Another Ms. Pac newbie call for help

Evewalker

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So after years of being in this hobby, I finally picked up my first Ms. Pac last week. It was non-working, and apparently was not turned on for quite some time. She is disturbingly clean on the inside and out, and only 6018 credits on the counter, though.

Since I've gotten it, I've gone over the usual. Resoldering questionable connections, reseating chips, checking fuses, etc. One problem I noticed was that the daughterboard ribbon cable z80 chip connector has a pin cleanly busted off of it on the last position. Removing the entire daughterboard from the equation, and after popping in a known good Z80 in that slot (from what I read was a good troubleshooting procedure) I figured I'd have the problem isolated....

However, the fast moving image photo below is what comes up now, along with a constant hum from the speakers. Before I start randomly shotgunning potential parts via Bob, I figured I'd ask people with a lot more experience with Pac setups than myself where I should be focusing my attention.

Thanks everyone
 

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Try adjusting your Horizontal Frequency pot on the monitor chassis. This is the same image I had on my Ms. Pac-Man after I did a re-cap and replaced the flyback, HOT, and voltage regulator. A slight adjustment of the Horizontal Frequency pot fixed it.
 
That's not a monitor issue.

You don't have a friend with a working pac board to test in the cab?

We need some pics of a few things:

The 4 position fuse block in the bottom of the cab
The edge connector
The pcb
 
Im going to guess bad connection on the vram card. Do we get a prize if we guess right?
You can rule out the monitor by coining up and seeing if it will play blind. Bottom left of the board are the four 161's Raymond mentioned. Alot of times one or two of those are socketed and the chips are the old TI ones with crusty legs....check those for bad connections or broke pins.
 
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Thanks everyone.

Here's what I've done so far today:

-Re-cleaned fuse holders/fuses. Strengthened a loose connection to the top 12v holder.

-Adjusted the horizontal freq pot. Didn't help, although the distortion pattern completely changed to fast moving small lines. Tuned it to near original position, and adjusted focus. The G07 has absolutely no burn. Creepy.

-Reseated the only socketed 74LS161, cleaned pins. Reflowed the other 74LS161 ICs nearby. Maybe its nothing, but they have faint white spots on the plastic cases, shown in photo.

-Completely cleaned the edge connector and pins, although it wasn't too bad to begin with.

-Noted that on bootup, sometimes I can now hear a weak series of 8 beeps, repeating indefinitely. I also saw what appeared to be something like a white circle amongst the graphics garbage during this, which is shown in the screen shot. I unfortunately don't always get this, but it is far more common after the above. It will not play blind, nor will it coin up.

-Noted that on or off, this Ms. Pac smells like distinctly like slightly aged, yet still edible, bacon. Searched for the source of the bacon in case a secret cache was hiding behind the G07, found nothing besides a dead spider. Disappointment ensued.

Photos are attached.
 

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Good call, Riptor. Some combination of reseating, cleaning, and reflowing around the vram card changed things. I also reflowed the C3 cap, and it is getting a fairly stable 5.01 to 5.08 across it.

I now have a stable picture of a pretzel and a small blue line. Bad video ram? Or something else?
 
It could be alot of things causing this, basically the program is not running. Usual culprits are 2114 ram, z80, sync bus card or the roms in row 6.
 
The Z80 I have in there now I can confirm is good (came from my recent Spy Hunter teardown and repair), so that can be ruled out.

One of the roms, 6H, is suspect. I haven't been able to remove it. I can only assume that at some point, the last pin was snapped or damaged, because the socket hole is filled with solder. It has continuity, but it is obviously a hack repair. In order to get it out of there, I'm probably going to have to remove the socket.
 
I swapped 4M and 4L to see if there was a bad ram at 4M, and it displays two objects, but different ones (a bright white Ms. Pac and full color Blinky).
 
If you want to send the board to me for repair send me a pm. At this point you probably need new sockets for the roms and those masked roms should be replaced.
 
I have a friend bringing by a Ms. Pac board to test a few things during the week. If I don't see any results there, I'll be sure to shoot you a PM and have you take a look at this thing.

How should the 2114 chips be behaving under logic probe? More is pointing to one or more of them being the issue.
 
You cant really test the rams with a logic probe. The quickfire way is to swap in a good set or a known good one, one at a time. If you have a logic probe it wouldnt hurt to check the clock and reset pins of the Z80. Umm, pin 6 and 26 I believe. Clock should show a steady pulse and reset should be high. If reset is low or pulsing low to high you have problems elsewhere.
 
Check the data buss on both sides of the 74LS245 that sits between the 2114s and the Z80 Sync Buss Controller. See if any bits are stuck. You may need to power the board off/on a few times to see if the bits are truly stuck or just temporarily stuck because of the CPU not running right.
 
Also, dumb question... did you unplug the daughter board's ribbon cable from the CPU socket and plug the Z80 straight into the socket on the main board?

That will quickly rule out a ribbon cable or daughter board issue.
 
Also, dumb question... did you unplug the daughter board's ribbon cable from the CPU socket and plug the Z80 straight into the socket on the main board?

That will quickly rule out a ribbon cable or daughter board issue.

Yup. Z80 directly on the board right now. I used a known good one as well, just in case.

I'll probe around the LS245 right now. Probing the Z80 clock and reset has clock with a steady pulse, but as expected, the reset does appear to be pulsing low to high. :(
 
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LS245 looks good.

Measuring reset at Z80 26 and 7L LS02 shows pulsing. However, measuring pin 9 on the LS161 at 9C shows stable reset, and responds to the switch by going low. I'm not sure what progress I'm making, but I feel like I'm making a little progress. :)

Thanks a ton, guys.
 
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