SPS160 Blowing GFI

[paradisecs]

I picked up a free SPS160 in great physical condition but the guy said he could never get it to work.  I didn't bother to power it up on site (didn't want to inadvertently fix it and then have to pay to get it).  Got it home, cleaned the mech and contacts.  Powered it on and instantly blew the GFI circuit.  I did some further checking and didn't like the 7.5 fuse socket so I replaced it and the fuse. 

Powered on and blew the GFI again.  I pulled the DCC4 and SHP3 out and tried them in another unit I had sitting there and they work fine and more importantly don't trip the GFI.

I mounted them both back to the SPS160 but didn't plug them in to power.  I then powered on the cabinet which turned on all the A/C lights.  If I then plug the AMP and DCC in to the A/C inside the cabinet they come on and work without blowing the GFI.  Turned the power off and back on and immediately tripped the GFI.

Any ideas?  A short in the toggle switch maybe? When I unplugged for the night i noticed that someone had put a 3-prong plug on.  Could this be causing a ground issue and blowing the GFI?  I know that the 3-prongs are bad on these units but I don't know why.

Stephen

[Ron Rich]

Stephen,
By law, all Seeburgs produced after the model LPC-1, must have 3 wire line cords ! Something is causing this problem--Plug in units one at a time and power it up- check the LPS circuit last, you may have a pinched wire there. Ron Rich

[robnyc]

First, do a simple continuity test from the plug AC prongs to the ground pin. Should be no measurable continuity.

Next, use a ground lifter adapter (3 into 2 wire) the type with a free ground wire meant to go under a screw on an outlet faceplate. Turn on and measure voltage from that ground lead to the ground on the outlet.

I have measured as much as 79 volts with no current behind it into a DVM in these tests and this goes away when you reverse the internal plugs. That voltage will trigger a GFI while not representing a actual danger. When you tried these units in another machine you may have just polarized the plugs to eliminate the leakage. All of my machines will exhibit some leakage if not grounded. I test for this and polarize-mark the internal plugs before reconnecting the ground.

RobNYC