*** THIS WAS RESOLVED AFTER DISCOVERING THE BATCH OF TIP102s BEING USED WERE FAULTY/FAKE ***

This is probably simple, but better to ask vs replacing a lot of TIP102's, pre-drivers, and logic over and over again.

Special solenoids aren't locking on at pwr on here, but Q75 blows up when triggered.

I initially replaced q75 as it was blown previously. Replaced the 4401 pre-driver and 7402 @ u45 as well, as the high signals on IJ18 were not present. Everything else tested fine in the area. Tested out U50 and U49 as well. Pop coil to Q75 was melted previously, replaced coil. Coils have proper voltages, aux pwr board coil diodes are good, TIP36Cs for slings are good. Switches tested ok. Fuse values are correct everywhere. I figured all was well.

But when in test mode, activating Q75 via pop switch causes it to violently fail, take out pre-driver + U45 7402. It seemed almost delayed, whereas I didn't see it coming to shut the game off immediately. All other special solenoids did not activate either, minus the right sling. Q75 was the last switch tested and it blew up and I had to replace the driver, pre-driver and U45 again.

With IJ18 & 19 disconnected, everything else is fine. I have barakandI's solenoid saver on the way before I test again.

Any ideas where to inspect next? PIAs? I've usually seen this the other way around where coils just lock at pwr on, and replacing upstream logic + drivers takes care of it.

i just realised i left the coil mounted diode on the replacement....yeah, that would do it.

Leaving this post in hopes it helps someone else to not overlook.

not so fast

got andrew's sss board to test SS section again, all working now except Q75 pop. Trigger that pop, locks on. Turn off game, turn on, locks on now. Unplug IJ18, still locking, so not a switch issue. Time to replace upstream U49 and retest U45 to see if it shorted it out again. But at least no blown TIP102 again. SSS board fuse did not blow. Didnt want to leave engaged long enough to test that though.

U45 isn't shorted, but I've got three blown TIP102s with the inline driver fuses in place. Q73, Q75, Q77. 3 pops. Getting closer.

Any ideas why it cascade failed like that and why fuses didn't pop? I must have some streams crossed somewhere.

Going to replace U50 & U49 now.

had the sss board upside down, which explains why the fuse didn't pop.... sucks having limited time, lots of mistakes.

uggghhh... Q75 keeps blowing. SSS fuse not popping. No clue. But TIP102s did not cascade fail, but tested that way in circuit after the Q75 short with 1J19 connected prior to socketing U50 & U49, so good clue there, like if a diode shorted.

Seems like something is connected wrong, but I've checked a dozen times now it feels like. Unless a PIA can do this sorta thing. Or another component failed now that was working previously. Going to recheck zeners. Aux pwr diodes are fine.

Replaced Q75 again. All other SS circuit components tested out again on the game. Everything checks ok, pre-drivers fine, drive transistors fine, Logic is good, Zeners all giving around 5k resistance, resistors compare fine to others, values all look the same. On a whim, I replaced the diodes on the aux pwr board again for the pops, but they tested fine out of the game.

With MPU in game, J118 & 19 disconnected, logic levels look right from U49 buffer to U45 & U50 lines on the NOR gate like it should to provide GND path when in test mode. Holds high outside of test or game mode, so nothing is getting stuck. PIA isn't negatively interacting anywhere from what I can tell.

Replaced SR19 since some of the readings were below 4.7k, but it tested fine outside. I've got my Swords of Fury MPU to A/B things now, because at this point, I'll never figure this out otherwise. But it really seems like it isn't board related. Coils all test fine, 4 ohms on all 3 pops, 14ohms on slings. Swithces test fine, no shorting between the score & activation switch, or mounting screws/pop body, etc.

Last time when I was at this point and plugged in 1J18 & 19, I got all the SS components working fine with repeated tests, with the exception of Q75 Pop, which fired about 3-4 times normally when triggered, then fried the Q75 and locked on again. So whatever it is that is causing it to fail after replacing the drive transistor, it takes a few times before the transistor breaks down. It definitely is failing like if you had a shorted coil diode.

Could I have created a current sink somewhere when it had that explosive failure initiallly? I have Leon's test rom to check PIAs if it really did travel that far upstream.

Good idea. I'll throw an LED in line with a resistor and eliminate that coil from the equation and see if Q75 still blows. Divide and conquer is definitely the way to troubleshoot at this point.

I replaced the diodes for the pops on the aux board again for good measure. I'm about to replace all of them in the lower coil voltage path at this point, even though they tested fine. Also replaced the pre-driver for Q75. Put sockets in place for Q75 & the pre-driver. It isn't ideal for long term, but for now, it will help if I have to keep replacing Q75. I also tried swapping coils with another.

Still blowing Q75. Pops 4 times, then blows out the collector side consistently. I'm going to swap power & gnd return wires with one of the other pops. After that, I guess it is time for Leon's test at this point, as every other logic IC involved tests fine.

I don't have a high wattage resistor at the right value on hand to do the LED test, unless there is some other way to kludge it together. The only 1+ watt resistors I have are either too low a value or too high. I think I need something in the 2k-5k range at 1 watt or higher to do that, right?

Thanks zaza, that clarifies things for tests. I was thinking of high power, and you were talking about probing +5v with an LED to see if it is stuck on I'm assuming. I had done probes with my meter previously to rule out all those logic IC areas. I'm going to focus on PIAs later tonight.

It has to be something on the aux pwr board, I've gone through everything at this point. MPU is fine. Leon test shows the PIAs are fine. Checked logic switching with an LED test and it doesn't lock on. Even took apart the entire pop. I still don't know why the solenoid saver board isn't popping fuses. Going to replace every single 1n400x diode on that board next here.

Thanks for the ideas DA. I will throw a diode on that coil as an additional EMF protection to rule out the Aux board for now. I'm leaning that way, since it consistently blows after 3-4 switch actuations. Make sense that would be some sort of blowback threshold for the TIP102 breakdown. I'll also disconnect 1J18 and let it rip in test mode and see what happens. I don't care about blowing TIP102s now that I have sockets in place. It has made it less painful to test ideas. Sometimes getting over the fear of blowing things up is 1/2 the battle.

When I was doing logic probing, I did disconnect 1J18 and stuck an LED+Resistor to watch the logic, triggering the pop switch over and over, let it sit, came back, repeated. Unfortunately I didn't catch it misbehaving at all or latching on any of the NOR inputs or the output.

What kills me about this is that is that it seems brain dead, whatever is going on. I'm like 8 hrs into debugging this now. It is isolated to the one area, so it should be easy to debug. I've got to be glossing over something dumb. No AH HA moments yet though.

With switch removed & diode running across the coil, Q75 does not blow!!! (in cpu activated test)

So the issue is the switch path. Locked on with switch activation when I reconnected it and burnt up Q75.
Going to replace the zeners now and inspect any other parts I haven't replaced yet in that switch path. I've only got 6.8v zeners on hand, but I'm guessing that is fine, since they're supposed to function as dumps for overvoltage anyway.

So that rules out everything else. Thanks again DA.

Replaced zeners. Still locking on with the switch and killing Q75. I honestly have no clue what to do at this point. I checked U45 again and it looks fine.. Same with SR20. Stuck my meter on the switch again and tested that out a bunch to see if it was a physical issue, but it checked out fine. The only part in that switch path I haven't replaced is C71 .1uf cap.

Unfortunately, i've replaced all parts on the switch, short of the leaf switches themselves. But it has to be the switch, otherwise Q75 would blow with CPU controlled test.
I'll replace C71 on the mpu for shits, and ill swap out the solenoid switch itself.
The red flag here is that the inline fuse for coil power to Q75 does not pop.
What would cause the TIP102 to short only with switch activation, and NOT also blow an inline fuse?

Ordered a replacement switch stack for that pop. I know it is fine, but need to rule out everything. Disconnecting that pop for the time being.

Switch replacement (and RC replacement) did nothing, as was expected. Replaced C71 on MPU as well to rule out ALL components related to Q75 driver path.

No change, still locks on, but ONLY with switch activation. Kills Q75.

Replaced components:
MPU SS section - all drivers & pre-drivers, Zener diodes, SIP resistor packs related to SS section, U45, U49, U50.
Aux Pwr - All 1n400x diodes.
Playfield - Pop switch stack & components.

The wiring is definitely 100%, no goofs there. I've done countless continuity traces, both from PF to back box, and on the MPU in those SS areas and further upstream. Leon's test looked fine, all wiggling, nothing latching. Nothing latching with logic testing of the switches, checked 3 times at least now.

A/B checks done with my Swords of Fury. SoF doesn't use 1J19, so not the best comparison there, but it made more sense than to use my Pinbot because SoF has the Aux pwr board and interconnect board. I didn't swap SoF's MPU into Taxi, but did component level metering checks. I'm probably going to have to do the swap now and risk damage because I'm out of options. Only thing left is that this is somehow MPU related still.

It gets more bizarre now.

I swapped MPUs with my SoF. Initially ran CPU controlled pop/sling tests, ran coil tests, let them sit on the pops and slings for a bit (30 actuations per pop). Everything looked good, so turn off, plug in 1J18, go back into test mode to check out switches. Slings are good. Upper right pop is good with switch, lower pop is good with the switch, left pop doesn't blow Q75 with the switch.... But after 2-3 pops, the power starts to get super weak and stops working, all pops affected. Poor SoF MPU probably needs work now.

Disconnect 1J18, fire it up again, run CPU controlled test again for pops....Nothing. +25 rail is fine, all the other coils have no issues, fuse is fine.

Checked the SS section TIP102s on the SoF MPU, none are shorted. Checked out U45/U50 (these were previously socketed on my SoF MPU), they're good as well.

So the issue is power related??? like a failing 25vac rectifier on the Aux pwr drv board or something, only all of the other +25v rail coils operate fine. Could that be due to the differences between pulse timing and manual switch activation? Really reaching here. Obviously there is also still something wrong with the Taxi MPU as well, since Q75 didn't blow.

im definitely going to pull the aux pwr brd tonight. I recapped it already, and I usually just replace rectifiers, but didn't this time. I may have forgot to reflow joints. I usually replace headers too, but they looked good on this game.

Pulled the aux pwr drv board. Everything looked good, zero ohms resistors are good, BR1 tested fine too, but reflowed solder everywhere and replace BR1 as well. Replaced the 2.5A fuse for the Red-White wire, as well as the 25VAC 7A fuse. Fuse clips have decent tension. No corrosion or anything. Checked ohms from red-white wire at the Aux Pwr drv directly to the coils - 0.1 ohms. Checked each pop's return wire @ 1J18 - 0.1 ohms. All good with power and return.

Fired up the coil test. Same result as before. During CPU test, the left pop just faintly attempts to power on, the others are even weaker. So it is MPU again, only now with the SoF MPU.

Unplugged 1J18 & 1J19 and manually fired all 3 pops just fine to the gnd strap, full power. Checked the SoF MPU, all the SS section TIP102s and pre-drivers tested fine on this MPU, along with U45, U50 that were previously socketed.

Next test is to remove the SoF MPU, checked it over deeper then pop it back into SoF to test and see if whatever is going on with Taxi screwed it up. At least that would give me insight into what it is doing and narrow it down further.

I put new ones on all three. Made 3 "22uF" bipolar caps from two 47uF Nichicons, (+) to (+) chained, (-) leads to switch solder tabs. The originals were really out of spec, as expected of low value 30+ year old electrolytics. I have done this before without issue in other games.

I have a scope I can use. Coils fire fine manually. Voltages at the coils check good so the Aux Pwr board is likely okay at this point, from a connection perspective. A lot of components have been replace on it now anyway (every single 1n400x diode, caps, BR1). I had it on the bench last night and ran through it to ensure it was good. I can still swap the board from SoF.
But because when I ran the coil test initially with the SoF board the pops fired fine, then the weakened behavior started after I connected 1J18 to test switch triggering, the issue is likely not Aux pwr, or power at all. It is something fudged up with the MPU(s) now as a result of some bad behavior with those switches. Like mentioned above, the SS switching looks perfect on a logic level. Everything gets enabled correctly in test/game mode, and all logic fires as expected. It is acting as if something is miswired, PF side issue, but I have thoroughly inspected that wiring dozens of times now, and I also can't be 100% because of the history of the SS repairs on the SoF MPU.

I picked this up in this state. Initially, the left pop coil was melted. No back story on it, other than knowing some work was needed on the pops and SS section.

I'm thinking I have two damaged MPUs here now, so any further looking into or troubleshooting with the SoF MPU is moot until I determine what failed on it. If I narrow down what failed on it, it MIGHT give insight. But because the SoF SS also had previous work, AND SoF doesn't use the switch path 1J18, it could have had faults previously that I didn't catch.

I'm uploading a video now because there definitely needs it at this point. Here are a few pictures.

Pops wiring
IMG_20200925_142000430 (resized).jpg
IMG_20200925_142004454 (resized).jpg
IMG_20200925_142021584 (resized).jpg
1J19 & 1J18 Connectors into SoF MPU
IMG_20200925_142055151 (resized).jpg
Taxi Aux Power Driver
IMG_20200925_142059914 (resized).jpg
IMG_20200925_142104781 (resized).jpg
Interconnection board point for +25v line
IMG_20200925_142117198 (resized).jpg
Taxi MPU & Trace damage/repairs
IMG_20200925_142251293 (resized).jpg
IMG_20200925_142257784 (resized).jpg
IMG_20200925_142308705 (resized).jpg

It is sloppy, I know. Especially the TIP102 areas that were zapped (previously).
My Hakko desoldering iron needed a new tip and lifted a trace topside on U45 before surrendering and buying a new one. But everything is fine there, no bridges anywhere, spent time buzzing out that board.

holy shit.. i have the wrong return wire on that lower bumper!!!!!

1:20 in - I said SoF MPU, Meant Taxi MPU.

thank you for the reference, helpful

They tested okay on the bench, but I'll jumper them all to rule that out tonight. Thanks for the idea.

That was the first thing I thought when I saw the picture, but i checked and it is the right one. I buzzed them out a dozen times, so im sure they are right. Good to know I'm not crazy. Thanks.

Caps were installed series, i mispoke.
I tried the jumper on W4, no dice there. I will attempt TIP gnd now and see.

Pops fire perfectly gnding the tab of the TIP102s

I put the Taxi MPU into my SoF. SoF has no issues with it, works fine in it so far.

I did briefly do logic tests again on the 1J18 switch path U45, U46, U49, U50 interactions all the way to the drivers for this SoF MPU in Taxi. Logic is functioning properly, being enabled where and when it should upstream. I can trigger that switch and see the pre-driver to driver voltage changes, was something like 1.6v for all them, which I believe is the right saturation voltage for a darlington pair, not getting blasted with 5v.

I put diodes across the pop coils temporarily to rule out EMF. Going to remove aux pwr again and remove 0 ohm resistors and solder in jumpers for peace of mind later. It shouldn't make a difference since gnding the tabs fires them without issue. They are getting power just fine.

My switching logic is good. I'm confident there. Those pop switches are functioning properly in every way (buffers, NOR, inverter, enable).

With 1J18 disconnected and the pop switches out of the equation 100%, getting no/ultra weak action with pulse fired CPU pop coil test means voltage is not getting to solenoid gnd properly. That it applies to all 3 pops means it is probably a shared/common path, PROBABLY because the left pop barely functions, the other two do nothing.

Ether way, bench time for the MPU again.