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Calling all electrical wizards

I know this is totally not something that shows up very often...  If anyone here happens to be particularly skilled at electronics or pinball machine repair, I could use some assistance.

I have a 1978 Bally Bobby Orr Power Play pinball machine that I have been trying to fix up for the past couple months.  It used to work a few years ago, then my dad had to put it in storage for a while.  It sat in a trailer in Missouri until he brought it back up to Wyoming for me.  Basically, when it got here we plugged all the connectors back in and switched it on.... nothing happened.  So I got out the DMM and started checking testpoint voltages.  Basically I have no voltage after the transformer.  So I figured that the transformer was bad and I started looking for a replacement.  It took me 4 months to track down a used one, I put that in just this evening and I still dont have anything.

I cant figure it out, I have the schematics of the transformer and rectifier baord assembly, and according to all of my continuity checks the board is in good shape and nothing is burned out inside the transformer.  I have a good ground all the way from the wall up to the board, and I can still verify 115VAC going into the transformer.  It seems as if something is grounding out the different outputs on the transformer, but I cant find it.  This is really begining to irritate me because I cant find the problem.  :mad:

Anyone have any suggestions?


Calling all electrical wizards

Reply #1 –
Can you post the schematic of the power supply?

Calling all electrical wizards

Reply #2 –
Does the transformer hum and/or get warm? If not, check for continuity through the transformer primary by putting your OHM meter on the pr0ngs of the power plug.

Calling all electrical wizards

Reply #3 –
Wow, Neat project!  Definitely continuity check the transformer per softtouch. The primary and secondaries should all have low ohms.

If the primary is open, you would have no AC on the the secondaries, as since you have several secondaries, its unlikely they all went bad.  The primary coil is common to all of them.

That board that is next to the transformer has full wave bridge rectifiers on it (the 4 lead square blocks), I have seen those go shorted before, but I'd expect that would make the transformer warm.

You could unplug everything from that power supply board except the transformer to get rid of the rest of the load and see if that brings things up.  It looks like each one of those rings labled TPn should have the DC voltages on them if things were working.


V6->V8HO 88 LS
5.0L V8 87 XR7

Calling all electrical wizards

Reply #4 –
First rule in trouble shooting a power supply with several secondaries on the xfomer... Verify the primary is OK and their is no open circuit back to the plug. Should be fused as well as a switch and maybe a safety that has to be bridged while the unit is open. I've only looked at a couple P/B wiring diagrams, so yours may very well be different..
 

Calling all electrical wizards

Reply #6 –
I had my father-in-law over for 4 hours this evening helping me troubleshoot the machine with me.  We couldnt figure out why we had 120VAC between the hot and return lines coming up to the transformer, but as soon as we hooked it to the transformer we had no voltage between hot and return, yet 120VAC to ground.  No fuses were blowing, the transformer just sat there and didnt act like it was shorting out anything.  I was seriously ready to shoot it and go watch SG-1 while eating Oreo's.  We finally found that a rat (or some other animal) had chewed through the return line on the power cord WAY back up inside the machine where we couldnt see it, and that was why were werent getting any voltages coming out.  By that time I was ready to just sit down and cry because I have been trying to figure the problem out for 4 months.  A $9 computer cord from radio shack solved the main problem, one that I should have checked when I first tried to turn the stupid thing on.:shoothead



Now I have to troubleshoot all the solenoids to find the ones that are locked on, fix all the feature lamps that arent working, fix the score displays, and stop feeling like a retard for not catching the power cord.      All but that last one should be easy.