Spy Hunter MCR Help (garbled screen)

Sheesh, I'm finally back at this one! I've got the boards spread out again and I hope this time I can find the problem(s).

A friend verified/burned all of the eproms, so I feel good about it not being one of those.


I've checked the reset pin, and it is pulsing about every 0.5 sec.
dont forget reset. Reset comes from the power supply and is often damaged when the original battery out gasses.


4.94v across the ram @ 5G. I swapped it out with Cmndr Brain's 6116 Nvram adapter, just in case the original ram was bad. No change.
so whats the voltage rating on across the RAM chip (5G) in question (pin 24 to ground). also I see in previous posts you've replaced the 6116 at 5G did you replace it with a low power 6116?

you need a low power 6116 in that spot when using the battery.
(and definitely you do need to make sure the reset is also working as gamefixer mentioned)

-brian
 
I just realized that I hadn't tried disconnecting the reset line yet, so I gave it a go (pic1). The board still resets over and over again via the watchdog, but the cheap squeak deluxe kicked right in with the opening sounds.

Use your logic probe to test pin 17 (should be purple) on the power connector on the CPU board.

Reset should start low and go high. If its stuck on either that may be your problem.

Like I mentioned earlier. For some reason disconnecting this wire or the grey wire some times gets these boards going. Also, I've noticed that connecting the grey wire to +5 (V.Batt pin 16 on that same connector) gets the game to boot as well. If your power supply is missing its battery or the charge circuit is not working you may not be getting enough voltage on that grey wire. I assume the board is looking for a logic high there which would explain why connecting that pin to +5 makes the board boot.


So, recapping what I've done thus far (mostly for my own reference)...
-New Z80b
-New 74ls04 @3F, 74ls161 @3H, and 4053b + socket @1G (the 4053b @1G had pin2 & pin5 jumped so that both pins pulled +5v from vBatt. Pin5 trace to +5v was cut. I socketed the chip & retained the jumper.)
-New Caps on all 3 boards
-Reflowed Headers
-Replaced Ribbon Cables
-Replaced RAM @ 5G with 6116 Nvram adapter
-Verified/burned ALL eproms
-Checked reset circuit from PS
-Tried with the PS reset line disconnected

I'm not sure which chip/logic path I should move on to next. Any suggestions?
 

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I have not. The ps has a cordless phone battery attached to it. Should I remove & modify?
 

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If you can remove the V.Batt wire from the connector either on the power supply or the board its worth a shot. Brian explains why some boards work with it and others dont above.

At least I think its v.batt. Could be the reset line. I really dont recall which one I've had to remove to make these things work.
 
I'm making PROGRESS!!!

Both the Video PCB and the power supply have been verified to be working, which leaves just the SuperCPU board.

I've updated the SCPU schematic with what I've verified good (green), replaced/repaired (grey), and parts that I still need to source a replacement for (red).

It still hangs on boot with temporary replacements installed in 12B & 6G.

What are the next most probable chips to verify?
The LS138 @ 8f? LS139 @ 9e? LS32 @ 9f?
Or would it be more likely something like the LS244 @ 4f/5f and LS245 @ 6f?

Or something completely different...?



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Ok, I think I may have found the deep end of the pool...

I've gone through the schematic and marked up the chips that have tested good with the logic probe (pic1).

Having gotten about as far as I can get with the tools that I've got, I probably should have sent this SCPU board
out to the highly-capable cdjump, but the stubborn/inquisitive side of me purchased an HP 10529 Logic Comparator instead.
What have I done...?

Now I've got to order a set of chips to compare, and learn how to use a new tool. It did come with a set of unused
reference cards, and a socket card.


@cdjump [or one of you that can follow my marked schematics]- Which chips should I make sure to have
on hand when I test this board (there are probably a bunch, the board appears to have more than 30 different ones)?

.
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