2246 passes all diagnostics successfully. Readout character dots are misplaced and appear distorted. Any suggestions or help how to fix the problem would be greatly appreciated.
I'd check if the eprom is correctly set in the socket as well as firmware checksum.
Dear RVALENTE thank you for the reply. I reseated both eprom and rom chips that were on bases and check the chesksum of readout rom as well as system rom through diagnostics menu and they are ok. Unfortunately the problem remains. I can see a change in the misplaced readout dots (they move but still out of place) when I scroll the underline in the service menu window.
The interesting thing is that the distortion is not consistent, the letter E for example is distorted in different ways in different positions. I wonder if it's related to the position of the character on the screen? I've seen vaguely similar behavior in old arcade game boards when there was a stuck bit on the output of a character RAM.
James_s thanks for the comment.
The problem is so weird that I cannot figure out where to start from. Same characters are not only distorted differently on the same screen but they chance every time I move the underline with the up or down cursor. Initially I thought that the problem might come from PS capacitor noise since 33 years had past from the day I bought the scope from TEK as a student in the states. I recaped the PS but the character problem remained.
I want to remind you to replace ALL 17 ZM diodes. See thread below:
https://groups.io/g/TekScopes/message/170804?p=,,,20,0,0,0::relevance,,17+diodes,20,2,0,762879242245, 2246, and 2247 Tek scopes all use the same power supply.
I have a 2245A and a 2246.
Thanks for the tip. I ordered the diodes and the old ones will be replaced as proposed.
How does the readout circuit work on these things anyway? Does it just step through eprom addresses and output the data to a pair of DACs?