Trying to get a 4 port to work again - only seeing snow

[brockj]

I have 4 port 5200 that is only displaying snow. The system powers on, and when a game is inserted with and the system powered on, you can see a change in the snow, a little color, but nothing discernible. I have been pouring over posts relating to the same things, first recommendation I came across was to replace the LM393N IC in the switchbox. I ordered up a couple from digi-key and replaced it, no change. The next process I came across was re-seating the chips on the motherboard, I did that and the colors in the snow became a little more vivid, but nothing drastic. Finally, I received a working 2 port and I decided to try swapping out the larger chips (I do not have the schematic, but I know that would include the CPU, GTIA, can't remember the other two offhand), I started one at a time, and with no change swapped all of them at once, still no change. I am sure there is more to do, and perhaps the chips from the 2 port would not work in the 4 port (not sure why that would be), but thought I would come here. So, what should I try next?

 

Thank you in advance for your help!

[zylon]

Sounds like box is working, but system not fully turning on. 1st thing to check is the little IC near the power switch. they are very cheap. 2nd possibility is the RF modulator.

[brockj]

Zylon, thank you for you help with this, sorry if this is a dumb question, but you mean U29 correct? Would that just be a CD4013BE? I am not 100% familiar with all of this, so I hope you don't mind me asking questions.

 

Thank you!

[zylon]

Yes. That's all it is. It handles the power to both sections of the 5200 circuitry- video and logic. Partial failure of this IC can give similar symptoms to having a dead modulator and is easier to replace.

The more I think about it, the more I am leaning towards dead modulator on your system, but would try the IC first.