Hi Applefritter, this is my first thread in this fine forum.
I have an Apple III bought on ebay. It was sold as defect, it was dead on arrival. Model A3S1 no 57901 motherboard 820-0043-00E 5V memory board, american keyboard. The power supply was dead. Defect KB lamp. A defect trace on the MB so no voltage to the KB. After replacing with a new PSU, new KB lamp and repair of the Mb the Apple III is partially working.
There is a videoproblem, there are vertical lines on the display. Sound is ok . Floppy drive is OK. There is no text.
Reset key is working. When I test Ctrl-OpenApple-Reset key sequence its probably starting in monitor mode. But no text
After reparing the AIII it is booting ( Apple III system utilities) and the keyboard is working, but no text .
I have reseated all IC, replaced the RAM on the 5V memory board with new RAMs but the same result.
According to Apple III service reference manual ( p 13.53) it can be defects in several IC on the motherboard. I have replaced the two 2114, switch positions of all LS374 and LS161 without any change.
The ROMs on the MB are not exactly the same number that’s printed on the MB. According to https://kb.pocnet.net/wiki/Apple_Chip-Bezeichnungen the ROMs installed on the MB have the same function except position G9 . The MB is marked with 341-0030 on G9, (Video elements/attributes generator) but the installed ROM is 342-0060. It looks like a EPROM ( D2716) with a label saying 342-0060. Not original Apple.
There are a lot of threads about Apple ii character generator in this forum .
Also about 2114 static RAM in A3
My question is if the G9 ROM is the problem. I have not found any information about 342-0060. I have read someware that its posible to try with ROMs from Apple IIE in Apple III . I have a working A IIE but I have not tried that. Is it better to burn a new EPROM 341-0030 from a ROM image?
Thanks for any help.