Teenage Mutant Ninja Turtles - Missing Some Graphics??

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Teenage Mutant Ninja Turtles - Missing Some Graphics??

Hi everyone,

I picked up a 4 player TMNT in pretty decent shape. The main issue is that there are some graphics that are missing. It is tough to explain, so I posted up a video. I also have posted the self check including the mask rom check.

Not really too sure where to go with this since from what I can see, the game plays and sounds fine otherwise. I already have removed the socketed chips and cleaned them down with rubbing alcohol with no change.

Self Test Video:
http://www.youtube.com/watch?v=lU_tPuVI6J8

Missing Graphics Example:
http://www.youtube.com/watch?v=6gacfo-QXEI

I would consider myself to be pretty technical however this is my first board and I have absolutely no idea where to start. I did repair a few G07's though..

Does anyone have any idea what may be going on here?

Thanks,

Matt
 
As it is a Konami from the early 90s the most likely fault is bad fujitsu TTL chips. Do you have a logic probe?
 
Thanks for the reply - I do not have a logic probe unfortunately :-(

However, I do have a DMM that has a "logic" setting -- it was somewhat fancy when it was purchased some 12 years ago.. Serial port and all. Do you think that would work? I will try and locate a manual for it..
 
OK - Do have a logic probe on my DMM. What would I need to be testing for.. I am not quite sure what TTL I would be looking at, I assume it would be something similar to the 74LS245 -- A quick google turned that up as a particular high failure chip.

I have the schematic for the board -- can anyone suggest some good quick reading on how to go about testing these things out?
 
Hey Guys - Finally ready to tackle this.. Can anyone suggest a proper place to start looking for such a faulty TTL chip? From what I can gather from online... each TTL has it's own truth table so it would be best to test all of one particular kind fist; no?

Does anyone repair these boards? I am not sure how far I can make it but defiantly want to try!
 
First off look for Fujitsu TTL chips, anything 74LSxxx, then go round those with your logic probe looking for pins that are neither high or low. If you find one then pull up the datasheet and see if that pin is unused, or if it is the inputs to an unused gate on the chip, ie only 3 of the 4 gates on an LS32 may be used. In many cases you will find floating pins on Konamis of this vintage. Thats a quick and dirty approach.
 
My TMNT is about 90% Fujitsu 74LS chips... I am trying to find a good easy chip type to understand as well as test. Would you be able to offer any suggestions as to what specific types are typically easier to troubleshoot than others?
 
Looks to me like you're missing sprite graphics on the left half of the screen... more or less.

Don't start with an LS138. Start with a simpler logic TTL chip, like ones with just basic logic gates (AND, OR, NAND, NOR), or perhaps the simplest to understand are inverters or buffers.

Not sure if TMNT schematics are available... I'll look for 'em.
 
For the ultra simple try a hex inverter - 74ls04

When the input pin is high, the output is low and visa versa. The hex in the name simply means there are 6 individual gates on the chip.

For slighlty more complicated try a 74ls32 - a quad OR gate.
 
Does anyone have any idea what may be going on here?

Looking at the schematics that Solder linked, you'll notice a few sheets of it are potentially more relavent than the others. The ones that interest me are:

"COLOR" pp15-16 in the PDF. Color is the final stage of video output, and often the data from different sources (tiles, objects, text, etc.) get put together and then color PROMs assign the final color to each pixel, and then its R G & B components are output.

"OBJ" pp19-20 in the PDF. This is OBJects, another term for sprites, which seem to be missing on the left half of your screen.

"VRAM" pp21-22 of the PDF. This is Video RAM, which tells the OBJects (and the tiles, etc.) what to display and where to display it.

Briefly glancing over those 3 sheets, I'd make the following observations:

1) I don't think the sprite EPROMs are to blame. They contain the data that defines what the sprites look like. Your sprites look fine... when they're on the right half of the screen. They're just missing when they happen to be on the left half.

2) We can just hope that the problem doesn't lie in any of the numerous custom chips in the video section of this PCB. There are several: 051937, ???60 (can't read it, the middle of the schems, between pages, didn't scan), 052109, 051962.

3) I might start my probing with the '151s on the left side of the OBJ schematic. Also kind of interesting looking are the '153s on the right side of the VRAM schematic. These appear to select among OBJect and other sources for which data to pass along to the COLOR section.
 
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Wow - DarrenF, thanks for that update. I will definately go take a look at some of the simple chips first as mentioned by Womble to verify I can actually test these things without going crazy..

Then I will look for the mentioned chips to start at and see if I can understand the truth table and go from there. I actually have the original manual for the game with the schematic, but don't really know what all of it meant.

On another note, "The Book" as suggested by channelmanic (in both my threads) was FANTASTIC and really made other fuzzy items super clear. The little schematic picture legend helped and it really is written quote well. It won't make coffee though..

Will keep you guys posted!
 
It could be a custom as they are the tile map generators, but it could equally be ojbect RAM, I have seen a few boards where the sprites are mashed but only in certain parts of the screen.
 
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