Help me repair this VA6 Mega Drive

Hello guys,

I bought this very mega drive, same model as I used to have back in the early 90's, for the sake (and pleasure) of repairing it. it was sold as "for parts / not turning on", but i managed to get the led on just by using a new power supply (9v 2A). And that was as far as I could get, results wise.... well, kinda.

I undid the PAL-M mod, got it back to NTSC-J and reverted the language/region mod. Also, i did the component mod because i don't have a MD1 AV cable with me. Still didn't get any audio or video. Note: the headphone jack outputs that low "hiss" sound when the console is turned on and the TV does display the "info" that some signal is being received. I thought that was it, but when I decided to give the board a nice clean things started to get interesting:

I basically cleaned everything with alcohol, wd40 and detergent/water. Let it dry, worked on all the mods again and, voilà, the console was back from the dead. But my joy didn't last long: the console freezes, sometimes doesn't show any audio/video, sometimes works for like 10 minutes and freezes again. It is totally random and I really can't blame it on overhearing because it happens even when everything is still cold.

That being said, I have to say that, even without messing with anything up again, the console now refuses to show any audio/video again. And this is the moment I beg for your help, lol:

Tests made so far:

Voltage regulators are fine: I even replaced them, both are getting around 8.2v and outputting 4.8~5v
Rams, CPU, Z80, IC4, IC8, rgb encoder (cxa1145p) are all giving a nice 4.8~4.9v read from their vcc pin

I didn't test the other components, including IC9, IC11, IC12, even thought they do get warm after a while. Will test them later.

QUESTION: Is it normal to read around 3v from pins 32, 33, 64, 65 and a couple of others in the VDP (315-5313)?????

I am worried about the corrosion around the 315-5433. The picture I am attaching was taken BEFORE the cleaning process, the green spot between pins 160 and 1 did damage a bit of the board (it is possible to see the brown layer right there), but I am not sure if it affected the contacts....

The cartridge slot doesn't show any signs of broken pins, but I can't say it couldn't be the problem.

Every time I think about what could be causing it, both the 315-5433 and the cartridge slot come to my mind. When I think that the console was (kinda) working just after I cleaned it (therefore, not 100% entirely dry), i think that the problem might be with contacts.

Among the crashes, Sonic 1 did show the "emulator line 1111" and "address error" messages. I dunno if we can use that to help finding out the culprit.

I have a complete set of capacitors and a spare cartridge slot to replace, but I would very much like to do some additional tests before that... the thing is: what and how to test?

Thanks in advance for your help.

note about the back of the board: like I said, i redid all those wirings and also wired CXA1145P's pin7 to its corresponding trace in the middle of the board (note that there is a cut trace right there). If needed, I can post new pictures of the board, just let me know).

Pictures are here: http://postimg.org/gallery/2uulvkw1u/466715e0/

 

Have u checked solder joins around AV port? Also check the cartridge slot pins for damage/ alignment. The soldering in the underside looks ropey and needs redoing. Also consider using a switch less mod as the traces have been cut. Check the caps around the video chips, these have a reputation for failing after a few decades of use. Failing that, it may be a case of the video chip giving up, which has no remedy other than replacing the video chip (no sure if that's even an option). Good luck.

 

Are you sure the AC Adapter is Center Negative? Because the Genesis/Famicom/PC Engine and other like consoles use that polarity.

Yeah, could definitely be the chips.

 

Full recap done and still nothing. I lost left channel sound sign (must have screwed up somewhere, still trying to figure out where).

I was redoing the soldering when this resistor popped out http://prntscr.com/bdvx67 . Not sure about my soldering after that, I will try to redo it.

The solder joints around av port seem fine. The cartridge slot looks ok, but I am really thinking about replacing it....

If nothing works I will desolder IC4 and IC8, give the contacts a good clean and solder again.

What is really bugging me is the fact that the console WORKED again for like 1-2 days (even though it was freezing/crashing) and then, OUT OF NOWHERE stopped working again...

Yup, center negative, 9v 2A, the console worked with that power supply, I don't think that is the problem.

I hope it is not the chips.....

Thanks for your help guys, hope to get some more clues on what to check next.