Atari 800 no video/ sound hum and pop issue.

[Scooter83]

Im trying to diagnose and repair that 800 i bought from one on the members on here. The one with the unbadged 800s. ( I bought the one with the engineering lab label on it.). Anywho. Ive gone though the usual suspects for no video ( not even getting the red screen he got when he made the post since he was having a video problem ).so kinda lost why now i cant even get that. Right now getting a black screen a little bit rolling sometimes and a hum/ popping sound from the TV.

Ive tried :

changing and clean the ram rom chips. ( the ROM had grease/petroleum jelly on the pins that went into the slot ). I cleaned it off and such . No luck.

Changed the ram chips. I need to get a spare 10K rom chip to try that.

Every chip on the board is socketed. so i tried to reseat all the chips.

checked for any bad resisters or capacitors, none that i could find bad swelling up or leaking.

Changed power supplies,

changed video cables.

nothing gives me at least the red screen that was shown in the picture.

Im thinking maybe if i get a different ROM chip maybe or it could be a bad CPU or video chip on the board that needs to be swapped out. Im not sure where else to go with it.

 

Just thinking from easy to hard how where do i go from here. Extra Rom CX801 is the next easy step before swapping chips off the board. but what else should i look for.

[_The Doctor__]

changed power supplies? or power supply side board?

did you check for 5v and 12v and no AC on those lines?

Edited September 24, 2018 by _The Doctor__

[Scooter83]

the power supplies themselves

[_The Doctor__]

Maybe I should be more clear.. the transformer pack to the wall or the power supply side board inside the 800

[Scooter83]

the external pack to the wall. I had 2 of them available and bounced back and forth and no change.i dont have a volt meter to check things so been trying to start simple and work towards the harder fixes

[_The Doctor__]

hum indicates ac inside the machine normally, and it cooks stuff.. You have to get inside the case and check the power board and it's voltages...

the rolling bars are called hum bars, you are getting hum bars and popping... Make sure to disconnect the power board from the main board then test the voltages dc volts then ac volts... then you can report back...

arm yourself with a sams as well as field service manual from Atarimania..

Edited September 24, 2018 by _The Doctor__

[Scooter83]

Well figured out where the issue laid. One of the chips on the cpu board was bad. I for now just swapped out the cpu board but as I get time I will swap out the chips and figure out which one was bad. But on the plus side the HCD eng dept system is up and running

[Scooter83]

Heres a few photos