New to me Gravitar can't start a game

woodmedic

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I just picked up a Gravitar. The monitor needs to be repaired (Waiting on Parts). The game powers on and I have 4.97 V at the main PCB. The dip switches are set for free play. The 1 and 2 player start buttons are flashing. When you press either start button, nothing happens. I took the game out of free play mode and when you insert a quarter, the credit sound plays but you still cannot select 1player to start a game. Edge connector looks great and wiring between switch and edge connector checks good. I am thinking that it may possibly be the buffer at N9 which is a LS224. Both start buttons go to this buffer according to the schematics. Just wanted to see if any of you Atari vector gurus had any input. Thanks!
 
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I'm not sure how to go into self test. I'll look at the manual. Can I do it with no monitor?
 
I actually have the hard copy of the manual. First thing I did before powering on was disconnect the monitor. I just didn't know if while in test mode does it make a sound on button presses or is the monitor needed to see something changing. Thanks for the posts by the way!
 
Ideally, if powered on, and not in free-play, the PL1/PL2 leds will be off.
Credit up and they should lite up. If not, then CPU issues or logic load, as you have implied is not recording coin switch etc.

Check your harness. Check your voltages. That's always a good start.
Go slow, don't want to make it worse. ;)

Page 1-8 of the manual discusses button presses and "beeps".
 
With free play off start button light are off. As soon as a quarter is inserted 1p lights up. 2nd quarter causes 2 p to light. Pressing either one does nothing. I did the procedure to get into the test menu but I'm guessing since 1p isn't working I'm not getting into test mode. I checked all of the voltage test points on the main pcb and they all look good. The credit sound plays when a quarter is inserted. I'm checking the wiring now but so far everything looks really good.
 
Power it on with the test switch enabled, and it will automatically go into self test, so you don't need to mess around with getting it into self-test via the CP buttons.

You should then be able to test the individual switches.

Before replacing the buffers, look for broken caps and resistors, which are located before the buffers. The glass caps can go bad, which will kill individual signals.

Also, check your wiring, and the buttons themselves, to make sure they are connected properly. Plenty of folks sell games incomplete, and will throw parts together at the last minute, and not actually test them. The cone buttons are easy to hook up wrong.
 
I just picked up a Gravitar. The monitor needs to be repaired (Waiting on Parts). The game powers on and I have 4.97 V at the main PCB. The dip switches are set for free play. The 1 and 2 player start buttons are flashing. When you press either start button, nothing happens. I took the game out of free play mode and when you insert a quarter, the credit sound plays but you still cannot select 1player to start a game. Edge connector looks great and wiring between switch and edge connector checks good. I am thinking that it may possibly be the buffer at N9 which is a LS224. Both start buttons go to this buffer according to the schematics. Just wanted to see if any of you Atari vector gurus had any input. Thanks!

I think you can verify the wiring and activity of the P1/P2 switches in one easy step. Connect your voltmeter to pins N9.15 and N9.13 respectively and push the buttons. If the levels toggle, the buttons are connected and working so the obvious assumption would be to replace N9.

If the input levels do not toggle, then possibilities include the following...
1) shorted inputs on chip, replace N9.
2) open pull-up resistors R119, R128 on start1 and start2 input lines.
3) open series resistors R108, R127 on start1 and start2 input lines.
4) Connect voltmeter to edge conn pins M and 11 or at the input end of any of the resistors listed above and see if the lines will toggle at that end. If the levels sit high and won't toggle then the problem is not on the board but is in the wiring to the switches or the switches are bad or the switches are not grounded. Of course, there's always the throughput of the harness connector P24/J24 to check.
 
I did as suggested above and pin 15 toggles with the p1 button. Voltage goes from 4.98 to 0 when p1 is pressed. Same happens with p13 when 2p is pressed. This would indicate that wiring, buttons,etc are working properly correct? If so should I replace the buffer?
 
Did you try checking test mode? It might give you more clues first.

It will let you check the dip settings too, to see if the board thinks they're set the way they are actually set. It may just be that buffer, or you could have other bus problems, which are showing up as those buttons not working. It helps to get as much info as possible before doing surgery.
 
I tried to boot it into test mode but I just get static from the speaker. Very strange.
My options are limited with the monitor being dead. I guess I'll get it going before I mess with the pcb any more.
 
Sorry I missed the note about the monitor.

What info are you using to conclude that the monitor is bad? Unless you've tested it with a working board, or have other obvious clues (blown fuses, etc), then it's possible you could have a bad output on the game board, and are missing the X or Y signal (or both), which would cause the spot killer to light on the deflection board.

It's also possible that a bad X or Y output (i.e., maxed out) could blow the monitor also. This is where a scope comes in very handy. But if you don't have one, you can measure the AC and DC voltages on the XOUT and YOUT test points of the game board. Post what you find, without the monitor plugged in.

Also, you should test all 6 frame transistors on the monitor (see the color vector monitor FAQ, Appendix B, for how to do this). If all fuses and transistors look good, you can try powering on the monitor without the game board plugged in, and see if you are getting HV, which you should possibly hear, and otherwise feel as static electricity on the front of the tube. This will give you more info before you start connecting things.
 
Thanks for the advice. Before I plugged it in I noticed that R100 and R101 are both fried. The guy I bought it from turned it on when I got there to pick it up and I noticed it had neck glow. I got -10.3 on XOUT and -11.7 on YOUT.
 
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For sure! I'm going to order a complete rebuild kit for the rest of it too. Even if I don't use it all, I'll have parts for later. Do the XOUT and YOUT voltages look normal? I have no clue what the should be. I assume just having voltage there is good.
 
If those are DC voltages, then that is not good. You should see around 0V +/- 0.5V DC during normal operation, and a few volts AC (as you want to measure both AC and DC, as mentioned). Those voltages indicate the X and Y signals are maxed out, which will definitely blow your monitor, and suggests other issues with the game board.

How quickly are the 1P and 2P buttons flashing? (i.e., how many times per second?) It's possible your board isn't fully booting, and may be resetting. You said you were getting a credit sound, and that's good, but it sounds like there could be something else going on.

If you are serious about working on this board (and others), so yourself a favor and get a logic probe. They aren't the end-all be-all tool, but for 20 bucks, they will give you important basic info that will be difficult to get with other tools.

Look up the Elenco LP-60. I have one and find it works very well. Should be around $17-22 shipped, depending on where you look, and how long you want to wait for shipping.
 
Thanks for the advice. Before I plugged it in I noticed that R100 and R101 are both fried. The guy I bought it from turned it on when I got there to pick it up and I noticed it had neck glow. I got -10.3 on XOUT and -11.7 on YOUT.

R100 and R101 can and will fry if the Q102, Q103 are shorted or if the game board drives the deflection super hard for an extended period.

Measuring -10.3 on XOUT and -11.7 on YOUT on the game board indicates something is definitely very wrong with that board. With both X & Y pinned to an extreme negative voltage like that, the monitor would have turned on the spot killer and shut down the HV but the deflection amps would have been running at their maximum current, perhaps long enough to damage several components. It sounds to me like your monitor and your game board both need work.

Andrewb is a wg6100 expert and his advice here is spot on. You can repair the monitor using original design components for now but you should install an LV2000 or equivalent module at your earliest convenience.

If you can buy or borrow an old analog scope, you can use it to test the video output of the game board and you should use the scope as your only video display until you can see that the game board is repaired and working properly. Repairing your wg6100 won't do you much good if you just blow it again by driving it with a bad game board.

Bill B.
 
I'm not sure that I am ready to work on the main pcb. Is there a recommended place to send these to get them repaired?

Could it be the AVG I have read about causing this?
 
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