 50 cabinet but I noticed the Dsp did say Dover on the board. Also we checked all the Pico fuses on the ssl they were all good. Best I can figure is there is something in the card rack shorted drawing the supply down. We did find if we leave the +12 unhooked and connect the -12 side of the supply we could get the cpu to come up. I think the cpu only uses the 5volt supply like you said so this doesn’t make a whole lot of sense?

It looks like earlier Tac50s did use the +/- 12v supply from PS1. Don’t think I’ve ever seen one. It probably doesn’t go anywhere but the rack though. I would think you could pull boards until the the voltage holds.

Got it fixed Ended up being a bad cpu the cpu was taking the 12volt supply to ground.