🚀 go-pugleaf

Last weekend I was at a local Swap'N'Shop (Amateur Radio related) and I
bought three "non guaranteed to work" Nintendo carts for $20.00.  They
apparently were from a video store that rented the things, and had gotten
trashed somehow.  I took three of the nine or ten the guy had, figuring it
wouldn't be too hard to clean the contacts or whatever, assuming it was 
something simple like that. =)  Anyway, two out of the three don't work
at all; one of them is screwed up - the graphics are all "trashed" - kind
of like what happens when your programs accidentally starts storing stuff`
where the video memory is mapped. :-)  Anyway, SOMETIMES, the last game is
playable, and the characters are just slightly skewed, other times it's
hopeless.

I took apart one of the non-working cartridges, and inside there was a
VERY tiny circuit board - which surprised me from the size of the plastic
case.  First question: Are all the circuit boards for Nintendo cartridges
the same?  This one says (C)1987 Nintendo on it, and has four ICs, two
resistors, and a capacitor.  It also has two "jumpers", one labeled "H"
the other "V".  The "H" jumper is connected while the "V" jumper is open.
Second question: What does this select?

The four chips are as follows:
 . 74HC161 - which is a 4-bit binary counter with asynch reset.  It is
             capable of being loaded also.  Third question:  Any idea what
             they do with this?  Is it used to divide the clock from the
             main NES box?  This one is easy to replace if it's the
             problem (although I doubt it... the easy ones never are the
             cause of problems!)
 . One labeled (C)1989 Nintendo (16 pin DIP)
             I assume this is a PLA; probably something to do with their
             monopoly on requiring something special in the cartridge for
             it to work in the NES.  Fourth question: Anyone know any
             specifics about this chip?  (Or maybe references to other
             articles on it?)  If this chip is the bad one, I presume it's
             impossible to get, and I'm SOL.
 Finally, there are two 28 pin DIPs that appear to be ROM's.  One is labeled
 as PRG, the other as CHR.  The PRG chip says "M38128B-13" on the second line.
 The CHR chip has six numbers on the second line; unfortunately, I'm doing
 this from memory and I can't remember what it says.  I suppose it's
 conceivable the ROM's are fried from a static zap to the connector.  Anyway
 to tell?

 The cap appears to be a bypass cap from the top of the circuit board to the
 bottom.

Anyway, anybody have any info on what all this stuff is?  Maybe pinouts on
the ROM's (if that's what they are?)  Anybody else take apart any other
cartridges?  Are they similar to this, or does each manufacturer use their
own boards?  I haven't taken apart the other two yet; I pretty much hacked
the first case, thinking the circuit board was going to be big.  If they're
all this small, it's a simple matter of sticking a screwdriver to pry the
case open near either of the screws at the connector end.  Slowly push in the 
screwdriver til the case pops - this allows enough room to let the cartridge
slip out, and the only damage to the case is that one of the screws is
missing.

Any information or references would be greatly appreciated;  I'll post a
summary to the net if I receive any replies.

aTdHvAaNnKcSe,
Eddy J. Gurney, N8FPW

--
      Eddy J. Gurney, N8FPW           THE ECCENTRICITY GROUP
eddy@jafus.mi.org -- gurney@frith.egr.msu.edu -- 17158EJG@MSU.BITNET
(Preferred)          (But this is OK too)     (Only if you have to :-)