Bally MPU not booting

thebman80

Well-known member
Joined
May 22, 2006
Messages
7,394
Reaction score
30
Location
Wallingford, Pennsylvania
I have a Bally Midnight Marauders and the MPU is not booting. The light stays on and never blinks. I tried the Wiki pin troubleshooting but really had no luck. It just keeps talking about acid damage and this board has NONE it's perfectly clean. I have the thing on my work bench hooked up to my test bench power supply. I have a logic probe and an O scope so I'm ready to go just have no Idea what to check now.
 
Do you have 5V on the MPU board? The LED will light if 12V is at the board but no 5V so get that checked first.

Make sure you get EXACTLY 5V as, if it's a little low, your fault could be the earthing mods that should be done on the solenoid driver board not on the MPU at all.
 
Last edited:
Well I have it on the test bench and I believe the 5v was around 5.3v or so when I put the meter to it. I turned it up a little to like 5.5V and down to 4.9v and the board wasn't booting with voltage differences. Its still set to about 5.3v.
 
From the "old Clay page":

No Flashes: the LED is Permanently On.
If you turn your Bally game on, and the LED stays on continually, this is one of the hardest problem to fix on these boards. A stuck on LED can be caused by any (or all!) of the following:

The reset circuit is damaged (after all, it's in the battery corrosion area!) This includes transistors Q1 and Q2 (both 2N3904), Q5 (2N4403), and diodes CR5 (1N4148 or 1N914) and VR1 (1N959B or 1N4738A).
The program ROM (read only memory) at U6 is bad.
The ROM jumpers are incorrectly set for the U6/U2 ROMs installed.
The U9 CPU microprocessor is bad.
The U11 PIA (peripheral interface adapter) is bad.
ANY of the sockets for chips U6, U9, U11 are bad.
The ground trace to U11, U6 or U9 are bad. U11 is especially important to check the ground trace, as it's right in the corrosion zone. And corrosion just loves to travel up the ground traces. Use a DMM set to continuity to check ground at U11 pin 1 (and U11 pin 20 for +5). Also check U6 pin 12 for ground (and U6 pin 24 for +5). U9 pin 1,21 (gnd) is less of a problem as it's well outside the corrosion area.

The first and last two points are probably the most common problems.

Go "Bare Bones" (What to Remove for the first "Flicker").
To get the initial flicker out of the MPU board's LED, you only need three chips on the MPU board. These three chips are U9 (the CPU), U11 (PIA) and U6 ROM (except on some Stern games, which also require the U2 and/or U5/U6 ROMs). Remove all other socketed chips! Once you get the initial flicker out of the MPU board, then you can re-install the other removed chips.

The Reset Circuit.
If the reset circuit is damaged, the MPU board will never start, and the LED will stay on at power up. Since the reset circuit is in the "corrosion zone", it is often damaged from battery corrosion. The reset circuit holds pin 40 (reset) of the U9 CPU low until +5 volts is "stable", and then sets pin 40 high (telling the CPU it can start the boot up process). While the reset section is holding pin 40 of the CPU low, the LED will be on. This is one part of the initial "flicker" seen when a working Bally board is first powered on.

Here's what to try first:

With the MPU board OFF, Put a logic probe or DMM set to DC volts on pin 40 of the U9 CPU. The logic probe will be "low" (or the DMM at zero volts).
Power the MPU board on.
In just an instant, the U9 CPU Pin 40 should go "high" on the logic probe, or about 4.75 to 5.5 volts on the DMM. Repeat this for U9 pin 2, which also should also go high.

If the above happens, the reset circuit is probably working fine. If pin 40 of the CPU is low and never goes high, there is a problem with the reset circuit. Since pin 40 never goes high, the CPU will never start the boot process, and the LED will stay on.

Here's some other stuff to try:

With the MPU board powered on and pin 40 of the U9 CPU high (4.75 to 5.5 volts), short the junction of resistors R1 and R3 to ground. To do this, find the junction where resistors R1 and R3 connect together (the right side of R1 is the junction of R1 & R3). With the MPU board on, use a wire and short this junction to ground (TP4).
U9 CPU pin 40 should now go low to zero to .5 volts while the R1/R3 junction is grounded.
Another short cut is to take a small screwdriver and short pins 40 and 39 of the U9 CPU chip together for a second. This again simulates the reset circuit. If the LED starts flashing, the reset circuit is damaged.

The above procedure is simulating what the reset circuit is meant to do. If shorting the junction of R1 and R3 does not pull U9 Pin 40 from high to low, then there is a problem with the reset circuit. Most likely there is a problem with Q1 (2N3904), Q2 (2N3904) and/or Q5 (2N4403). Replace them all (they are cheap!) and repeat the above procedure. Also check/replace diode CR5 (1N4148 or 1N914). Finally check/replace diode VR1, which is a 1N959B (1/2 watt) or 1N4738A (1 watt), 8.2 volts (note VR1 is mis-labeled in the manual as "1N9598"). If you still can't get U9 CPU pin 40 to go low, there is some other problem in the reset circuit (corroded traces?).

Here are some other points to check. Turn the MPU board on and test:

U9 pin 3 = 2.4 volts
U9 pin 36 = 2.6 volts
U9 pin 40 = 4.75 to 5.5 volts
U9 pin 5 = 2.8 volts

If the above voltages check out, then the reset section is probably working correctly. This means your problem probably lies with chips U6, U9 or U11 (or their sockets), or incorrect MPU board jumpers.
 
Ok that will give me something to work with tomorrow now I need some freaking sleep my brain is fried at this point of the night. I believe on the Wiki pinball troubleshooting page there was a section where it told you to remove some chips and see if the LED blinked I know I removed them and it still stayed a solid green. I can resocket those 40 pin chips tomorrow as well Since I have some sockets handy.
 
Last edited:
Ok so after going through that list of stuff here is what I got:

U6 pin 24 is reading 1.92V

I took out all nonessential chips.

pin 40 of U9 is Stuck Low

U9 pin 2 is always High



U9 pin 3 is 3.09v
u9 pin 36 is 4.11V
U9 pin 40 is 0v
up pin 5 is 4.12V


So should I be rebuilding the reset section then? There is no battery corrosion at least that's plus...
 
pin 40 of U9 is Stuck Low

That tells you the reset circuit is not working. Reset should start low briefly, then go high.

I would recommend conversion to a DS1811 reset circuit. There should be instructions on pinwiki. Alternatively, you could troubleshoot and repair the problem with the original reset circuit. Personally, I wouldn't just rebuild the whole original reset circuit but that's an option. Too much work for a reset that's too short (IMO). Bally MPUs won't like to boot with PC power supplies a lot of the time using the original reset circuit but will boot after a manual reset. The original reset is too short. That's not your problem if the reset is never going high but something to keep in mind should you rebuild the original circuit.

When troubleshooting MPU problems I always start by checking voltages, then the reset and clock circuits. If you don't have that stuff the MPU will never boot.
 
Yeah that will be the next step ordering the kit.

I'm not sure If I can do that conversion Circuit or not. I believe C3 or C5 on Midnight Marauders uses A different component than other bally boards. In fact its the only different part on the board from other games.
 
Says hes out of stock:) I will be ordering the rebuild kit today how is great plains in shipping? Fast? Not fast?

Two thumbs up from me for Great Plains. Trusted, reliable, and highly recommended.

If you're going to install the kit you should consider troubleshooting the problem first and replacing only the bad component(s). See if it works, then install the other stuff if you want. Of course, you don't have to do that but might as well take the opportunity to learn something while you're at it. And then you'll know how and why you actually fixed the problem.

Just my $.02.

Good luck with the repair.
 
Last edited:
Well I was going to start with Q1 and Q2 first and try the board off and on in between replacing each part, then move on from there.


Two thumbs up from me for Great Plains. Trusted, reliable, and highly recommended.

If you're going to install the kit you should consider troubleshooting the problem first and replacing only the bad component(s). See if it works, then install the other stuff if you want. Of course, you don't have to do that but might as well take the opportunity to learn something while you're at it. And then you'll know how and why you actually fixed the problem.

Just my $.02.

Good luck with the repair.
 
I couldn't agree more, ED is a great guy really helpful and knows his stuff.

Two thumbs up from me for Great Plains. Trusted, reliable, and highly recommended.

If you're going to install the kit you should consider troubleshooting the problem first and replacing only the bad component(s). See if it works, then install the other stuff if you want. Of course, you don't have to do that but might as well take the opportunity to learn something while you're at it. And then you'll know how and why you actually fixed the problem.

Just my $.02.

Good luck with the repair.
 
Well the kit came last Friday, that was fast shipping. I finally had time tonight to actually start messing with the board. I replaced C1, C2, C3, C5, C13, C80, CH5, CR7, CR8, CR44, R11, Q1, Q2, Q5, and VR1. I replaced them all one at a time and powered up the board after each replacement so far nothing has made the Green LED not stay lit all the time. I have a handful of resistors to replace still in the kit and I the U8 RAM and Socket as well.
 
Well the kit came last Friday, that was fast shipping. I finally had time tonight to actually start messing with the board. I replaced C1, C2, C3, C5, C13, C80, CH5, CR7, CR8, CR44, R11, Q1, Q2, Q5, and VR1. I replaced them all one at a time and powered up the board after each replacement so far nothing has made the Green LED not stay lit all the time. I have a handful of resistors to replace still in the kit and I the U8 RAM and Socket as well.

That's the problem with trial and error troubleshooting. Sometimes it takes a while.

You should be checking the reset. You might have fixed the reset but still have a problem with something else.
 
Ok finished off with the resistors almost... after going through the list the first R113 was a diode but suppose to be that way for my board. :D I figured that much out, that's the one I was thinking of that you can switch out to change the type of MPU. Now this next one had me scratching my head... at location R12 there is a N4007 diode big black sucker... What has me confused is that the original schematics for Midnight Marauders says its suppose to be a 270ohm 1/4w resistor. The Corrosion repair kit says this as well. So could this be screwing up the voltages in the circuit? I know I didn't put this thing there. Other than that I replaced all the parts in the kit so far except for the U8 RAM. Nothing has made the LED blink yet.


Just want to get an opinion on R12 before I try anything else.
 
R12 might be changed to a diode if one was using a remote battery holder and did not wish to charge the batteries. Most folks leave the resistor at R12 and add the diode in the battery holder.

That isn't why the mpu is locked, sorry.
 
Eh worth a shot was the only thing that was totally different from what it was originally suppose to be. Any other suggestions now that the reset section is rebuilt?
 
Back
Top Bottom