Seeburg SHP-1 - Short

So taking a break from my Seeburg USC-2 until I get a new DRD-1....

SO I have a SHP-1 amp that seems to have a direct short somewhere. I have it connected to my dim bulb tester and shows me a short. I have removed the transistors on the heat sink, the 2 boards and still shows a short. It was doing this prior to recapping and still after so I would doubt it is cap, and yes I replaced the 2 large can caps and I know the 2 are reversed in polarity (C66 red+/black- & C65 black+/brown-). I have checked every wire to see if there was something loose or cut but nothing.

The only thing that I can think of is a transformer, but which one? I have it on my dim bulb tester as it will blow a fuse immediately otherwise. What would be the best way to trace down a problem like this? I can take 1 transformer off the grid at a time to see but is there an easier way?

Ron, a shorted diode in the supply can easily cause this problem.

Beyond that, remove the preamp board, test, then remove the driver board (unsolder the jumpers that should be added) with the finals removed the culprits are reduced to a short in a transistor socket or wiring to the capacitor that couples to the output trans. The trans are not likely the problem as they are DC blocked by the coupling caps.

Rob

I would have checked for the shorted diode(s) first, before even touching a soldering iron.

Well thats the beauty of humanity Matt, we all work differently . I would and do the obvious pieces first which is typically replacing 40 years old capacitors before I even put in on my dim bulb tester.

Plus some of us are still learning and willing to learn. This is not a competition, this is a hobby for most of us.... Always remember DHPL!!!!!

Where can you get a 100 PIV -3A diode? Or what is an acceptable replacement?

Well I figured out a replacement and they are on order... 1N5408

Ron,
Hint--replace all 4--- Ron Rich

Thanks Ron, yeah I figured I would. I ordered 20

Ron,
I don't think I have used that many in the last 20 years--I think I still have the in stock with the Seeburg house number on them--By any chance, is this a Code A, SHP-1, or did someone "jump" the internal 2A.fuse ? Ron Rich

It was a pack of 20 that I got online... I will stash the rest, you never know what will come later

This is a SHP-1 Code B and has the 2a "pigtailed" fuse inline by the transformer diodes. 3 of the 4 diodes tested over 500 the other 1 (CR5115) tested at 0.

Ron,
Code "A's" had no fuse installed, and if/when the PRVC, or Mic was shorted, it would take out the diode--if you were "lucky"--if not, poof, went the transformer ! Ron Rich

rvalkenburg wrote:Where can you get a 100 PIV -3A diode? Or what is an acceptable replacement?

1N5402 (200 PIV @ 3 amps) Radio Shack # 276-1143:

http://www.radioshack.com/3-amp-diodes/ ... HS2KmcrhTQ

1N5404 (400 PIV @ 3 amps) Radio Shack # 276-1144:

http://www.radioshack.com/3-amp-barrel- ... ck&start=3

Both of the above would be an improvement over the original 100 volt rating, plus you can get them locally.

Replaced all 4 transformer diodes and at least that problem is solved
Showed to be OK, no more shorts on my dim bulb tester and double checked all caps and connections before I put it into service. Had it connected and turned on for about 10 minutes, did not engage the mech or anything, machine sitting idle. At that point it started... the resistor R5176 (560) on the right channel side of the driver board started to smoke. I know that resistor is tied to pin 17 (-32v) but have not been able to track down what would cause it to fry.

Ron,
I strongly suggest that you stop repairing that amp, and purchase, and read, ( also, read the sticky above about errors in it) (the late) Tony Miler's "SHP amp book", before you have a fire in that amp !
R-76 ( and others) should NOT be 560 ohms !!!
Ron Rich

I took the amp off-line immediately and would not put it back until I can figure out this issue and I will try and get a copy of Tony's book.

What should R-76 be, in the schematics it lists it as 560 and I do not see anything in the Doc Error Sticky about this error.