Tempest display issues but don't think it's monitor

JustinZ

Member
Joined
May 14, 2007
Messages
30
Reaction score
1
Location
Mesa, Arizona
Tempest display issues but don't think it's monitor

Hello,

I am pretty much completely new to working on arcade machines, so please bear with me as I ask some pretty basic questions.

I have a two-board Tempest which suddenly one day started not displaying correctly. I do not think the issue is the monitor because it is doing things that don't make sense from a monitor perspective -- crossing text over other text, drawing lines that do not intersect or meet at the points they're supposed to, etc. Also on the title screen there's a big chunk taken out of the lower left corner of the "zooming box" or whatever you want to call it.

I do not have a lot of equipment but I do have a multimeter so I checked the little test rings on the boards and found the following:

+22 and -22 on the logic board are at +/- 25 or so.

The ROMS are getting about +4.3, except ROM 5, which is getting +3.3ish.

Everything else is basically normal.

Um, some other common questions I've seen in searches that may or may not be pertinent . . . Big blue has definitely been replaced. There's an LV2000 on the monitor.

I am not sure what else to check or what to do if one of the above issues could be causing the problem. I have attached some crappy webcam screenshots to explain what I mean with lines not intersecting and the like.

Thanks a lot in advance everybody.
 

Attachments

  • Image9.jpg
    Image9.jpg
    41.8 KB · Views: 39
  • Image10.jpg
    Image10.jpg
    44.2 KB · Views: 33
  • Image35.jpg
    Image35.jpg
    60.8 KB · Views: 29
  • Image36.jpg
    Image36.jpg
    32.9 KB · Views: 29
  • Image37.jpg
    Image37.jpg
    53.4 KB · Views: 27
Low voltages can indeed make a game finnicky. Test out your ARII boards (the one with the big black heat sink) and make sure youre getting correct voltages there. It may be time to rebuild that puppy.
 
Thanks drewster!

"+10.3vDC UNR" on the AR II is at about 11.4. -5 is at about -6.25, -22 is at about -24.0, +12 is at about 11.8, +22 is at about 23.9.

I also found two 36VAC points which both gave me 18.0vAC. There was a "+SENSE" that peaked at 4.99 in DC but was all over the place. I hope it is not AC and I'm not screwing up the multimeter.

I appreciate the help in what to look for. Now if I just knew what any of this meant . . . :D
 
Were you testing the AC with one lead on ground, or both leads on the AC? If you had the lead on ground, what you measured is normal.
 
Ground -- I didn't even think about that, which is silly since that's the obvious reason why there are two points even if you don't know what you're doing, lol. But I should've remembered that, thank you.
 
Double check them and make sure youve got a ground as stated above, then tell us what youve got.
 
Yeah, once I put one lead on the left 36vAC and the other lead on the right 36vAC I got 35.9. Before, I had put one lead on either the left or the right 36vAC and one lead on GND, so that's when I got 18.0. Makes perfect sense, right?
 
After you get done looking at the +5 line, Put it in test mode and get to the big plus + screen.. this is the BIP test screen. Take a pic of that.

It looks like a BIP problem, but since you didn't touch anything and it just started doing it on it's own it would be unlikely that the BIP pots were moved.
 
Thanks Talon. I went ahead and took pics of all the test screens. Here they are. I again apologize for the quality -- they're taken with a crappy webcam that is hard to hold steady or particularly straight. Regardless, you can see that the hatch pattern in #2 is especially pretty and the plus in #3 is, well, not a plus. :D
 

Attachments

  • Image44.jpg
    Image44.jpg
    22.3 KB · Views: 18
  • Image45.jpg
    Image45.jpg
    35.5 KB · Views: 17
  • Image46.jpg
    Image46.jpg
    10.9 KB · Views: 13
  • Image47.jpg
    Image47.jpg
    21.2 KB · Views: 13
  • Image48.jpg
    Image48.jpg
    21.9 KB · Views: 13
I also just noticed +6.8 is running a little low at 6.54, and according to this page,

http://www.kfu.com/~nsayer/games/tempest.html#cant-tune

"Possible VSM analog power problems
The most common cause of an inability to tune the video properly is the power supplies to the analog vector section of the main board. Check the +15, -15 and +6.8 volt power loops and make sure they are absolutely correct. Any variance beyond 2% or so is a Bad Thing."
 
Well it couldn't hurt at this point, but find the x, and Y bip pots. I think you will need to adjust y. See if moving them does anything.

Yeah that 6.54 is a bit low.. It could be one of the MC1495's is shorting out. and pulling down the voltage.

So far my best guess would be a bad am6012 at f10, or if yours has the alt circuit mc3410 at e10un less it's the X. I forget which is which. In that case it would be a10, and b10
 
Last edited:
Awesome, Talon. Messing with the y-bip while I'm on the crosshatch part of the self-test, the characters now go straight across the screen instead of being at an angle, but the hatch is still all over the place. So I barely touch x-bip and now I'm pretty damn close on the hatch. Here's a shot of it.

In-game, lines are much closer to where they need to be. There are still minor problems like the "1 coin 1 play" overlapping "bonus every 10000" but I'm sure that can be adjusted for, as can the termination points of the lines. This is fantastically better!

Edit: The first self-test screen is interesting! Check out the other two attachments. I can't get the data rows to line up without them overlapping each other, so there has to be this extra space.
 

Attachments

  • Image50.jpg
    Image50.jpg
    35.1 KB · Views: 19
  • image52.jpg
    image52.jpg
    27.9 KB · Views: 19
  • image54.jpg
    image54.jpg
    55.7 KB · Views: 17
Last edited:
Yeah go back to the big + sign. You need to adjust it so that the center point or cross section just touch. You'll need a mirror or a friend. I've got a large mirror that when the CP is open you can rest it in there, and look through the cab to see the center.

If it adjusts that's a good thing. Could have just developed a little corrosion on the pot. Looks like you may have gone a little over in y.


IE your + sign left line would be lower than the one on the right.

Like I said adjust them just so the tips touch, and don't overlap.
 
Yeah I've got a big mirror, though I am about to kill whoever programmed the pokeys on the self test (were those really the best four notes you could come up with dude? Come on, lol) but I think I've got it.

In game, everything now lines up perfectly too. Thanks a million!
 
Back
Top Bottom