Gauntlet Power Problem

MagicMarc-er

Member
Joined
Apr 14, 2011
Messages
404
Reaction score
21
Location
Worthington, Ohio
I've been playing my recently restored Gauntlet and everything has been fine when one day, all the sudden it dies, right in the middle of a game. I checked the fuses and both F2 and F3 fuses had blown. I replaced them, powered it back on and watched them fry again instantly. I checked the power coming in and I have a good 120V going to the switching power supply and 5V coming out where I need it. The problem is with the two fuses just downstream of the transformer.

It looks like I have about 12.6VAC at F2 and 13.5VAC at F3. F3 seems a little high but F2 should be ok shouldn't it?

Anyone have any ideas as to what might be the problem?
 
Check for a shorted diode on your audio board (CR1 thru 4).
Check for a short in the coin door lamp wiring.
 
All four diodes on the sound board tested ok but there is a small dark spot on one of the leads for CR4. Might be nothing.

I did notice that the metal housing of the potentiometer for the sound volume had come in contact with one side of the R3 resistor. Could that have been the problem?

Also, when I blew the fuses the last time, I noticed a spark on the bottom of the inlet side of the transistor. Would that be normal?
 
Ugh...two more fuses fried. I thought maybe one of the contacts on the back of the sound board had come in contact with a metal staple on the cabinet where the board sits. I moved it, moved the potentiometer away from that resistor, fired it back up and fried them again.

Any other ideas?
 
Ok, DarrenF, looks like you were onto something. I checked the coin door and did find a possible short. It looked like one of the lamp holders was touching the metal of the coin door. I removed all 4 lamps and made sure nothing was in contact, replaced the f2 & f3 fuses and powered it up. This time f3 had no problem but f2 fried again.

Any other suggestions?
 
If the fuse is blowing instantly, there's still a dead short somewhere. It could be a wiring or inadvertant contact issue, or could be an internally shorted component. You need to isolate the problem.

The 12VAC out of the xformer goes to the audio board. There, one leg of it goes off to the coin door for lighting, and both legs are rectified & filtered to form +15VDC & -15VDC. These DC voltages are then used on the audio board to power the amplifiers, and they also go to the main game PCB (didn't bother looking to see what for).

I'd recommend disconnecting the power connector from the main PCB. If the fuse still blows, your problem lies on the audio PCB (or in the wiring). If it doesn't, then there's a problem on the main game PCB.

If the problem is on the audio board, then some causes include:
-physical damage / inadvertant contact, causing short.
-shorted diode (in spite of your above contention that they aren't shorted)
-shorted capacitor
-shorted amp IC

If the problem is on the main PCB... I'd have to look at the schematic to see what +/-15VDC is used for.
 
The saga continues. I bought a second sound board, powered it up, and no fuses blew...but nothing came on either. The lights in the coin door are working, I can hear the monitor humming but the light on the main board is not on so......

I took the main power connector off the main board and tested all the connections. Good power on all the 5 VDC lines but 17 VDC coming in on the gray wire from the sound card. That seems high (it's supposed to be 12 VDC.

Suggestions?
 
I'm at the end of my ability to fix this thing. Maybe someone has some suggestions. Let me recap: Gauntlet was working fine but shut down in the middle of a game. I checked and two fuses (F2 & F3) were blown. I replaced and they blew again. Checked several things and nothing was obvious so I bought a replacement sound board. When I power this one up, there are no blown fuses but....no light on the main board. Checked power on each pin at the main board and everything looks good except that instead of +15 VDC and -15VDC I have +18VDC and -18VDC. Checked back at the fuses and I have 13VAC on both red wires between the fuses and the sound board instead of 12VAC. The lights on the coin doors are on.

At this point, unless I'm missing something, I guess the problem has to be the main board, right?

If that's the case, anyone have a place you'd recommend for board repair?
 
Back
Top Bottom