Tempest Plays Blind

bstnguy

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Hi Group,

Looking for some input for a Tempest that plays blind. I'm not a EE and don't play one on TV, so bear with me.

The Known:
Game plays blind
Verified monitor is not the issue
Spot Killer On
Big Blue replaced, PS putting out 5.05VDC
Turning up Screen shows one line from the center of the screen straight down, nothing else
VR1 & 2 putting out +15 and -15 and getting good 5V
Input to MC1495 (C12 pin 9) swinging +/-
Outputs of MC1491 (C12 pin 2,14) both steady at 9.8V

So I'm not sure if C12 is bad, or D/E12 (the TL082) is bad and flooding the outputs?

The deeper learning for me is does the MC1495 split the small +/- signal and amplify it into two larger signals, one + and the other -, and then the TL082 amplify them more?

Any info would be helpful.

Thanks!
 
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Check the legs of the adjustment pots. Often these will be broken, and you will loose x or y, or both. I've seen them where they look good, but will be broken, so use a meter to check them on the solder side of the board.
 
What makes you think its the Vector generator circuit on the board?
I believe the MC1495 is part of a sample-and-hold circuit for the vector generator.

You may want to have a few of the bottle cap (TO-3) style transistors on hand for the Y side of the deflection. They mount underneath the deflection board and on the side of the chassis. They are a 2N3716 and 2N3792 pair that control the Y deflection output. While it doesn't sound like these are you problem they might need replaceing anyway.

You could check the yoke wireing to see if there are any broken windings, you can inspect visually but it would be better to put an ohm meter on the windings with the power off.

Luke
 
Do you have a 2 channel Oscilloscope? If so, hook them up to the board to see if the vectors are being generated...
 
On the scope, if I check the X-out and y-out, I'm getting said one line like in my description. Is there a good place upstream of the signal to check?

And my monitor was rebuilt with the pimpin' Bob Roberts rebuild kit.
 
When you say the monitor is good, do you mean you've tested it and seen an image? Also, have you checked the X and Y outputs on the gameboard itself for voltage swing?

Make sure when you're checking for output from the game that you do it in game mode AND test mode. I've had boards that put out video in test mode, but refused to display game graphics.


Re the MC1495s...

I've had 2 Tempests and numerous Space Duel/Gravitar/Black Widow boards where the MC1495 chips were the culprits. Since you're getting swing on the 1495 inputs your DACs are probably ok. If you're getting no output at the x y testpoints, try replacing the MC1495s.
 
Tested the boardset on a known good monitor and cabinet with the same results. I can turn up the Screen to override the Spot Killer and I get a 4 inch vertical line starting at the middle and going straight down (with no width).

Question on the outputs of the 1495's: Is one output supposed to be negative and the other positive?

Additionally, any good sources for those? My usual suspects don't have them.

Thanks
 
Thanks for the list, I must have zoned out on ArcadeChips.com

got a couple on order.

I'll repost when they're in.
 
Both connectors were reflowed for exactly this reason. However, those IDC connectors always give me the heebie jeebies. I might try to reseat them for kicks...
 
Both connectors were reflowed for exactly this reason. However, those IDC connectors always give me the heebie jeebies. I might try to reseat them for kicks...

Hmmm... that reminds me... someone asked for pole position interconnect cables ;)
 
I've rebuilt those connectors using molex headers, and plugs. You don't get the 90 degree bend for the wires, so it makes it a little tighter sliding the game board in. But it works well with the gold connectors.

Just got finished working on a BZ, and the header solder joints actually look good on that board. Much better than any tempest I've ever seen. So I left them alone, and so far it all works great. I did replaced all the sockets for the roms, and cpu with machined ones.

I know someone was building new cables for these, did they use the IDC connectors or something else?
 
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