• Please review our updated Terms and Rules here

Cbm 2001 Pet strange boot

Desperado

Veteran Member
Joined
Nov 25, 2017
Messages
6,786
Hi guys, i'm always desperate because without your help I can never fix anything :(
I have this 2001 Pet (no crtc ic) with with a problem that has never happened to me...
When i turn on, i can see for one second a random chars screen which immediately collapses into a horizontal line!
Do you think the cause is in the monitor? Dave i know, you ' ll hate me ;)
Thanks so much!

 
Your first guess is the same as mine...

I would guess the problem is somewhere in the vertical drive of the monitor.

However, to be clear that it is, check the video, horizontal and vertical drive signals from the PET main logic board (with the monitor disconnected to prevent damage) to ensure that the vertical drive signal is not disappearing.

Dave
 
Your first guess is the same as mine...

I would guess the problem is somewhere in the vertical drive of the monitor.

However, to be clear that it is, check the video, horizontal and vertical drive signals from the PET main logic board (with the monitor disconnected to prevent damage) to ensure that the vertical drive signal is not disappearing.

Dave
Hi Dave, J7 connector?
Thanks :)
 
I saw that J7 pin3 is directly connected with G10 pin 11... unfortunately also in this pin i have no square wave :(


and

 
You have proven that it isn’t the copper track then.

If G10/11 is not oscillating, what is going into the gate at G10/12 and G10/13 then?

Hang on, have we both got the correct schematic? Is your machine a 2001-N?

Dave
 
Last edited:
You have proven that it isn’t the copper track then.

If G8/11 is not oscillating, what is going into the gate at G8/12 and G8/13 then?

Hang on, have we both got the correct schematic?

Dave
G8 or G10 Dave?
 
You have a 2001-N then not a 2001?

Check H8 pins 12, 2, 3, 5 and 6. That should tell us everything we need to know...

Dave
 
You have a 2001-N then not a 2001?

Check H8 pins 12, 2, 3, 5 and 6. That should tell us everything we need to know...

Dave
Ok so:
H8
PIN 2: 0,16V no wave
PIN 3: 4,7V no wave
PIN 5: 4,7V no wave
PIN 6: 0,16V no wave
PIN 12: 0,24V no wave

This is a disaster :(
 
I have this board:
 

Attachments

  • Schermata 2022-04-24 alle 16.11.17.jpg
    Schermata 2022-04-24 alle 16.11.17.jpg
    176.4 KB · Views: 18
It’s NOT a disaster!

It is telling me (and it should be you if you put your observed logic levels onto the pins of H8 on the schematic) that H8 is OK and the problem is the missing clock on H8/12 (called NEXT).

This is sourced from G8/9, so the next set of measurements are G8 pins 8, 9, 11, 12 and 13.

Dave
 
G8

pin8: 3,9 V no wave
pin9: 0,24V no wave
pin11: 1V and wave
pin12: 0,24V no wave
pin13: 3V and wave
 
That flip-flop gate in G8 looks OK, but we are missing the signal on pin 12.

Are you following this on the schematics?

This takes us back to schematic sheet 7 and gate G1 pin 3.

I would check G1/1, H5/9 and H5/10 to see what is missing, and work back from there...

Dave
 
G1 PIN1: 3,7V square wave
H5 PIN9: 4,7V and pulse signal
H5 PIN10: 4,3 and pulse signak
 
Vertical collapse... I think you need Hugo! What diagnostic tools do you have... how competent do you feel?

Assuming that this is actually a monitor issue...


If you have the tools then firstly inspect C9 and then then diode junctions of Q8... Q10.

We have already proven that the monitor is not getting the vertical drive signal from the PET logic board - hence the horizontal line...

Dave
 
Just been out for the evening.

Those signals look OK.

Can you just move forwards now and check G1 pins 1, 2 and 3.

Dave
 
Back
Top