Refurbed MsPac work

Sid723

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Hey guys, I have a Ms Pac recently and it was in very bad shape.

It was sitting outside at this one place for about 6 to 8 months. So far, I put a cap kit into the monitor and got that working pretty well.

I am now working on the logic board. After hooking the logic board all up and to the monitor, I see jibberish on the screen. After removing some of the ROMs, I found the older ones at 6E, 6F, 6J and 6K (2532 type) all have at least 1 pin that fell off. I will have to replace these and probably the sockets for them as well.

Question 1: I am pretty sure I can use a 2732 as a replacement with a rewired socket or rewiring the traces on the logic board. Has anyone ever done this before?

Question 2: I am finding it hard to find a MAME site that has the ROM image for these chips. Does anyone have a link to a site that has them? The last one I went to wanted you to sign up for all kinds of surveys and junk just to download a copy.

Any help is greatly appreciated.
 
PM me your email address and I will send you the rom files.
Why not use 2532? I dont see any reason to modify the board. If your going to go through that much trouble you could just single rom it.
 
My eprom programmer only handles 27xx chips. I guess I could make a modified chip socket to convert the programmer to accept 25xx chips. But then I would need to order 2532 chips.

I don't want to change the board if I don't have to. Does anyone have the 2532 roms already burned for sale?
 
@Channelmanic:
I found the 2532s on your site. If I order 4 of the roms, can you program them with the mspac row 6 images?

If so, let me know or PM me.

Thanks.
 
Yup. For KLOV'ers you order the EPROM then order the Programming Fee for the first chip ($3.99) and I'll program all 4 chips for you.

Non-KLOV'ers pay $1.99 for programming each additional chip on the same order.

Just PM me your name and order # and I'll take care of it.

RJ
 
Yup. For KLOV'ers you order the EPROM then order the Programming Fee for the first chip ($3.99) and I'll program all 4 chips for you.

Non-KLOV'ers pay $1.99 for programming each additional chip on the same order.

Just PM me your name and order # and I'll take care of it.

RJ

I am on the site, but I don't see where you specify "Programming Fee". I am using the site link that you have on your custom signature line.
 
OK, I replaced the EPROM sockets and put the programmed EPROMs in. I made sure that the leads on the board do make continuity with other contacts on the board where the diagrams say they should.

Next problem: I am still getting white vertical lines all over the screen and some mixed up sprites. Every now and then I see a buzz in the picture. I believe this could be the watchdog signal resetting the Z80.

I put the logic probe to the board at the reset to the Z80 and I see the watchdog is triggering. Can I leave the small boards off the motherboard and have it running? I would just like to eliminate as many factors as I can to get the main board working first, then I will move on to testing the invidual smaller boards.

I think I read somewhere that you can take the cabled board off and just put the Z80 in that socket and have it run without some features. Can I also leave the other two smaller boards off and troubleshoot it from there?

Need more advice please.

Thanks in advance.
 
You need both of the smaller boards on there to boot. You can remove the ribbon cable from the main board and install a z80 in its place to eliminate the daughterboard. Your characters will look funky with the mspac character roms but it will run just fine that way.
 
Ok, thanks Riptor. So, the two smaller boards need to be in place, and I can put a Z80 in place of the ribon cabled board.

So, somewhere the program must be getting lost. That is why it is being reset by the watchdog. I will start going over the board with a logic probe in the next few days to see if any signals are hanging up or not changing as they should.

Anyone ever troubleshoot the logic on this board before?
Any suggestions on where to start?

I will probably start with the usual, address lines, data lines, then take a look at the support chip signals.
 
Since I see a reset signal at pin 26 of the Z80, I decided to check out the watchdog circuit first.

The V-blank signal is the counter signal for the 74LS161 (9C). Pin 15 also has a signal which means that the counter is reaching the end and sending a reset pulse to 7L (NOR gate), then to reset of the Z80. Pin 1 on 9C also has a signal which is supposed to clear the counter before it reaches the carry point which is the reset for the Z80. Since I do have a signal on pin 1, then I can only assume that a watchdog reset is being generated, but the counter is not being cleared before it generates the reset signal.

So, the 74LS161 could be bad, or the watchdog reset signal is not making it at the correct time to clear the counter before it reaches the reset point.

This is a picture of the circuit from a manual I found online.
 

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  • MsPac_Watchdog.jpg
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In troubleshooting the watchdog circuit, I can see that a clear watchdog signal is being generated. This seems to be happening twice, then doesn't happen again and then the watchdog goes into reset.

This must mean that the CPU is accessing some of the ROMs and runninng part of the startup program, but then it gets lost somwhere along the way after that. I already replaced the row 6 EPROMs.

If they are not the problem, then I believe there are two more EPROMs on the MsPac board that may be the problem (5E and 5F). Only problem is that I am not able too program or verify the contents of these two EPROMs. The book says they are Character ROMS.

Any ideas?

Thanks.
 
Update:
I checked continuity on all the daughter boards and all is fine.
I moved the 2114 RAM chips around and found something changed on startup:
- The watchdog now clears and doesn't get to the point of sending a reset to the CPU.
- The screen now shows a few other objects, but still doesn't start up.

When I tried to move the 2114 RAMs again, I found that the very old one had pins that fell off.
I replaced it with a 2114 RAM from another board, but it still is not starting up.

I think my next move is to replace all of the 2114 RAMs.

I also found a site that has some PAC/MsPAC repair tips. They suggest that the bars I saw originally could be symptomatic of the 2125 RAMs at 2A, 2B, 2C & 2D. I guess I will get some replacements for these too and see if it hellps.

If anyone out there has any ideas, I would really appreciated it.
 
Not sure if you have encountered this web page, but it might help you troubleshoot:

http://www.arcadegameover.com/pactrouble.html

Thanks MajorHavoc, very interesting site. I managed to find and repair a couple of traces on the board that were broken. Now when I start it up with one of the RAMs out of it's socket, I get all zeroes just like one of the screens in your link.

Here's something new: I took another 2114 from another board and plugged it in. Now I get nothing on the screen at alll.

Then, when I put that same RAM back into the board and take a different RAM out, the screen now comes up with the zeroes again. There are 2 RAM locations I can do this to. If all RAMs are in, I get nothing on the screen. But, when I take one of these RAM locations out, I get garbage or all zeroes on the screen.

Weird!! I also checked the watchdog in all cases. It was ok. Any ideas?
 
MsPac CPU timing - the clue thickens

OK, I replaced all the 2114 RAMs, still the same.

I have an HP1650A that I bought years ago, so I thought I would play with that. I hooked a pod up to monitor the address lines from the Z80 CPU. The HP was set to display the addresses seen on the address bus and the clock I used was the PHI signal at pin 6 on the Z80.

I then powered on the board and checked to see that the watchdog was not barking and it wasn't. The HP was set for a single trigger so it was armed and would trigger when it was address 0000 Hex on the address bus.

I then took a wire and did a quick short of the reset on the CPU (pin 26) and the HP then triggered and below is what it showed:

-0007 3000
-0006 3000
-0005 3000
-0004 3000
-0003 3000
-0002 3000
-0001 3000
+0000 0000
+0001 3000
+0002 3000
+0003 3000
+0004 3000
+0005 3000

Clearly, there must be a loop at address 3000 that the CPU is caught in. This loop must also have an area where it is sending the watchdog reset signal, which is why I am not seeing a watchdog reset occur.

Question to you all is: What is the routine at address 3000? If I know more about what is happening there, I may be able to find out what hardware maybe associated with this and get a clue where the problem is and repair it.

Any ideas?
 

Thanks Hewitson. I found a loose connector on the ribbon cable and now the board shows more addresses when I hooked the board up to the logic analyzer. I did see it following the program addresses as they are listed in the document you linked me. I also see the address going to various places, but I still have no clue why it isn't starting up yet.

There is something new it does now: The screen stays blank, but after about a minute it sends a very fast beep to the speaker in bursts of 8 beeps and repeats this pattern 16 times. Then it waits about 5 minutes before it repeats the pattern again.

Could this 16 groups of 8 beeps mean something like maybe it sees a bad ram or something?

The plot thickens even more. Any ideas out there?
 
Uncle!!

OK. UNCLE!!!

I just about had it with his fix. I checked the support logics and I don't see anything amiss.
I know the row 6 roms are new and most all the websites I have visited tell me that the game should still play even with bad row 5 ROMs.
I tried both ways: with ribbon board on or with just a Z80 in the socket.
I checked continuity on all RAMs, ROMs, CPU and other areas with some repairs, but I can't find any more problems.

When I set the dip switches to freeze, the game comes up with mixed characters all over the screen, so I am guessing that the video RAM and ROMs are working fine.

I am still wondering if the row 6 ROMs are of the correct program, but I have no way of checking the original ROMs since the legs have fallen off.

I also traced the program with my logic analyzer (HP1650a) and found that the program does seem to follow some of the right code.

So, my final question to all is this:

Is there anyone that can repair this board that is located close to the 60448 area code?



Let me know. Thanks for your help up to now.

I give up.
 
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