800 hum

[russg]

Got one of my 800s out. It booted fine. When I load a game, or even do some graphics 8 from BASIC, it hums,

pretty loudly.

Since the hum seems to be when graphics are being displayed, I'm thinking Antic or GTIA. I have some

test modules and chips. Any ideas what may be causing the hum? If I hit Reset and exit the game to

DOS, the hum quits.

[atariksi]

Got one of my 800s out. It booted fine. When I load a game, or even do some graphics 8 from BASIC, it hums,

pretty loudly.

Since the hum seems to be when graphics are being displayed, I'm thinking Antic or GTIA. I have some

test modules and chips. Any ideas what may be causing the hum? If I hit Reset and exit the game to

DOS, the hum quits.

 

Interference of video with audio line.

[Rybags]

Check your TV tuning if it's via RF.

 

POKE 77,128 and let it cycle through the colours - attract mode is good for generating weird sounds if the TV isn't tuned properly.

 

Probably a good idea to check that the power supply isn't going bad. Check the +5V to GND on the SIO port with a multimeter - since the 800 does power conversion both in the PSU and the power supply board internally, that's 2 potential sources for overvoltage, which can potentially kill a machine.

[Justin Payne]

Maybe it hums because it doesn't know the lyrics to the song.

 

Sorry, I couldn't resist.

 

...but so message wasn't chock full of gut busting humor, I did a little Googling and I'd have to go Rybags suggestion. It appears hum can come from transformers in the power supply. The other option is trying to plug it into a different display and do the color cycle thing.

Also, might also be the video switch that's plugged into the TV, but I would say the chances of this are probably slim.

 

I'm not sure if that helps you any, but at least the joke might cheer you up a bit.

[Rybags]

Note that "hum from power supplies" doesn't necessarily mean the hum you might get from the PS itself.

 

Overvolting Ataris often show the symptom of unwanted audio through the TV - one I bought with a dodgy PS did it and it stopped as soon as I put it on my good supply.

[OldAtarian]

Have you tried passing your RF cable through a ferrite core?

Edited October 2, 2010 by OldAtarian

[russg]

Maybe it hums because it doesn't know the lyrics to the song.

 

Sorry, I couldn't resist.

 

A good one.

 

...but so message wasn't chock full of gut busting humor, I did a little Googling and I'd have to go Rybags suggestion. It appears hum can come from transformers in the power supply. The other option is trying to plug it into a different display and do the color cycle thing.

Also, might also be the video switch that's plugged into the TV, but I would say the chances of this are probably slim.

 

I'm not sure if that helps you any, but at least the joke might cheer you up a bit.

Thanks to those who responded.

The RF cable thru ferrite core. The 800 in question has a ferrite core on the RF cable inside the case.

I'm using the composite monitor port. I believe I removed the RF cable on one of my 800s as it is

in the way and I never use it.

I made progress. I substituted the power supply/RF board and that stopped the hum.

Now, I tried a burn in and after about one hour, the computer froze up, but it did pretty good just booting

and playing Sargon III.

I don't know what caused the crashes, probably heat related, as it takes an hour to happen.

The computer should go overnight without locking up.

I don't know how to service the hum power supply board. It has about four really large capacitors. I understand

old capacitors can fail, and they are probably forty years old. It also has diodes of course, and a rectifier

I recognize. I have two complete 800s and some extra ROM boards and a spare motherboard, I used my spare

RF/PS board for this.

These 800s are built like tanks.

Thanks

[AtariNerd]

Didn't the early 800's have problems with the memory boards overheating as well, because of the cases around the boards? At least I've heard that that can also cause a similar buzzing problem. The solution was to of course remove the cases and plug the boards back in. It's unlikely to be the cause, but just another oddball suggestion.

[russg]

Well, another day. I believe the crashing was a personality board problem. I tried to fix it by substituting

Antic, GTIA and CPU, but that didn't work, still had crash. So, I put in a spare personality board and

am going to see if it will survive overnite.

Thanks for listening.

I have two 800s, one is much lighter in color than the other. Did Atari make different color 800s?

[atariksi]

Well, another day. I believe the crashing was a personality board problem. I tried to fix it by substituting

Antic, GTIA and CPU, but that didn't work, still had crash. So, I put in a spare personality board and

am going to see if it will survive overnite.

Thanks for listening.

I have two 800s, one is much lighter in color than the other. Did Atari make different color 800s?

 

Could be more yellowing on one unit which produces sort of sun-tan look.

[russg]

Well, another day. I believe the crashing was a personality board problem. I tried to fix it by substituting

Antic, GTIA and CPU, but that didn't work, still had crash. So, I put in a spare personality board and

am going to see if it will survive overnite.

Thanks for listening.

I have two 800s, one is much lighter in color than the other. Did Atari make different color 800s?

It is done. Replaced the personality board and let run Pacman overnite and no lockup.

Thanks everyone who responded.