Strange colour from a Wondermega MK1

So, recently my Wondermega Mk1 has been producing some very odd colours.
Upon switching on the machine it can look normal however within a few minutes the red from the image seems to drop out however it will return after leaving the machine on for 30 minutes. I'm running the picture from the S-Video port.
Take a look below.

Colour after 5 minutes of use


Returns to normal after 30 minutes


In game it's the same. After 5 minutes of use


After leaving the game running for 30 minutes


I hope it's not time to replace the caps but it sure looks that way.

 

You might be right that the caps need to be replaced.

 

It's weird that it fixes itselt after 30 minutes. Checking the caps next to the video outputs, with a multimeter, might confirm if any or more are out of spec.

Found this website while looking for info: http://www.meulij.com/wondermega_disas.html

 

Thanks for the link, Johnny. I once took apart a Wondermega and do remember it being a real pain in the arse to put everything back together.
Looking at the pictures it seems the cap numbers are listed on the board. That's really handy but first I need to figure out which are the video caps.

I've never replaced caps before but how hard can it be? Just desolder the old one and pop in the new, right?

 

I was looking for schematics and found that link. Thought it would be nice to post it as a disassembly guide. It does look a bit complicated.

I'm not really that experienced in soldering either, but i would suggest trying desoldering / soldering a broken and common system to test yourself before doing anything on the Wondermega. Actually, i would try figuring out the issue before doing anything on that expensive console.

Maybe it's something that can be discovered just by looking at the board (caps leaking, cold solder joints,... ) or with a multimeter. I would even try using another AC Adapter to remove all variables.

 

Any updates on this @Yakumo ? I'm actually curious to known if you found where the issue is / was.

 

Man that looks like a ball ache to disassemble. Definitely looks like a cap issue. As the cap 'warms' up it settles down. It seems to be the 'Blue' channel that's playing up as you have both 'red' and 'green' in the beginning. As you are getting this on S-Video, it suggest maybe the problem is happening before the RGB is processed into Y/C at the Sony CXA1145 encoder. Yakumo, do you have pictures of your Wondermega board specifically around the Sony encoder chip?

 

I don't see any surface mounted caps at first glance, which is surprising yet reassuring. Should be an easy job, you want to get a low-powered iron for this circa 20W to limit any possible damage ie traces popping off. Even then beware of leaky caps that would corrode traces, I had a few nightmare situations recently with an old MSX2 and leaky SMD caps, hate them!!!

Let me know if you need any help!

 

I would go straight after the capacitors connected to pins 13 (if any) and 14 (usually 10uf 16v) of the CXA1145 chip. Those filter the voltage which set the bias voltage for the Y/C filter/delay circuitry. A fault there gets you PAL systems have blinking green spots/wedges on areas with red color. On NTSC you get bad/wrong tint.

I believe once these caps get replaced you won't need to wait the unit to heat up to work properly. No need to replace all caps if they're not faulty.

 

Citrus3000psi restored my Sega Wondermega, replacing the caps and diagnosing further problems (since caps were only part of the issue) until the core problem was addressed.

My CD-Rom was taking 15+ minutes to "warm up" to an operational state, and it turned out to be a combination of caps, voltage regulators, and a diode after some investigations along the way. Now it works like a Day 1 system again and sits paired to workshop PVM.

I made the mistake of looking at the complexity of the Wondermega firsthand and I knew better than to dig into that. Great component fitting rationally, but man, too much for me.

 

My model 1 megadrive does this

 

Pictures of boards here
http://meulij.com/wondermega_disas.html

I have the full sized on my hdd if needed