Bally Black Pyramid Pinball MPU toasted?

mert8431

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Need some advice or a suggestion from someone on where to get a new MPU board or some tips.

So I just went to fire up my Bally Black Pyramid and instead of starting up like it normally does, I just got the general lights and nothing from the score read out or other lights. Checking the manual, I'm told to pop open the back box and check out the the LED light for status...

Flipped power switch on:

Light flashes 1 to confirm power and then flashes quickly 5 times and then LED goes off. It should flash 7 times for the game to start up properly. Game manual suggests removing J1, J2, J3, and powering up the game. Same deal. Pulling J4 gets no lights as this is the power to the board.

Checking the Bally repair manual it says for 5x flashing, check some ciruits and pins...I have to go get a multimeter tomorrow...

In the mean time, if a chip is dead is there a good place anyone can recommend to send it?

The MPU-A4 is a bally midway a084-91624-aa44
 
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Fifth Flash Completed:
The Fakers Guide: a fifth flash means the U11 PIA (6821) is good. No fifth flash means U11 (6821 PIA) or its socket are bad. Note the flipper enable relay will usually click on/off at about the fifth flash. The lack of a fifth flash could also be a bad resistor connecting to U11 like R134.

Techno Guide: Same test is performed on U11 as was performed on U10. See above.

Sixth Flash Completed*:
The Fakers Guide: a sixth flash means the PIA at U11 (6821) and the U12 timer (5550 chip is good. No sixth flash means either PIA U11 (6821) or its socket is bad, or the U12 (555) timer is bad. Lack of the 6th flash (five flashes only) can also mean a problems with the zero-crossing detector. Often this is the MPU board's R113 resistor (2k ohm, near the J4 connector) is open. This resistor takes the 43 volt DC coil power to the zero-crossing detector circuitry and normally runs hot. Hence it may eventually go open, so check it if only 5 flashes from the LED are seen. Thanks to Ray J. for this tip.

Techno Guide: The U9 CPU chip monitors PIA2, port CA1 (U11). If transitions from high to low are detected, the CPU decides the Display Interrupt Generator is working. If U12, a 555 timer, or any associated circuit component fails, the CPU will not flash the LED the sixth time.

* Note on Baby Pacman and Granny and the Gators, this flash step is skipped and not tested.

Seventh (Last) Flash Completed**:
The Fakers Guide: Getting the seventh flash means the CPU board has passed all self-tests. After the 7th flash, the LED should have a very dim glow to it (this "dimness" occurs because the game is strobing the switches), and the game should be in 'attract' mode. No last LED flash generally means there's no +43 volts DC for the solenoids (power transformer fuse F4 is probably blown), PIA U10 (6821) or its socket are bad, or U14 is bad.

Remember the 7th flash is looking for 43 volts (or 6 volts AC in the case of Baby Pac's last flash) on the MPU board. Note this test for voltage is performed on Baby Pac too (the prior flash step is skipped, giving Baby Pac a total of 6 LED flashes). This is done thru PIA U10's CB1 port. The PIA is looking for the zero-cross of the 43 volts (or 6 volts for Baby Pac). If 43 volts is not present (rectifier board F4 fuse blown), the last flash will not occur.

If the game locks_up after the 7th flash, try unplugging the sound card and reboot. If it then works check the isolation power diode CR3 on the sound card - sometimes this bad diode on the sound board can lower the 43 volts enough to stop the MPU board's 7th flash (Star Trek comes to mind). Also Check the solenoid driver board cap C23 is in good condition. There is also a chance the 555 timer chip and/or C17 could be bad on the MPU board.

The 43 (or 6) volts can be "faked" and not supplied (for example if you are booting the MPU board on the work bench), and the last LED flash can happen. Just connect the top leg of resistor R23 (leg closest to chip U12) to the top leg of resistor R17 (leg closest to TP3) using an alligator test lead.

Techno Guide: The U9 CPU chip monitors PIA1 port CB1 (U10). If transistion from high to low are detected, the CPU decides that the zero crossing detector is working. If U14 fails and the CB1 line is stuck high or low, the test will also fail. The zero crossing detector circuit input is the +43 volts DC line that is used for the solenoids. If the fuse in that line (F4 on the power transformer module) is blown when the game is turned on, the CPU will not flash the LED the seventh time.

** Note on Baby Pacman and Granny and the Gators there is no 7th LED flash.** These games only had six flashes instead of seven. The easiest way to determine if the MPU board is a -133 designed for Baby Pac/Gators and 6 flashes is to look at the J4 connector (lower left corner) around pin 19. Between L1 and L2 (the very large inductors that look like 2 watt resistors) is either a diode (cr52) or a resistor (r113). If it's a diode, this is a -133 MPU board and there will only be 6 flashes. If it's a resistor, it is a -35 or -17 MPU board and there should be 7 flashes. Converting the -133 MPU to a -35 MPU is very easy do. Just replace the 1N4148 diode at CR52 with a 2k ohm 1/4 watt resistor. New EPROMs will need to be burned too of course For more information on the -133 MPU board see
 
Sixth Flash Completed*:
The Fakers Guide: a sixth flash means the PIA at U11 (6821) and the U12 timer (5550 chip is good. No sixth flash means either PIA U11 (6821) or its socket is bad, or the U12 (555) timer is bad. Lack of the 6th flash (five flashes only) can also mean a problems with the zero-crossing detector. Often this is the MPU board's R113 resistor (2k ohm, near the J4 connector) is open. This resistor takes the 43 volt DC coil power to the zero-crossing detector circuitry and normally runs hot. Hence it may eventually go open, so check it if only 5 flashes from the LED are seen. Thanks to Ray J. for this tip.

Techno Guide: The U9 CPU chip monitors PIA2, port CA1 (U11). If transitions from high to low are detected, the CPU decides the Display Interrupt Generator is working. If U12, a 555 timer, or any associated circuit component fails, the CPU will not flash the LED the sixth time.

Many thanks, that way more helpful then the Bally repair guide. I wonder if I should try removing the chip and putting it back in. Are these chips tough to come by?
 
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