There's probably a bad chip somewhere in the video refresh circuit as daver2 indicated. We will find it. The fact you get a good raster scan says the most difficult circuitry is working. Just go slow and sure during troubleshooting. With the RAM/ROM replacement board and other gadgets you have, we should be able to get this PET on the air.
Time to break out the ancient oscilloscope.
Any suggestions on where to start? UD2,UD3 and UD4 I can't seem to locate on the schematics, as for the expansion boards I have them all installed now (replacement Video Rom, Video Ram and the Tyemouth - set to replace everything system Rom and Ram) I have also removed all original ROM chips as well as all original system ram except for the one in J 1-2 and I 1-2 was that a good course of action?
Yes I agree with that remark.
According to CPU-World:
What do you mean? It's bandwidth is 200 KHz. It's as good as my old Dumont of 1950!
...
Sadly it seems as though it was thrown out in the last purge of the schools science department.... so I will need to replace it with something else.
As far as I am aware they are the same chip just a 6503 is a special part number for Apple, you know how Apple likes to be special ha ha ha, but the 6502 out of the pet worked fine in the mac.
Thanks Alan!
What are you thoughts on the https://www.amazon.ca/Hantek-Digita...72&sprefix=osc,aps,85&sr=8-15#customerReviews Hantek? it is 20mhz, Adrian Black did a review on them recently and said they where OK for most use, I am also thinking I can use this as part of my Computer Science course next year and the ability to display it on a computer screen to cast to a tv is handy, thoughts?Yes I agree with that remark.
The scope that would be most use fault finding is an Analog scope of at least 20MHz bandwidth. (You don't require math functions, USB interconnectivity---you want to see what is there and not have to worry about digital scope issues such as aliasing and sample rates).
One of the better compact reliable choices is the vintage Hitachi V-509 (it also has a delay timebase and is 50MHz rated) but these are harder to get (in good order) compared to the V-209, the 20MHz version. I would recommend then the V-209, like this:
Also get the manual for it:
Hitachi kindly put the schematic in the manual too. Though these oscilloscopes practically never require any repairs. Their features are being super compact, optional 12V operation, super bright trace with a 10kV CRT final anode voltage. A beautiful scope and its hard to imagine that you could get something so marvelous and so well made for the price they sell for nowadays. These make most USB scopes look like piles of junk.
Never buy a physically beaten up or cosmetically damaged looking vintage analog scope, likely it will have multiple issues. In that comparison it would be better to buy a wide bandwidth, at least 50 to 100MHz new digital scope, or you will spend a lot of time restoring and repairing the analog one.
Generic x 1 and x10 probes are available cheap on ebay.
One of my favorite analog scopes is the Tek 2465B. 400MHz rated. But it can do something quite amazing that no 400MHz rated digital scope can do.What do you mean? It's bandwidth is 200 KHz. It's as good as my old Dumont of 1950!