Space Duel Upright Issues

Klankster

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I thought I'd start a topic on my Space Duel upright, which developed a problem a while back -- The screen would "collapse" in the Y axis partially, with bands of the display working and at the edges of the properly-displaying bands, you'd see a bunch of vectors overwriting themselves on one horizontal line (IIRC). Sound familiar to anyone? (I'm kind of thinking DAC issue, with one or more bits feeding into the DAC getting dropped, or something like that).

So, it was doing this to me one day and I already had the back off, so I looked around the back just in time to see one of the discrete transistors (I believe it was Q12 -- at least that's the one I have marked) start smoking. I killed the power, ordered up some replacement transistors and promptly got busy with other things in life and haven't gotten back into there until now.

I took the board out last night and started looking at it, and noticed that in addition to that transistor having smoked, C107 (associated with -15V supply circuit) is totally toasted:

CookedCap.jpg


C107 is a 2.2uF, 35V tantalum cap. Just for grins, I'm also going to replace the 7915 voltage regulator and the other electrolytic filter cap.

I'd appreciate any input you all might have on this -- any reason this cap would fail like that which would indicate a problem elsewhere? Might it have hosed something else? I ask because the -15V is used in the DACs, and Q12 is part of the DAC reference and bipolar current reference circuit. And the Y output looked questionable with what looked to me like a DAC issue before things went really bad. Coincidence? Or might there be a bigger issue?

This is an -02 version PCB, BTW.
 
They just fail. I've seen this many times before. Just be sure to put a tant cap back and not an electrolytic.

-15 would cause graphics issues you speak of if it starts drooping. Good idea to replace the reg as well since its been strained from the shorted cap.
 
Just got the parts from Mouser today, so I swapped out the cap with a new Tantalum and changed out the known bad 3904 at Q12.

Before testing I decided to check out the power supply and am glad I did -- Fuses 4 and 5 (4A, 250V slow-blow) were both blown. I guess I'm not surprised; With C107 bad (due, I assume, to a dead short inside) that would have easily blown the -15V fuse. The only thing I thought was odd about that is that both +15V and -15V were out, and C107 is only on the -15V side -- I haven't looked at the schematics but assume they're connected.

Anywho, I now have clean +15V, -15V, 5V.

Testing with the main board connected next.
 
OK, just tested with the main board connected, and it runs but the video problem I had before is still there. Some stills of the five test screens are below. Does this fault ring a bell with anyone?

Screen1...
Test1.jpg


Screen2...
Test2.jpg


Screen3...
Test3.jpg


Screen4...
Test4.jpg


Screen5...
Test5.jpg
 
And here is a video of the screen during attract mode. You can see that some output looks almost normal, like the high score table, but then it's distorted at the top (player1/player2 lettering). I'm still thinking serious DAC problem, converting the digital form of the display to analog vectors. So strange that it's kind of selective, though!

Maybe a monitor problem, since some of the output looks almost normal?

Any thoughts on what this could be?

Video link here
 
Did a little more investigation on this -- I believe this is a monitor problem.

If I rap the cabinet, the monitor image sometimes corrects momentarily. And there is a red LED toward the rear of the monitor's deflection board that is flickering -- I believe this is the "spot killer" LED? -- I futzed around with a connector or two back there and at one point that LED turned off and I had a solid, complete image on the monitor!

So, I'm going to try taking out that board and will check it for loose connections, cold solder joints, etc. because I believe that is the problem -- something making intermittent contact that is making the spot killer come on and fouling up the image.

Can someone give me a little feedback on this and let me know if I'm on the right track?
 
I have a Black Widow board with the exact same issue and it isn't a monitor problem. I have yet to get it working right, and I'll be watching your thread closely.
 
Well, not sure about yours, but mine was definitely a monitor problem! Here's what I found on mine:

I pulled the deflection board from the monitor and flipped it over. The bottom of the poor thing had really gotten a hack job from somebody back in the 80's! Several repairs done with scraps of wire where they had done a crappy job replacing some power transistors, big blobs of solder, but those were solid at least.

What wasn't solid was the PTC Thermistor! All three leads on it were loose, I could easily rock it around on the board like a loose tooth. This matches what I found in a PDF FAQ document on the Wells-Gardner 6100:

While you are at it, resolder the three pins of the PTC thermistor (in the middle, along the left edge of the deflection board) as they are almost always loose for some reason.

The bottom of the board with the area of the PTC pointed out with an arrow:

DeflectorBoardSolderSide.jpg


The top, showing the PTC Thermistor:

LoosePTCThermistor.jpg


That was the only problem I could find on the board, so I reassembled and fired up the game, and voila! The display was working perfectly:

Fixed1.jpg


Fixed2.jpg


Time to put it back in the game room and turn on FREE PLAY!!! :)
 
I was curious about what that PTC thermistor actually does in the monitor, so I did some checking -- Turns out that it's part of the monitor's degaussing circuit! When the monitor powers up, the degaussing coil is activated, with current going through this device. As the degaussing goes on, the thermistor heats up, slowly reducing current to the degaussing coil until it shuts it off. Then the monitor is in normal operating mode.

I guess what was happening to my display is that with this component loose, the degaussing coil wasn't ever really getting shut off, causing the strange distortions in the image.

You really do learn something new every day!
 
Today I moved the machine into the rec room and turned it on -- black screen, spot killer LED on solid. Hmm.

The back was still off, so I jiggled the wiring harness that runs to the monitor and the spot killer LED went off and the display was perfect. Started playing with the wiring a bit to see if I could narrow it down and ran it down to one of four wires that run to points on the back of the board -- a slight movement would light the LED and kill the display.

Powered it down, took the deflection PCB out again and started examining all those wires, checking for loose/cold solder joints etc. -- A slight tug on the yellow wire and it popped right out! The connection with the little metal ferrule where it is soldered to the board was totally loose.

I desoldered the ferrule, stripped the wire back a bit and soldered it directly into the board. Replaced the board, fired up the game and it was working. Jiggling the cable at this point does nothing, so I guess I'm really back in business.

I also re-thought the FREE PLAY option and decided to leave the machine in coin-op mode because when it's on FREE PLAY mode, there is no attract mode -- just the game selector -- and I don't want that to get burned into the monitor.
 
I also re-thought the FREE PLAY option and decided to leave the machine in coin-op mode because when it's on FREE PLAY mode, there is no attract mode -- just the game selector -- and I don't want that to get burned into the monitor.

I think DogP did a ROM mod so you can have free play and attract mode.
 
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