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A buddy asked me to repair a few Atari Dig Dug PCBs for him and the following PCB has been very problematic.
Thanks to @lilypad19 for his information and assistance. Unfortunately, that did not resolve the issue. My testing was completed using logic, documentation, schematics, a logic probe, and a multi-meter. My scope is not currently working.

Atari Dig Dug PCB #3 (B, with factory, yellow wire)

This PCB had a lot of problems, so I took a more systematic approach with it, starting with the CPUs.

Symptoms:
  • Burnt edge connector
  • Board does not boot and only displays a weird, orange/red and distorted grid.
Troubleshooting #1
  • Clean all NAMCO custom chips and PROMs (first revision PROMs)
  • Clean all CPUs
  • Confirmed voltages are correct (even varied them a little)
  • Left the factory, yellow wire, and resoldered the damaged cap that was factory soldered to 3R
  • DIP switches match another repaired and working Dig Dug PCB.
  • Dig not observe any issues with the original PCB caps, so they were not replaced.
Troubleshooting #2
- Swap locations of CPUs, then replace the one bad CPU. The PCB is trying to boot, but still showing
video trash.

Troubleshooting #3
- Replaced 2016 RAM at 4K.
- Board now boots, but graphics are still screwed-up, everything is still orange/red, there are lines through
background characters, some background characters are blocks, and text is hardly readable.

Troubleshooting #4
- Swapped multiple NAMCO custom chips with no change.
- Swapped half of the ROMs with known good ROMs, and this revealed minor corruption in the 114 ROM
(I could have verified these using my EPROM burner, but this way was faster).

Troubleshooting #5
- The orange/red garage is still present, so I began reviewing the object related schematics. Between these
sections there are only 11-12 chips and two in particular, 7A and 9B (SN2149H-3), caught my attention
when performing the heat test (touching every chip with your finger). These two were super hot.
- Socketing and replacing these two eliminated the orange/red and messed-up text. It plays, coins-up, and
the background looks great. NOTE: I tried multiple 2148 and 2149 before getting exact replacements,
SY2149H-3. I observed no on-screen differences between these 2148 and 2149 variations. However,
there may be an important distinction since the SY2149H-3 is 55ns RAM and the D2149H is 70ns RAM.

Troubleshooting #6
- While the colors, text, and background are fixed, there are zero foreground sprites or moving object
sprites showing in the demo, title screen, and gameplay.
While I initially wondered if slower 2148/2149
RAM could cause this, replacing with exact SY2149H-3 shows speed is not the issue. Further, I believe the
symptoms of slow RAM would be visible, such as multi colored blocks, but not a complete absence of sprites.
- In reviewing KLOV, someone mentioned in 2018 similar issues, including the missing foreground sprites,
based upon these 2149 in 7A and 9B (9B specifically being the cause for the missing foreground sprites).
- While reviewing the PCB again for any damaged traces, any previous work I missed, bent legs, etc., I noticed
a small crack in 8M (SN74S174N). I did not have the "S" only version of this, so I socketed and replaced it
with a SN74LS174N. No change in the foreground sprites, and installing an ordered SN74S174N made no
difference.
- Using my logic probe, I documented the 2149 at 9B on a working Dig Dug PCB, then compared to this Dig
Dug PCB. All the D2149 outputs are showing as High with no pulsing. Ditto for the inputs. On a working
board, all of these outputs and inputs are showing as High and pulsing.
- I completed this same comparisons for the 2149 at 7A, as well as the four (4) 161 at locations: 9A, 8A, 8B,
and 7B. Same missing inputs, which causes weird outputs. This feels like something further in the circuit, but
I have replaced ROMs 116, 117, 118, 119 with no change (interestingly, the game will boot and play the
same even if these ROMs are missing). It will also play, with the same missing sprites, with 9B missing.
- Have been hunting high and low (no pun intended) for missing clock signals and so far I have not found it
missing.
- I piggybacked a number of chips looking for any change at all, including the four 161, 74LS138N, 74LS157N,
74LS365AN at 8C and 9C, the PROM (111) at 8F (from a spare parts board), etc. All of these in the two
respective video sections of the schematics (fourth revision).
- Replaced all of the Namco customs in the video motion section with known good customs with no change.
- The SN74LS298N at 8D was acting weird, so I socketed and replaced it. No change.
- Legs 1-8 looked questionable on 9J (SN74LS175N), so I resoldered those (did not replace or socket).
- There are likely numerous other testing, checks, etc. that I have done, but this is what I documented.

Anyone have any ideas? If so, please be specific in your suggestions and requests.
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