Genesis plays in black and white...sometimes

[Sectorseven]

Hi, I've been having some odd problems with the Genesis model 2 I just hooked up. Sometimes when I start it up, the game will be in black and white and have vertical lines going through the screen. If i turn the power off and back on it will usually fix it, but not always. Sometimes I have to cycle the power multiple times for the color to work.



After a few restart attempts:


I took a look at the board and I think there's an added circuit board, but I'm not sure. Here's a pic:


There's also a couple wires on the bottom side that were soldered on/near the power input, but I forgot to grab a picture of them. There's two chips on the board. It's glued down so it's hard to get a good look at it, but it says ©1993 Sega, so I guess it's a factory mod.

Any thoughts?

[ooXxXoo]

The Genesis aside having a few different models out there, its one of the systems to have a whole bunch of revisions, different boards, and modifications here and there done to the boards as well....

By the looks of it, and by looking to the sources of those new added wires, there is possibly a problem with Sync, vsync and/or Hsync...It seems that the video encoder is not getting a clean / strong sync signal, therefore rendering the black & white image....

Check your PM box...

...

[raylydiard]

could be just dirty cart connectior

[InsaneDavid]

Possible it's some kind of 50Hz / 60Hz softmod? Looks like one of the lines may run to pin 46.

[Sectorseven]

I compared the voltage on the CXA1145M and the two chips on the added board, as well as the solder points across the board, and the voltage is the same on all of them in both b&W and color mode. Tempted to disconnect that add on board, but I'm guessing that will only cause more problems. I'm limited by the tools at my disposal, but does anyone have a schematic of the model 2 genesis 1.8 board?

[Sectorseven]

I hooked up a 32x for shits and giggle, and I have actually not been getting any B+W problems with the games now. The 32x has it's own video encoder, correct? So, would that point to the Genesis' CXA1145M as being the culprit?

[FABombjoy]

Maybe the 1145, I'd look for a problem in/around the color oscillator circuit first.

[Sectorseven]

Maybe the 1145, I'd look for a problem in/around the color oscillator circuit first.

Hmm, assuming it's the oscillator I'd have to test it with an oscilloscope, yes? Or just flat out replace it and see what happens.

[FABombjoy]

I would suspect a cold solder joint first. See if anything in that area responds to pressure or temperature, or reflow all of the connections and see if that makes a difference. I wouldn't jump to conclusions and start replacing parts without further diagnostic tests.

A scope or frequency counter could be used to test an oscillator.

[FABombjoy]

Oh, I just realized you have a unit with the 1145. You'll also want to check external Y/C filter area as a problem there could also remove color. I can't remember the exact pins, check the datasheet for CIN COUT YIN YOUT