ROTJ - RESET Line is Pulsing

Arcadenut

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When I test the RESET test point, it is pulsing... Comparing against a working ROTJ board, it should be HIGH.

Any pointers on what might be causing the RESET to be pulsing?

Watch Dog is HIGH (witch matches the other board).

All EPROMS have been verified good.

Thanks!
 
It's most likely the watchdog barking, which keeps resetting. The watchdog pin you're testing is probably the watchdog enable pin, which is actually an input. There's LOTS of things that'd cause the watchdog to bark, but first I'd do a very thorough visual inspection for broken traces, burnt resistors, broken/bad caps, etc.

Assuming the watchdog pin you tested is the enable (maybe labeled WD_EN), you can ground that, which will disable the watchdog, but most likely it'll just stop resetting, and not actually work any better (unless the watchdog circuit is at fault, which is rare).

DogP
 
It's most likely the watchdog barking, which keeps resetting. The watchdog pin you're testing is probably the watchdog enable pin, which is actually an input. There's LOTS of things that'd cause the watchdog to bark, but first I'd do a very thorough visual inspection for broken traces, burnt resistors, broken/bad caps, etc.

Assuming the watchdog pin you tested is the enable (maybe labeled WD_EN), you can ground that, which will disable the watchdog, but most likely it'll just stop resetting, and not actually work any better (unless the watchdog circuit is at fault, which is rare).

DogP

The test point is labeled WDOG. The schematics show WDOG and WDIS, but I don't see any test points for WDIS.
 
Ok, follow up:

The issue has been resolved. It was a two traces that were shorted together on the RAM at 14B/C.

Fixed the traces and the board booted and played.
 
There ya go!

When the CPU is running, it trips a counter to keep the watchdog at bay. If it's not running then the watchdog itself will trip and smack the reset line in an attempt to get the CPU running again.

BUT...

If you have a problem with the CPU, program ROMs, program RAM, address decoding, address or data buffers, interrupts, and more, you'll end up with a watchdog timer tripping the reset line. Gouged traces in those areas of the board will do it too, as will corroded traces from liquid or rodent damage.

If the reset line had never done this before replacing something then check what you replaced. Did a pad or platethru get pulled? Did a pad or trace get bridged with solder? Was the replacement installed backwards? Was the replacement ROM programmed with the correct code?

If the board does it right off the bat then check for gouged traces and the items listed above.

Have fun with the ROTJ board! There's a HUGE satisfaction that comes from fixing a board. :D
 
There ya go!

When the CPU is running, it trips a counter to keep the watchdog at bay. If it's not running then the watchdog itself will trip and smack the reset line in an attempt to get the CPU running again.

BUT...

If you have a problem with the CPU, program ROMs, program RAM, address decoding, address or data buffers, interrupts, and more, you'll end up with a watchdog timer tripping the reset line. Gouged traces in those areas of the board will do it too, as will corroded traces from liquid or rodent damage.

If the reset line had never done this before replacing something then check what you replaced. Did a pad or platethru get pulled? Did a pad or trace get bridged with solder? Was the replacement installed backwards? Was the replacement ROM programmed with the correct code?

If the board does it right off the bat then check for gouged traces and the items listed above.

Have fun with the ROTJ board! There's a HUGE satisfaction that comes from fixing a board. :D

Yep, learning new stuff all the time. I was fixing 2 ROTJ boards for a friend, both were DOA when I got them. I fixed the first one no problem, it had quite a few issues:

3 Bad EPROMS
4 Bad RAMS (12S, 4K, 5K, and 5P)
and Q2 was bad.

The second one (which this post is about) was driving me crazy because I didn't see the trace issue until JROK stopped by and spotted it.

I want to thank JROK for helping on this board.

This board also had issues with the PIXI board, which had 2 bad 74LS374's (1/2C and 2B) and a bad RAM (2A).

The reason the RESET keep resetting (and no Watch Dog barking) in this case was because the two traces where shorted together, which corrupted the RAM. This is the RAM the 6502 needs to boot with. Since the RAM was "bad" the 6502 couldn't boot and we were stuck with Garbage on the screen and the processor constantly resetting.
 
Wow that's one basket case board - I have never come across one that bad. Was this out of a cabinet or from a stack of boards? If I get a board from a stack of boards, I go over them with my magnified light to look for gouged or shorted traces and bent over shorting leads on the solder side. I always check the roms before I start because they have a tendency to have bit rot. I'll print and file this repair log. Thanks for sharing.

Bill

Yep, learning new stuff all the time. I was fixing 2 ROTJ boards for a friend, both were DOA when I got them. I fixed the first one no problem, it had quite a few issues:

3 Bad EPROMS
4 Bad RAMS (12S, 4K, 5K, and 5P)
and Q2 was bad.

The second one (which this post is about) was driving me crazy because I didn't see the trace issue until JROK stopped by and spotted it.

I want to thank JROK for helping on this board.

This board also had issues with the PIXI board, which had 2 bad 74LS374's (1/2C and 2B) and a bad RAM (2A).

The reason the RESET keep resetting (and no Watch Dog barking) in this case was because the two traces where shorted together, which corrupted the RAM. This is the RAM the 6502 needs to boot with. Since the RAM was "bad" the 6502 couldn't boot and we were stuck with Garbage on the screen and the processor constantly resetting.
 
Wow that's one basket case board - I have never come across one that bad. Was this out of a cabinet or from a stack of boards? If I get a board from a stack of boards, I go over them with my magnified light to look for gouged or shorted traces and bent over shorting leads on the solder side. I always check the roms before I start because they have a tendency to have bit rot. I'll print and file this repair log. Thanks for sharing.

Bill

Wasn't a stack of boards, but these Atari boards seem very fragile when it comes to the traces, so it probably didn't take much.

The boards were plugged in upside down, so I'm thinking that was what did the most damage.

It was a fun learning experience!
 
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