Dig Dug Atari PCB - repair help

[WestSun]

Hello there,
   I've had an original upright Atari Dig Dug cabinet for quite some time now.  It's worked pretty well, but recently developed a few issues that i'm struggling with.  Perhaps the gurus in these forums can help!

ISSUE #1) Sound
    The sound is now a very high-pitched version of the correct dig dug sound.  At first it would occasionally turn high pitched, but was fixed with a power off/on.   Now it is constantly high pitched, and quite annoying.  It sounds like it's like 3 octaves above where it should be, and very strained.  But the notes definitely change where they should.  I've replaced the ICs 2L (4066) and 3D/E (LM324) on the mainboard.  No change.  Plugging a speaker in the Audio output of the mainboard results in the same sound, so i know for a fact it is a sound generation issue, and not at all related to the ARII.  Does anyone know what could cause this issue?

ISSUE #2) humming
   Related to above, there is a constant hum coming from the speakers.  When the game is being played, it's not very audible.  But when its sitting idle, it's quite obvious.  Just as above, i can hear it from the PCB, and know it's generated there.  Perhaps the two are related?

ISSUE #3) dig dug has turned blue!
   As of yesterday, mysteriously the white body of DigDug has been replaced with a black background!  It's the main one that runs around and digs.  I have NO idea which ICs control the colors of the individual sprites in the game. ALL other graphics seem just fine, including the dig dugs at the bottom which show your life count.  It's really strange.  Any help on this new issue would be greatly appreciated as well.


Aside from these issues, the game runs and plays quite well.  The problems are relatively minor, but still quite obvious and annoying.  I'm hesitant to drop $100+ on a full blown PCB repair, when the issue could simply be an IC or two.


Things that i've done:
- I've redone the power supply with a kit from Bob Roberts.
- Re-capped the ARII board, along with some of the ICs. (also a Bob Roberts kit)
- Physically, i can see nothing wrong with the PCB.  no burn marks, bloated caps, or other obvious signs of damage.
- Probing the voltages on the mainboard PCB doesn't show any anomalies.  5V is a solid 5.00V.  The 10.3 is running a bit high at around 12.3V, but that's expected, since its unregulated.
- Resistors around the replaced sound ICs all check out.


So, if anyone has experience with these issues, or any suggestions, i would be most grateful!

Thanks.

[WestSun]

SUCCESS!!    (well, partially, anyway)
Issue #1 => SOLVED.
I took the repair to the logical conclusion and replaced a bunch of ICs in the sound generation circuit.  I decided to start with the readily available ICs first.  If that didn't work, i would change out the RAMs, and then finally, change out the custom ROMs. I am happy to report that i didn't have to go that far!  This is what i did:
1) Gave the mainboard PCB a thorough cleaning with alcohol.  Lots of scrubbing (with a medium brush), and washed it down a few times
2) Removed the following ICs, installed sockets, and installed new ICs.
    - 1L (LS237)
    - 2M/N (LS174)
    - 1M (LS283)
    - 4K (LS157)
    - 3M (LS158)

Like i mentioned before, since these are all commercially available, this was the easiest step to do first.   
I'm happy to say that the sound issue is solved!  The high-pitched version of the sound is completely gone, and has been returned back to the normal, pleasant Dig Dug sounds.
Now since i did them all in one fell swoop, so i don't know which one was the culprit.  But since they are now socketed, if this issue ever reappears, it will be easy to replace one at a time, and i will definitely update this post with that information.

The humming (Issue #2) is still there, and honestly, its not really that big of a deal.  But the above fix confirms that the problems are not related.  I would guess that it's pickup from a noisy ground, or something like that.  I'm willing to live with it.

The BAD NEWS?  Dig Dug is STILL BLUE!  (Issue #3)
So, if anyone has any suggestions and knows which specific ROM or RAM controls the colors on the individual sprites, i would be most grateful for that information!

Thanks.

[yoharv]

I would suspect it's a continuity issue... maybe a break on the G07 controls.  Check/verify all connections are clean and stiff.  Did you try the output to another monitor?  You could rebuild the G07 ~ that would improve video quality at the very least.