BabyPac help pls

Alright. I got my hands on the GATG mpu board. u6 and u2 were the same type chips, so the jumpers were the same. I swapped out u2 and u6 and fired it up. On it comes. hooray,,I guess. Swapped u9,10,and 11, all good. So the problem on the bad some must lying somewhere in the smaller components or a bad trace? OHH where to start.
 
OK, started probing the two boards to see if I could find any major differences. The big thing I am finding is that on the bad board, pins 27, 28, and 29 are all dead with 0 voltage on u9, 10, and u11,,where as on the good mpu board, there is activity of some sort on these. I am having trouble identifying any factor that these three pins may have in common. Not the greatest at trying to read schematics.
Last page of this shows the mpu
http://mirror2.ipdb.org/files/125/Bally_1982_Baby_Pac_Man_Manual.pdf
 
OK,,still kicking at this and running out of things to check to get that initial flicker. Here is what I have so. A completely rebuilt reset section, with the exception of the 82ohm resistor, but it checks out. Confirmed working, U2,U6,U9,U10,U11,U15. All these part work in the good MPU board. U16 was bad, swapped the one from the good board, still no flicker. Essentially, there is no reason why I should not be getting at least the first flicker. Voltages are all good.
Any suggestions??????
 
I didn't catch where you checked the MPU for clock - pins 3/37 - if there is no heartbeat there, there is no life...
 
armis2000 said:
I didn't catch where you checked the MPU for clock - pins 3/37 - if there is no heartbeat there, there is no life...
Click to expand...

I did check for clock signal. None. According to the manual, it states either a bad U15 or U16. I tried with 2 working chips there and still nothing. No pulse, just a high probe, actually, all pins on U9 are high.

Double checking s ome things here. Q2, 2n3904 seemed weird. I pulled it and tested good, but on the pcb was ohming between the collector and the base, but was open on the good board. Does this mean something is shorted somewhere?
 
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Found shorts between the points of CR5 and also C13. Checked everything for continuity and cannot find any shorted component. Checked and double checked with a magnifying glass for any bridged joints. Here's what's weird. Pin 21 and 22 of U8 are shorted. On the good pcb, they are not. I pull the 6821 out of the socket at U11 and the short goes away, I put a new 6821 in and the short comes back, pull it and it goes away. But this is only affecting the short at U8. Still there at CR5 and C13, plus a few other spots in that area.
Are there any tricks to finding a short other than visual inspection and lifting legs?
 
Running out of things to try and also patience. Confirmed all chips working, all worked in spare board. New sockets, checked all traces of sockets with DMM. Rebuilt reset circuit. Test the reset, ground junction of R1 and R3, pin 40 of U9 goes low. Release and goes back high, but the mpu does not reset. Cross pin 39 and 40 of U9. led does not blink. Manual states the reset section is good. Checked for clock signal, yes, pin 3, 36, and 37 of cpu pulsing. Clock is present. Next, traced the VMA signal through it's path and it all checks good and is exactly as the working board as well. Voltage is correct as the good board boots on bench and in machine. Still can't get that first flicker. I must have tested every component on the board and can't find anything. Trying to think if I forgot anything.
 
drewscruis said:
did you check the 555 timer?
Click to expand...

No. The manual makes no reference to this at all. What/where is this and what should it be doing? Is that the small 8pin ic? I remember checking the voltage and probing it, can't really remember what it was doing. Just checked the matic,,will see what it is doing on the good board and compare with the bad.

That checks out good.
 
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Just a quick update on this. Got an order in from Riptor (7days from USA to CAN with a holiday, super fast) and replaced the sockets. Still no go, led solid.

Been driving myself insane checking trace to trace. I found something I cannot find the source of. Comparing with the working MPU board, I found that on the non-booting mpu, U8, pins 13 and 14(tied together) are shorted to pin 2 and also pin 16 of U6. On the working board U8 pin 13 and 14 only connect to pin 16 of U6. Why they are shorting to pin 2 I cannot find. I pulled all the chips and the short is still there. Tried to follow the traces but don't seem to see where they would cross or any common components. I'm not great at reading schematics but don't see anything sticking out there. Anyone give me a hand at this? Thanks
 
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Long last, this bitch is finally working!!!!!

At first, this game was brought to me with the wrong CPU in it. I think it had a 6809E, can't quite remember. Also had a bad 9602. A few broken traces easily fixed but the last short was the hardest to find. With no visible bridged joints on the parts side or solder side, and testing EVERY component for shorts, the last thing was to check the sockets. Seems on U9, a pad had lifted slightly and moved ever so much, just enough to make contact with the trace running between pins under the socket. Hooked up to the test bench, still solid led, crossed pin 39 and 40 of the cpu and it started the boot process. Wanted to see how far it went into the boot, so I put it in the game and it booted with no help at all. Played a few games and worked great.
 
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