Arcade Collecting > Restorations & repair

I don't believe it, another classic added => Centipede ! FINISHED !!!!

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Level42:

--- Quote from: RayB on March 12, 2007, 05:58:36 pm ---Level, is it safe to assume at this point, that you've given the board a proper scrutinizing, looking for broken traces, broken capacitor legs or missing caps? Bad/Broken caps feeding power to the RAMs will also result in RAM errors.


--- End quote ---
Mmmm, well I did a lot of looking at the board, but didn't specificaly look for that. However, since the two lines that run directly from one of the two 2114's to the bus driver (74LS245) mearure very differently to GND then all the others I think that one of those 2114 is the cause for the problem.

The 2114's are first in the memory map of the Centipede PCB, and the service manual (and self-test beeps) check these two rams first. This added to the info Fredster gave and the info  I found on 2coinsperplay.com leads me to being pretty sure about this....

However, there is a good chance that there may be more problems of course. By looking at the sodlerings you can easily identify if any chips have been replaced already. Three chips of the "main" (Playfield) RAM had already been replaced. However these all measure the same on the same leads per chip. So I expect them to be OK.

There were two or three other chips replaced as well, and the soldering job looked not too good, so I tried re-flowing it. I instantly learned from that that soldering an old PCB like this is a risky and delicate job. The old flux seemed to be baking away !

Anyway, it's definitly worth visiualy checking again the PCB and the parts for any other problems for sure.

I'd love to have a CAT-box ! It shouldn't be too hard to "emulate" one with a PC and some hardware should it ?

RayB:

--- Quote from: Level42 on March 12, 2007, 06:44:31 pm ---I'd love to have a CAT-box ! It shouldn't be too hard to "emulate" one with a PC and some hardware should it ?
--- End quote ---
That's a good question. They are rare and fetch a high price on Ebay. I have not ever heard of anyone trying to build their own.

Level42:

--- Quote from: RayB on March 12, 2007, 08:19:00 pm ---
--- Quote from: Level42 on March 12, 2007, 06:44:31 pm ---I'd love to have a CAT-box ! It shouldn't be too hard to "emulate" one with a PC and some hardware should it ?
--- End quote ---
That's a good question. They are rare and fetch a high price on Ebay. I have not ever heard of anyone trying to build their own.


--- End quote ---
Yeah, but I think the high price is based mostly on the collecting value. I have seen someone who had some plans about it, but it seemed to have never materialised.

I must be missing a lot, but as far as I understand, basicaly you put adresses on the adress bus and write data to it that then gets read back and compared. You can also put in a range and the have it pulse through all the adresses in that range and compare....looks pretty simple to me,but although I'm an electronics service man, I'm not an electronics designer :)

It would be a powerful tool and a fun project.

Level42:
I ordered a set of all sort of RAMs that are on the Centipede PCB plus the buffer IC and the High-Score memory from www.arcadechips.com
Ordered yesterday, shipped today  :applaud:

The IC I could not identify turns out to be a 82S25 and not a 82525....this is also available at www.arcadechips.com

Hope it will solve the problem !

fredster:
Level42,

I screwed up more than one trace by soldering an old area.  You have to check continuity of each of the traces around the chips.  Somebody may have screwed up the repair and gave up on it.

Check each one and then make sure it's good.  They are pretty big traces.  Use the multimeter to track them down from edge to edge and see if they are okay.

It's easy to fix if you find one dead, get that really small wire at an electronics store that's made for this.  All you have to do is touch it to the trace and you have a new one.

Go ahead and look at the board.  Really really look at it with a magnifying glass and a bright light.  Look at each repaired area and see if you see anything that is burnt or lifted.  That could be a problem.

Most of the time, you can see what's wrong.  You may have a dead trace. One that was okay for a while, then went bad later in use.

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