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Cbm 2001 Pet strange boot

daver2 said:
No need to unsolder the sockets.

This is the test screen I was talking about previously that wasn't passing.

IF the video characters that are present on the screen are correct (to my PETTESTER documentation) THEN this indicates that the 6502 CPU can't (correctly) readback the characters that were put on the screen.

The issue is likely to be one (or more) of the data bus buffers between the CPU and the video RAM.

I am currently on my way out of the office now...

Dave
Click to expand...
ok Dave...so for now do I leave everything like this?
 
Ok, i have Nivag bodge pettester on Ud9, nothing on UD8 and original Edit rom on UD5.
 
For the avoidance of doubt... The UD9.bin shows checksums of all B but only the first 2K of F and E. The bodged UD9 should show the checksum of the first 2K of B and E and the whole of F. Hence the plan to put the editor ROM in the B socket.

Not sure why it gets stuck. I guess we are all getting a little desperate now 😅

Maybe the edit ROM is truly knackered.

Does the machine start with just bodge UD9 and all other ROMs removed?
 
I suspect the EDIT ROM is toast. This is why the machine probably doesn’t work with the Commodore ROMs in but does work with the PETTESTER ROM. The solution is to either (a) checksum the existing Commodore EDIT ROM as Nivag has suggested and (b) download and burn a new 2K EDIT ROM (if the checksum is incorrect).

The reason the test gets ‘stuck’ on the video RAM test screen is that the CPU is not reading the video RAM characters back correctly.

Are there pulses on E7 and E8 (74LS244) pins 1 and 19?

If pulses are present, E7 and/or E8 could be faulty. Try the piggyback test...

There are TWO different issues addressed in the ONE email.

Dave
 
As mentioned in post #378, i i already burned a 2716 eprom with edit rom file bin but i have always same screen stucked :(
 
So try the piggyback trick with E7 and E8 to see if that fixes the problem.

Try E7 first. Then try E8 second. Then try both E7 and E8 at the same time.

Dave
 
daver2 said:
So try the piggyback trick with E7 and E8 to see if that fixes the problem.

Try E7 first. Then try E8 second. Then try both E7 and E8 at the same time.

Dave
Click to expand...
Unfortunately i have only one 244 spare...i tryied to piggyback first on UE7 and after on UE8 but nothing changes... :(
I have always pulse on 1-19 pins and scrambled screen :(
 
daver2 said:
The reason the test gets ‘stuck’ on the video RAM test screen is that the CPU is not reading the video RAM characters back correctly.
Click to expand...
Ah... fair enough.

; Check that the first 1K of screen memory has taken the value that has been written.
; If not - keep looping. If it has, perform a delay and move on to the next test.
Click to expand...

I won't complicate by bodging again.

It's interesting that it fails to read back what it writes... the screen looks OK so it must be a problem with reading not writing.... that's a mystery.
 
I have seen this exact same fault before. It was the read halves of the buffers that were faulty.

>>> scrambled screen

You don't have a scrambled screen, the screen is correct for the test being performed. It is just that the diagnostics have detected a fault that you can't physically see. If you had a better oscilloscope you could simply test the buffers in circuit and find out exactly what was faulty.

>>> Maybe must i reburn correct pettester bin file??

The PETTESTER is showing you a fault. It is asking you to fix it!

Dave
 
daver2 said:
I have seen this exact same fault before. It was the read halves of the buffers that were faulty.

>>> scrambled screen

You don't have a scrambled screen, the screen is correct for the test being performed. It is just that the diagnostics have detected a fault that you can't physically see. If you had a better oscilloscope you could simply test the buffers in circuit and find out exactly what was faulty.

>>> Maybe must i reburn correct pettester bin file??

The PETTESTER is showing you a fault. It is asking you to fix it!

Dave
Click to expand...
Ok Dave so i think that the best option for me it's to buy the new 244 ics, right?
 
Yep. There are two further buffers upstream, but these are used by the DRAM aswell and we have already proven that the DRAM works (haven't we?).

I am not sure how we did that without MY hacked PETTESTER code that sits in the EDIT ROM socket though...

I suspect we are all getting confused with all of the different version of PETTESTER floating around and no clear view of which variant of the PETTESTER was used for which tests...

Dave
 
daver2 said:
Yep. There are two further buffers upstream, but these are used by the DRAM aswell and we have already proven that the DRAM works (haven't we?).

I am not sure how we did that without MY hacked PETTESTER code that sits in the EDIT ROM socket though...

I suspect we are all getting confused with all of the different version of PETTESTER floating around and no clear view of which variant of the PETTESTER was used for which tests...

Dave
Click to expand...
Yes you have reason! Can i burn a standard pettester version and use always this?
 
You should be able to.

We have proven that the Kernal ROM works ok, as the checksum matches what we expect.

If my PETTESTER doesn’t work in a 2716 in the EDIT ROM socket then you have either burnt it incorrectly, or there is something wrong with the decoding of the EDIT ROM or the EDIT ROM socket is potentially faulty.

In any case, the PET won’t work at all without the EDIT ROM - so it has to work!

Dave
 
daver2 said:
You should be able to.

We have proven that the Kernal ROM works ok, as the checksum matches what we expect.

If my PETTESTER doesn’t work in a 2716 in the EDIT ROM socket then you have either burnt it incorrectly, or there is something wrong with the decoding of the EDIT ROM or the EDIT ROM socket is potentially faulty.

In any case, the PET won’t work at all without the EDIT ROM - so it has to work!

Dave
Click to expand...
Ok Dave, so i burn your 2k PETTESTERV4.Bin in 2716 eprom and after i put this on Ud8 socket, correct?
 
daver2 said:
I suspect we are all getting confused with all of the different version of PETTESTER floating around and no clear view of which variant of the PETTESTER was used for which tests...
Click to expand...

I believe the PETTESTER didn't work in the Edit ROM slot before which is how we got to this point.... either that or I was just trying to make your life more interesting.
 
Nivag Swerdna said:
I believe the PETTESTER didn't work in the Edit ROM slot before which is how we got to this point.... either that or I was just trying to make your life more interesting.
Click to expand...
Mmm....maybe you have reason Nivag...but at this point i want to try again....
Cross my fingers :)
 
Ok, i burned original Pettester on 2716 eprom and i fitted on Ud8...now seems working but i have always this screen in picture...
With Nivag pettester version on Ud9 instead I could also see the next page with the ram and rom test ... Why???
 

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