Midway Galaxian basics

drbible

drbible

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Starting to look at this galaxian as i picked up a 2 non working originals to practice on. Interesting ref the pacmans just posted......I would never have spotted that shorted solder/trace so that's useful info.

This board is actually in pretty good condition on visual inspection. Gave it a clean and pulled, cleaned and reseated the roms. Havent checked them but i have swapped them out with the other boards and no change to screen display.

CPU and clock active and not in reset.

The display is mostly garbled data but with an occasionally readable bad ram (2 and poss 3) message.

Having realised it's supposed to have a 7v supply im now wondering whether to carry on or not until i sort that.
I can max my power supply up to show the board is getting nearly 6v and it does look like its trying.

The question is, is it worth continuing with the ram fixes without sorting out the power feed or is my supply in all honesty enough to troubleshoot with at this stage?

1000036637.jpg1000036636.jpg1000036584.jpg1000036583.jpg
 
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Mc-Q

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are you using a regulated 5v psu?
if yes then remove the regulator and fit a jumper from the diodes at the edge connector to the regulator output pad

dont trust the sockets the romboard is pushed into,
and you probably need to socket the rams.
if you have the skills, it's a good idea to get rid of the romboard and fit a 27c128 to the mainboard with a modified socket and put all the code in one chip,
you can also pull the 2x2114 rams and bodge in a 6116 that will give double the ram and allow a lot of conversions to run
 
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NivagSwerdna

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IMHO convert it to 5V DC and run from a regulated supply. You don't need to worry about the 12V until you get to the audio output.

The originals have an AC input not DC... You probably just want to use a modern PSU unless you have specific needs.
 
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Mc-Q

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depends on if he has the cab or plans to sell it really.
if it was mine i would convert it to dc for jamma use.
but a cab owner wouldnt buy it from me afterwards
 
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NivagSwerdna

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I've never done it but I think an AC board requires 7VAC to get going.

Measure between the corners of a chip and see what is actually making it to the board after regulation
 
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Mc-Q

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it will probably need more than 7, the diodes have a .7v voltdrop and the regulator has overheads - i'd say 7.5 minimum
 
drbible

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Mc-Q said:
are you using a regulated 5v psu?
if yes then remove the regulator and fit a jumper from the diodes at the edge connector to the regulator output pad

dont trust the sockets the romboard is pushed into,
and you probably need to socket the rams.
if you have the skills, it's a good idea to get rid of the romboard and fit a 27c128 to the mainboard with a modified socket and put all the code in one chip,
you can also pull the 2x2114 rams and bodge in a 6116 that will give double the ram and allow a lot of conversions to run
Click to expand...
Can, and will, put new sockets in for the rom board and ram chips. However the motherboard etc is out of my league.
Yep, using a standard psu which maxes out at just under 6v....1000036512.jpg1000036694.jpg
 
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Mc-Q

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if you keep the romboard it shouldnt be in chipsockets,
it should be in female pinstrip sockets.
thats why it's not reliable - it's held in by about 3mm of pin!
 
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NivagSwerdna

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# You say DC and I say AC... let's call the whole thing off!

I think that arrangement and adapter wires A&B and 1&2 together as GND. Which is wired to JAMMA GND on A&B, 1&2,...
It presents 5V on C&D and 3&4 from JAMMA C&D, 3&4.

Now an AC Galaxian... would expect GND on A&B and1&2
but... 7V AC on C&D and 3&4

The conversion is pretty straightforward. Basically remove the diodes and voltage regulation parts and then run the 5V to where the emitter of the regulating transistor would have been.
Basically nuke the area... and then that red wire brings the 5V back into the circuit... something like that...

CaptureGalaxianPSU2.png

CaptureGalaxianPSU.PNG
 
drbible

drbible

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Great info thanks all. Getting 4.5v at the most distant chips which may actually work i guess. However I'm going to go with the DC and the single ROM mods I think. Not least to expand my skills....wire wrapping etc. Anyway will report back when it's fixed. Wanted this fix log not to be another running commentary of my ineptitude so need to stop now!
 
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