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Major title repair

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Lurch666 View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Lurch666 Quote  Post ReplyReply Direct Link To This Post Topic: Major title repair
    Posted: 04 Dec 2018 at 4:50pm
I'm attempting to fix a major title board for stegrey but I'm not getting very far.
When I first got it it just booted to a white screen.
After wobbling some of the jumpers I got a white screen with two big vertical light brown bars.
Checking with my scope I found activity with the cpu,program roms and ram as expected if it was booting.
No sounds or signs of life though.
I replaced an ls373 at D6 on a hunch but no difference.
I then went to my usual path of "it must either be the ram or cpu".
Got some replacement CPUs coming from America but got some ram today.
Now the ram is tms 2063 but found the equivalent is cxk5064 that was in a gals panic 2 that I have with a graphics fault so I pulled them from that board (but one didn't survive so I had to wait for replacements) and tried it in the major title but still no difference but the rams from the major title don't work in the gals panic 2 so I'm assuming they were bad.

Now I'm back to the blank white screen.Still seeing activity in the circuit but wondering if I'm missing something.

Lack of documentation or schematics is slowing me down and there doesn't seem to be much info I can find so if anyone could give me a pointer that would be great.

I will keep on trying though as I can never leave these things alone.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Flinnster Quote  Post ReplyReply Direct Link To This Post Posted: 04 Dec 2018 at 5:41pm
Oh Confused Good luck. Can't say I've seen one of these whitescreen, but for sure it's probably not getting as far as a rom / ram check then Cry


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Post Options Post Options   Thanks (0) Thanks(0)   Quote TheDaddy Quote  Post ReplyReply Direct Link To This Post Posted: 04 Dec 2018 at 6:05pm
I have 2 with just a brown screen and 1 with a with white screen. No audio but cpu/mem seem fine, both are receiving and sending info as it should ( as far as i can tell ). I feel your pain i really do.

Good luck !

Dave.

Edited by TheDaddy - 04 Dec 2018 at 6:05pm
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Lurch666 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lurch666 Quote  Post ReplyReply Direct Link To This Post Posted: 04 Dec 2018 at 6:27pm
Forgot to say I also checked the program roms and they matched mame so they are ok.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote caius Quote  Post ReplyReply Direct Link To This Post Posted: 07 Dec 2018 at 3:07pm
First of all you should narrow the fault(s) in a the CPU or VIDEO board, also the bottom board can prevent the boot.After done it you can focus your troubleshooting in the specific board.But I guess you have no working set.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lurch666 Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 2018 at 12:25pm
Tried looking at the bottom board and I'm seeing activity there as well so something is going on.

Noticed the cpu is NOT watchdogging so either there is no watchdog or the system is running ok but I'm still getting no video output apart from a white screen.

Waiting for a replacement cpu just in case but I doubt it's that.

Next I'm going to check all the 74ls chips to see if any of them are giving the wrong outputs.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Equites Quote  Post ReplyReply Direct Link To This Post Posted: 11 Dec 2018 at 12:33pm
Originally posted by Lurch666 Lurch666 wrote:

Waiting for a replacement cpu just in case but I doubt it's that.
 

Is the CPU warm?  A stone-cold CPU usually points to a dead one.
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