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CBM PET 3032 STRANGE BOOT

But you are not telling me whether they are stable on the oscilloscope trace or not...

You must tell me what I am asking!

Dave
 
Ah, if you slowly advance the video you have an almost page of E characters but with a band of none E characters moving across the page.

Can you scope the pins of F9 please. The data input and output pins should be stable and correspond to the logic levels of the 'E' character that we have configured on the video RAM outputs.

Pin 11 should have the video latch clock and pin 1 should be LOW.

Why do you wave the white flag when we have a new lead to follow?

Dave
 
daver2 said:
Ah, if you slowly advance the video you have an almost page of E characters but with a band of none E characters moving across the page.

Can you scope the pins of F9 please. The data input and output pins should be stable and correspond to the logic levels of the 'E' character that we have configured on the video RAM outputs.

Pin 11 should have the video latch clock and pin 1 should be LOW.

Why do you wave the white flag when we have a new lead to follow?

Dave
Click to expand...
I will do these test tomorrow morning...have a good evening guys! Thanks so much for your help!
 
F9:

pin 3: H
pin 18: L
pin 4: H
pin 17: L
pin 7: L
pin 14: L
pin 8: H
pin 13: L

pin 2: H
pin 19: L
pin 5: H
pin 16: L
pin 6: L
pin 15: L
pin 9: L
pin 12: L

On scope signals are stable high or low... :(
 
Excellent work.

Can you now check the following pins of the character generator (F10) using your oscilloscope:

5, 4, 3, 2, 1, 23, 22, 19, 18, 20 and 21.

These should all be static logic levels as well. I want to know if they are HIGH, LOW or dynamic.

Dave
 
Excellent work.

I haven't finished with F10 yet, so we will come back to it presently.

Can you check E11 pin 2 for a stable 8 MHz clock.

Can you also check E11 pin 1 for a stable signal. Can you report the frequency you observe.

Dave
 
E11 pin2: I AM DESPERATE!!!
as soon as I touch pin 2 of e11 with scope probe, I hear a strange buzz and the screen fills with noise!!
 
No need to be desparate...

That should be an 8 MHz clock. It should be there to get anything at all on the screen...

Try with your probe on the x10 setting. You will have to change your oscilloscope Y scaling by a factor of 10 as a result. See if that makes any difference to your measurement.

Dave
 
Ok this is signal when i probe E2 pin 11....if i touch pin with probe, i can see some more noise on screen...
 
I would stop doing that!

I suspect your oscilloscope is loading that pin up too much. Not sure why just yet. Let me think about where to measure that by looking at the schematics. If I ask you to measure this (or a similar pin) again, just 'dab' the oscilloscope probe on for a very short period of time. Too long could damage the monitor.

However, one thing I did notice from your screen, is a perfect load of 'E' characters. You have waited for the logic to warm up BEFORE taking all of the above measurements haven't you? If not, all of the previous measurements are invalid. We are trying to measure things when the display is incorrect...

Dave
 
daver2 said:
I would stop doing that!

I suspect your oscilloscope is loading that pin up too much. Not sure why just yet. Let me think about where to measure that by looking at the schematics. If I ask you to measure this (or a similar pin) again, just 'dab' the oscilloscope probe on for a very short period of time. Too long could damage the monitor.

However, one thing I did notice from your screen, is a perfect load of 'E' characters. You have waited for the logic to warm up BEFORE taking all of the above measurements haven't you? If not, all of the previous measurements are invalid. We are trying to measure things when the display is incorrect...

Dave
Click to expand...
Yes sure, the previous measurements are made when display is incorrect....in this last case i measured also with correct display but i have always same noise!
 
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