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That's looking pretty good from where I'm standing! Good job!

G3 pin 1 is nSEL0 G3 pin 2 is nSEL1 Considering G3's gate to be an OR with inverting inputs (an exercise for the reader as to why that works)... it's inputs become SEL0 OR SEL1.... so it's output should be high when either SEL0 or SEL1 were active. I would therefore expect the ON period of pin...

BTW... the reason I suggest working on your dual trace skills is.... you'll get a lot of support from Hugo et al. as you try.

The difference between 4K working and 8K working is really only nSEL0 and nSEL1... this can manifest itself two ways.... either nSEL0 and/or nSEL1 isn't getting to pin 19 of I3 and/or J5 or the buffer logic is wrong due to G3 (and possibly the buffers). Note that many of these devices are...

BTW we are obviously playing a bit fast and loose by poking random locations but in this case we will probably get away with it. If you are interested in how a PET really works then read... http://www.primrosebank.net/computers/pet/documents/The_Commodore_PET_revealed.pdf I remember reading it...

You really need to work on your dual trace skills... It would be nice to see the input and output of G3

Given you can get a Basic working but use onboard RAM you could write a program to POKE/PEEK a location at say 6K in a loop and then observe the Chip Selects.

Suspect G3 or poor connections.

That seems quite extreme.

Now seems the time to test your 6550s I also note the D checksum is still wrong now correct! D=5045 PS If you use the character ROM you had before... that would free up the OMNI ROM... which could be configured as a 4K ROM... replacing 2 bad ROMs... finally if you reconfigure the PETTESTER...

Just for the ROFLs... found this picture... This is a vintage 1980 ROM adapter from Skyles Electric Works.

My ROM replacements can do pairs as suggested... using exactly the decode logic you are talking about. It really depends on the aesthetics you are after... some people like only originals, some people like adapters, some people like every socket populated. My personal take, is that making...

That's a bit disappointing... I don't think that is the correct D answer... Maybe clean the legs and contact clean the sockets? Being Checksum-16 you can add 31FC+1E49=5045 BTW... These checksums are quite weak with respect to errors... It is a suggestion they are correct rather than a...

BTW... I think E85F is probably quite rare it... It is the original Basic 1 ROM with all the initial release bugs! My PET has the E7CB variant. A true collector would probably appreciate the bugs!

Assuming you have a typo you could populate H1, H2, H3 and H6. H2 and H6 form a pair so that might make the D checksum match daver2's documentation. Looks like the rest are dead... You need to go ROM shopping. Over to daver2 for RAM testing....

The way that variant of PETTESTER works is that it creates a checksum for the E socket (which is H3) on the basis of the single device there... you can cycle your ROMs through there to get individual 2K checksums... rom-1-c000.901439-01.bin 0xe85f rom-1-c800.901439-05.bin 0xe4fe...

CA92 is the correct checksum for rom-1-e000.901439-03.bin which is currently in H3! Mark it as H3 and take it out and put it aside... move another ROM into H3 and repeat the test

@daver2 I believe the ROMs are also not in their correct locations? I cannot read most labels but I would expect a -013 to live in H2 not H6? A -016 does look correct in H4. I always found the numbering very confusing. I believe it would be 901439-01, 901439-02, 901439-03, 901439-04...

You must have a very dead ROM... remove some until it works... try and work out which causes it to get stuck.

I mean H1 and H2 and H3 and H4 and H5 and H6 and H7 (PETTESTER)! And take a photo of the screen!