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

[Steve Larkins]

Nice thanks for sharing.

On Saturday, 20 February 2016, John Robertson <jrr at flippers.com> wrote:

> 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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Steve Larkins
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