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Bad Cbm 3008 PET, time to desperation again?

Why are you replacing components again without testing signals first?

Most of this is probably a waste of time...

Notice the letters "NP" on the capacitors. This stands for "non polarised". Replacing them with polarised electrolytic capacitors may result in premature failure and damage (either to the replacement component, the monitor or both).

Use your oscilloscope, the monitor schematics and the expected oscilloscope traces from the Commodore Monitor manuals to identify where the faults are within the monitor first.

Dave
 
That number doesn't seem to appear in the Zimmers archive documents.

You are going to have to do it the hard way - print out the PCB layouts from the Zimmers website and 'eyeball them' with your PCB.

You can fix something without the schematic and PCB layout - but it will take a darn side less time with them!

Dave
 
daver2 said:
That number doesn't seem to appear in the Zimmers archive documents.

You are going to have to do it the hard way - print out the PCB layouts from the Zimmers website and 'eyeball them' with your PCB.

You can fix something without the schematic and PCB layout - but it will take a darn side less time with them!

Dave
Click to expand...
However, I have changed almost all the electrolytic capacitors, the screen is no longer squashed but the writing on the basic is not stable... they dance a little..
 
I assume you have changed the main power supply smoothing capacitor on the output of the monitor voltage regulator?

What does the ripple and noise look like on the output of the voltage regulator? Measure this with your oscilloscope set to AC coupling.

By 'dance', do you mean that the display is possibly affected by the magnetic field from the transformer (possibly)?

Dave
 
>>> where is this cap please?

On the monitor PCB. But I don't know which one it is as I don't know which monitor PCB (and schematic) you have...

>>> yes possibly but i am not sure...

Does the 'dancing' get less if you reorientate the monitor with respect to the transformer? I.e. turn the monitor via 90 degrees.

Perhaps post a video of the monitor screen?

Dave
 
daver2 said:
Does the 'dancing' get less if you reorientate the monitor with respect to the transformer? I.e. turn the monitor via 90 degrees.
Click to expand...
no...it is the same...

I suspect that this is the correct schematic....
 
Maybe I solved it!
I sprayed some electrical contact cleaner on a small potentiometer, turned the potentiometer slightly left and right and now the screen seems very stable.
 
daver2 said:
>>> where is this cap please?

On the monitor PCB. But I don't know which one it is as I don't know which monitor PCB (and schematic) you have...

>>> yes possibly but i am not sure...

Does the 'dancing' get less if you reorientate the monitor with respect to the transformer? I.e. turn the monitor via 90 degrees.

Perhaps post a video of the monitor screen?

Dave
Click to expand...
Layout seems to match the original 2001 video https://www.zimmers.net/anonftp/pub/cbm/schematics/computers/pet/2001/video-layout.gif
 
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