I always recommend checking the display high voltage before removing your driver board for service. I’ve written about this before, sometimes the circuit can fail allowing the full 230VDC to pass through the regulator to the displays.

When this happens I’ve found that Q21 (the transistor on the heat sink) is dead shorted allowing the full 230 volts to pass right through. The first time I found this I replaced it and it blew right out again. That’s because Q23 (the transistor with the fins on it) is also blown. When Q23 blows it takes Q21 with it.

Replacing both usually solves the problem. While I’m there I also replace Q22. On this Bobby Orr Power Play the displays stopped working. The fuse was blown but not for any obvious reasons. At the 190 volt test point I was getting 230 volts.

I replaced all 3 transistors and the capacitor, (C26, the big filter cap) serviced the rest of the board and tried it out. I still had no displays and the voltage was low and fluctuating between 120-150 volts.

R51 was burned up and open when I measured it. I’ve seen them burned up before but they usually still read good. Either way do yourself a favor and replace it. I also replaced the two capacitors next to it (C27 & C28), CR21 the 1N4004 and VR1 the 1N5275A zener diode.

When that zener fails you’ll get a low voltage condition, about ~25 volts or so.

The displays seem to be able to take the full 230volts but who knows for how long. Don’t take any chances. Check your high voltage section if it hasn’t been checked recently.