black and white picture with static noise on a Jr

[jarreboum]

Hi there, I'm having some problems with my 2600Jr. I had been working fine when I got it, but after a while, and after changing games, the console started to randomly display a snowy black and white picture with static noise coming off the TV speakers. Sometimes unplugging the power cord and turning the power switch on for a few seconds did the trick to bring back the colours, but now it doesn't do that any more: now when I turn the console on, the pictures very briefly appears in colours but quickly switch to black and white with noise. The games are otherwise playable.

 

Being able to have a brief normal picture after the console is fully discharged made me believe that it may be a capacitor problem. But which one? I tried changing the big 2200µF 16V one, but that didn't help. It's quite possible that the "new" capacitors I used could be bad too, I've had trouble sourcing them. I haven't touched any other cap in the machine, there are lots of them all over the place. None look bad, but I don't have the eye for it.

 

I tried installing the Tim's RGB mod, thinking it could be something in the RF modulator, but I couldn't get an image out of the mod. my problem may be interfering with whatever the mod does to output RGB.I've completely uninstalled the board for now. I also installed his new linear voltage regulator, which I'm still using.

 

What could be the problem here?

Edited April 9, 2018 by jarreboum

[Electric-Dreams]

Hi,

 

Maybe you can try another power adapter ?

[+save2600]

Sounds like a dirty or bad connection out of the RF out to me. Or he's using a modern flat screen that doesn't sync well to the 2600.

[Electric-Dreams]

An old thread about same issue here, worth reading i guess :

http://atariage.com/forums/topic/199541-atari-2600-4-switcher-intermittant-fuzzy-reception/?&p=2547333&hl=+fuzzy%20+reception

[jarreboum]

I'm using a CRT TV. The setup hasn't changed at all between when it worked and when it stopped working. The degradation was very progressive, at first it just happened once in a while, then it happened all the time but I was able to restart the console properly, and now restarting doesn't do anything

 

Could it be the power adapter? I don't have an original one, but a cheap one from Chinese eBay. I replaced the voltage regulator with the new one that's part of Tim's RGB mod kit, that didn't change anything.

[jarreboum]

An old thread about same issue here, worth reading i guess :

 

http://atariage.com/forums/topic/199541-atari-2600-4-switcher-intermittant-fuzzy-reception/?&p=2547333&hl=+fuzzy%20+reception

 

Indeed! Now my problem would be to identify the guilty cap, as I don't see anyone with a Jr in those threads.

[Electric-Dreams]

I'm no specialist, but i guess the guilty cap lays probably near (or at least is linked to) the 7805 voltage regulator. It is said that those caps on 6 and 4 switches models are green chicklets. But on my 2600 Junior there is no such cap next to the regulator.

I do not know if your 2600 Jr is NTSC or PAL, but you can look here for PAL Jr Schematics :

http://atariage.com/2600/archives/schematics_pal/Schematic_2600_Junior_PAL.html

 

I would begin by replacing C36 (top left). Again i'm no specialist and i'm just guessing. Sorry I can't help more.

[jarreboum]

 

I would begin by replacing C36 (top left). Again i'm no specialist and i'm just guessing. Sorry I can't help more.

 

Comparing the schematics, that would be my guess as well. I doubt it's anything before the voltage regulator, though I did order some more caps just in case.

 

Hopefully that's the one.

[+Stephen Moss]

Being able to have a brief normal picture after the console is fully discharged made me believe that it may be a capacitor problem. But which one? I tried changing the big 2200µF 16V one, but that didn't help. It's quite possible that the "new" capacitors I used could be bad too, I've had trouble sourcing them. I haven't touched any other cap in the machine, there are lots of them all over the place. None look bad, but I don't have the eye for it.

I don't understand this fad on AA for leaping to the conclusion that every problem is caused by a bad capacitor with absolutely no proof that they are the problem in any particular instance, potentially resulting in pointlessly changing every cap in the system and the problem persisting.

Just because you briefly get a good picture after the console has been off for a while (or discharged as you put it) in no way implicates a capacitor, it can suggest there is a thermal related issue in that that an IC is failing or a component such as a resistor/diode/transistor specification/value is changing either because it is faulty or a fault elsewhere is causing it to become hot or a bad solder joint opens up as the system warms up.

 

Is it a gradual change from good to snowy or instant like the flick of a switch?

If a gradual change it could be that the RF carrier frequency is changing slightly and thus the TV is not longer in tune. Have you tried adjusting the tuning on the TV to see if you can once again get a good image or is a snowy video and poor sound all you can get once the problem occurs?

 

Do you only use that TV with the 2600 and if that is all you use it for do you also turn it off once the problem appears and you turn the 2600 off?

If so how do you know the fault is with the 2600 and not with the TV, have you tried the 2600 on another TV or running another RF source into the TV for the amount of time it takes the fault to appear to positively identify which of the two is at fault?

 

To eliminate any problem with the power unit/regulator you would need to measure the input & output voltages of the regulator both before the problem occurs and after.

[jarreboum]

I have absolutely no proof of anything, one way or the other. I'm not an electronic engineer, I'm coming here with a console problem asking for help. I'm sharing my doubts and experience in the hopes that people with actual knowledge could help me, and correct my wrong assumptions.

 

It is sort of gradual, but happened in less than a second. When I was able to get a correct picture, that picture could hold as long as I would use the console, but I never did extended tests. When that picture would change, I would get a correct picture for less than a second, then it would quickly fade to black and white with audio noise. Then after a couple of tries, I could get it working properly again. I noticed that unplugging the console, flicking the switch and waiting a bit, before using it again was a reliable way to make it work.

 

I'm using that TV with other consoles, but only the 2600 uses RF. It's the only console I have that uses RF, and it's the only TV I have that can take RF from the 2600. The TV is digitally tuned. Could it drift the way you are describing?

 

The problem now happens all the time and I cannot correct it any more. Whatever was partially faulty in the console is now completely faulty. I can't do before/after tests any more.

Edited April 13, 2018 by jarreboum

[+Stephen Moss]

You could try tapping/toggling the BW/Colour switch if you have one although I doubt that is the issue as that would only explain the video and not the audio. I have a 15" LCD I use for gaming which has manually adjustable digital tuning and I cannot correctly tune my 7800 into it for both clear video and sound as the tuning increments are not fine enough.

 

Personally I would think the fault comes down to one of two things...

1) Incorrect voltage out of the regulator - effects are system wide. If you have access to a multi-meter you should get 4.5 - 5.5 volts DC.

2) If it is not a power issue then it has to be something common to both the Audio and Video which would suggest either the TIA or the modulator.

You could try the finger test, put your finger on top the IC, switch on and see if it gets hot, you could do that with all the IC's but I would start with the TIA (has C010444 or C011903 written on it)

and the modulator IC (has 3086 written on it).

 

As you have no other RF source to try the TV with thereby eliminating it as the problem there are two ways to help try and resolve the issue if both the regulator output is ok and finger test does not indicate the problem...

1) Take the 2600 to a TV repair store (if they still exist) who should be able to look at the signals coming from the TIA and RF modulator and determine if the problem is before the modulator, with the modulator or neither (your TV), the last two of which I would expect them to be capable of repairing.

2) If that is not an option then fit (or in your case refit, you might have made an error the first time) an AV mod. The AV mod should tap into the Audio and video before they get to the modulator. Consequently, if the 2600 is working correctly and the mod is working and correctly fitted I would expect you to get an output on your TV. Installation of the AV mod should require you to either remove the modulator altogether or isolate it, if it has no such instructions I suggest either removing the modulator altogether or open the modulator and remove the 330 ohm resistor (Orange, Orange, Brown colour bands), at least initially. That should ensure that the modulator is not interfering in anyway with the AV mod, then even if there is a problem with the video you should get clear audio if the TIA is functioning correctly.