CBM PET 3032 STRANGE BOOT

[Nivag Swerdna]

It may be worth you reading the group of posts starting at #284. This was an interesting test we did with the video RAM and CPU removed and 'forcing' specific characters to be displayed on the screen. See if the results align with (or disagree with) your thinking.

I like those.... looking back now the ? < etc sort of tests are in the same range as the working ones? i.e. below 0x3F? Might be worth repeating and going higher? Aim for a Z perhaps?

 

[daver2]

Good call.

Dave

 

[Desperado]

I am desperate! What can i do now please?

 

[daver2]

We just told you in post #521...

Can you make sense of it?

Dave

 

[Desperado]

We just told you in post #521...

Can you make sense of it?

Dave

Unfortunately i can't understand what i do

 

[Desperado]

We just told you in post #521...

Can you make sense of it?

Dave

Time to little wires again o can i try to change F9?

 

[daver2]

No, don't change F9!

Remove the two video RAM chips and get your eight little wires out.

Also remove the CPU.

We need to wire the four (4) data lines from each video RAM socket (making eight pins/wires in total) to form one of the uppercase letters 'A' through 'Z'.

I am in town at the moment, so I will post the pattern of 0V and +5V links we require when I get home.

In the meantime, see if you can work it out for yourself - but don't actually insert the wires just yet until I have reviwed your thoughts. Think PETSCII not ASCII...

Dave

 

[Desperado]

Also remove the CPU.

Cpu is now inserted on Nivag s' board....must i remove the diagnostic board with cpu?

 

[daver2]

No, just the CPU.

Dave

 

[daver2]

This should give you a capital letter 'E':

F7 pin 11 = L.
F7 pin 12 = H.
F7 pin 13 = L.
F7 pin 14 = L.

F8 pin 11 = L.
F8 pin 12 = H.
F8 pin 13 = L.
F8 pin 14 = H.

You will find L (0V) on pin 9.
You will find H (+5V) on pin 18.

You should get a screenfull of letter 'E' - but are they 'stable' or not?

Dave

 

[Desperado]

You should get a screenfull of letter 'E' - but are they 'stable' or not?

So need waiting for some minutes, right? Thanks!

 

[daver2]

Yes, you should get the EEEEEs filling the screen (to let us know you have wired things up correctly) and then wait for everything to warm up...

Dave

 

[Desperado]

Yes, now i see screen full of "E"....im waiting to warm up!

 

[Desperado]

I am desperate!!!

 

[daver2]

Why are you desparate?

This is giving us data points to the problem (like a trail of breadcrumbs).

We know now that the problem we are hunting for is either after the video RAM or is something to do with the video timing logic.

Can you oscilloscope the HDRIVE and VDRIVE signals and see what the frequency is and whether they are stable or not. This looks like VDRIVE is misbehaving - and may also account for why your previous oscilloscope trace of the video signal wasn't stable.

This board is a fighter isn't it!

Dave

 

[Desperado]

This is horizontal drive
View attachment IMG_20230317_182415.jpg

 

[Desperado]

This is vertical

 

[Desperado]

This board is a fighter isn't it!

This board it's been the most difficult job for me But thanks to her, I had the opportunity to buy a Nivag card!

 

[daver2]

But are the signals constant/stable like I asked you (when you have the strange image on the screen)?

Dave

 

[Desperado]

But are the signals constant/stable like I asked you (when you have the strange image on the screen)?

Dave

yes these are the signals when i have strange image on screen