Would bad ram cause a Stargate not to boot?

gameguy1957

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I've got a Stargate that I've converted back from a bad conversion of Jail Break. Today is the first time I've tried to get it to run and I don't get anything on power-up except speaker hum for a couple of seconds and one coin door light that comes on.

It has good voltage at the power supply and coming in to the board. I also get decent voltage at the ram, I think. It's 4.85 and 11.97.

I've done all of the basics like reseating chips, cleaning contacts points for cable, etc.

The monitor is also known good. I rebuilt it recently and used it to test a machine a few days ago. There is glow at the neck on it.

I don't have any spare ram on hand, but on the other Williams machines I've dealt with I would at least get some output to the screen or sound to let me know that it has something going on with it. Even with bad ram.

Any suggestions?

Thanks,

-JM
 
bad ram has a code for it on the main pcb if this is the case. Have u turned up the brightness on the monitor to see if u have raster with the pcb disconnected? Checked all the connector pins?
 
Got raster after turning up the brightness for the monitor. That makes me feel stupid, but it was plenty bright on the last game I tested with that monitor a few days ago.

On the ram code, it doesn't show anything, but the the ram is physically in bad condition. I though I had a couple of Defender boards with ram on it here at the house, but they are both empty.

The LED doesn't even flicker on boot, but it does briefly flash when I shut it off.

I may just order a set of ram for it instead of borrowing it from another working machine. While waiting I can reflow all of the header pins on it.

Thanks,

- JM
 
Yes - if the RAM is so bad that there effectively is no RAM at all for the CPU to do anything then you wont get any error code at all.
 
Yes - if the RAM is so bad that there effectively is no RAM at all for the CPU to do anything then you wont get any error code at all.

That's kind of what I'm thinking, but was thrown off by it not appearing to get anything on the video. Now that I've got that I'm going to get the ram and do some other basics like reflowing the solder and paying some attention to the interconnect cables.

Thanks,

- JM
 
It should only need to have the CPU and a subset of the ROMs working to get through most/all of the rug test. The prerequisites for these would obviously include CPU/ROM power, CPU clock, correct ROM contents, and any other intervening logic or inter-board connectors. If you have isolated RAM failures, it should still be able to get through the rug test and display the results.

Not sure if later games fixed this, but on Defender if you have an issue that is corrupting RAM on a large scale (e.g. bad power or incorrect decoding), it will get to the end of the rug test and watchdog reset. This happens because the CPU sets up a stack in RAM in order to call the drawing routines for the self-test results screen (yes this is a terrible idea); if the stack RAM is corrupt it will go off into the weeds when it tries to return from those routines. On Defender this manifests itself as a quick blue screen in between endless rug test cycles.

LeChuck
 
I'm going to need a set of roms for it too. They are as bad as the ram chips, but not noticeable from the top like the others.

I only lifted and reseated them without completely pulling them. When I pulled them today, about half of the legs on some of them remained in the sockets.

So, where can I get a set of roms for it?

-JM
 
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