Dig Dug Watch dog won't stop barking

kb0jjn

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I have tested about all of the customs and cleaned the legs, only two fell off, a new record. The z80a cpu chips are new and working in another board. I had one ram chip a 2114 that got very hot and burned my finger. I replace that one, a 2114-2, with a 2114-3 < don't think a 100 nano secs would make a difference here but I may be wrong.

This board I am working on is a different ver. than the working one. This board has all of the cpu chips on one side but the working board has the cpu chips in the middle of the board.

this is the type of board I am working on right now

http://www.ebay.com/itm/DIG-DUG-ATA...574?pt=LH_DefaultDomain_0&hash=item2320ae522e

and this is what my working board looks like.

http://www.ebay.com/itm/DIG-DUG-not...933?pt=LH_DefaultDomain_0&hash=item232182e975

Is there a rom difference in these two types of boards?

I am thinking right now that is my problem as just about everything I have tested seems to have tested good. Even changing the inputs gives correct results. The first thing that gets tested is usually the ram then roms, Right?

I have dumped the roms but have not tested with mame. Probably not zipping them right or something.

The only thing I seen that may be an issue is an 74ls159 right next to the first cpu chip. The enable lines are not doing anything.
 
Check all data and address lines with a scope to make sure they are there, look right, and are of valid logic level. Failed data/address buffers can/will bring the set down. One stuck or otherwise bad line will cause the constant resets. Clean *all* socketed chips and verify the socket pins make contact with the chip pins. And then there's those damn customs....
 
normally the cpu writes to an address to keep the watchdog from reseting.

so either
a) the logic that controls the watchdog is bad
b) the cpu is never getting to the code to issue the watchdog clear/reset.

i would check each address line on the code roms, and ram to make sure toggling, and the oe/en pins, etc, address decoders.
 
Progress:

I am not sure if I am going forward or backward but now instead of a long period of time until a reset, it just starts out resetting almost right away.

I replaced a few of the buffers as I don't have some of the parts I need.

The address lines don't look right on a few pins and are missing on pins 1,2,3

Pins 4 and 5 don't look right at all and pins 40 to 30 (a10 to a0) look the same on each pin. So there is something rotting in Denmark.

For ref. only here is the z80 pinouts

http://www.cpu-world.com/info/Pinouts/Z80.html


I am fairly certain the 74l159 right next to the first z80 cpu is bad so I will be putting this project up till I can get some more parts.

In my efforts to understand the z80 processor better, I found this.

http://z80.info/zip/z80cpu_um.pdf

Is there other good reads on the addressing magic, other than posted in the sticky?

I have some time now to do some reading and posting here :).
 
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