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FYI Patched PETTESTER attached.... this is the version that can live in a Kernel ROM socket.

That could probably be arranged. Also, can we have an idea of your test equipment and experience... what do you have to hand? You can then be guided according to your experience.

Hi Well the good news is that for a moment you got some good behaviour! There probably is a FAQ somewhere but... Do the standard things first... check voltages at the voltage regulators... then as it was so close to working... remove the ROMs... maybe a sprinkle of contact cleaner and...

The W65C21N is plug replacement of NMOS 6521 and 6821 devices with current limiting resistors on outputs ports and TTL input thresholds.

The purists probably crave old unreliable MOS hardware but IMHO 6520s should be consigned to history. Even the most obvious replacement a 6821 is a bit obsolete. W65C21N6TPG-14 is the way to go; order yourself some stock! 6520 -> W65C21N6TPG-14 6522 -> W65C22N6TPG-14

FYI.... FDBF is the Checksum-16 of edit-2-n.901447-24.bin and DD67 is the Checksum-16 of 2K worth of 00s followed by PETTESTE2KF04.bin :) What would actually being tested would depend on if the ROMulan RAMulator were fitted and if it were which jumpers were in which positions... Assuming...

There are quite a few timings in this thread... Post in thread 'Commodore pet 2001-8 no video from logic board' https://forum.vcfed.org/index.php?threads/commodore-pet-2001-8-no-video-from-logic-board.1240575/post-1285323 Not sure how accurate my scope is in absolute terms but it might be...

The PETTESTER F800 variant... can checksum the editor ROM, if I remember correctly.... I would like to see it producing the correct numbers for the real editor ROM. (And in particular those numbers to not be changing) Alternatively use the VOSSI tester which does a simple sum on the editor ROM...

I recommend burning the PETTESTER variant I attached a few posts ago into a ROM, you may need to repeat the 2K twice if using a 4K ROM and put it into whatever socket covers F800. That way we at least eliminate the editor socket, although obvious we do still have Desperado's ROM choice and...

If @Desperado has the technology to make ROMs then we could always burn PETTESTER into a ROM using the version that works at F800; that would eliminate the editor socket for a while? PS I should really add that to my board if I ever make any more. There is an alternative, more primitive...

Perhaps we should checksum the PETTESTER ROM?

Following Gary C's instruction above... with 9AB & CD set to OFF... What do you see on the first screen? What checksums are you seeing? PS I realise this board has PETTESTE2KV04.bin i.e. the original editor ROM version so you will need E and F enabled and may have to move some ROMs around...

When we get to it... We can test the PET ROMs by using the PETTESTER but we need to do some jumper moving to not test the substituted ROMs! I will have to check but I think we also have the F800 version of PETTESTER so we can even test the E socket. But I take it we are not there yet. PS...

You can stick with PETTESTER but switch to PET RAM.... I believe you were testing substitute RAM?

This is very interesting... How does it relate to the damp finger test? Does the capacitance of a wet finger make that test unreliable? 140pF sounds like a very small number?

Which Logic Tester do you have? Only a very very fancy one would be able to detect a marginal part. Most cheap testers don't check voltage levels nor do they operate that a representative frequency; even worse some assume CMOS levels when testing TTL parts.

Probably better with no CPU? @daver2 ? You can remove the ROMulan RAMulator for now too... we really only care about video rendering for now.

Of course the purists would say that waving your finger at a circuit was a really mad idea. In fact the lack of an earthing strap would give some people cold sweats. :) I'm wondering what @Hugo Holden is thinking about the observed behaviour? The finger test is more suited to finding broken...

+1 That looks like a good next step. PS @daver2 Maybe some wires in the F10 socket?

It could be any of the ones mentioned in #591... I'm going to make a guess here... G11 Although I'm not sure earlier tests agreed with this I think that the correct character being rendered means that most of the early logic is OK... so I'm inclined towards G10, H10, G11... and I'm going to...