Donkey Kong Jr PCB Repair

wxforecaster

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I am trying my hands at a first ever PCB repair, and was hoping that with the help of existing material and folks here I could bring this board back to life and gain some nice experience from the matter. This was a spare PCB that I had pondered getting Double DK'd at some point.

Initially, I heard the analog sound mix upon firing it up, but got nothing but a scrambled mess afterwards on screen. I found both the H and V pots were broken away from the board. I soldered them back and have a nice stable picture. The game plays fine, but there are three what I would call "major" issues.

1.) The analog sounds (walking, jump, falling, etc...) work perfectly and are the correct volume, but there is no music, coin up sound, etc.. However, I say this with a caveat that I thought I could hear the music very very faintly (basically inaudible) in a couple places. (7K)?

2.) There is no red on screen, although once in a great while I've seen the red "flicker" in for a fraction of a second. (Note the Sanyo monitor was recently recapped and is in perfect working order with other Nintendo boards)

3.) Almost all of the motion objects have a solid rectangular block associated with them that is of the same color as the primary object color. (bad 7C, 7D, 7E or 7F?... tough to tell with the red color mising)

I do have a probe, but admittedlty have no idea how to use the darn thing. I do have schematics for the game. I imagine there are others here like me that would love to learn more!

Evan
 
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Check and clean the legs of your Proms located on the CPU board. Blocky character would be a Eprom issue related in the 7X series of chips.
 
OK, I reseated the EPROMs, which were suprisingly clean. In fact this board is in exceptionally nice condition overall. I also brushed the TV-out contacts which looked a bit tarnished.

The red is back with a nice stable picture. With this, I have confirmed that 7C is bad and producing the blocky objects above the characters identical to Brasington's site.

After removing the back panel and listening carefully, I can also confirm that I can hear music, but EXTREMELY faintly. This would suggest that 7K is bad (Brasington says LM234, but did they mean LM324?), but I'm not sure which side of the board (can I assume the side with the rest of the analog audio stuff?). Both of these look similar and neither are socketed.

Where can I acquire the needed chips (and socket?) to repair this board?

Evan
 
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As far as the volume have you tried the volume pot on the board?
That is one most miss.
 
Per the original post, the analog sounds are fully functional at the correct volume. I wasn't aware the DK Jr PCB has a sound pot, but looking at the schematics, I'm fairly certain this is an amplifier issue specific to the digital sounds.

Evan
 
Interesting followup.

Replaced the 7K op amp and the 7C EPROM this morning.

Plugged in the game and was greeted with missing red color and a split screen with random garbage on the right half and a compressed DK board on the left half. When you'd start the game, DK Jr would die instantly. However, the music was fixed so I know the op amp replacement worked.

Obviously 7C should have had nothing to do with this new problem (confirmed by putting back in the old one).

I wish I had taken a picture of the bad screen because the fix is a real strange one, and thankfully I found it fairly quickly. Given the symptoms and knowing the board previously worked fine outside of the issues mentioned above, I took out the Z80s to clean them figuring that could be the problem. I noticed that one of them was a replacement and the previous owner had apparently broken a couple legs in the process. Instead of putting in a new chip, there was a solder attempt to reconnect the legs and in two separate areas solder was sloppy and barely touching an adjacent pin. Good gravy. It must've been a fluke that I didn't see this a few days ago when I first powered up the board for testing. I cleaned this off carefully with a wire brush, plugged it in, and the game works perfectly!

Thanks to Mike's Arcade for the quick shipment of the two chips and socket.

Evan
 
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