What hack is this...

melchman

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I acquired a working Ms. Pac-Man this weekend. Spent some time replacing the usual failure points. I have a strange hack on my PCB. I am hoping for help identifying and advice on removal strategies.

Brief description and photos are here.

A microswitch was attach to pin 2 of the chip at C9 and pin 11 (of 14) of the chip at C8. Pin 11 was lifted out of the socket.

A third wire is attache to the microswitch but not attached to the PCB or ground.

Does this sound like a "worthy upgrade" or a bad hack that needs repaired?
 
Hmmm.

If I momentarily close the switch (like pushing a button and releasing) it resets (restarts) the game. If I hold it it keeps resetting and does not start.

If I disconnect the switch it puts an odd pattern with two ghosts and some fruit on the screen.
 
Do you have schematics? It would really help to figure this out if you had schematics and could figure out what signals are being tied together.
 
I acquired a working Ms. Pac-Man this weekend. Spent some time replacing the usual failure points. I have a strange hack on my PCB. I am hoping for help identifying and advice on removal strategies.

Brief description and photos are here.

A microswitch was attach to pin 2 of the chip at C9 and pin 11 (of 14) of the chip at C8. Pin 11 was lifted out of the socket.

A third wire is attache to the microswitch but not attached to the PCB or ground.

Does this sound like a "worthy upgrade" or a bad hack that needs repaired?

I'm looking at the schematic now. If your board matches it, then perhaps I can talk usefully...

9C pin 2 looks to be vblank, and 8C pin 11 is also vblank.
(9C is below and to the left a bit of the Z80 on the schematics. 8C is just left of the Z80).

Pin 11 of 8C is the source for the vblank IRQ, if I'm reading this right. And 9C feeds into some logic that synchronizes it and holds it disabled at some points?

My guess is that the switch is a normally closed type (NC type) so that normally the two things are connected, and the board works. If you push the button, they are disconnected (no VBLANK to the CPU) and the board doesn't work.

Someone's failed attempt at a pause switch, perhaps? Without vblank, one could think that the CPU would simply do nothing, thus allowing one to walk away. Given that they proceed to leave the input floating (instead of tying to gnd or +5 when not connected to vblank), I'm unclear whether it's not working because that simply won't work, or if it's because they left the input floating and it's flipping out the CPU.

Obviously it doesn't work, so I'd remove it, put pin 11 back in it's socket, make sure pin 11 is really getting VBLANK (the trace on the board is probably good), and call it a day.
 
Vblank

I believe it is NC as well. If I remove the switch (nicely placed a MOLEX in the hack for me) it does seem to pause (I call it freeze) on boot.

There is a third wire that looks like it was soldered to something but my searches have not found the connection point.

I had not considered +5 or GND, though.

I don't think there is enough left of the pin to restore. I may need to purchase a new one. Or leave it in place. Or close the circuit without the NC switch?
 
I got it....that wiring probably went to a 'security lock' of some sort. It's a keyed lockset with an integrated microswitch iinside. Turn the key one way, the game works. Turn the key the other way, the game wont work.

I've seen these kinds of locks installed on some games in the past. Some extra layer of security or something OPS put on machines.
 
I believe it is NC as well. If I remove the switch (nicely placed a MOLEX in the hack for me) it does seem to pause (I call it freeze) on boot.

There is a third wire that looks like it was soldered to something but my searches have not found the connection point.

I had not considered +5 or GND, though.

I don't think there is enough left of the pin to restore. I may need to purchase a new one. Or leave it in place. Or close the circuit without the NC switch?

How much do you want to clean up the board? If you want to clean the board, then get a new chip, remove all the wires and be done.

If you can't get a new chip (It's just 74 logic, but I don't know availability on that particular one - I think they are still commonly available), then you could take another socket, put the chip with the cut leg in the socket, solder a wire from cut leg to appropriate point on the socket, then drop the socket in where the chip goes (so you'd have one socket acting as the new leg for the chip, but the whole thing is still removable if you need to change it).

If you don't mind the board looking a little hacked up, then just cut the switch off, run the wire from the cut leg to the other chip and call it a day. When next you need to work on either of those chips you'll have to deal with the wire, but they aren't likely to go bad.

I don't recommend leaving the switch in line, that just creates more things to go wrong. If you don't do a 'proper' fix of replacing the chip with the cut leg, then at least cut out the switch and shorten the wire as much as you can.
 
I got it....that wiring probably went to a 'security lock' of some sort. It's a keyed lockset with an integrated microswitch iinside. Turn the key one way, the game works. Turn the key the other way, the game wont work.

I've seen these kinds of locks installed on some games in the past. Some extra layer of security or something OPS put on machines.

Or a motion/slam switch to stick it to machine abusers. Get pissed off and shove/smack/kick the cabinet, lose your game and your credits.
 
Or a motion/slam switch to stick it to machine abusers. Get pissed off and shove/smack/kick the cabinet, lose your game and your credits.

I don't buy it. If you wanted a slam switch, or even a cut-off, you'd wire to the reset line, not hack vblank like this. A reset hack would only need 2 wires, and dorking around cutting chip legs. I really thing the intent was some thing else.
 
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