TECH: Baby Pac-Man issues - MPU?

Pimpbot5000

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Hello,

I've been working on bringing a Baby Pac-Man back to life, and after rebuilding the rectifier board and the MPU I managed to get it working.

It worked for several weeks, and then I accidentally left it on for 24 hours. Now the Vidiot board is flashing correctly (10 times) and the MPU is flashing correctly (6 times) but the game will not boot.

After the MPU flashes it looks like it tries to reset everything. All the playfield lights turn on and then off. Then... nothing. No attract mode.

I'm thinking this is an MPU problem? Previously, even with a non-working Vidiot board, the MPU would boot and the playfield lights would flash, and I could conduct the light and solenoid tests.

Any suggestions on how to track this down are appreciated.
 
Even though both boards complete their boot, the communications between the vidiot and MPU can be bad. Did you repin the connectors between the 2 boards and reflow the solder joints on the mpu and vidiot?
 
Even though both boards complete their boot, the communications between the vidiot and MPU can be bad. Did you repin the connectors between the 2 boards and reflow the solder joints on the mpu and vidiot?

I didn't do that since the game was working. I suppose leaving it on for 24 hours could have stressed the connectors to the point of failure? My only concern is that even with communication between the two boards not working, I think the MPU should be able to run the playfield, but aside from the initial flashing of all the lights, the playfield is dead.

I should have also mentioned that pressing the coin door test switch does nothing. Pressing the Vidiot test switch brings up the communications test, with zeroes in all the columns. From there I can cycle through all of the game audits, etc.
 
If you don't have sync between the two boards, nothing happens. I think I have seen it give me all zeros before. I want to say I forgot to plug in one of the MPU-> Driver board connectors. Re-seat all your connectors a few times? Check your tilt and slam switches too, they can cause strange stuff.
 
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So I was probing the 555 chip on the MPU board with a logic probe and the game came back to life. The game boots properly every time now. It's the craziest thing.

It's still not quite back to normal though. Sending Baby Pac down into the pinball portion does not activate the pinball. In fact the playfield goes back into attract mode even though a game is in progress. MPU reset?

The communications test now shows all values correctly.
 
check the fuses underneath the playfield
if one or more is blown, check the components in that circuit like the solenoids(flippers, drop target reset) to see if they are mechanically working and OHM out the solenoids with a multimeter to see if they arent shorted
 
check the fuses underneath the playfield
if one or more is blown, check the components in that circuit like the solenoids(flippers, drop target reset) to see if they are mechanically working and OHM out the solenoids with a multimeter to see if they arent shorted

Thanks. I confirmed all fuses are good. Also I can now run the solenoid test, which confirms all solenoids are working.
 
Sounds like a bad socket on the chip, clean the legs of that one and try it, cant remember if its socketed there, or once you get the game running put some pressure on the socket and see if it acts funny, twist test it.
 
Ok, after a hiatus from repairing video games in order to regain my sanity, I'm now back working on Baby Pac-Man trying to figure this thing out.

I'm still convinced this is an issue related to the MPU. I need the Bally MPU gurus to help me figure this out. I think what's happening is: upon booting the MPU instantly goes into test mode, as if I'm continuously pressing the test switch. It runs a fraction of a second of each test. So it flashes the playfield lights once and fires the kickout hole solenoid.

Check out this video to see what I mean:



I should mention that I've re-pinned the connections on the MPU. I've also replaced the PIAs and replaced the 555 timer.

Also, I don't think this is a problem with the test switch itself. If I disconnect the coin door, the game does the same thing. And if I have someone press the test switch while I probe U10, pin 40 is high and then goes low, which all seems normal to me.

MPU gurus... help!
 
You're going into factory reset upon boot up meaning the CMOS RAM is not retaining your settings. You either have bad batteries or a bad 5101 CMOS RAM.
 
You're going into factory reset upon boot up meaning the CMOS RAM is not retaining your settings. You either have bad batteries or a bad 5101 CMOS RAM.

Thanks for the reply Dokert. There's actually not a battery on the MPU. I didn't think it was required, and the game has worked previously without it. I did swap out the 5101 with no change in the behavior. The other thing is if I cycle through all the audits until the game resets, it never goes into attract mode but instead the MPU cycles through its tests again.
 
Well, the problem is definitely on the MPU board.

I picked up a nice damage-free MPU on eBay.

CIMG5719.JPG


The first thing I did was remove the battery. Then I reseated the chips. I plugged it into the game and everything works again.

CIMG5720.JPG


I still want to figure out what's wrong with the other board. It should be easier with a working board to compare to.
 
I had a similar issue recently. The MPU needed a battery. Some of them will work fine without it, this one did for a while but then stopped. I was told by a bally mpu guru that sometimes without a battery the old cmos will get filled with junk upon start up and not be able to function. I am not a guru and took the advice and made the Li battery mod to the MPU and it works perfectly now. It is an easy and cheap repair, try it your only out $2.
 
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