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Commodore 3016 scrambled screen

It should work!

It looks like the CPU is not correctly reading the PETTESTER EPROM.

That looks like the usual random power-up screen...

Dave
 
That is probably the machine code monitor (TIM) - so everything is not well with the world.

Why are we jumping all over the place with different tools? Why isn't my PETTESTER working when it has been. That is the first question to answer.

Dave
 
If i use you're pettester now i get the scrambled screen. If i replace pettester with original rom then i get the code monitor.
If i place the defect H4 back the pettester only show the first screen now (With all the characters) what's also in your manual.
It's really strange.
 
Can you post a photograph of the PETTESTER screen with the defective H4 please?

There is something that has happened between replacing H4.

I suspect firmware can write to the video RAM but not read correctly from it. This doesn't account for why the PETTESTER isn't working with a new H4 - other than a soldering issue on the H4 socket...

Dave
 
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What was wrong?

Of course, the memory test failed there - so you are not out of the woods yet...

It looks like the first bank of 16K data bit D1.

But I would give it a number of runs to see if you get consistent errors.

Check the HDRIVE and VDRIVE signals are consistent (with an oscilloscope) when the 'jumping' is happening. This would isolate the problem to the logic board or the monitor itself.

Dave
 
daver2 said:
What was wrong?

Of course, the memory test failed there - so you are not out of the woods yet...

It looks like the first bank of 16K data bit D1.

But I would give it a number of runs to see if you get consistent errors.

Check the HDRIVE and VDRIVE signals are consistent (with an oscilloscope) when the 'jumping' is happening. This would isolate the problem to the logic board or the monitor itself.

Dave
Click to expand...
I replaced ic's in it's socket. i think i was bad conection.

Also switch the mainboard to the 3016 monitor and the 'jumping' is also there, so it's on the mainboard.
After another test, there is no error.
I will continue this evening..
 
Welcome to the world of annoying vintage computers...

I can see the 'correct' text below there - but there is a 'mess' on the screen.

Is the image 'fixed' or is it varying? A video might help more.

Eventually, you will get to the bottom of all the problems - honest.

Dave
 
It looks like a character generator issue (or socket).

A [SPACE] character is turning out as a different character - but I can't tell what from the actual photograph you posted.

I suspect the other characters are turning out to be something else as well. Hence the screen looks right (as to be what is displayed) even though the characters themselves are in Romulan!

Dave
 
There is activity on the screen with Pettester. I see the same kind op activity as when it was correct. only now the screen looks like my last picture
I will check the character rom first (Socket)
 
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