Midway Guided Missile repair

Nama

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Ok, going to take a break from trying to fix my Space Invaders while I try to track down a D3245 ic.

Started working on my Guided missile.
What I have done so far.

- Built up a JAMMA adaptor. Presently controls aren't wired up.
- Jumpered the board for 2716 EPROMs
- Unlike the SI and SI deluxe, I have to manually reset the CPU.
- Have burnt the new Space Invaders Test ROM to an EPROM and installed.

So this is what it does.

https://youtu.be/JChfZBB7_v0

Petty funky stuff...but it actually looks like it's running the the Test ROM code!!!
It's the same test ROM as can be seen here: https://www.youtube.com/watch?v=J0KvcoGKL-4
...so you can see the change in pattern on my screen as if it's drawing the rows of text..'RAM, CRC ROM E, CFC ROM F' etc etc.

This all looks promising, just not sure what to make of all that scrolling stuff.

Any advice or if anyone has seen something similar, I'd love to hear from you.

Cheers

Phil
 
Built up a JAMMA adaptor

double check all the video wires especially the sync through the adapter are in the right place is all I got

hopefully someone can chime in with the answer but I would love to see what the fix is

good luck
 
Looks like the syncs missing or not connected to screen correctly if it connected correctly start at the sync line from output and work your way back until you find the issue
 
For screen output, I'm just tapping into the composite output line from the edge connector pin 18. Should I trace this line back and have a probe around?
I'm not sure where sync is generated.

Thanks again

Phil
 
Ok..that was easy.
Noticed that the input on 74LS55 at A6 pin 4 was low, traced that back to pin 12 of E6 (9316), and it was indeed low where as all the other outputs were pulsing. Piggy-backed a 74LS161 on the 9316 and it fire right up!!!!

It's late here now, so I'll do more testing in the morning.

Cheers and thanks for the insights.

Phil
 
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Thanks Stoog,
Ok, I should have said it 'fired right up with the Test ROM'...

The Test ROM shows the RAM is fine, but fails on the BIT test. I'm hoping that this was because I was using the SI Test ROM, and not a test specifically coded for the Guided Missile board.

Anyway, I burnt a set of Guided Missile ROMs to 2716's.

Now I get a screen of black and white lines that scroll up, then down (or is it left and right???)

https://youtu.be/7FyA7S_ejjU

More funkyness.

I've also been trying to find a video that shows Guided Missile powering up as it may give me a clue to what mine is doing. Unfortunately I can't find anything.

Phil
 

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Ok, some progress.
I was able to get the machine to boot properly. I have no idea how I did it, and I've only been able to do it once :-(

Basically I powered up the board, then I manually reset, which involves shorting the reset line between GND and 5V, and then the screen starts to do the up down curtain action. Then I reset the machine again (applied 5V to the reset line) and hey presto. It was up and running.

Now, however much I try I can't seem to do it again. It was a pure fluke.
So I'm wondering if it's my manual reset that is the issue. Not sure how to go about applying a real reset as I only have the boards and I don't have the original power supply. Maybe there is a circuit I could build???

Or then again, maybe this has nothing to do with the reset.

Anyway, at the very least this confirms my ROM strapping.

Cheers

Phil
 

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Seems I can get it to work once in about 100 reset!!!
Had it up and running 3 times now. Last time I even hooked up some jumper wires to some of the controls and played a game all while shorting the wires to GND. Fun times.

I will look into the exact needs of the reset line.

Phil
 
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Ah...now there's the answer I was hoping for.
Who would have thought GM had a RAM test, and that it looked like that.

Switching the DIP setting has solve the problem...if you can call it a problem!

Much thanks to Stoog, and blinddog for making me feel humble.

Next I'll complete the JAMMA harness adaptor with all the controls, and hook up the speakers (I see there is a left and right speakers, is it ok just to tie these together?) and see what sounds are working and whats missing.

Phil
 
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For completeness here is the rest of the fixes for the sound board:

• Generally many sound missing - Replace 74174 with stuck outputs at E3 brought back some sounds, but not all.
• No Jet sound - Replace LM3900 @ P3
• No Tank sound - Replace LM3900 @ R4
• Left Missile sound not right - Replace LM3900 @ H4, but that didn't fix it the problem. After tracing though the circuit I found a dead resistor R825 150 Ohms. Visually it looked fine, but once removed it fell apart!

Thanks again

Phil
 
Nama how do you know what sound comes from what LM3900? I am trying to learn. Thanks
 
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