Stargate died while playing

dahnz

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I was trying to get in a game or two before bed last night and my Stargate just died on me in the middle of play. The monitor still works, there's no just no input to the screen. I had time to only check the fuses and the voltages to the CPU board (all looked fine). Hitting the reset button does nothing and there's no life on the ROM board display. The sound board works fine when I hit the test button. It's not playing blind.

This game uses both the linear power supply and a switcher (it was like that when I got it). Tonight I'm going to measure the voltages at the ROM board and try disconnecting the interface board. What else should I be looking at?

Thanks in advance, Dominic
 
I was trying to get in a game or two before bed last night and my Stargate just died on me in the middle of play. The monitor still works, there's no just no input to the screen. I had time to only check the fuses and the voltages to the CPU board (all looked fine). Hitting the reset button does nothing and there's no life on the ROM board display. The sound board works fine when I hit the test button. It's not playing blind.

This game uses both the linear power supply and a switcher (it was like that when I got it). Tonight I'm going to measure the voltages at the ROM board and try disconnecting the interface board. What else should I be looking at?

Thanks in advance, Dominic

Is it flashing a sequence of numbers on the LED?
 
No, that's what I meant when I said there was no life on the ROM board display. In other words, there's no life - no digits, no error codes, no nothing – on the LED display on the ROM board. That and the fact it just went straight from gameplay to orange screen makes me think it is a power issue. (It's not an orange screen anymore - when I powered up again it was just white.)
 
This game uses both the linear power supply and a switcher (it was like that when I got it). Tonight I'm going to measure the voltages at the ROM board and try disconnecting the interface board. What else should I be looking at?

Thanks in advance, Dominic

Check all of the voltages, both from the linear and the switcher. Switchers will drift over time. If you are lucky, it drifted down and it just needs to be turned up. It should be at 5.05-5.10V at the CPU and ROM boards.

ken
 
No, that's what I meant when I said there was no life on the ROM board display. In other words, there's no life - no digits, no error codes, no nothing – on the LED display on the ROM board. That and the fact it just went straight from gameplay to orange screen makes me think it is a power issue. (It's not an orange screen anymore - when I powered up again it was just white.)

Strange screen colors are often the result of bad +12VDC power. Check which power supply is being used to provide +12V.

ken
 
I'd bet it's the switcher. You might need to replace it. Do you have another one to test it with?
 
No, I don't have another switcher. The 5, -5 and 12 voltages were fine at the CPU board (though the 12 was a bit high - 13V) but I haven't tested at the RAM yet or on the ROM board and I haven't broken out the logic probe. The sound board works, so the voltages there are presumably okay. I'd like to ditch the switcher and just use the original PS, because I lose my high scores and settings. I don't know why they decided to use both, but at least they didn't strip out the PS. The switcher in it is at least 11 years old.

I might have to call on Dokert for a new harness, depending on how much they hacked it up.

I don't know if the screen colours mean anything (I suspect not). When the game stopped, the whole screen went completely orange (just like in the colour test), until I tuned it off. Now when I power it up, the screen lights up but that's all. When I said "white", I just meant to say the monitor was working but apparently wasn't receiving any signal.
 
The sound card has its own power rectification system, so it is difficult to tell anything useful from that. It normally takes the +12V unregulated and converts it to the required voltages. So even when the power supply is hosed for CPU & ROM logic levels the sound card will work.

Measure the voltage at the 4 corners of one of the RAM chips.

The voltages should be
Pin 1 = -5V,
Pin 8 = +12V
Pin 9 = +5V
Pin 16 = Ground

The pins are numbered starting in the upper left corner (notch being up), going counter clockwise.

If any of them are low or are fluctuating more than 0.1 V you need to replace your power supply.

ken
 
OKay, I finally got to checking the voltages. The 5v was a little low so I cranked the switcher up a bit and now I have spot on 5v at the RAM. The other voltages are all okay (well, the 12v is about 13v, but I thought I'd read once that this would not be a major problem). But still no joy.

I got my logic probe out and it's not reading anything at all on pin 14 of the RAMs (that's the one you check, right?). I checked pin 37 of the CPU (as per the recap manual) and it's stuck on low, and hitting the reset button makes no difference. I then checked pin 13 of 5H (the watchdog circuit) and it's stuck on low.

That's as far as I've got and I'm a complete beginner at all this, so any help would be most appreciated.

PS. Interestingly, the switcher supplies only the 5V, and they just stripped a bit of the original 5v line from the PS and soldered a lead from the switcher on. Without the switcher, the original PS is supplying about 2.5 v, so hopefully I can fix that one day and get rid of the switcher all together.
 
It sounds like you have some CPU board issues. There are a number of things that can go wrong with the reset circuit. You may need to pull the schematics and work backwards from the CPU to see what is holding the reset line.

If you want to get your power supply board fixed or replaced, I rebuild Williams power supplies (and sell replacements). It is $20 + shipping for a rebuild and $30 for a replacement. PM me for details.

ken
 
It sounds like you have some CPU board issues. There are a number of things that can go wrong with the reset circuit. You may need to pull the schematics and work backwards from the CPU to see what is holding the reset line.

If you want to get your power supply board fixed or replaced, I rebuild Williams power supplies (and sell replacements). It is $20 + shipping for a rebuild and $30 for a replacement. PM me for details.

ken

I would start here with a known good power supply, prior to shooting it any further.
 
I'm in New Zealand, so while it would be nice to send the boards (CPU and/or power) to someone for work, postage costs mean it's not an option. I may be able to find someone here to do work on it, but because that will likely not be easy, I'd like to do what I can.

I do have a spare power supply I can swap in, if need be, but I checked the voltages again and found I was misremembering what they were - at the RAM, they're reading -5.21v, +12.21v, and +5.15v. The power supply in my Stargate is the Defender style model (ie, no overvoltage protection, heatsinks on the one board).
 
The voltages sound a little high, but not unreasonably so. If you have a scope or a sensitive DMM you can check for AC ripple, becuase sometimes when one of the bridge rectifers is going it will allow AC to bleed over.

Based on your comment about the reset line, you may need to trace the logic chain back through the reset circuit to find what has gone south. You should also walk the clock path to make sure the clock signals are getting through both the reset circuit and the normal forward path to the CPU.

If you have a spare CPU you could try swapping it in. That has worked for me once or twice.

Or you could just buy a known working spare boardset, so you only have to pay shipping once. I've got a working Stargate set I was about to throw on EBay, if you want to go that route. $100US + shipping.

Sorry, diagnosing board issues remotely is like brain surgury via email. It can be done, but it is not always pretty.

ken
 
Thanks Ken. I have two spare CPUs. I'm not sure if they work or not, but I'll try swapping them in. Is your Stargate set CPU, ROM, and I/O or just CPU?
 
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