Hi pinsiders,

I'm new here, and new to pinballs in general. My step family had a Data East - Back to the Future pinball sleeping in their garage for almost 20 years.
The pinball is from 1990, they forgot about it after it broke down. I'm trying to repair it.

I've had a specialist (in France where I am at the moment) who repaired the power supply and CPU boards. The CPU board had battery acid damages. So a lot of components are new on those. I had to fix a transistor on the PPB myself to get 50V to the flippers. The pinball worked for one day, but while I was testing some lamps, I think I got a shortcut. While I was levering the playfield, lights started twinkling, and I heard a clacking noise. I turned it off, but when I turned it back on, no more booting. Had a couple fuses blown out, on the power supply and PPB boards. I replaced them, the pinball still doesn't boot, with the 5V and PIA leds always lit.

What it does :
- 5V and PIA leds always lit on the CPU (no flashing of any of the leds)

- low 5V on the power supply board, only 2.3V. 12V ok (14V/-14V). If I disconnect CN6, I get the 5V back. Something is wrong when CN6 is connected (I got that it supplies the other boards?)

- The fuses are all fine, the capacitors look ok on the power supply (and have been replaced very recently), I get the right voltages at the fuses of the power supply, and 43v at CN3 (where it should be 34V, but I guess it's ok?)

Before a couple months ago, I knew nothing at all about pinball, and really not much about electronics. But I have the manual and the willingness to learn.
Any help would be much appreciated ! Thanks !

Thanks, I found the pinwiki, that's great !

For my problem I see that I have to check this :

4.5.5 Low or Missing 5VDC
If you have low or missing 5VDC, the game may reset or will generally not function properly. Several components could be the root cause for this condition. Ordered in probability of failure, examine...

fuses at F1 and F2, both 7ASB fuses. Remove them and buzz them with an ohmmeter -> Done, they are OK

C2 (100uf 25v), C3 (47uf 63V), and C7 (330uf 25V). These caps tend to leak their corrosive contents on the PCB and kill the 5VDC circuit. Replacing these three caps is always recommended when 5VDC problems occur -> It's been done by the tech less than 2 months ago, they look fine

bridge rectifier (DB1, CM3501). Test the bridge first. Lug style bridges are tough to remove while avoiding board damage -> Not sure how to do that

LM723 voltage regulator. If the DC voltage with respect to ground at pins 4 and 5 differ, the regulator has failed. -> Will check tomorrow

TR5 (2N6057) on the power supply board (use 2N6059 or 2N6284 to replace obsolete 2N6057) -> Will check too

C1 (1000uf 25V) can also be replaced when you have problems with the -12V supply too -> Doesn't apply here

Another condition affecting the 5VDC power circuit is failure of the 18,000uf/25V smoothing capacitor at C4. This cap is probably way past it's spec life. Replacing it is advised. While the original capacitor was specified at 18,000uf, the more common 15,000uf/25V cap will work fine in this application -> not sure it's been replaced, but doesn't look like it leaked.

While trying to test the LM723 chip, I think I made it worse ...
Suddenly the blanking led lit on the CPU, and I now have 14 V on the 5V test! Slight burnt smell too.
I stopped there.

I had 3.8V at pin4, 5.14V at pin5. Maybe I should not have tested the other pins ? At pin 8 or 9 I got the blanking led to switch on.

Here is the power supply board

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