Dokert
Well-known member
look here http://www.therealbobroberts.net/xtal.html
Crystal or Clock Oscillator $2.50
first item on the parts page after the last capacitor
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Please post all monitor technical topics in the Technical - Videogames - Monitors section, not in the General Help section.
Williams Stargate arcade. Where's my +12v?
- Thread starter mitchschaft
- Start date
look here http://www.therealbobroberts.net/xtal.html
Crystal or Clock Oscillator $2.50
first item on the parts page after the last capacitor
OP
OP
Ok, I didn't see 3 legs on it so thought it wouldn't be it.
OP
OP
Well I just discovered the sound-test button on the sound board. It sounds awesome so I know that part works, too. I do need a new speaker since this one is dried up and has tears in it.
Off to order some more parts.
Off to order some more parts.
OP
OP
I replaced the main ribbon cable and headers. I didnt do the little board ribbon stuff yet.
That made no difference. Was still getting a weird screen and no lights on the rom board LED. So I did the ram upgrade from Bob to 4164 chips and put the power adapter on. Now I consistently get a rug screen (8 out of 10 times) and the LED on the rom board comes up with '2' and stays there. No flashing or other numbers so maybe it just freezes up before it gets to the next number.
If you look in the last pic with the 3 caps near the power connector, the red-circled cap only measures to .5v while the other 2 are 4.80. Is that a problem?
Other than that maybe I need a new CPU chip. I get a consistant 4.76v to all the socketed chips positive legs if that means anything.
That made no difference. Was still getting a weird screen and no lights on the rom board LED. So I did the ram upgrade from Bob to 4164 chips and put the power adapter on. Now I consistently get a rug screen (8 out of 10 times) and the LED on the rom board comes up with '2' and stays there. No flashing or other numbers so maybe it just freezes up before it gets to the next number.
If you look in the last pic with the 3 caps near the power connector, the red-circled cap only measures to .5v while the other 2 are 4.80. Is that a problem?
Other than that maybe I need a new CPU chip. I get a consistant 4.76v to all the socketed chips positive legs if that means anything.
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kb0jjn
New member
The 4.76 is a bit low and needs to be addressed.
OP
OP
Ok, cool. How would you start with that one? Is it changing out resistors? Or I can google I guess.
kb0jjn
New member
People often complain of resets during game play. There are some
software bugs (at least in Robotron) but more often than not the resets
are due to the +5 VDC supply dropping below what TTL devices can operate
with at the logic board itself. The Molex connections to and from the
power supply board will often show signs of overheating. Try measuring
the +5 at the power supply and again at the logic boards. If there is
much of a difference and especially if the logic board is seeing less
than +4.7 or so you have problems.
That was copied from this link. Hope it helps you.
http://www.mikesarcade.com/cgi-bin/spies.cgi?action=url&type=info&page=Williams-hardware.txt
OP
OP
I bumped it up to 4.86 just by changing out some connectors. I'll finish that up and see about adding a pot to the +5 resistor adjust.
OP
OP
Here's an update. I replaced all the connectors for the power supply and CPU board. I swapped out the cable/headers for the interface board, too. After that, not much changed, but I was getting more flickering on the 7-digit number LED. Rug pattern.
So I thought about pulling the battery and turning it back on for the heck of it. With the battery out, I was able to get the table reset screen then a ram error consistantly. When I put the battery back in, it would just do the rug test like usual.
So I thought about pulling the battery and turning it back on for the heck of it. With the battery out, I was able to get the table reset screen then a ram error consistantly. When I put the battery back in, it would just do the rug test like usual.
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OP
OP
I figured I needed the +5 a little higher. I went ahead and installed the little pot/resistor and it works great. I installed it and turned the wheel until it matched the ohm reading of the resistor that was in the R25 slot before I took it out. Then I powered it up and adjusted 'til I got 5.01v to the ram chips. It was at 4.86v. From the power supply board, the reading is +5.08v. Not sure if that's too high or not. I get consistant ram errors now. It changes anywhere from 1-3-1, 1-3-4, 1-1-1, etc etc, after each power cycle.
But now I can no longer make the table reset or ram errors come up on the screen even if I pull the battery. It tries to load the game it seems. It moves from a partial screen of the game to a rug test, makes a weird chiming, and turns itself off. It loops that over and over. I tried a couple different voltages, a little higher and a little lower. It still loops. I need to learn how to trace signals more thoroughly. I have trouble reading the schematics sometimes. For instance, I'm not sure which cap should have which voltage. Check out the video and see what you guys think my next plan of attack should be.
http://www.youtube.com/watch?v=hjiUABnvMDU
I'm exausted, it's bedtime
But now I can no longer make the table reset or ram errors come up on the screen even if I pull the battery. It tries to load the game it seems. It moves from a partial screen of the game to a rug test, makes a weird chiming, and turns itself off. It loops that over and over. I tried a couple different voltages, a little higher and a little lower. It still loops. I need to learn how to trace signals more thoroughly. I have trouble reading the schematics sometimes. For instance, I'm not sure which cap should have which voltage. Check out the video and see what you guys think my next plan of attack should be.
http://www.youtube.com/watch?v=hjiUABnvMDU
I'm exausted, it's bedtime
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Sooooo close.
Do you have any extra RAM chips? If the error is consistent, try replacing that one chip and moving forward.
Measure for any AC ripple on the voltage lines at the RAM sockets.
This is looking pretty good.
Do you have any extra RAM chips? If the error is consistent, try replacing that one chip and moving forward.
Measure for any AC ripple on the voltage lines at the RAM sockets.
This is looking pretty good.
OP
OP
The ram error is different at each power up. I've tried swapping chips around but it doesn't follow or anything.
I'll read up on ac ripple and test that out. Would I measure that from the bottom of the board?
I'll read up on ac ripple and test that out. Would I measure that from the bottom of the board?
OP
OP
would a 15MHz scope be useful on these chips? My tektronix 2467 is under the weather with a possible u800 chip failure so the ol' B&K will have to be resurrected.
Dokert
Well-known member
Remove the pot that you installed on top of R25. If you want to make the +5vdc adjustable, remove the resistor at R25 and install a 5K pot where R25 was.
If you are reading +5.01 at the power supply 4J2 and 4.86 at the board, you have either a bad header or a bad connector. Most likely you have a bad header or cold solder joint on the mpu (1J1 IIRC) or at 4J2, and when you bumped up the +5vdc you are too high on the ROM board now.
If you are reading +5.01 at the power supply 4J2 and 4.86 at the board, you have either a bad header or a bad connector. Most likely you have a bad header or cold solder joint on the mpu (1J1 IIRC) or at 4J2, and when you bumped up the +5vdc you are too high on the ROM board now.
OP
OP
I thought you were supposed to add a 1k resistor inline with the pot. Maybe I read it wrong. But the original resistor is gone.
I'll check the other stuff shortly. It was 4.86 on the board before I made the adjustment and 4.94 at 4J2. Now it reads 5.01 to the chips and 5.10 at 4J2. The rom readings are at 5.09.
I'll check the other stuff shortly. It was 4.86 on the board before I made the adjustment and 4.94 at 4J2. Now it reads 5.01 to the chips and 5.10 at 4J2. The rom readings are at 5.09.
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1500points
New member
6 pages of tshooting? you are tenacious. 
I went with a switching powersupply and that little conversion finger board from arcadeshop, which makes it plug and play, after dicking with bogus resets and ram errors for a month.
i'd never go back to the old powersupply. way too stable with the new PS.
I went with a switching powersupply and that little conversion finger board from arcadeshop, which makes it plug and play, after dicking with bogus resets and ram errors for a month.
i'd never go back to the old powersupply. way too stable with the new PS.
On a stock board these caps should read -5V, 5V, 12V. Since you're using the 4164 adapter, 12V is connected to 5V, and -5V (red circle) is floating .. so that is in line with your measurements (although the 5V rail is low as others have pointed out).
LeChuck
It sounds like it is time to try swapping parts from a known working set to isolate which board(s) are working and which are bad. If you don't have an extra set, try a shout out in the main forum, we must have somebody near you with a working Stargate.
A long shot would be to unplug the I/O board on the off chance that the PIA chip (which sits on the CPU bus) is freaking out and messing with the signals. It doesn't happen all that often but I have seen it happen twice.
I know you want to do it yourself, but you might want to send the boards off to be repaired. It is sounding more and more like there are multiple issues in that boardset and that is a pain in the a** even for somebody who knows how to repair these boards.
ken
A long shot would be to unplug the I/O board on the off chance that the PIA chip (which sits on the CPU bus) is freaking out and messing with the signals. It doesn't happen all that often but I have seen it happen twice.
I know you want to do it yourself, but you might want to send the boards off to be repaired. It is sounding more and more like there are multiple issues in that boardset and that is a pain in the a** even for somebody who knows how to repair these boards.
ken
OP
OP
I just unplugged the I/O board (the little one, right?) and it does the same thing. I guess it doesn't even make it that far.
Yes, it is the little one. I did say it was a long shot, but it is always worth trying.
Usually when you are seeing random RAM errors, it is some chip that is on the CPU bus that is acting up or one of the clocks is not working. These can be somewhat difficult to trace.
ken
