I am resurrecting this thread because I am having a similar problem with a Medusa. The bottom right pop bumper locks on when the game is started and blows the playfield fuse. I have replaced the q14 transistor and resistor and installed a new coil on the pop bumper.

I followed Quench's advice and tested the following voltages on the SDB. Here are the measurements. They appear to be okay.

Measure the voltages on the SDB at:
a) Pin 14 of U2 3.68vdc
b) Pin 10 of U3 .92vdc
c) Pin 9 of U3 .55vdc
d) The banded side of diode CR14 1.28vdc

Thanks in advance for the advice.

Quench,

Thank you. I have should have known that - still learning.

How do you know what the correct voltages should be at the different pins and locations?

This is really helpful. Thanks!

I replaced U3 and everything worked fine for a while. Then the same pop bumper - bottom right decided to quit working. Q14 had failed. I replaced it and all was good for a while and then Q14 failed again.

It is a new coil with diode so it should be good. I did not replace the cr14 on the sdb. Will do that and report back.