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(Topic ID: 272875)

Kings of Steel MPU Fault?


By GPrince

3 months ago



Topic Stats

  • 15 posts
  • 4 Pinsiders participating
  • Latest reply 73 days ago by GPrince
  • Topic is favorited by 1 Pinsider

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20200720_133316.jpg

#1 3 months ago

Hello,
I'm having a few issues with bringing my Bally Kings of Steel back to life. Upon startup, 2 thumper bumpers are firing and not releasing which is blowing the playfield fuse. I've replaced the transistors to both on the solenoid driver (one had blown up, and only upon replacement did it cause the 2nd bumper to pull in) but the constant voltage remains to the solenoids. Also, the drop targets aren't resetting. They flick slightly at the start of a game, and oddly when the ball goes into the saucer right before it ejects the ball, but do not pop up as they should. I've replaced all the playfield coils, but the saucer is the only thing to come back to life. I'm wondering if I'm not having an MPU fault causing the thumper bumper problem, but not sure about the rest.

#2 3 months ago

hmmmmmmmm.

Is the ground braid attached in the head? https://pinwiki.com/wiki/index.php?title=Bally/Stern#Inspect_Harness_Wiring

Is the polarization correct on the coil diodes? .... https://pinwiki.com/wiki/index.php?title=General#Testing_the_coil_diode

Are ALL the connectors on the boards "keyed" and installed correctly? https://pinwiki.com/wiki/index.php?title=Bally/Stern#The_Importance_of_Keying_Plugs

Is there corrosion on the MPU (sadly quite common) https://pinwiki.com/wiki/index.php?title=Bally/Stern#Repairing_Alkaline_Damage

Post some pics of the boards in the head

1 week later
#3 3 months ago

Thanks for the advice! I just started looking, and found the ground braid was in fact broken. Reattaching it didn't fix anything right away, but I'll continue on with your list of recommendations. Here's a shot of my MPU and solenoid driver.

20200720_133316.jpg
#4 3 months ago

You might want to look at the pre-driver chip U1 or U3 on the solenoid driver board if some coils still lock on after replacing the transistors. U2 can also fail causing the coils to lock on... same for the drop target reset coil. I would look at that before fooling with the MPU.

#5 3 months ago

Am I looking for voltages leaving the U1 trace going to say, Q1 that is causing it to fire? R8 was burned up, which I replaced. Also, I bought an Atlas esr70, but it doesn't test fractional farad caps. Is there another way to know if they're bad?

#6 3 months ago

Take a look at pinwiki. There is a section with a nice write up on how to test U1 which is a transistor array. It is a 3081 chip. All you need is a multimeter. Check U3 and U4 while your at it. If those check out ok, then look at U2. U2 is best checked with a logic probe while the power is on.

#7 3 months ago

Don’t worry about the caps unless they’re cooked. Then just replace. they are inexpensive

#8 3 months ago

Will do, thanks for the insight!

#9 3 months ago

Step 1: cut the yellow nasty 1984 battery off of your mpu before it pukes on your mpu.

Also :

https://pinside.com/pinball/forum/topic/vids-guide-quick-bally-driver-board-repair-bulletproofing

#10 3 months ago

from Clay's repair site "Now we need to test the chip that drives the diode and driver transistor. This chip is a CA3081 (NTE916) transistor array. Basically it's several transistors packaged in a chip format. This is known as the "pre-driver transistor pack". You can test this too:
Turn the game off.
Remove the Solenoid driver board from the game.
Put your DMM on diode setting.
On the component side of the board, put the black lead of your DMM on the GND test point just to the left of the U1 chip.
Put the red lead of your DMM on the two pins of the pre-driver chip (one at a time) that you noted above.
For the pin that connects to the 1N4004 CR diode, you should get a reading of .1 to .2 volts.
For the other pin, you should get a reading of .7 to .8 volts.
Reverse the DMM leads (red lead now on GND). You will get the same .1 to .2 volt reading for the pin that connects to the CR diode. The other pin will read 1.1 to 1.3 volts. Note this test is far less conclusive than the first test with the black lead on GND.
If you get any other meter readings, replace the pre-driver CA3081 (NTE916)

#11 3 months ago

I replaced U1 and U3. That brought back my thumper bumpers. After also replacing Q3, 4, 7 and 11, I now have an outhole. The right slingshot still isn't getting voltage, and the new Q11 for the drop target reset exploded.

#12 3 months ago
Quoted from GPrince:

I replaced U1 and U3. That brought back my thumper bumpers. After also replacing Q3, 4, 7 and 11, I now have an outhole. The right slingshot still isn't getting voltage, and the new Q11 for the drop target reset exploded.

Do a resistance check on that reset coil (and or diode)

1 week later
#13 88 days ago

We have drop targets! I had replaced all the playfield coils, and one of the drop target reset coils had a reversed diode from the factory. Installed a new transistor (and did the recommendations from Vid for bulletproofing the solenoid driver) and Bob's your uncle!

#14 88 days ago
Quoted from GPrince:

Bob's your uncle

I have an uncle Bob. He's always saying the same old shit everytime I see him: "Have ya chopped off that yellow 1987 battery of your MPU yet? Hope it don't puke nastys all over your board."

Lol Uncle Bob lol.

Also, congrats on making progress!

2 weeks later
#15 73 days ago

Thanks for the help! Further tracing found that the slingshot was punched down on J2 slot 3 (the key) from the factory, instead of slot 12, so it never worked. I relocated it, and we're slinging! It rapid fires occasionally, but it's great having it work.

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