Converting -12vdc from the +12vdc of a JAMMA harness

Tornadoboy

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Converting -12vdc from the +12vdc of a JAMMA harness

Hey dudes, here's more proof I'm a newbie:

I've got an Exidy Spectar PCB that needs the usual +5/12 voltages along with -12vdc and I was wondering if someone can point me to a simple yet reliable circuit for converting it out of the standard +12 in a typical JAMMA switching supply? I know computer ATX supplies can provide all the needed voltages but I wanted to make an adaptor that'll plug into a jamma cab without having to change anything.
 
Traditionally the -5 vdc supply is used for this purpose.

In order to supply a true -12vdc you will need to build a fairly elaborate circuit, converting the +12 vdc is not really an option.
 
I found this circuit on the web which claims to convert +12 to negative using a common 555 timer, although the source webpage doesn't say how many amps it can handle:
 

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Cheaper to put another power supply in.

Mouser has part #: 580-BWR12-625-D5A-C

Which takes +5 in and gives you +/- 12v out at 625ma of juice.

$117.10 - EEEK!

They have cheaper parts but they put out less than 100ma of current.
 
I just spent a couple of minutes looking through the Spectar manual and I don't see where -12 vdc is used. It is possible that it is generated strictly for the coin counter, many of the old coin counters operated off of 24vdc. If it is used as a logic signal as described in the manual the conversion circuit you show will not be able to handle the load.


Do you see where the -12 vdc is utilized in the circuit?
 
I just spent a couple of minutes looking through the Spectar manual and I don't see where -12 vdc is used. It is possible that it is generated strictly for the coin counter, many of the old coin counters operated off of 24vdc. If it is used as a logic signal as described in the manual the conversion circuit you show will not be able to handle the load.


Do you see where the -12 vdc is utilized in the circuit?

Yep, although it looks like it's only used for the audio amplifier on the sound board which uses a couple of LM739's, so if I wanted to get cute I might be able to just bypass the amp alltogether and replace it with something that uses +12, but I'd rather not hack things THAT much! :) Not to mention if I figure this out it will be usefull on other Jamma adaptations.
 
Yep, although it looks like it's only used for the audio amplifier on the sound board which uses a couple of LM739's, so if I wanted to get cute I might be able to just bypass the amp alltogether and replace it with something that uses +12, but I'd rather not hack things THAT much! :) Not to mention if I figure this out it will be usefull on other Jamma adaptations.

It's only used on the Op Amps (LM324 and LM379), so substituting -5V for the -12V rail should work just fine.
 
An easy way would be to get a PC PSU, like an AT model. It should have +/- 12v,5v. Just be sure you stick some fuses in there since the PSUs do push a little harder than the ones in your arcade cab. YOu most likely can snag one for less than $30.
 
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