TI-99/4a PHP1260 32k Memory Problems

[TI-99/4a PHP1260 32k Memory Problems]

I forgot to add that I have disk controller with 2 drives and the rs232 cards - both work without any problems.

-BoBc

[TI-99/4a PHP1260 32k Memory Problems]

I have some strange memory problems with 2 php1260 cards. ( well at least with card 1 )

 

 

Card 1: When I "size" in ExBasic it will not normally show the memory in the PEB. And when it does the amount of memory displayed changes.

Any attempt to run a program from a disk drive will cause the system to either error out or crash the system. I wrote a small basic

program that writes 0 to 255 in each memory location and peek that location to make sure the data is there. I realize this is a modest

approach as it will not completely give a true test of the memory. This small prog will not run in ExBasic. I could only get it to run

using the minimemory cart. It ran fine and showed no errors. Took a long time! i can do the "call load" with the minimem module

but not with the ExBasic cart. I have 2 ExBasic carts and both do the same thing.

 

Card 2: I have another card that worked fine for the two weeks after I powered up the system, then it failed. Using the mem test proggie,

it has multiple memory errors, but the EXbasic cart does show the memory card when you do the size command. Running any program

using the ExBasic cart fails because the loaded prog is corrupted.I have already cleaned all the connections and checked power supply voltages on the mem cards, all is well there, no apparent electrolytic cap problems, I pulled all the caps and they checked

ok.

 

I have cleaned all the connections from the console to the peb. checked solder connections on the peb cable and to the flex cable

interface. Power supply voltages in the peb are nominal. Voltages on the memory cards are correct out of the regulators. no ripple on the +- voltage buss. I can load a file from a disk drive in ti basic and with the minimemory module - i cannot with the ExBasic cart with a mem card in the peb.

 

Is there a memory test prog available that will run in assembler that can perhaps tell me which memory chip is failing. or give me an idea of

where the failure may be?

Any help will be appreciated.

Regards,