CBM 8032 - What does the startup chirp actually mean?

[MikeP]

Hi Daver2 and Dave_M,

I have completed the surgery on the motherboard, removed the 6545-1, put in a socket and a new Motorola 6845P. I think we have some progress... For the first time I see something on the screen. Unfortunately, just a single line (See attached). The line was very bright, so I switched it off quickly.

Any thoughts?
Thanks
MikePET_has_a_line.jpg

[MikeP]

sorry, I forgot to mention that I am now seeing activity on J7 on the Video, Horizontal drive and vertical drive pins (so, the new CRTC seems to be working) - so, the fact that the monitor only displays a single horizontal line - does this mean that there is a problem on the CRT board?

[dave_m]

No 60 Hz pulse Vertical sync on UB13 pin 40 and J7 pin 3?

[MikeP]

Hi Dave_M,

This is what I see on Pin 40 of UB13 and J7 Pin3PET-CRTC_Pin40.png

[dave_m]

Hi Dave_M,

This is what I see on Pin 40 of UB13 and J7 Pin3PET-CRTC_Pin40.png

That is noise. The signal should be 60 Hz frequency (16.67 mS period). There should be a skinny negative pulse every 16.67 mS. Use a negative edge sync with a time base of about 5 mS/ division. The vertical should be about 2 V/div with a 1X probe or .2V/div with a 10X probe.

See http://www.zimmers.net/anonftp/pub/c.../321450-03.gif , photo3.

[daver2]

One step forwards ...

+1 for Dave’s post.

Dave

[MikeP]

Hi Dave_M and Daver2,

I have made several attempts to find something on the Vertical Sync pin, but, I am 99% sure it is just stuck at -5Volts with only +- 200mVolts of noise.

Mike

[daver2]

Back in post #42 you stated that you saw activity on the H, V and Video pins of J7?

In post #47 you state ‘stuck at -5V’. Do you mean +5V?

I am not doubting you, but can we make sure that we are not getting ourselves confused before we move on.

Dave_m suggested an oscilloscope setting to measure the V DRIVE back in post #45. Have you used those settings?

Do you have a logic probe? if so, can you probe the H, V and Video pins of J7 (with no monitor connected) fir signs of activity please and report if the pins are High, Low or Pulsing please.

I am suspecting a monitor fault, but (for this to be true) we need to see all 3 signals as correct from the PET! I would just like to make it 100% that we don’t have an operational V Drive signal...

Cheers,

Dave

[dave_m]

I would just like to make it 100% that we don’t have an operational V Drive signal...

Yes, it is important to know the proper voltage on the Vertical drive signal. If we have a noisy LOW level signal then we may suspect a shorted signal. +/- 200 mV is a lot of noise. Do you see this on other signals?

Also let's keep the J7 connector disconnected from the monitor until the H and V sync signals are correct to protect the CRT. This is a difficult problem. Hang in there.
-dave_m

[MikeP]

Thanks for the encouragement. Attached is the output from Pin 3 (Vertical Drive) of J7. (I have kept the monitor disconnected). I think the scope is setup as Dave_M requested. (I see a square wave on the Video pin and Horizontal drive).

SDS00006.png