Arcade Collecting > Restorations & repair
1981 Ms. Pac-Man restoration
Finalheaven:
--- Quote from: RayB on July 01, 2010, 11:16:48 pm ---I think the way I have seen it done is to piggy-back the chips, and bend a couple specific legs up (maybe the ones that take power?) and you link those to a switch (2 or 3 position switch depending on how many chips you wish to support).
This is all fuzzy memory of how I *think* my Galaga's fast shoot chip is set up. Think about it, no soldering of dozens of little wires!!
--- End quote ---
I wanted to create the switch board so that I can swap eproms and not worry about bending pins. When I was pulling the 30 year old eproms out of the PCB some of the legs fell right off, and that was with perfect extraction technique. I'd rather screw with little wires and get that right and leave the eproms untouched. Sockets and wire is cheaper for me than finding 2532's, plus I really enjoyed it.
As for the voltages, I read a few data sheets regarding 2532's and discovered pin 21 is Vpp, pin 24 is Vcc, and pin 12 is Vss. From a TI datasheet (http://www.downloads.reactivemicro.com/Public/Electronics/ROM/2532%20EPROM%20Data%20Sheet.pdf) I read that Vpp is +25V power supply and the Vcc is the +5V supply and Vss is the ground.
In the old Ms. Pac-Man schematic, There's no record of the 24 pin on 6F, but it does show pin 21 as Vpp with a straight line pointing out and then ending at a diagonal line. Any thoughts on which pin I need to open in order to disable the eprom?
RoyalScam:
First off, let me say excellent progress on the restore! I have absolutely no experience repairing Ms. Pac-Man or any other arcade machine for that matter, but Vpp is usually the programming voltage supply for an EPROM. Should that voltage be present, I would think that it would be very possible to randomly reprogram, or even irreparably damage your ROM. I would leave that pin unconnected. Should you want to verify this with the original mainboard, use a dc voltmeter set to read in excess of 25 volts and check to see if Vpp is actually being supplied to the EPROM. I would guess not.
Regards,
Scam
<edit> Thinking about it a bit more...That pin may be held high Logic1 or +5volts or even held low Logic0 or GND, easily verified with the voltmeter.
Finalheaven:
--- Quote from: RoyalScam on July 02, 2010, 10:34:23 pm ---First off, let me say excellent progress on the restore! I have absolutely no experience repairing Ms. Pac-Man or any other arcade machine for that matter, but Vpp is usually the programming voltage supply for an EPROM. Should that voltage be present, I would think that it would be very possible to randomly reprogram, or even irreparably damage your ROM. I would leave that pin unconnected. Should you want to verify this with the original mainboard, use a dc voltmeter set to read in excess of 25 volts and check to see if Vpp is actually being supplied to the EPROM. I would guess not.
Regards,
Scam
<edit> Thinking about it a bit more...That pin may be held high Logic1 or +5volts or even held low Logic0 or GND, easily verified with the voltmeter.
--- End quote ---
I did that and found Vpp was not being supplied 25 volts. Pins 21 and 24 were being supplied +5 volts. I rewired the switch so that pins 21 and 24 would be operated by the DPDT switch, but it still didn't work. I was getting artifacts. At this point I've settling for the original speed rom and closing her up.
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