Crazy voltage issues

[demogo]

Anyone have any thoughts on what's going on my with my voltage in my Gauntlet Legends? Here's the deal:

I fired up my Gauntlet Legends game today and it was acting funny. It was rebooting during the demo mode, and once it came up and started making an odd buzzing sound instead of the normal demo audio, etc. This is all new behavior -- the game has been behaving well for quite a while.

Anyway, I checked the connections and everything looked okay so I pulled out my DMM and checked the voltages at the buttons (which experience has shown me is the same as at the ROM). It was only at about 4.65 volts which is pretty crazy since I hadn't touched the power supply adjustment.

Anyway, I tested the voltage at the ROM and got the same number so I tweaked the power supply up to 5.0v, let the game run for a while and all was well.

Then I tidied up the inside and installed some cable clamps to tame the wild wiring inside.

As a side issue (which MAY be related), 6-8 months ago I'd been having a very intermittent issue where the GL and NBA Jam boards (which share the cabinet) would freak out shortly after powering the game up and someone suggested that it might be the ballast in the marquee light. So 6-8 months ago I unplugged the marquee light from the power supply and everything had been fine so I figured this other issue really *was* with the marquee ballast. Since I had the game open anyway I went ahead and opened the top up, cut out the old ballast, replaced it and the starter, and put things back together.

So I fired up the game (this time with the marquee light lit) and low and behold, the game locks up during the intro mode again. Sure enough, I check the voltage and it's again around 4.80 volts (at the buttons). So I tweak it AGAIN to 5.0 volts and then the game is fine, demo mode works, and we play a long game of GL.

So what the heck is going on here? Why did I have to turn the voltage up so much to get back to 5.0v the first time? And after hooking the marquee light up again (plugs into the aux power socket on top of the power supply), why would I have to tweak the power up again?

I replaced the power supply earlier in the year so it's pretty new. (Last one worked but caused interference lines in my picture).

I did check the voltage level at the buttons with NBA Jam running and got the same low voltage levels so I don't think it's a GL specific issue.

Thoughts? Opinions? Why do I have to keep cranking my power supply up?

 

[demogo]

Anyone? Bump.

 

[Oryk Zinyo]

A drifting power supply is a sign of weak caps. You may want to check out the "new" switcher.

Another possibility is faulty connectors drawing down the voltage level. However, this almost always shows a reduction in voltage levels after the game has been on for a while, not immediately upon power up.

 

[demogo]

A drifting power supply is a sign of weak caps. You may want to check out the "new" switcher.

Another possibility is faulty connectors drawing down the voltage level. However, this almost always shows a reduction in voltage levels after the game has been on for a while, not immediately upon power up.

I guess I should check the voltages before the jamma extension connector and immediately after it?

I hope it's not the power supply; those are like $70 supplies. And it was new.

 

[Oryk Zinyo]

Yeah, checking the output at the first available point is a good start.


Also, it is possible that something in the cab is drawing off a lot of the amperage and that is causing the voltage drop you are experiencing.

 

[demogo]

Does it make sense that when I hooked up the marquee light again that the additional draw from the aux power plug on the top of the power supply would cause the power supply to need to be readjusted?

I can't think of anything that would be sucking up a lot of the amperage -- nothing has really changed.

 

[Oryk Zinyo]

No, the power output from the switching power supply shouldn't be affected by the marquee light. The power draw I am hypothesizing would have to be coming something after the switcher.

 

[mecha]

did you happen to catch my lengthy reply in that one MK or MK2 thread last week about power supplies?

I'm going to assume you have the larger box unit power supply with the molex plug in there. sometimes the adjustment pots just get oxidized or covered in shit and you have to wipe them. (which means with the machine turned off, you turn the pot back and forth between its extremes several times -- the wiper on the pot self-cleans it in ways, think of it as disc brakes being covered in rust and braking self-cleaning them ) the only safe way to do this however is with the game board not plugged in (see: disconnect the JAMMA harness) and the optimal way to do it without damaging the power supply is by putting a load on it, like one of your coin door lights.

I rigged up a lamp tool that plugs into the molex connector, I crimped male pins on it... alternatively I can also use it with screw terminal units via alligator clips. if you have several cabs I encourage you build one of these so you can do some preventative maintenance on your PSUs.

although failing electronics in the unit can always be a possibility, I figure if you have the full range of voltage adjustments (your 4.65 sounds a bit low however) the unit should be ok for the time being.

my recommendation, seeing as how this has been a recurring problem now, would be to replace the power supply and be done with it. your marquee light isn't going to affect it, unless you have your meter probed into the incoming AC going to the power supply and you see a noticeable drop somehow while you have the machine turned on. (VERY doubtful, as that would mean your monitor would be getting pulled down as well -- there's no iso in that cab)

 

[demogo]

did you happen to catch my lengthy reply in that one MK or MK2 thread last week about power supplies?

I'm going to assume you have the larger box unit power supply with the molex plug in there. sometimes the adjustment pots just get oxidized or covered in shit and you have to wipe them. (which means with the machine turned off, you turn the pot back and forth between its extremes several times -- the wiper on the pot self-cleans it in ways, think of it as disc brakes being covered in rust and braking self-cleaning them ) the only safe way to do this however is with the game board not plugged in (see: disconnect the JAMMA harness) and the optimal way to do it without damaging the power supply is by putting a load on it, like one of your coin door lights.

I rigged up a lamp tool that plugs into the molex connector, I crimped male pins on it... alternatively I can also use it with screw terminal units via alligator clips. if you have several cabs I encourage you build one of these so you can do some preventative maintenance on your PSUs.

although failing electronics in the unit can always be a possibility, I figure if you have the full range of voltage adjustments (your 4.65 sounds a bit low however) the unit should be ok for the time being.

my recommendation, seeing as how this has been a recurring problem now, would be to replace the power supply and be done with it. your marquee light isn't going to affect it, unless you have your meter probed into the incoming AC going to the power supply and you see a noticeable drop somehow while you have the machine turned on. (VERY doubtful, as that would mean your monitor would be getting pulled down as well -- there's no iso in that cab)

No, I missed your earlier thread -- that's interesting.

The voltage issue I observed today was the first day that I've ever seen this. It's not clear that the possible ballast related issue is the same thing or not -- the game has behaved fine for the last 6-8 months with the marquee light unplugged so I tend to think that was a different issue.

I'll open the damn thing back up tomorrow and probe the voltages as they leave the power supply all the way to the ROMs. If I don't see any losses there then it sounds like the new power supply is going to get replaced AGAIN.

I have a spare 300 watt power supply I just pulled out of a computer -- would that do the trick? I don't think there's a voltage adjustment screw on it, and I also don't believe there's a plug for the marquee light...

It would take some cable hacking but the price would be unbeatable.

 

[mecha]

oh, your marquee runs off the AC plug on your power supply? that's odd, I thought those cabs would've been identical to the other Midway cabs and have 3 separate AC feeds for the power supply, marquee and monitor.

in either case, I was under the impression that the AC out on those power supplies directly fed off the AC plug that you insert into it.

I, like many others here, would frown upon the PC power supply solution, mainly because of the amperage they throw out. I've seen supergun applications with them where you insert inline fuses on the 5 volt power lines, but that's a little too much bullshit work than I'd be willing to put up with. you also, of course, lose out on the +5 adjustment.

were you implying that you've replaced the power supply before?

 

[demogo]

oh, your marquee runs off the AC plug on your power supply? that's odd, I thought those cabs would've been identical to the other Midway cabs and have 3 separate AC feeds for the power supply, marquee and monitor.

in either case, I was under the impression that the AC out on those power supplies directly fed off the AC plug that you insert into it.

I, like many others here, would frown upon the PC power supply solution, mainly because of the amperage they throw out. I've seen supergun applications with them where you insert inline fuses on the 5 volt power lines, but that's a little too much bullshit work than I'd be willing to put up with. you also, of course, lose out on the +5 adjustment.

were you implying that you've replaced the power supply before?

Mecha,

There may be a separate power plug for the marquee light but there's also one on top with a standard electrical plug and that's what the marquee light had (I don't remember why). Easy enough to cut off the connectors and switch to the other plug but it sounds like a moot point.

And yes, this power supply is a new replacement from the manufacturer that I installed earlier in the year. The previous power supply worked fine but was responsible for an annoying ripple in the video.

Could you please explain this a little further?

"I, like many others here, would frown upon the PC power supply solution, mainly because of the amperage they throw out."

 

[demogo]

OK, this is crazy.

Plugged the game back in and the voltages at the buttons were about 5.16 -- definitely higher than when I last had the game on.

I am running a very unusual wiring harness for wiring:

Power supply -> cab jamma plug ==> Bob Roberts jamma extension harness. I recorded 5.48 volts where these plug together.

then this is routed up to my control panel where there's another BR jamma extension harness which feeds back to the GL boards. I recorded 5.35-5.40 volts here.

I recorded 5.30 volts at the GL gameboard jamma plug.

That's a lot of wire and connectors to push electricity through so it doesn't seem like it's an insane loss.

But when I re-probed the spot that I got 5.35-5.40 at, I got 5.60 volts.

This whole thing is giving me the creeps.

I sure hate to spend a ton of money on a new power supply but does that sound like what's needed here? I'd say my DMM was acting up but the game is having issues so there's obviously a problem here.

Any other thoughts?

 

[Oryk Zinyo]

Well, you should check the batteries in your DMM. I have seen them give erroneous readings when the batteries are close to dead.

As for the rest of it, the power loss seems extreme. I am worried that your power supply is not holding the output voltage properly, and that would indicate that it needs to be rebuilt or replaced. Did you try wiping the pot as mentioned above?

 

[demogo]

I replaced the batteries in my DMM a few months ago and it hasn't been used that much but I'll double check them tomorrow. The last batteries lasted a couple of years so I don't think it's that.

I haven't tried the wiper thing yet. I'll do it tomorrow although I confess that this power supply thing is freaking me out. I'll dial the voltage way down -- I don't want my boards being fried by the power supply and I'm concerned that's what's happening now.

 

[tonyh22]

I bought a Gauntlet Legends a few weeks ago and the light was burnt out in the marguee, so I replaced it. A day later I was having the issues you are having with it resetting pretty regularly. When I checked the volatges the +5 was around +5.7. I adjusted the voltage down to +5v even and then the systems wouldn't boot and had errors pop up. I turned the voltage up to 5.17 and I haven't had an issue yet.

But like you I thought the marguee light was causing it but it appears that was not the case.

 

[CamW]

just look on ebay buy one that has a return if that fixes your prob. there you go
if it still doesnt work return the power supply

 

[demogo]

I bought a Gauntlet Legends a few weeks ago and the light was burnt out in the marguee, so I replaced it. A day later I was having the issues you are having with it resetting pretty regularly. When I checked the volatges the +5 was around +5.7. I adjusted the voltage down to +5v even and then the systems wouldn't boot and had errors pop up. I turned the voltage up to 5.17 and I haven't had an issue yet.

But like you I thought the marguee light was causing it but it appears that was not the case.

Tony, I believe I am having both those issues but I don't believe they are related.

 

[demogo]

OK, I just posted the followup to this thread here:

http://forums.arcade-museum.com/showthread.php?p=1469754#post1469754