Commodore 3016 scrambled screen

[TheMatrix]

Yes, but i see the same with my other CBM3016 monitor.

 

[TheMatrix]

This is my working 3016 board with the 3032 monitor



i forgot the picture…

 

[daver2]

>>> Yes, but i see the same with my other CBM3016 monitor.

I understand what you are stating. But, as of yet, I have not seen a valid VDRIVE signal oscilloscope trace to substantiate that statement...

Dave

 

[TheMatrix]

I will continue tomorrow. See if I can get good signal with scope

 

[TheMatrix]

i think i first should buy a analog scope. I use digital. It's terrible. I used to work with analog , never had any problem getting the right signal

 

[daver2]

All you have to do is to slow down the timebase...

Dave

 

[TheMatrix]

All you have to do is to slow down the timebase...

Dave

And that's the problem. There is a function but i don't see a good signal.

 

[daver2]

Can you post a photograph or a video of the VDRIVE signal?

Dave

 

[TheMatrix]

 

[TheMatrix]

With adjusted time base ( what I can find)

 

[TheMatrix]

It’s really annoying

 

[daver2]

Well, I can't see any evidence of problems on the signals displayed on your oscilloscope.

I would go with a VDRIVE signal timebase even slower than post #169 though. We are not trying to actually see the detail, but the overall 'pattern' and then trying to see whether it is changing and causing the anomalies on the monitor.

The monitor display jitter looks quite pronounced now, so it should be easy to locate the issue...

Dave

 

[tsky]

It looks to me like the VDRIVE signal is exactly twice as fast as it should be. That could be one bit in a counter somewhere not working.

 

[daver2]

Good spot...

So he needs to look around G10 and H8 of schematic http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001N/320349-6.gif.

It is not that the signal is changing, it is just confusing the hell out of the monitor!

Dave

 

[TheMatrix]

This is the slowest I get.
H8 and G10 itself are ok. Checked it with retro chip tester and swapped with working machine

 

[daver2]

What you are telling me is that the chips work, not whether the input signal NEXT is correct or that the PCB tracks between the pins of the IC gates are intact.

Please use your oscilloscope on the pins of the ICs on the schematic and state whether a signal is HIGH, LOW or what the frequency is if it is oscillating.

Dave

 

[TheMatrix]

Signals on H8
P1
P2 P3P4

P5 P6P8P9

 

[TheMatrix]

P10 P11P12

 

[TheMatrix]

Checking G10 and pcb tracks tommorow.

 

[Hugo Holden]

If the V drive signal is twice the rate it should be, this would correspond to the V scan amplitude being half the height, because the peak scan current in the yoke is proportional to the time the V drive pulse is high. Interesting that it was intermittent though, being the correct frequency at times and not at others. Though TTL IC's can go intermittent, I have had a few.

Sometimes it is hard to see the time and amplitude scale on the photos/videos, so it is always better to state the the volts/cm and the time/cm settings for the recordings as it helps a lot for others to spot defects in the recordings.