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

[John Robertson]

On 02/20/2016 11:31 AM, John Robertson wrote:
> This is now working!
>
> 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 :-#)#
Ah, all I needed was a 2K2 pullup resistor bank on the Data pins. Now I 
get clean ROM and RAM tests.

I've included photos of the setup for those who are interested...

John :-#)#

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