My Falcon went to black screen

[exxos]

So the CPU is stuck in a loop of doing nothing at all...

What do you get for BERR, & HALT ? pins 129,130 ?

Also, power down machine, power up again, does your results for Address & data bus ever change ?

[christophe.griard]

I re-checked all Ax addresses: no switching.

Yes I saw for a very little number of Ax adresses with different value after a reset : for example A0 can be High or Low.

On the scope I have a stable +5V on pin 129 and on pin 130 (as already seen on the expansion port) : the CPU seems not to be halted and no bus error is detected...

[exxos]

I re-checked all Ax addresses: no switching.

Yes I saw for a very little number of Ax adresses with different value after a reset : for example A0 can be High or Low.

Right, so you need to press reset and re-check all Ax Dx pins again and see which ones change after reset..

[christophe.griard]

Ok. I will do it tomorrow morning : my eyes are quite tired and the pins are very small... :-).

Thanks a lot for your help : I very very much appreciate.

Have an nice end of day Exxos.

See you.

[christophe.griard]

Hello,

I have done the measurements (and made a sheet to summarize all the data). In fact, all the measurements I gave yesterday are still valid (unless pour A0 that is at 0V instead of +5V; maybe a mistake...). Yesterday I thought that some fugures could change as I saw 0V and +5V on A0 but probably a measurement mistake.

All these figures do not change after 5 different resets and after a power off/power on sequence...

I put a column "Comment" with a comment about the behaviour while reset button is pressed. I have still some +4V and +5V.

CPU signals.jpg

[exxos]

So yesterday you said this...

Yes I saw for a very little number of Ax adresses with different value after a reset : for example A0 can be High or Low.

So are you now saying there is no activity on the pins whatsoever now ?

Note that this would only be apparent right after reset..

[christophe.griard]

Yes.. I did not succeed today to see another value on A0 than 0.

To try to answer your question, on the scope, if I look at A9 (pin 51) with the pin 51 triggered to reset (set on channel2), when I release the reset button I can see the reset signal going from 0 to +5V with no effect on A9 (remaining at +5V).

Still on the scope, for A0, I can see 0V and when I press the reset button, then A0 goes to +5V : I can clearly see the step down for the reset (going from +5V to 0V) and at the same time the step up for A0 (going from 0V to +5V).

Then after I release the reset button, reset signal goes from 0 to +5V and at the same time A0 goes down from +5V to 0V (comment column of my excel sheet).

This is the only activity I can before and after the reset. Once the reset button is released it seems there is no activity.

I don't know if it answers properly your question...

[exxos]

Thanks, OK another test.. Hold the reset button down and test Ax Dx again... you can test with meter, but important to hold reset button down constantly while doing the measurements.

[christophe.griard]

That's the measurement I indicated in my comment column with the voltage value when I press the reset button and keep it pressed. I did this for each Ax and Dx.

For example (see my excel sheet), when I press the reset button, A4 (pin 56) goes from 0V to +4V (until I release the reset button, A4 remains at +4V) and when I release the reset button goes to 0V.

[exxos]

That's the measurement I indicated in my comment column with the voltage value when I press the reset button and keep it pressed. I did this for each Ax and Dx.

For example (see my excel sheet), when I press the reset button, A4 (pin 56) goes from 0V to +4V (until I release the reset button, A4 remains at +4V) and when I release the reset button goes to 0V.

Right, that's not what I meant in that test, I mean press reset to trigger your scope to see of bus activity when reset switches high...

So if your chart is already with reset held down.. something isn't right as the Ax pins should all be high...

In that case, take a pin like A16 which you have as zero (unplug PSU from machine) use your meter on A16 to 5V on resistance, and see if you read about 10K resistance there...