Hi There!

I´m an Atari 8-Bit veteran and doing repairs and enhancements of old Atari XL/XE.

Several times I have timing / temperature problems if the CPU was manufactured by Synertek. It makes no difference which datecode was on the CPU.

The failure is always the same. After 6-8 hours of operation with full loading (for example: running an intensive memory check program) the CPU begins to make disturbance on his data-/address-lines. Sometimes it only crashes / hangs up, but in the most way only data hold in RAM are written or readed wrong. The bad adresses are floating in the whole address-space of 64K.

After a long time testing all components I found out that the problems depends on the type of CPU. For example, NEC or Rockwell build 6502 works very well of about >12 hours permanent usage under stress.

When you cool down the Synertek CPU (for example: using a coolant spray) rapidly, the the failure is gone while CPU works ahead.

Has anybody make the same experiences with Synertek CPUs?

Remember that the Atari 800 XL/XE uses an special type of 6502, the 6502C. It´s difference is the HALT-Signal, which enables using of DMA with a videocontroller for example. It´s possible, that these problems belongs only to the for Atari produced 6502C. But I´m not really sure.

Thanks, Juergen

Only my first home-made computer had an NMOS 6502. I never left it on that long, and never did much with that computer. After that I always used CMOS. But how about a DIP heat sink?

I also remember Apple II computers with NMOS parts having an optional fan box that would hook on the slots along the side.

Hi Garth,

Thanks for that information. I have ordered some pieces of that heat sink.

Also, with the help of the german atari community, I found out that this problem occurs only a few series of Synertek CPU. Some guy remember, that atari service germany in the Eighties also build heat sinks over this problem-based series.

Thanks & Regards, Juergen