Firepower keeps burning driver transistors

Raikus

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I had my bottom left pop bumper coil lock on and burn out. So I replaced the solenoid in the pop bumper, made sure the wires were soldered back on correctly, replaced the power transistor that matches up to the pop bumper solenoid (in this case, second row, middle section of the special solenoid drivers on the driver board), turned it on and *SNACK, CRACKLE, POP*

It flamed out another one.

My next step is replacing the 2N4401 transistor and 3 resistors in this section in addition to another 5A-8977 transistor (which are listed as TIP122 on the schematic, but the Marco ones that I ordered based on part number read as TIP120). Before I do that and potentially fry another batch of transistors, is there something else I need to check or look at?

Additional info: Firepower is a Williams System 6 and I'm using the driver board schematic made by Phil Butcher for part numbers and solenoid locations.

Appreciate the help.
 
Well, for one thing I'd use a TIP102 instead of a TIP120 or TIP122. Much better power handling ability.

Then I'd double check that the diode on the coil is wired correctly. Remember, it's all about the diode facing on the coil, and sometimes they are reversed.

If it locked on, was it a misaligned switch on the pop bumper? or was it a problem on the driver board?

-Hans
 
I ordered a new coil with diode already on there. Lined side of diode points to the two red wire solder -- at least that's how it was and how it is on all my other coils.

I ordered 10 of the part number from Marco and they're the 120's. Hate to have to place another order, but will if that's causing the problem. I doubt it is though, just that the 102's are hardier, right?

At first I thought it might just be the coil ad the diode was busted in half when I removed it burnt. I replaced the coil with a new one, turned it one, and fried the transistor. Replaced the transistor, fried again. So most definitely a driver board issue as the transistor it fried both times is the special solenoid driver for that pop bumper.
 
If you already ordered the 120's, then you're fine. They are closer to the original part, just that the 102's are hardier.

What I'd do next is replace the transistors but NOT connect the special solenoids yet. Pull the solenoid fuse too. Then add JUST the power connector for the specials, and if that's ok put back the fuse (for testing, consider using a smaller fuse too, it IS the correct fuse size, I assume). Then add on the switch connector.

Being that it is a pop bumper, have you checked for a short of some kind at the coil area? There's a lot of stuff going on in the area of those pop bumpers.

-Hans
 
When you put in a new transistor. Check the traces around the legs for continuity. Easy to lose through or across board continuity and that tends to blow things up.

LTG :)
 
Thanks LTG. I did that last night. Installed the new and checked points of contact along the line. Also checked to make sure there weren't any shorts. Whatever the problem it crispied it as soon as I switched it on.
 
Burning transistors and coils do not necessarily stop at this stage. Literally, one has to consider the entire chain through which the solenoid circuit is activated:

Coil - TIP102 - 2N4401 - 7408 - PIA

If you continue to hav eproblems after both the TIP102 and 2N4401 have been changed, it's time to suspect the TTL driver circuit and the PIA that drive the solenoid. A burning coil often pulls enough current to create damage up the entire line. I have worked on hundreds of these boards, they can be tricky, but even a DMM will help you find out where the problem is. Keep us informed.

Chris
 
Ok, here's the progress today. Double checked the switch stack and tugged on all the resistors on the switches. Well, the white one pulled back from the middle switch. Soldered it back to the switch point where the cap meets.

Then changed the TIP122 and 2N4401. Checked the above transistors. The 68 Ohm is definitely toasty. Change it. Change the 560 and 2.7k Ohm to just to be sure.

Run checks on the resistors. They don't show the same numbers as the ones around them. Each was measured with the black lead on the gold side, red on the opposite. Here's the data on the ones I replaced:

R11 (68 Ohm) - .085
R10 (560 Ohm) - .294
R12 (2.7k Ohm) - .788

Here's the same readings from the surrounding resistors:

68 Ohm - .086
560 Ohm - .536
2.7k Ohm - .677

As you can see the 560 and 2.7k are both way off. I decided not to put the board back in before trying to get some feedback from the board here. Also, I checked the capacitor/resistor combo found at the top left of the board and got very different readings on the 1st pair (R3 and C3 on Phil Butcher's Driver Board Assembly schematic) than the rest of them.

Any advice on the next step that WON'T result in my frying my new components? :D
 
Any advice on the next step that WON'T result in my frying my new components? :D

My advice would be to disconnect the coil from the circuit. This will remove the load and the diode. This way you can test the circuit without fear of burning any more parts. Remove one lead from the coil and put your DVM in a voltage scale in the place of the coil. Use diagnostic mode to turn on and off the coil and watch the meter. When the coil fires, you should see a blip of voltage. If this is the case, and you do not see a continuous voltage, then the circuit is running correctly, if you do see the continuous voltage, then the 7408 or PIA is bad.
 
Ok, here's the progress today. Double checked the switch stack and tugged on all the resistors on the switches. Well, the white one pulled back from the middle switch. Soldered it back to the switch point where the cap meets.

Then changed the TIP122 and 2N4401. Checked the above transistors. The 68 Ohm is definitely toasty. Change it. Change the 560 and 2.7k Ohm to just to be sure.

Run checks on the resistors. They don't show the same numbers as the ones around them. Each was measured with the black lead on the gold side, red on the opposite. Here's the data on the ones I replaced:

R11 (68 Ohm) - .085
R10 (560 Ohm) - .294
R12 (2.7k Ohm) - .788

Here's the same readings from the surrounding resistors:

68 Ohm - .086
560 Ohm - .536
2.7k Ohm - .677

As you can see the 560 and 2.7k are both way off. I decided not to put the board back in before trying to get some feedback from the board here. Also, I checked the capacitor/resistor combo found at the top left of the board and got very different readings on the 1st pair (R3 and C3 on Phil Butcher's Driver Board Assembly schematic) than the rest of them.

Any advice on the next step that WON'T result in my frying my new components? :D

Looks like the controlling TTL chip is toast, hence your invalid resistor measurements.
(since you changed the resistors, and have new TIP and pre-driver transistors installed.)
 
Sorry for the delay. I ordered more parts and finally got some bench time on the boards yesterday.

After replacing IC 8 & 9 for the special solenoid with sockets and new 7402 chips, and replacing the 6820 in IC5, the readings came into line. I plugged the board back in and nothing fried... until the machine went to kick in the solenoids and then the F2 5A fuse on my power board blew. So I guess I solved the problem on my driver board only to find another one in the under playfield wiring?
 
I mistakenly called the Solenoid F2 fuse a 5A when it's a 2.5A. I guess my next step is testing for 28v and then pull the solenoid/flipper connector and test with fresh fuse?
 
Noticed something last night when looking under the pin. The pop bumper above the one I changed (in the picture it's the bottom left one) has the solenoid in the different direction than the rest. It's also a 900 DC whereas the others are 850 DC. Could this be causing the overload?

6880850422_89e19669d6_z.jpg
7026950689_4b3d6d50bd_z.jpg


Also, I'm in danger of having four posts in a row so if someone could break up my monologue with their own post it'd be great!
 
850 or 900 should not make the difference. But where is the diode on that coil?
 
It's connected on the inside of it, but the entire solenoid is positioned backwards. All the others have the lug side closest to the playfield. This one has the lug side at the end of the pop bumper bracket mount.
 
It's connected on the inside of it, but the entire solenoid is positioned backwards. All the others have the lug side closest to the playfield. This one has the lug side at the end of the pop bumper bracket mount.

You can place the coil either way, it will not make a difference on how it works, it will generate a magnetic field that will pull the plunger in either way.
Typically, you want to place the lugs on the end farther away from the coil stop so the solder joints see less vibration, but for operation it does not matter.
 
Voltage on the solenoid fuse (F2) measured 37v. Driver board is testing fine though (and changed with another with same result). What should I look at next? I'm quickly depleting the world's supply of 2.5a slow-blow fuses.
 
Check that the red wires on all those coils are on the banded side of the diode. The three that I can see look to be correct, but that 900 I cannot see the diode to tell if it's correct.

Get an ohmmeter on the coils themselves, make sure they are all within specs.... should read about 3-4ohms or so.

Pull all three coil connectors from the driver board, power it up and see if anything blows. If not, add ONE connector, power it up, see if anything blows. Repeat until the fuse goes, and then you at least have it narrowed down to a few coils.

-Hans
 
Thank you HHaase. All hot wires are on the banded side of the diode. I tested the coils across the lugs and 3 registered .005 on my ohmeter and one registered .006. I pulled connectors and tested the voltage at the fuse block and each time it registered right around 37-38v (with time in between for the voltage charge to diminish). I was out of fuses to test each connector with one it.

So if my coils are testing higher (I'm guessing they were supposed to read .003 to .004?) am I back to looking at the driver board?
 
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