Dig Dug Graphics Problem

kestep

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I have an Atari Dig Dug board sold to me as "working".

It boots up and plays fine, but there are some problems with the graphics.

At boot up, the crosshatch is not the normal white grid. The grid is mostly there, but some red and black blocks are present. I would have assumed a RAM problem, but the self test says that the ROM and RAM are OK.

The intro screens have a number of horizontal lines present.

During gameplay, everything looks normal EXCEPT for the bottom most area of the playfield. The are horizontal lines covering parts of the "dirt" in that area.

Voltages are good and the problem is repeatable at every boot. Is this symptomatic of a custom chip issues? The 6116 RAM?

Any thoughts would be greatly appreciated.
 

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I highly suspect the sockets to be dirty on both the ROMs and the custom IC's. Try reseating them and cleaning the legs, but be careful with the custom ICs, its VERY easy to break off a leg and VERY inconvenient I might add.
 
I've removed and cleaned about half of the socketed chips.

No change so far, but I'll hit the rest later.

It plays like a charm and the corruption doesn't affect play at all.
 
I believe there are two 2148 (can also be 9148) RAM chips which will cause graphics
problems. Could also be the TMM2016 Ram chip.

That board has a bunch of custom ICs and is really hard to troubleshoot if
you don't have a known good board to compare parts with.

JD
 
Looks like it could be a logic issue in the Playfield Generator or Video Color Controller circuits.

Do you have a logic probe or scope, and are you interested in that level of diagnosis?
 
Looks like it could be a logic issue in the Playfield Generator or Video Color Controller circuits.

Do you have a logic probe or scope, and are you interested in that level of diagnosis?

I have a scope. I'd be quite interested in DIGging in to this (pun intended).

I need to finish reseating and cleaning the socketed chips.

I do have a working Galaga and was going to see if I could swap some of the customs.
 
Is that an LCD? Make sure the VGA cable is nice and tight if it is.

You got me. To be fair, this is all mounted in a non-dedicated cab in order to troubleshoot and to play.

The VGA cable is fine and everything else on the game display is fine. I think the CGA to VGA converter and the LCD can be ruled out.
 
I have a scope. I'd be quite interested in DIGging in to this (pun intended).

I need to finish reseating and cleaning the socketed chips.

I do have a working Galaga and was going to see if I could swap some of the customs.

OK, finish reseating/cleaning, and try swapping what you wish.

If none of that does the trick, you need to determine which version of Dig Dug you have, and get the appropriate schematics. A good pic of the PCB will help. IIRC, the older PCBs have all the ICs oriented the same way, but the newer PCBs have about half a dozen ICs oriented perpendicular to the rest (include the 3 Z80s at the end opposite of the edge connector).
 
Bumping this eight year old thread.

I've almost completely fixed my last Dig Dug board. Several TTL had to be replaced. Now passes all tests and plays.
But my last puzzle to solve is the same as shown in this thread - static horizontal playfield lines.
I've looked through the PF Generator and Vid Color Controller sections and have not noticed anything unusual.
Anyone have any other hints?
 
I'll preface this with this could all be a bunch of bs, but I like logic problems so I looked a the dig dug schematic, I dont own the board but I have had similar problem on double dragon. Anyway, coming off the 4c custom are 1v 2v 4v 8v etc. I'm thinking this is vertical position in binary. If this is true the 2v should have half the frequency of 1 v and 4v half of 2v. 1v 2v and 4v address into the pf rom at 4f. If one of those were stuck you might get bars. That's were id start, the path from the 4c custom through the couple gates to the 4f rom, but maybe you tried this already. Good luck.
 
No, not the V or H timing signals. All scope out correct.
The custom(s) are known good. So has to be one of the TTL.
Still looking ...
 
I am sure you have already done this. If the ram checks ok but you are getting noise in the test pattern then try looking around the playfield generator, video color and video output for any noise or signals that are marginal levels. If you have other boards then try swapping the custom ic's to eliminate those. Use dipsw 5 to freeze the test pattern that way you can use the scope to look for the problem without worrying about what other circuits are introducing as the code runs.
 
The CPUs, ROMs and all customs come from a working PCB so they're good.
This particular board, however, has been worked on before and there are alot of extra sockets or replaced sockets. So these and any hidden issue under the sockets might be of concern.

But all tests pass and I've taken the dead board to this point where it plays perfectly but it just has those lines. Disabling the playfield data removes the lines, so I know it's in that section .... somewhere. Checking R/G/B shows line are consistent with each color. I would have suspected RAM but it does not seem the case here. Freezing the test pattern is an interesting idea ... I'll try that next and go hunting. I also suspect the 112 BPROM in the PF GEN section, so I might have to pull that and test it.
 
Also for problems like this a video probe can help narrow down the problem. Connect one end of a 470 ohm resistor to a test clip and the other end to a wire and test clip. Clip the wire to the green or blue game board video output pin. Probing shift registers, mux's, ram, prom and other outputs to find something similar can help track down the area of concern or eliminate sections of the circuit. I think the galaxian service manual vol 2 talks about using it.
 
I've known the fix for the left-to-right static playfield lines on my board for awhile now.
Just been patiently waiting for Mouser to deliver the replacement part so I could verify the fix.
And the bad parts was ....

REVA Dig Dug
10R 74LS298 Quad 2input MUX (feeding 136007-X12 BPROM)

Can't recall completely, but this was the board with which I used the Fluke 9010A, and strategic read/writes to the A000 to A007 playfield addresses to find the error (in test mode with static display). I really should take better notes. LOL :)
 
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