jimerson

I wonder if you may be measuring phantom voltages. I would connect appropriate-sized resistors to the DC power rails to simulate the normal computer load, then check the voltages under load.

If you click the "3 sold" link it shows the sale price was £2.67 haha ?

Not really, without opening it up again. I have this photo from before the ANTIC replacement. I hope it is readable. There is no date next to the copyright symbol on GTIA.

If you did any soldering to install the mods, I would double-check carefully for any solder bridges, blobs, stray wires or anything that could be jumpering between components or traces. Especially in places like J202 where it appears from the diagram 5v and 12v are in close proximity. I always use a strong magnifier or microscope when inspecting boards.

Thanks for all the excellent assistance, it works now. On the CPU I soldered a donor leg from a bad C=64 PLA. Replaced ANTIC chip and video is now good!

Ack, not anymore! I decided to pull the chips from the cpu board and look at the legs and sockets. I noticed some brown crud on pin 8 of the 6502B, and that leg broke off when I pulled the chip. Looks like pin 8 is Vcc so it was probably going to fail soon anyway. The board is very clean and all solder very shiny, looks almost brand new. I should have the replacement ANTIC and 6502B before Friday.

Thanks for all the advice. When I reseated the chips I just pried them up a bit then pushed them back down. I will remove them and check for damage and corrosion. If that doesn’t work I will order an Antic and swap it (I don’t have any spare parts). Will report back in a few days.

Hi, I got an older Atari 800 beige s/n 946-2193 a couple weeks ago. It came with the ROM and 16K module. Also Centipede, Star Raiders and Basic cartridges. The cartridges all seem to work and I can play the games but there is always "garbage" scrolling down behind the text characters. I believe this has a GTIA because "GRAPHICS 9" (and POKE 623,64) command shows a black screen. Also because I saw it when I re-seated all the chips I would appreciate any help troubleshooting this, I don't really know where to start. To make the photo below, I used GRAPHICS 2:PRINT#6;"ABCDEFG..." to enlarge the text to get a much better look at the problem. I hope the video works. Thanks, Jim 19-12-31 16-08-39 3085.mov

I got this a couple weeks ago, my first Atari 8-bit. The only problem is a slight video glitch. I will be asking for repair help in another thread