Static when powered on

[SlowCoder]

When powered on, shows static.

Have checked ...

channel switch

swapped coax cable

Verified good power supply

Checked power switch using voltmeter.

Adjusted color POT.

 

I'm not sure what I should look for as far as corrosion on the silver box on lower right. I don't see anything outstanding such as leakage or discoloration other then a little rust.

 

I see what appears to be a POT in the silver box, but I don't know what it does. Can someone explain?

 

What else can I check?

[BigO]

The static changes from what's there when the console is powered off?

[tetrode kink]

Yeah, BigO, just what I was thinking. SC, do you mean no change in "static" from when the power is off? Or do you mean it shows a black screen with static? Or a game screen, where you can see the game is running, but a really static-y picture? Random colors with static? What happens to the sound?

 

A pic might help, if it's hard to describe.

 

-tet

[SlowCoder]

Pure static. No change in picture on TV when console is turned on. This is not a power supply issue, as I'm using known good supplies. Power is getting at least through the power switch.

[Trinity]

now test the power switch then the voltage regulator.

Edited August 13, 2010 by Trinity

[SlowCoder]

now test the power switch then the voltage regulator.

I already verified the power switch is working properly, as power is flowing through it. Where is the voltage regulator?

 

Never mind ... I found the voltage regulator. I'll check that out tonight. I've got another board I can swap with if that's the case. I'm assuming the white paste under it is heat sink paste? If so, I've got more I can apply.

Edited August 13, 2010 by SlowCoder

[BigO]

now test the power switch then the voltage regulator.

I already verified the power switch is working properly, as power is flowing through it. Where is the voltage regulator?

 

Never mind ... I found the voltage regulator. I'll check that out tonight. I've got another board I can swap with if that's the case. I'm assuming the white paste under it is heat sink paste? If so, I've got more I can apply.

I wouldn't bother swapping from a second board if you have a Radio Shack or similar store nearby. That 5 volt regulator is a cheap, readily available part.

Edited August 13, 2010 by BigO

[SlowCoder]

Ok, I bought a voltage regulator, but I don't think I needed it. I tested the current one, and it does get warm when on for a while. Also, using a voltmeter, I determined it is properly dropping voltage from the 12v supplied to 5v.

 

Next step?

Edited August 13, 2010 by SlowCoder

[A.J. Franzman]

First, the silver box on the lower right of the motherboard or switchboard (depending on console model) is the RF modulator. The adjustable part you can see through holes in the sides of that box is the ferrite core of an adjustable choke, and I advise that you don't mess with it at this time.

 

The symptom you describe (no change to snowy TV picture when powering console on) is in my experience usually due to a bad wall wart or voltage regulator. However, since you say you tested the regulator and saw 5 volts on the output, my next questions are: exactly how did you connect the VCS to the TV? Have you tried TV channels 2, 3 and 4, each with the console's channel switch in both positions?

 

If the console is hooked up properly and you've tried all of the above channel combinations, the next likely suspects are the RF modulator and the TIA IC. The modulator has a couple of discrete transistors, some passive components, and an IC (really a transistor array) inside, and it can be a real pain to open up. But I've had to replace the IC transistor array in a couple of units, so I know they have a tendency to fail. However, swapping TIA chips is a lot easier, so if you have one available, try that first.

[tetrode kink]

...If the console is hooked up properly and you've tried all of the above channel combinations, the next likely suspects are the RF modulator and the TIA IC...

But if it were only a bad TIA, wouldn't the RF modulator still generate a carrier? At least produce some change on the screen between power-off and power-on?

 

-tet

[A.J. Franzman]

Hmm, probably so, but what effect would a TV display if receiving an unmodulated carrier? Solid black screen? In that case, disregard the bad TIA option -- my mistake.

[SlowCoder]

...If the console is hooked up properly and you've tried all of the above channel combinations, the next likely suspects are the RF modulator and the TIA IC...

But if it were only a bad TIA, wouldn't the RF modulator still generate a carrier? At least produce some change on the screen between power-off and power-on?

 

That was my thought too. I had already tried a different series of chips on it without success. For the time being, however, I have pulled the chips from this board and placed them in another Atari that was down. That atari now works, so it definitely wasn't the chips. One day I might attempt revival of this board and replace the RF modulator.