My Falcon went to black screen

[exxos]

Conerning your question, the signals remains like this for at least one minute without changing in shape/level.

So the CPU is trying to boot then..

Check out the ROM chip enable line.. pin 3...

[christophe.griard]

I removed the Sim RAM and I measured +5V on pin 3 of U51 (see picture for the point on the motherboard at which I measured the +5V).

Pin 3 of U51 Comment.jpg

[exxos]

I removed the Sim RAM and I measured +5V on pin 3 of U51 (see picture for the point on the motherboard at which I measured the +5V).

To make sure.. you had trigger set and can confirm it never goes low after reset line goes high ?

[christophe.griard]

Yes I confirm Exxos: the channel 2 that was used as a trigger was connected to Pin 1 and pin 17 of expansion port.

Once the reset button is released, then the reset signal remains at +5V as seen in the pictures of my previous message (1 division corresponds to 5V) and never goes done to 0.

[exxos]

Yes I confirm Exxos: the channel 2 that was used as a trigger was connected to Pin 1 and pin 17 of expansion port.

So the CPU seems to be running, and yet its not accessing ROM. I would next measure A0- A23 and D16 - D31.. Document, high, low or switching for the signals.. no need to post scope images.

[christophe.griard]

Thanks Exxos: I do it right away and come back to you right after.

[christophe.griard]

Exxos,

Below are the measurements I made (both with the meter and the scope especially some 4 Volts values measured on some pins):

A0 (pin 21) : +5V
A1 (pin 22) : +5V
A2 (pin 59) : 0V
A3 (pin 58) : 0V
A4 (pin 56) : 0V
A5 (pin 55) : +5V
A6 (pin 54) : 0V
A7 (pin 53) : +5V
A8 (pin 52) : +5V
A9 (pin 51) : +5V
A10 (pin 48) : 0V
A11 (pin 47) : 0V
A12 (pin 46) : 0V
A13 (pin 45) : 0V
A14 (pin 43) : 0V
A15 (pin 42) : 0V
A16 (pin 41) : 0V
A17 (pin 40) :+5V
A18 (pin 39) :+5V
A19 (pin 38) :+5V
A20 (pin 37) : 0V
A21 (pin 36) :+5V
A22 (pin 34) : 0V
A23 (pin 33) : 0V

D16 (pin 96) :+4V
D17 (pin 97) :+4V
D18 (pin 98) :+4V
D19 (pin 99) :+4V
D20 (pin 101) :+4V
D21 (pin 102) :+4V
D22 (pin 103) :+4V
D23 (pin 104) :+4V
D24 (pin 106) :+5V
D25 (pin 107) :+5V
D26 (pin 108) :+4V
D27 (pin 109) :+4V
D28 (pin 111) :+4V
D29 (pin 112) :+4V
D30 (pin 113) :+4V
D31 (pin 114) :+4V

It is the first time I see some +4V but seen both on meter and scope...

[exxos]

Below are the measurements I made (both with the meter and the scope especially some 4 Volts values measured on some pins):

Are none of them switching ? You would have to check on scope for that...

[christophe.griard]

Ok. I re-check that at once with scope and come back to you as soon as it is done.

[christophe.griard]

Exxos,

First results : enclosed 3 pictures of what I can see on the scope as an example (I will continue to check all pins).

For these examples, no switching can be seen (I push the AUTO function on the scope to define voltage and time base; if I change the base time, nothing more to see: no switching).

For pin 47, signal close to 0 with fluctuations (I set a small scale on voltage axis).
For pin 51, +5V with some small fluctuations (I changed the base time from 5ns, 10ms, 50ms, 100ms) with quite the same picture and no switching.
For pin 56, an example of what I can see with a higher scale on voltage axis (same result than pin 47 if I had the same scale for voltage thzn pin 47).

So I will re-check all pins but I fear to find no switching. Let's check all the pins in case I missed something the first time.

A11 (pin 47) CPU.jpg

A9 (pin 51) CPU.jpg

A4 (pin56) CPU.jpg