Dig-Dug up in Smoke

mikejmoffitt

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I have a Dig-Dug cabinet I've had for a while that I've been slowly working on for a few years (I got it back in 8th grade for $158 off of eBay with local pickup - wasn't the worst deal!).

Long story short, I have an extremely busted up Pac-Man PCB that I managed to get working. The previous owner had totally fried the original AC-DC circuitry, so of course I have it running on 5VDC natively. The old edge connector was in such poor shape that I, for testing's sake, used some fingerboard to give it a Dig-Dug compatible edge connector. I installed it in my machine to test, and Pac-Man worked fine. Pac-man isn't the focus.

When I put my Dig-Dug back in, I plugged it in, and checked that it was not backwards - I'm not a fool. I turned it on, and got video, and a faint hum, though the monitor was on (Sanyo EZY, a whole other trip). The power LED on dig-dug was on, but very faint...

Anyway, after about 10 seconds of this nothingness, I poke my head back around the back of the cabinet again to see if anything had changed and- WHOAMYGODWHATISTHAT - Smoke was billowing out! It isn't clear where it came from - it looked near either the bottom of the Dig-Dug PCB, or the top of the AR-II board. I of course shut the machine off immediately, and the smoke stopped quickly. After nervously fretting around and assuring my mother that "that smell is just what old arcade PCBs smell like, don't worry", I pulled out the PCB.

Visual inspection returned no anomalies - everything looks fine. I put it back in, VERY carefully making sure the connector was not out of alignment (what a mess that could cuase). With much fear, I powered it on. It then worked perfectly fine, just like it had before. This still has the original PSU and AR-II board with no mods, as well as the PCB, and it's been running fine (apart from the monitor that I had to re-cap and other things).

Should I be worried? Has running Pac-Man on the AR-II pissed it off somehow? I tied all of the 5V lines together so I don't expect the SENSE line was getting anything out of the ordinary. I'm just very freaked out and would like to know what I did wrong so I won't do it again!
 
I tied all of the 5V lines together so I don't expect the SENSE line was getting anything out of the ordinary. I'm just very freaked out and would like to know what I did wrong so I won't do it again!

Where did you tie the 5v lines together? On the main PCB or the AR-II board?
 
Where did you tie the 5v lines together? On the main PCB or the AR-II board?

This is just in my Pac-Man adaption. I followed the Dig-Dug pinout from mikesarcade, and everything labeled 5V is tied together on the adapter, so by plugging my adapter into the Dig-Dug socket in the cabinet, they are tied.

With the Dig-Dug PCB installed, everything is stock.
 
I bet if you look at your AR-II board, you'll find that resistor R29 is fried. This is a very common problem w/ the AR-II boards. It's a 10 ohm resistor. Long story short, the sense line on Dig Dug "returns" the voltage from the main PCB back to the AR-II board. If there is a difference between the +5v on the board and voltage being returned, the AR-II cranks things up to make up the difference. Many times the edge connector on Dig Dug doesn't make a good connection and returns low voltage on the sense line in which the AR-II ramps things up. R29 is between the +5v and the sense line. It's only a 10 ohm 1/4 watt resistor and takes the brunt of the extra power. Up to 2.5 watts through a 1/4 watt resistor will let out the magic smoke. If that is the case, either replace R29 with a new resistor or there is a "sense mod" you can do to prevent that problem. Some people suggest against the sense mod because it defeats the purpose of it. If you have good connectors and good solder joints, you shouldn't have any problems. These games are going on 30 years old and new connectors and reflowed solder isn't such a bad idea.
 
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When I get a chance I'll pop my AR II out and take a look. If R29 is fried, though, then why would the game run perfectly fine after my reseating it? Is it possible that by shutting it off I saved the resistor at the last minute, hence it still functions? Either way, it may be wise to replace it just for longevity's sake.

When I get a chance this weekend, I'll take some pictures and I can turn the whole thing into a restoration log. The machine was a pretty decent deal, especially to the 14-year-old me, but it does need some work.
 
Yes, you probably started burning it up but caught it before it was completely destroyed. Once you reseated the connector, it made a good connection and alievated the stress on the sense line.

When you order that resistor... get a handfull of them, they're a couple pennies each and you may have the problem later with another game or with this one again.
 
Yes, you probably started burning it up but caught it before it was completely destroyed. Once you reseated the connector, it made a good connection and alievated the stress on the sense line.

^^^
Yep, what he said. You can actually bump up to a 1/2 watt flame resistant resistor. It will actually buy you a couple more seconds. With Dig Dug, you have to make sure you have a good connection on the edge connector before you replace the back panel and put it back in place. If you see the new resistor start to glow, turn off the machine and reseat the edge connector. Good luck. And yes, kudos on getting pac to run on DD.
 
I may solder in a little switch to allow me to enable / disable the SENSE line. I can see how the SENSE line can cause issues and one may wish to disable it, but it's cool that Atari would try to engineer a "smart" power supply like that, and I guess if it has a solid connection it's not a bad design. They should have simply implemented a ceiling limit...

Also, if anybody has an empty Pac-Man or other Midway-type cabinet in New York near Suffolk county, I'm interested ;D
 
I may solder in a little switch to allow me to enable / disable the SENSE line.

Unless your talking of a switch to bypass/enable, sure it can be done but that's seems to be overkill and a waste of time. If you just want to disable the sense line, no can do. If you put a switch in and disable the sense line, then the sense line will be at 0v and you will fry that R29 in no time. If you want to "disable" it, you need to jumper it at the AR-II molex connector. Here's a link to what's involved. http://www.stickycarpet.com/pinx/ar2mods.html Some people will swear to do the mod. Others, like myself, believe if you take care of your machine and make sure the connectors and the solder joints are good, you won't have a problem. On one hand you have removed a possible problem, on the other you lose the sense line "feature". If you do get a little corrosion or something is causing a slight dip in the +5v line, then the sense line will detect that and adjust accordingly. Which on the main pcb side might prevent intermittent troubles due to low voltage to the chips.
 
Unless your talking of a switch to bypass/enable, sure it can be done but that's seems to be overkill and a waste of time. If you just want to disable the sense line, no can do. If you put a switch in and disable the sense line, then the sense line will be at 0v and you will fry that R29 in no time. If you want to "disable" it, you need to jumper it at the AR-II molex connector. Here's a link to what's involved. http://www.stickycarpet.com/pinx/ar2mods.html Some people will swear to do the mod. Others, like myself, believe if you take care of your machine and make sure the connectors and the solder joints are good, you won't have a problem. On one hand you have removed a possible problem, on the other you lose the sense line "feature". If you do get a little corrosion or something is causing a slight dip in the +5v line, then the sense line will detect that and adjust accordingly. Which on the main pcb side might prevent intermittent troubles due to low voltage to the chips.

No, no, I'm well aware of the design of the AR-II. The switch would disable the SENSE adjustment circuitry by simply connecting 5V to SENSE, and thus SENSE will read 5V and do nothing.

However, my machine has had no problems and the edge connectors are clean, so for now, I will stick with the AR-II stock.
 
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