Contra repair log

ifkz

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SYMPTOM: So bad off I did not attempt power up.

FIXES:
1. Scratches on the bottom of the board, some very deep. All bad looking traces beep tested okay.
2. Several pins on various components touching and smashed around. Everything bent back.
3. Amp missing heatsink. I got lucky and found a heatsink that would work on the amp. After two screws and some thermal grease all was good.
4. Parts broken on component side replaced: Three disc capacitors replaced, one tantalum cap replaced.
5. Component side robbed of all EPROMS. Three of seven program EPROMS burned.

At power up these fixes gave the board some life. I have full sound. I could coin up and play a game resembling a black and white Atari 2600 game. Good! I will continue this log once I find four 2Mbit EPROMS (I have none) and when my cheapo USB EPROM programmer gets here. Time to learn some Engrish :)

EDIT (see below)
6. Using 27c400 chips with doubled code and pin 1 on each tied to ground, I was able to duplicate the mask ROMs.

Game works!!!
 
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So this rounds out my repair setbacks for the weekend. After writing the replacement EPROMs and installing them in the old mask ROM slots, I am greeted by a screen of junk. The pinouts must be different from the mask ROMS and the 27c2048's that I used. Dang it.
 
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Masks are often different pinout that eproms of the same capacity, often they have fewer pins as they dont need the programming pin. On chips larger than 1Meg capacity you haev to be very careful as the power pins can be in different places, so you can actually destroy eproms if you use them without confirming the pinouts first.
 
My smart friend says I likely need 27C2100 to match the pinout in the schematics. Anyone know where I can find four of them? Ebay strikes out.
 
Use a 27C400, program the bottom half of the chip, and make sure that pin 1 is grounded.

I have those in stock on my site...

RJ
 
Yes, this is looking more and more like I need to wait for a parts Contra to come along that still has the four mask ROMs populated.

No one I know can program 27c400s, my USB GQ-4X certainly can't do it either.

Ah, Konami and their 'fruity' ROM sizes and types!
 
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Those 4Mb ones are common ROMs in the CPS1/2 world.

I can program them easily.
 
Update!

Using information here, I bought a few 27c400 EPROMS and a better EPROM programmer than the GQ-4X Time to get to work!

I learned how to double the binary program files and programmed them onto four of these chips. I tied pin 1 on each to ground which made only the lower half of the chip visible to the game (per the above). I powered up and was greeted by a happy game!

Another one saved from the junk pile; as always, it was a KLOV group effort!!!
 
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Glad to hear you got it working. Contra is awesome. I sunk so many quarters into that game back in the day.

P.S. Congratulations on your 1000th post.
 
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