The electronics

Before switching on the pinball machine for the first time, I checked the input voltage settings on the main transformer and the fuses there and I checked the fuses on the power supply board. I needed to replace one fuse, it looked good, but when I measured it with my multimeter it failed the test.

Then I finally switched the machine on. Nothing happened. Then I plugged in the power cord and tried again… Lights came on, displays flickered at random and then went out. That was it.

Clearly things are not working as they should, time for some troubleshooting.

So where to start? With the power supply ofcourse!

The first thing I noticed was no -5VDC due to a defective 7905. Off to the store I went and now the power supply has a brand new 7905.

New 7905

The new 7905

Unfortunately after fixing the -5VDC I tested again and the 170VDC was gone. After a few measurements I noticed that TR3 (2N3440) had come loose from the PCB. Shabby soldering? That knocked out R6 (47 Ohm 3W) as well. Off to the shop I went again. I had to use a 5W resistor, but that’s not a problem.


The new R6 (47 Ohm 5W)


The new TR3 (2N3440)

I reconnected the power supply board into the pinball machine and tried again. Except for a pop from the loudspeaker when switching on nothing changed. I disconnected everything except the sound board and after pressing the test button on it, the LED blinked 5 times and the pinball machine started talking to me 🙂

The Sound Test video, best viewed with VLC media player (see my links section).

I disconnected the sound board and reattached the CPU board. It would not boot. After some reading on (see my links section) I checked the Power Fail signal coming from the power supply board and yes, it was the wrong signal 🙁

So I did what all good technicians do and disconnected the lead from the connector. Problem solved. I promise to get the power fail circuit fixed later on. I promise!

The Power Fail circuitry

I promise to check this power fail circuit later on...

The power fail workaround

The power fail workaround

After retrying to boot the CPU, it actually did… sort of. I starts booting but then keeps hanging somewhere. When measuring the test points, I don’t get the pulse signal on TP6. Further testing and digging in the schematics is necessary. To be continued…