Pacman - broken Sync Bus controller board?

[spurcap]

I was installing a high score save kit in my Pacman which involved removing the sync bus daughter board on my Pacman PCB. After installing, I put in the cabinet and powered on and go nothing on the screen. Removed it again to inspect and finally figured out that I had broken a capacitor on the daughter board during removal labelled ".1MF 50V AX. CER" in the schematic from the manual (there are 3 of them on the board). In an attempt to fix, I had what I believed is the same cap on the "filter board" that I have never used so I borrowed it and moved it to replace the broken one. Still no response from the game with the original ROMs installed. With the high score save/multigame ROMs I get a blue screen and no response from machine.

Should I replace the daughterboard and see what happens or is there potential for damage elsewhere in the board? Can't seem to find anything on how to start testing ... But I am new.

 

[KenLayton]

That sync buss board can be "accidently" installed backwards? By chance did that happen?

 

[spurcap]

That sync buss board can be "accidently" installed backwards? By chance did that happen?

Not to the best of my knowledge (I knew this and was careful) and definitely not installed backwards now. I understand if it were installed backwards, it could have fried the board but is it possible a broken cap on the board or if it were installed backwards that it damaged other areas of the PCB?

 

[smalltownguy2]

A malfunctioning sync buss controller board would leave you with a static image of jumbled sprites on the screen, not moving. If you don't have that, you have other issues.

 

[spurcap]

Is it possible that damage to the Z80 CPU would cause a blank screen? I am not sure what else it could be given only the sync daughter board and Z80 were removed and still used with the High Score kit. And both with the save kit and the original roms installed I am not getting anything other than a blue screen when the save kit roms are installed.

I could check that I am getting power to the PCB I guess, but not sure why I wouldn't given I was minutes before I took it out. I already checked all the cabinet fuses with my multi-meter.

 

[LyonsArcade]

Yes the Z80 could absolutely be the problem, it creates everything. Look closely at the socket with the chip out and see if the pins inside the socket look bent all to hell, sometimes you'll get one bent over at a weird angle and it no longer is touching the pin on the chip.

Look @ the crystal on the board and make sure you didn't snap it off while you were messing with it.

Look @ the edge connector of the board and see if one of the pins has folded over and came delaminated from the board. Look inside the edge connector and see if any of the pins look screwed up or pulled out.

try to boot it up without the sync bus controller installed and see if you get something different on the screen

Use your multimeter and check for continuity from the pin in socket to the back of the board where the socket is soldered in for each pin on the z80....

Make sure you didn't install any of the roms in backwards, then look again to make sure again, then look again to make sure again.

If you installed any of the chips backwards or the Z80 backwards or the controller board backwards they'll likely be fried.

You should get some kind of movement on the screen though other than just all blue.

 

[mecha]

I'm intrigued that Midway didn't silk the orientation of the chip notches. but all the U-shaped notches of the chips face the same direction. the sub boards pay attention to the notches, plug them in so the sub board notches are facing the same direction as the ones on the main board.

bad or missing Z80 will give you garbage on the screen. blank screen means you have inadequate or missing power, which is incredibly common on these games. if you've never replaced the fuse holders in the base of the game (there are 2 of them, 2 for 120V AC side of the isolation transformer and 4 for the 7 and 14V AC supplies off the other transformer) then you will have problems. the most famous symptom on a "working" game will be the "hum bar" effect.

Pac-Man and Ms. Pac-Man take AC voltages in from the right transformer and rectify them on the board. there is thus no traditional power supply in the game. bad fuse holders will in effect produce a bottleneck of the voltage going into the boards, and that trips up the rectification hardware to the point it will burn up the card edge, specifically the 7V AC contacts if I'm not mistaken. the excess heat also damages the pins of the harness, they'll become pretty melty and flatten out and make increasingly poorer contact over time. eventually you'll reach a point like where you probably are now where they barely make any connection at all, meaning no voltage getting into the board.

the only reliable solution I've found is replacing the burned contacts with copper tape. I'm sure a multitude of tutorial videos exist for how to do this. before you do anything though, read my PSU guide, there's instructions for how to measure voltage at chips. if you're well below 4V, then you have an issue with the juice coming in. which I'll reiterate can be a combination of bad fuse holders, bad harness pins, and burned contacts on the card edge that the harness plugs onto.

 

[spurcap]

For future reference to anyone reading this thread, I got it fixed. While not sure exactly what happened, this is my best guess:
1) Plugged in originally and didn't work due to broken cap on z80 bus board
2) Checked fuses after it didn't turn on and no issues
3) Replaced broken cap on bus board and put it in backwards (guessing but plausible, but definitely did something to blow the fuse that wasn't blown when the board was first plugged back in ...)
4) Tried swapping direction of cap but system still did not work as fuse was now blown (which I did not think of as I just checked it to be working)
5) Last night, saw broken fuse, replaced and all is good.

I do note that when I first turned it on, the picture was dark and one of the joystick directions didn't work, I pushed hard on the edge connector and all is now sorted. While I have another edge connector that I was going to wire into the cabinet, would it be advisable to add some solder to the PCB side of the connector?

Thanks all for the help

 

[spurcap]

So....
Had a 100 percent working pacman and then decided to pull the board to try again to get the high score save kit. Did it per instructions, triple checked, put on and blank screen...
Huh..
So removed the save kit to go back to original Pacman roms and same thing....
Took board out to take a look and realized that while I had labeled all the original roms when I removed them to make sure I didn't put them on backwards I must have screwed up the first one and as a result put them consistently ALL on backwards (with the exception of the sync bus daughter board). How much damage did I do???

Board still appears to be getting voltage. Perhaps I fryed the z80? Either way had everything right when I put the multipac high score save kit on and it didn't work and it was working before... so lost for ideas....

 

[KenLayton]

Any rom chips put in backwards are immediately destroyed upon power up.

 

[spurcap]

Thanks. Could they be fixrf with eprom burner or dead for good?

 

[nmantas]

Any rom chips put in backwards are immediately destroyed upon power up.

Had a couple of cocktails a few weekends ago and started doing some Rom programming.......been doing this stuff for years and put a rom in the wrong way twice. Especially love the light-bulb effect going inside the UV window. I wrote the first one off as a silly mistake......I was able to make the call that it was time for bed after the second. Definitely toast after that but the damage has always been just the ROM and nothing else on the board.

 

[tmoger]

That sync buss board can be "accidently" installed backwards? By chance did that happen?

Good Evening sir,

I am working on a ms pac board for a friend that botched the his highscoresaves.com high score save board. i noticed right away he installed the z80 sync board in backwards, would fry it by chance?

any suggestions would be great, i have a working pac and can swap parts off my board but i dont want to do anything that will break my board as well.

Hope all is well,

Tony Moger

 

[mecha]

Good Evening sir,

I am working on a ms pac board for a friend that botched the his highscoresaves.com high score save board. i noticed right away he installed the z80 sync board in backwards, would fry it by chance?

any suggestions would be great, i have a working pac and can swap parts off my board but i dont want to do anything that will break my board as well.

Hope all is well,

Tony Moger

Ken Layton is no longer with us. installing any of those boards backwards will destroy them. I believe Mikes Arcade sells the custom chip replacements still though.

 

[smalltownguy2]

Ken Layton is no longer with us. installing any of those boards backwards will destroy them. I believe Mikes Arcade sells the custom chip replacements still though.

As in "dead." That's an important distinction to make. RIP, Ken.

Mecha's advice is sound, you'd be wise to heed it.

 

[mecha]

they have the JROK VRAM addresser, but no Z80 sync bus controller.

here's replacement boards: https://www.mikesarcade.com/cgi-bin/store.pl?sku=SBCVRA

 

[Onji]

It seems that sometimes you'll get lucky and it'll just blow a fuse, and the bus controller will be ok. Something worth checking anyway.

 

[mecha]

It seems that sometimes you'll get lucky and it'll just blow a fuse, and the bus controller will be ok. Something worth checking anyway.

I've never heard of this, that's wild

 

[tmoger]

Ken Layton is no longer with us. installing any of those boards backwards will destroy them. I believe Mikes Arcade sells the custom chip replacements still though.

thank you for the reply,

Very sorry to hear about Ken. I really appreciate the info.