The lower pop bumper on my Cyclone does not work during game play or through diagnostics. I'm new with Sys 11s and have been reading the repair guide and doing various tests tonight. I am looking for some validation on what I have done and what I intend to do.

The center pop bumper is a Special Solenoid driven by Q77. I have the same, good voltage on both coil lugs, and the coil fires when I ground the coil directly at the lug. So, the coil has power and is good. Likewise, when I ground Q77, the coil fires. Based on my understanding of the repair guide, that means everything between Q77 and the coil itself should be fine.

I still need to check the Q77 pre-driver and if that checks out, I believe that narrows my problem down to a bad 7402 TTL issue at U50.

Q76 (left pop bumper) has been replaced (before I got the game) and is working fine both in game and in diagnostics. U50 controls both Q76/Q77. Is it possible that if Q76 shorted that it damaged the 7402?

My plan is to replace the 7402 at U50. Since the coil does not fire in diagnostics, and the coil driver itself seems to be fine, I am assuming the 7402 has a bad gate, and when the CPU signals it to fire Q77, nothing happens.

I would appreciate any feedback or additional thoughts about this.

Thanks for the replies. @vintageclub: The bumper switch does register in the switch test and during game play (plays a sound when it is hit) so I assume the switch matrix is working fine. As you said, when the switch is hit, the coil never fires, which is what lead me to the TTL. I wasn't sure about the special solenoids situation but knew this particular one was CPU controlled. Thanks for that bit of info. Seems like Williams was making a lot of design changes at this point in time.

I only have a photo copy of the manual and it's difficult to follow the schematics. I have a logic proble but I am not sure I have the pin outs to check on the TTL. You wouldn't happen to have that, woudl you?

I'll check the pre-driver tonight.

Thanks again for the replies.

Thanks again for the info. I will check the voltages on the 7402 and see what I get.

Ok - it looks like the 2N4401 Q76 pre-driver is bad. I got .4 on one side but .9 on the other. I checked Q78 for comparison and got .4 and .5 as I should. I checked U50 and pins 1-3 gave me proper values which also matched what I read on pins 4-6. I'll pull the board, replace Q76 and will let you know what happens. I appreciate the guidance.

No love ... I replaced Q76 and the coil still does not fire through diagnostics.

However, the voltages for Q76 now check out properly. It looks like R102, R103 and R104 are in line past Q76, so I checked those and lo and behold, R102 shows 0 ohms. So that's next on the list of components to replace. I know the resistor is 2.7k ohm (per the bands and the schematic) but I don't know the wattage. I assume 1/2 watt since that's what the others appear to be. Do you know for sure?

Looks like R102 is a 1/4W and not 1/2W. Off to the Shack again tomorrow ...

This is why I am not a EE and I ask for help.

I removed R102 from the board and it tested fine - 2.7k just like it should be. So that is not the issue. With the resistor removed and the board on my bench, I started poking around a found something very strange: from both of the R102 pads, I have continuity to the emitter AND base of Q77. Given the crap solder job on Q77, I know it has been replaced in the past I also found that I have continuity between the base an emitter leads of Q77 itself -- which I know is not correct.

Given the continuity between the Q77 base and emitter leads, I am now convinced Q77 has to be bad.

I tested the original Q76 after I pulled it out, and it was indeed bad too.

So I believe both transistors (Q76 and Q77) were bad to begin with.

Success! I replaced Q77 tonight and voilà! The lower pop bumper is now working. @vintageclub - thanks for the help and support.

To summarize ... both Q76 and Q77 were bad. I also will strongly recommend the Hakko FR300 desolderer. After years of using braid and mechanical solder suckers, I broke down and bought the Hakko and it made this job a cake walk.