Atari 400 power on successfully only now and then

[Atari 400 power on successfully only now and then]

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.

[Another 800 with a whacking price on Ebay]

4 hours ago, TGB1718 said:

 

Shockingly it says 2 available "3 SOLD"

 

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

[Calling All 800s!]

19 hours ago, Scooter83 said:

That's a really nice looking one.  Any info on the chip dates inside?

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.

[Atari 400 power on successfully only now and then]

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.

[Atari 800 video problem]

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!

[Atari 800 video problem]

2 hours ago, Rybags said:

Can you try some other stuff - like maybe GR. 7 : C. 1 : PL. 0,0 : DR. 100,100

 

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.

[Atari 800 video problem]

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.

[Atari 800 video problem]

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

[Calling All 800s!]

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