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Ive blown (at least) the tip120 on Q17 the last three times I turned the game on and I’m looking for help to avoid blowing it again.

Background: bought a well-used flash over the summer. Turned it on and ‘played’ maybe a game or two. At that time everything seemed to ‘work’, but the coils for the drop targets were all sticking. Then I started to ‘refurbish’ the machine including touchup and clear coat on the playfield and cleaning all of the mechanisms and replacing all coil sleeves. I couldn’t remove the sleeves on the drop target coils, so I put in replacement coils. There are three drop target coils…I put SA3-23-900-DCs in two of them Q19 & Q21 (this is the correct coil, I believe) and a SG-23-850-DC in the third Q17 (I understand that this is a suitable substitute).

When I turned it on the first time, something started burning. Eventually I found this to be the Q17 tip120. After researching a while, it seems that the new coils had the diodes wired opposite the original coils. I swapped the wires to the coil leads.

Turned it on again, and immediately the Q17 tip120 sparked and blew. I took it off and replaced it thinking a may have not soldered it correctly. This time checking for continuity and shorts on the driver board for this tip120. All looked good, so I turned on again and it immediately sparked and blew the same Q17 tip120.

This time I diagnosed the rest of the solenoid circuits on the board more thoroughly. It seems that the Q17, Q19, and Q21’s were all blown. The Q16 Q18 and Q20 were also checking out funny…so I replaced these too. The resistors and the IC 7408 seems to test fine.

Now I am afraid to turn on. What else can/should I check so I don’t blow everything again?

Photos below. Don’t be too hard on my soldering. I have checked to ensure I don’t have shorts and I do have continuity where I should.
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Hi thanks for the response.

The tip120s blow the second I power up. The Q16, 18, & 20’s are the predrivers and I replaced them all this time.

I will try without the connectors to see where the problem is.

Thanks, I appreciate it. Let’s see what happens this time.

Thanks, I didn’t realize that. I’ll definitely check them out before firing it up.

This was 100% correct. Coil diodes on my drops were all shorted. Thank you for this suggestion before I turned it on again!

Once they are replaced, I will turn game on without any solenoid connectors connected to board.

Making progress. With everything connected, nothing sparked and I don’t think I blew anything. I only turned the machine on with the three drop target coils connected for a second or two and it seemed that they were locked on in the charged position so I quickly turned the pin off. I pulled the three wires for those solenoids from the connector to the driver board and turned the machine on and tested for a while and everything else seemed fine. I’ll troubleshoot those three one by one this week.

Ive been working on/off on my Flash.

At this point, I have 2J11 pin 7 shorting to ground as soon as I turn the game on. This would be for solenoid 3 coil for drop targets.

I don’t believe there is any problem under the playfield, as I swapped the wire for solenoid 3 to one of the working pins on 2J11 and it worked fine in test mode. Likewise, whatever coil I connect to pin 7 on 2J11 locks on.

When I leave the 2J11 connector disconnected, and I put alligator clips on pin 7, the pin shorts to ground as soon as I turn power on. None of the other pins short to ground. When the game is off, the pin is not shorted to ground.

The associated tip120 seemed to test fine in circuit, but I replaced it anyway. Likewise, the 2N4401 tested fine, but I replaced it. I also replaced the IC7408.

Pin still shorts to ground as soon as I turn the game on.

What could it be? What could I check/test next?

Could it be an issue on the MPU? IC5? IC7? IC9? I’m just guessing at this point.

Help appreciated.

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What should I be measuring? DC voltage to ground?

I dont really understand how the IC’s work.

Anyway, IC1 pin 1 is reading 0VDC to ground. Pin 4 is reading 1.5vdc to ground.

Does that make any sense?

Pins 3, 8, and 11 are all at about 0.27v.
Pin 6 is 2.35v

…my 1.5v reading to IC1 pin 4 seems incorrect. Does this mean I should be looking at IC5 next?

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You’re suggestion is beyond what I’ve done previously.

That leg on IC5 is also reading 1.55v. Are you suggesting to cut that leg of pin 4 on the IC5? Why? Are you thinking that voltage is coming from somewhere else?

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This is what I have. I don’t think I can cut the leg off IC5 pin 4 with these.

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Thank you both for the tips.
I will try lifting the leg (pin4) of IC5 tonight.

I just replaced the transistors and the 7408 yesterday. Since then, with the connector attached, I’ve only turned the machine on for a second to verify whether the coil was locking. As soon as I see the coil locking, I turn power off. I suspect my 7408 is still good but will do the simple test on that tonight, as well.

After tonight, I’m going to be away from the machine for a couple of days, so I’ll go quiet. I do appreciate the help/input youve both provided. Thanks.

My solder work is so ugly…but I did have good continuity everywhere and no shorts, so I think it’s good. Will run your proposed tests tonight anyway, because…why not.

My life experience so far in pinball: the problem is usually the thing you assume is working fine.

I could cut pin4 on IC5.

Instead I desoldered the whole IC5 and removed the chip. Would it be a mistake to install the board and turn the machine on without the IC? Even if it doesn’t do any harm without the IC5, can I still learn anything without it?. Should I just remove the one leg and reinstall…or at this point should I just install a new IC5 regardless. (I don’t have one, so I’ll have to place an order).

For what it’s worth…desoldering that IC5 was a real pain in neck…but maybe a decent learning experience on using my desoldering gun.