Constructing A 6502 NOP card

The NOP card can be hand made and involves hard wiring the NOP instruction 
(Hex = EA) onto the data bus.  This in effect keeps the processor constantly in the NOP instruction and so forces it to act as a counter.  Therefore we now have constant known data to work with.  You can refer to the following link for further information on NOP cards and Signature Analysis in general.

http://www.spies.com/arcade/TE/SigAnalNotes.pdf

To Make The NOP Card

You will need

40 pin DIL socket
6502 processor
Some small gauge wire
Soldering iron, pliers, wire cutters.

1.	Bend out the following legs on the processor by 90 degrees  
2, 4, 6, 26, 27, 28, 29, 30, 31, 32 and 33.
 
2.	Place the processor (with bent out legs) into the DIL socket.

3.	Using the small gauge wire link the following legs.
	a) 2, 4, 6, 26, 27, 28, 30 and 32.
	b) 21, 29, 31 and 33.

4.	Cut a couple of lengths of wire about 2 inches long.  Attach one to pin 25 (A15, the highest address line) and the other to pin 39 (clock).  Strip back about half an inch of insulation on both flying wires.

Your NOP card is now complete for the 6502 processor.

To check the NOP card, remove the game processor from the PCB and replace it with your NOP card.  Set the 5004 up as follows

Start  	-ve
Stop  	-ve
Clock 	-ve

Put both the Start and Stop onto the same point, which will be pin 25 of the NOP card.
The clock will go on pin 39 of the NOP card.  The following pins on the NOP card should give the corresponding signatures

9	UUUU
10	FFFF
11	8484
12	P763
13	1U5P
14	0356
15	U759
16	6F9A
17	7791
18	6321
19	37C5
20	6U28
22	4FCA
23	4868
24	9UP1

If your signatures match then your NOP card is good.