Finding tron

studiopaul

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Im returning to try to learn how to fix Tron that i picked up a while ago.
When i purchased it ..guy stated that he smelled a little bit of burn..so powered off.
I assume cap or the like has burnt out.

Anyhow.

Tron along with the Tanks, Bikes are missing.
On test..I can not see what im selecting as there is no scroll icon.

I have checked:

1. all connections
2. main PSU
3. cleaned legs of chips
4. replaced video chips

where would burn out to cause this issue?
I have a DVM and scope as test gear..

Thanks guys
 
I wouldn't order a set just yet. I know that bad ROMs can display corrupted sprites (see this thread http://forums.arcade-museum.com/showthread.php?t=218828), but I don't know if bad ROMs would be the only cause for missing/bad sprites. The RAM (93422) on the Vid Gen board can also corrupt graphics. Maybe wait and see if cdjump or someone else responds with any ideas. If not, you could then resplace the ROMs. I can recommend Steph @ HobbyRoms- great communication and quick to fill my order.
 
Missing tron

last time I was told to replace video ram..purchase tested ..same thing.


my concern was the seller.

"it was working..then i smelt a slight burning smell and now no tron"

looking over board for burnt resistors and such.
 
Hmm. Yeah, sounds like looking for burnt out components would be a good place to start. Problem is if it's a bad capacitor or diode, it probably won't visually be bad. Time to start hitting everything with your DMM. If you can't find anything, maybe then go for the ROMs.
 
It sounds like you have a problem with one of your logic chips in the foreground part of the video gen circuitry. A logic comparator is a handy way to check the ls157's (there are a lot of them). Going through some of those chips with a logic analyzer would also be a good idea. You need to find a place in the foreground graphics area where a chip is receiving data but not sending it down the chain...
 
able to do this on a 2 channel scope?

was hopping that there was a 5 v or such.. that was feeding the beginning of logic circuit.

A three or four channel would be better. There are a few chips that combine signals, so you will have two lines entering the chip, and one line leaving. Being able to see all three in real time is important. A two channel won't cut it.

Of course, a simple logic probe or a single channel scope can tell you if one
of the chips is 'dead dead', i.e. no output at all.

The 5v on these boards is on a common rail--if 5v was dead shorted somewhere, it wouldn't be a subtle failure.

Btw, do you have new ribbon cables in place?
 
So I'm heading back in to look for tron today.

Thus far I have switched out the ribbon cables.
Fault stays the same.
Resoldered and cleaned connections.

I'm starting to look at the video board.
Double checking video ram etc.
Removing and cleaning ics.

The board has an alphabetical and numerical grid to show placement of components on circuit board.
Reading the manual is helping. But I'm having trouble with bad printed schematics.
Are there any other resource to explain each area of the video board?

I'm wondering if the CPU board is outputting the signal for the missing graphic or if the video is not outputting the image.

Thanks.
 
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