I1 repeating error with Diag Cart

[PhilC]

Hi All,

Two of the boards that I got the other day have the same error when booting, white border with black screen which is usually memory as you know.

Putting the diag cart into the board gives me the following error codes repeatedly

Capture.PNG

The vague description in the service manual says a data line is stuck. Do you guys have any idea whether this means its stuck in 1 or 0 state, as in faulty ram or maybe corroded contacts etc. In fairness, these two boards look pretty good, so I suspect I just have a dodgy ram chip.

[exxos]

Id assume the 1 is the error, but never seen that screen before.

[PhilC]

It looks like its something to do with CAS not pulsing on the higher bank? CAS stays high all the time.

[exxos]

If its a 16 chip RAM bank, then likely you have bad ram chip, whichever is going to bit 14 by the looks of it.

[PhilC]

Ok, that explains the error message, cool, thanks for that exxos.

Now to track it down (well, maybe tomorrow anyway)

[czietz]

Like exxos said: Probably the RAM chip for bit 14 is faulty. Other possible causes are the buffer (74xx244) or latch (74xx373) responsible for that bit. Due to the multitude of Atari board layouts it's not possible to give you the component designators, though. If in doubt, look into the schematic and trace it on the board.

[PhilC]

Thank you, yes I've looked and just need time with the scope to verify which chips against the schematic.

All part of the learning process.