Atari 2600 Jr Repair (please be prepared for nerd details)

[Osgeld]

So I got a dead 2600 JR from Ataribrian to tinker with ... cause I have fun fixing dead machines, and have never done a 2600 before. He had said that the unit only produces a black screen.

 

Once I cracked the unit open I removed the giant electrolytic cap and tested it with a meter, the 2200uf cap measured out to 2830 something which is fine. I also replaced the 7805 regulator since the stock unit apparently was never screwed down to the PCB plane and was seriously discolored from heat abuse, but otherwise worked fine. I used hot air and solder paste to bond the new 7805 to the ground plane and its running much better.

 

I did a quick n dirty composite mod and did a little cut to the trace feeding video to the RF modulator (thinking maybe something there might have blown). On the oscilloscope I get a nice color burst signal and chroma signal, though I do not see any sync signal ... and the picture on my TV tuner seems to confirm this as sometime it rolls, or flickers (of course no lama signal since the screen is black).

 

Also poking around I notice that I get a nice clean 3.57Mhz signal from the oscillator section of the board which goes into the TIA, the clock out of the TIA though is a funky rounded over saw tooth wave, that does not meet the voltage / timing requirements of the 6507 nor the 6532, which are both in an idol state.

 

For anyone that knows me I hate shotgunning chips that are getting more and more rare, but it does seem in my inexperienced with this system mind, that I might have a faulty TIA chip, can anyone confirm?

[AtariBrian]

I thought I read somewhere way back that it might just be a bad power button . But I cant remember for sure .

[Osgeld]

well I am getting good clean voltage to everywhere it needs to be with minimal ripple, input is a snotty bench supply

 

edit: I will admit the power switch is a bit junky, but in its most extreme its ok

Edited August 17, 2013 by Osgeld

[Osgeld]

bump

 

tried a new riot chip, still getting nothing on address lines, getting video out of the system but no function