[Techtoolslist] 9010/9100: Floating the 6502 Data and Address buses

[John Robertson]

This is a work in progress.

I have a couple of Gottlieb sound boards with two 6502s on each that are 
soldered to the PCB. The only 'easy' way to do tests is to socket the 
6502s, isn't it? The 6502 does not support floating the Data/Address bus 
(except for the 6512), does it?

Well, no, there is an easier way - it seems you can float the 6502 
Address and Data lines using the following technique:

1)  Clip off (leave a bit remaining) of the Vcc pin 8.

2) Find a 40 pin glomper clip and ribbon wire to a 40 pin header.

3) solder 2 40 pin IC sockets back to back after first removing pin 32 
from the inner socket (this will contact the cut off pin 8 via the 
glomper otherwise and power the 6502 CPU) and bend out pin 8 of the 
other (outer) socket.

4) solder a short jumper wire on the bent out pin and connect it to a 
jumper that you will hook to Vcc.

5) plug the double 40 pin socket on your 40 pin header and move the 
connectors on the glomper so pin 1 & 40 move to the correct pins on the 
outer 40 pin socket.

6) Hook glomper on 6502, connect jumper to Vcc

7) run your 9010 tests! OK, it isn't perfect...need to work on the 
loading because if I get inconsistent reads from the Eproms on a 
known-to-be-good board. And the RAM test craps out if the Eproms are 
installed - sometimes. Need to play with some pullup resistors 
next...but the RAM short and long tests pass on 6116s.

John :-#)#
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