My Falcon went to black screen

[christophe.griard]

Ok understood Exxos.

The columns "After reset n°x" are voltage after a sequence made with reset button pressed followed by the release of reset button. So it is not the information you wanted.

The voltage I measure while the reset button is held down is in the "Comment" column of my chart and is the information you want. So when reset button is held down, I measure +5V or +4V on all Ax and Dx addresses.

I unplugged the PSU and just did some resistance measurements : for all Ax, I measure 4,6 kOhms as a resistance between the pin and the +5V.
For all Dx pins, I measure 10kOhms.

[exxos]

All the information is in your chart...so all looks correct..

The problem is the very first sequence after reset should see all the address pins at 0 V, but the some reason you are not seeing that... Unless I guess it is possible you did not see the switch down to zero before the voltages as documented in your chart ?

Consistently going to that address does not really make sense... I suggest you remove the ROM and repeat measurements on a few address pins..And see if any of them in your chart change...

[christophe.griard]

I think I got what you meant Exxos.

I made a new measurements with a different time base to better see the phenomena and enclosed are two pictures (one for pin 21 and one for pin 22) during power on phase.

You have in red the signal for the CPU pin and in yellow the reset signal.

We can see on A0 that the signal goes from 0 to +5V and then goes to 0V. On A1, the signal goes from 0 to 5V and stay at +5V. SO we can see on these two pins that just after power on these two pins are at +5V.

If needed I can check in the same way all the pins for Ax and Dx.

I hope this time it answers properly your question...

CPU pin 22 (A1) during power on(1).jpg

CPU pin 21 (A0) during power on.jpg

[exxos]

If needed I can check in the same way all the pins for Ax and Dx.

Please remove the ROM and test the same with with a few more Ax pins.. No need to test Dx currently..

When RESET goes HI, the CPU should put all Ax low...

[christophe.griard]

Ok I do it at once.

One question : should I keep installed the Sim RAM to make these measurements with the ROM off?

[exxos]

Ok I do it at once.

One question : should I keep installed the Sim RAM to make these measurements with the ROM off?

You should leave RAM and ROM out of the machine during all these tests.

[christophe.griard]

Here are the results : only two pins (A1 and A2) are High (+5V). All others are Low at 0V.

Remark: when I push the reset button all these 0V go to +5V and when I release the reset button they fall to 0.

CPU Ax pins w-wo RAM.jpg

[exxos]

Here are the results : only two pins (A1 and A2) are High (+5V). All others are Low at 0V.

Remark: when I push the reset button all these 0V go to +5V and when I release the reset button they fall to 0.

So I wonder if those A1 & A2 are correct.. I will try and verify this on my Falcon later... I assume they should be zero... unless someone else reading can repeat the test sooner...

[exxos]

I quickly tried ADD1 & ADD2 as its on pin 48 & 47 of the expansion connector, and with and without ROM it goes to 0V and stays there.. So the question is.. why are you seeing A1 & A0 at 5V...

Check those pins under magnifier on the CPU...

[christophe.griard]

Thank you so much Exxos. It is very kind...

I made the measurement again on pin 22 and 59 and I confirm the +5V. I made during these two new measurements a picture during power on on these two pins.

CPU pin 22 wo ROM.jpg

CPU pin 59 wo ROM.jpg