Gorf powersupply -5v line too high.

Finch

New member
Joined
Apr 27, 2006
Messages
104
Reaction score
0
Location
Santa Cruz, California
I'm trying to get a gorf cab up and running but no luck yet. Replaced some blown resistors in the audio amp while I'm waiting for my monitor repair kit (no real good way to test before that)

Anyways I tested the voltages coming out of the PSU (its original) and noticed that the -5v is currently measuring at -6.35 and the pot on the PSU does nothing to adjust this. Is that too much voltage and might it cause problems?

Looks like the PSU board was repaired once before, so perhaps something was done to bypass the pot, or it doesn't work anymore.
 
A bit of a bump. Perhaps specifying it as a Gorf power supply is a bit too specific.

Mostly I'm wondering, is -6.5 volts way way out of spec and in danger of frying things. What do games usually use the -5v line for?
 
I think your level of specificity was appropriate.

I'm not too familiar with the PS in question, but it appears to have 3 different pots; one each of +12, +5 & -5 suppies. I assume you're certain that you are adjusting and measuring the correct one? Also, where precisely are you placing your DMM leads to measure your -5VDC?

There are only a handful of components in the -5V supply circuit; a couple of diodes, a few caps, couple of resistors, the pot, and the 7905 regulator. My even shorter list of suspects would include the 7905 and the 2000uF cap.

In general, I've seen -5VDC is used by: some old (70s era) memory ICs, audio amps, and some other "special" ICs (some speech synthisizers, etc.)

As far as Gorf specifically... It appears to use the -5VDC its video output. Just took a cursory look as the schematics, so I'm not sure if there's anything else.
 
The PSU looks to be about the same as the old Galaga PSU and the same used in a lot of old midway cabs.

I'm measuring the voltage by just sticking the meter into the end of the plug while it's not plugged into the game. I just read recently that I should meter while It's plugged in, but with it running a bit high I wasn't sure I should keep it plugged into the game.

I've adjusted all 3 pots while metering all 3 lines, 2 pots successfully adjust the +5 and +12 but the 3rd pot doesn't do anything to the -5 line.

The PSU has a resistor stuck onto the side of the IC on the PSU, and 2 caps piggybacked on top of each other as a replacement for one of the original caps, so that may explain the funkyness. Probablt going to get the Bob Roberts repair kit for it but in the mean time I'm just a bit concerned about it ruining other things I'm trying to fix.
 
get a switcher kit. those linear supplies are too old to keep games running correct. all components by now would need to be replaced.
even if you fix a prob now, they will go bad and continue to fry your boards.

ever since i have thrown a switcher kit in my gorf and wizard of wor, williams games, etc, ive had zero probs. the voltages are too flakey with linear setups and they run too hot.
...thats why they dont make them anymore.
 
Back
Top Bottom