Diagnostic cheat sheet and/or help for Atari 1040STF

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banedon
Retro freak
Retro freak
Posts: 16
Joined: Mon Feb 24, 2014 1:51 pm

Diagnostic cheat sheet and/or help for Atari 1040STF

Postby banedon » Sun Sep 24, 2017 4:13 pm

Hi guys

Now that I'm done (for the moment) upgrading my 520STFM, I've decided to take a look at a 1040STF which I bought on ebay a few years ago, but which turned out to power up but not display anything and there's no flopy drive activity (no clicking, no access light).

This could be an ebay lemon (i.e. someone has stuck a ton of duff parts on a duff PCB and sold it), but I thought I'd have a quick go at seeing if the poor thing can be brought back to life as I'd hate to dump it or carve it up for parts.
So far I've checked basic voltages and I'm seeing +5V and +12V out of the main PSU cable to the PCB and +5V on the two red/blue cabling pairs which branch out from the PSU area to the other parts of the mainboard (tested at the far end). So PSU *seems* ok.

My main question: Beyond reseating the PLCC and DIP socketed ICs/cleaning contacts can anyone offer any advice or (hopefully) know of a general diagnostics guide for the Atari ST line. I.e. Check pin 15 of the CPU for the clock - which I'm going to do anyway, but serves as an example - etc.?

My plan of attack in the mean time is to:
- visibly check entire PCB for damage/corrosion
- check signals (CLK, RESET, R/W) and the buses to ensure nothing is being held hi/low permanetly or running in an indeterminate state.

I'm not sure I can do more than the above as my knowledge of of the M68000 and the ST architecture is near to zero (for the moment :)).
Last edited by banedon on Sun Sep 24, 2017 4:20 pm, edited 1 time in total.

banedon
Retro freak
Retro freak
Posts: 16
Joined: Mon Feb 24, 2014 1:51 pm

Re: Diagnostic cheat sheet and/or help for Atari 1040STF

Postby banedon » Sun Sep 24, 2017 4:18 pm

[deleted as double post]

banedon
Retro freak
Retro freak
Posts: 16
Joined: Mon Feb 24, 2014 1:51 pm

Re: Diagnostic cheat sheet and/or help for Atari 1040STF

Postby banedon » Sun Sep 24, 2017 4:52 pm

I made a mistake with the power lines from the PSU area out to the PCB: one set is running at between 12 and 15v which I assume is for serial/RS232C as it's the cables connect to that section of the PCB.

Results so far:

CLK is running at 8MHz. The "square wave" is certainly not perfect, but is maintains it's pattern and definitely hits +4.5V and 1V with a rise time of approx 31-41 ns and fall time of approx 21 to 27ns.
Tested the data and address bus and the data bus is coming up as a steady HIGH and the address bus is tristating (HIGH-Z). However, on system reset therre is activity for approx 3-4 seconds and then they go solidly HIGH/HIGH-Z again. Checked the HALT pin on the CPU and that goes low at that time. The R/W line changes as well until HALT goes low, then R/W goes high (read).
So the CPU seems to be running some initial code then halting.

Something of interest: The BERR line pulses low every 20us then goes solidly high when the cpu halts.

Interrupts / CPU state:
IPL0 and IPL1 remain HIGH at all times and IPL2 remains LOW at all times. So we have 011 (IPL2 (MSB)/IPL1/IPL0 (LSB)).
FC0 has activity then ends on HIGH at halt, FC1 has activity then ends on LOW at halt and FC2 has a tiny bit of noise but is HIGH at all times - Supervisor Data mode?

Conclusion (guess!): An interrupt is firing and the CPU is then either executing a HALT instruction or it's halting itself due to an unrecoverable issue. From the M68000 data sheet I can't see what the 011 code means, but I'll have a hunt around. Note: doesn't seem to be a bus error as BERR goes high


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