Comet pinball slingshot not working

[Lindsey]

I've installed wires onto a coil with the wires reversed on the diode because the new coil had the diode on opposite of the old one. This was the resulting symptoms. It was a pain.

A reversed coil diode caused a bank of coils to lock on when the game was turned on? Weird. That shouldn't be possible. I'll have to take a closer look at the schematic.

 

[shardian]

A reversed coil diode caused a bank of coils to lock on when the game was turned on? Weird. That shouldn't be possible. I'll have to take a closer look at the schematic.

Refer to my Jurassic Park thread for further reading. It made all of the tip36c's appear shorted (that shared that power wire). Q5,4,3 all appeared shorted, because the swapped power wire was on the ground trace after it blew through the coil diode.

 

[R3LL1K]

Re-test all of the transistors. You probably did it wrong. If any test bad, take them out and test them again. If you find a bad transistor, you have to check everything in that circuit.

I clipped the black lead to the ground strap in the backbox and touched the metal tabs on the TIP122's with the DMM set to ohms and then again with the DMM set to diode test.

EDIT: I would pull the connectors coming from the special solenoid switches and the connector going out to the coils. If you've still got continuity to ground on the tabs of the driver transistors you know they're stuck on for one of the reasons I mentioned above.

Pulled the connectors and the TIP122's read open/infinite.

A 7402 IC could be shorted internally if the transistors are being energized when you turn the game on. Either that or a bunch of the special solenoid switches are stuck closed. Or all the driver or pre-driver transistors are shorted.

on U6 7402 with black lead to pin 7/ground
pins 3, 6 and 8 are shorted to ground

on U7 7402 with black lead shorted to pin 7/ground
pins 2,6,8,9 and 11 are shorted to ground.

So I guess this means the 7402's are bad?

 

[shardian]

I clipped the black lead to the ground strap in the backbox and touched the metal tabs on the TIP122's with the DMM set to ohms and then again with the DMM set to diode test.

Wrong test. That is the test you do to test down stream wiring when the game is on. You need to do the test where you touch one lead to an outside transistor pin, and the other to the center pin or the tab. One way should give you a beep and a reading within a range of .4-.6. The other way should be a null reading.

on U6 7402 with black lead to pin 7/ground
pins 3, 6 and 8 are shorted to ground

on U7 7402 with black lead shorted to pin 7/ground
pins 2,6,8,9 and 11 are shorted to ground.

So I guess this means the 7402's are bad?

Yeah man, you have major fried board components if all of those are showing shorted. Pull your board and do the proper transistor tests for all of the drivers and pre-drivers. If your 7402's are bad, then the drivers are also bad most likely.

 

[R3LL1K]

Wrong test. That is the test you do to test down stream wiring when the game is on. You need to do the test where you touch one lead to an outside transistor pin, and the other to the center pin or the tab. One way should give you a beep and a reading within a range of .4-.6. The other way should be a null reading.

This is how I read to test them on the pinrepair.com site.

2d. Before Turning the Game On: Quick and Dirty Transistor Testing
Transistor Testing.
Whenever I get a new system 11 game, before I ever turn it on, I test all the TIP122/102 solenoid transistors. I do this because I'm already in the backbox (examining the fuses and the GI connectors), and a blown transistor can really confuse a system 11 game. This is the procedure I use, and it takes about 20 seconds to test all the TIP122/102 transistors:

Make sure the game is off.
Put your DMM (digital multi meter) on ohms (buzz tone).
Put one lead on the ground strap in the backbox.
Touch the other lead to the metal tab on the TIP122/102 transistors. These are the 16 transistors at the lower left side of the CPU board, the six transistor at the upper right, and the eight transistors at the far lower right of the CPU board in a vertical row.
If you get zero ohms (buzz), the transistor is bad! (shorted on)
I replace the bad TIP122 transistor(s) with a more robust TIP102 immediately before I turn the game on. I also usually replace the associated pre-driver 2N4401 transistor too.

Yeah man, you have major fried board components if all of those are showing shorted. Pull your board and do the proper transistor tests for all of the drivers and pre-drivers. If your 7402's are bad, then the drivers are also bad most likely.

Luckily I ordered these driver and pre-driver transistors on Monday so I already have them on hand. I can pick up the 7402's tomorrow at Fry's. In reading the repair guide on pinrepair.com it says the PIA could be bad as well. Is there a part number or a way to test this part? Better yet, where is it and what does it look like.

 

[shardian]

The special solenoids are not CPU controlled. 7402 is as far back as they go.

 

[shardian]

I never use that method except for live testing for non-working coils.

Has someone worked on this before you? Maybe someone replaced the tips, but not the pre-drivers or the 7402 chips. Either way, pull the board from the game and follow the instructions for bench testing the transistor logic. It's a little farther down in the coil troubleshooting section of Clay's guide.

 

[R3LL1K]

I never use that method except for live testing for non-working coils.

Has someone worked on this before you? Maybe someone replaced the tips, but not the pre-drivers or the 7402 chips. Either way, pull the board from the game and follow the instructions for bench testing the transistor logic. It's a little farther down in the coil troubleshooting section of Clay's guide.

I don't know if this board was worked on previously.

 

[Lindsey]

Refer to my Jurassic Park thread for further reading. It made all of the tip36c's appear shorted (that shared that power wire). Q5,4,3 all appeared shorted, because the swapped power wire was on the ground trace after it blew through the coil diode.

The path to ground is still through the driver transistor. I get it though... the wires were reversed.

 

[Lindsey]

on U6 7402 with black lead to pin 7/ground
pins 3, 6 and 8 are shorted to ground

on U7 7402 with black lead shorted to pin 7/ground
pins 2,6,8,9 and 11 are shorted to ground.

So I guess this means the 7402's are bad?

Are you testing this with the game on or off? In any case... a meter set to continuity is going to be tough to troubleshoot with here. Is that what you're using? A logic probe would be better. The signal at the pin could be high and still show continuity to ground because the semiconductor in the IC is biased making you think it's low (shorted to ground).

I don't usually suggest this kind of thing but you should just determine which NOR gate (7402) is in the circuit for the coils that are locking on and shotgun it. I won't be shocked if that fixes the problem. They're cheap.

EDIT: Wait a sec...

Pulled the connectors and the TIP122's read open/infinite.

Are you saying that the transistors are biased (on) when the connectors for the switches and coils are attached but not on when you remove them? If that's the cast you need to determine which connector causes the problem to reappear and you probably don't have anything fried on the board.

 

[R3LL1K]

Are you testing this with the game on or off? In any case... a meter set to continuity is going to be tough to troubleshoot with here. Is that what you're using? A logic probe would be better. The signal at the pin could be high and still show continuity to ground because the semiconductor in the IC is biased making you think it's low (shorted to ground).

I don't usually suggest this kind of thing but you should just determine which NOR gate (7402) is in the circuit for the coils that are locking on and shotgun it. I won't be shocked if that fixes the problem. They're cheap.

EDIT: Wait a sec...



Are you saying that the transistors are biased (on) when the connectors for the switches and coils are attached but not on when you remove them? If that's the cast you need to determine which connector causes the problem to reappear and you probably don't have anything fried on the board.

I was going to replace both 7402's and probably shotgun all of the pre-driver and driver transistors for the special solenoids if replacing the 7402's didn't do the trick.

I used the testing method described on the pinrepair.com repair guide. I read resistance on all of the transistor metal tabs except for Q85 which read open but isn't used. Unlugging the connector all of the transistor read as open. I did this with the game off.

 

[shardian]

Before you go all Rambo with an iron, just test everything with the board out. Especially if your soldering skills aren't the best in the world. You could potentially make things worse.

If with the connector installed you get short conditions and with it off the board is fine, that's a wiring issue like I was trying to say in my JP example.

 

[R3LL1K]

Before you go all Rambo with an iron, just test everything with the board out. Especially if your soldering skills aren't the best in the world. You could potentially make things worse.

If with the connector installed you get short conditions and with it off the board is fine, that's a wiring issue like I was trying to say in my JP example.

lol at Rambo with a soldering iron. I can solder well enough to solder transistor leads and some IC's on this board. I'll test them while I have the board out.

I didn't read any shorts. With the connector plugged or unplugged.

 

[Lindsey]

Yeah... I only suggested shotgunning the 7402s. Everything you've said so far points to that as the problem.

If you want to test them the outputs of the NOR gates (pins 1,4,10 and 13) should not be stuck high. If they are the associated coil will be stuck on.

EDIT: They should not be stuck high with the game on. Should be clear about that

 

[R3LL1K]

Sorry for the delay in updating this. The issue was the 7402's and one driver transistor. Everything works fine now. The driver transistor that was bad is Q77, this is the one that drives the right slingshot which I originally posted about. The 7402's cleared up the blowing fuses/stuck coils. Thanks for everyone's help! I really appreciate it.

 

[shardian]

See, now that makes much more sense that the driver transistor was dead.

Congrats on figuring it out.

 

[Lindsey]

Sorry for the delay in updating this. The issue was the 7402's and one driver transistor. Everything works fine now. The driver transistor that was bad is Q77, this is the one that drives the right slingshot which I originally posted about. The 7402's cleared up the blowing fuses/stuck coils. Thanks for everyone's help! I really appreciate it.

You mean the first thing I suggested to look at was the problem? Shocking

Congratulations on fixing it. That one was kind of a pain.

 

[R3LL1K]

You mean the first thing I suggested to look at was the problem? Shocking

Ha ha, maybe...