TAC Scorpion PSU Issues

[Siegfried Meier]

Hey guys,

We also have an old '87 Scorpion here that is in pretty good shape.  The PSU is as well, but I'm having issues with the +48v side.  Initially, I saw that the LED was out on the PSU, so I stuck another 1A fuse in there.  Fired it back up, and slowly over the course of about a minute, the LED burnt out again.  Now, this could simply be because the fuse blew right away, and the LED burnt out slowly because the caps were draining.  Don't think I put a slow blo in there, but I didn't think +48 would care about that?  Any thoughts?

Thanks,
Sig

 

[mitsos]

Those fuses are on the secondary side, I've used normal fast fuses there.  The primary one you want a slo-blo.  Looks like something is shorting your 48V.  If it burns out without the console attached, check the PSU, if not, it's in the console.  good luck.  While you're working on it, if you haven't already done so, recap and also modify the PSU to remove the TO3 sockets.  Ask colin about it at AM, he has nice instructions with pics, it's very simple.  good luck!

 

[Siegfried Meier]

She's blowing without the console attached...

...what should I be looking for inside the PSU? 

Thanks for the help.

 

[mitsos]

Shouldn't be too hard to find. Here's a schematic:
http://www.gearslutz.com/board/geekslutz-forum/38192-amek-tac-series-350-power-supply.html

Could also be an intermittent connection in the TO3 socket.

This is from an ebay ad for servicing this PSU:

THE most important part of this rebuild in the heat-sink and regulator mounting modifications to make your PSU run much cooler and eliminate the poor regulator electrical contact that causes voltage drops and spikes. We eliminate these problems with the GRS Power Module Heat-Sink Upgrade modifications. The board above and the heat-sinks will be stripped down of all components and then new upgraded parts will be installed. Then the black heat-sinks will be modified to eliminate the intermittent regulator & transistor connections and to improve heat transfer. All of this increases reliability and eliminates voltage drop-outs, thermal shut-downs and poor voltage regulation!

I've had problems with TO3's before, so I did the mod, even though the PSU was working fine. Put some new heatsink compound on as well.  The TAC I have is likely getting hacked into two 12 channel hotrod "sidecars", so I'll do 2 smaller PSUs, basically the same as this, just smaller trafo.  I've already gotten a cAPI ACA-bo board working in there, they splice right in because, like API, all the summing uses inverting amps, just they're TL072s in the scorp!

anyway, good luck with it!