Turbo Duo Video Problem. Please help.

[Shaggyneo]

Hello. First off I have been reading these forums for a while and am very grateful for all the knowledge and kindness that is shared. I have worked on a lot of systems and a lot of pcengine/turbo grafx systems and have never seen this so I hope a fresh set of eyes can help. I was given this duo to do a sound cap replacement. I noticed quite a few more caps that looked bad so I replaced those as well. I put a game in and let it run for a while to test the sound and after a bit I noticed a flash in the video and the it looked like a scrambled cable channel. I have tried everything I can think of and have searched the web and can't find any other topics on a problem like this. I tapped pin 44 of hu6260 and attached it to the composite to even get the stable image shown. That image seems to have no white at all. Any help would be great as I hate to tell the guy his US Turbo Duo is shot. Thanks so much.

[Keith Courage]

There is most likely some broken traces somewhere but it could be a bad chip. I will let someone else chime in on that one since I have never encountered that particular problem before.

I repaired a DUO using thesteves Composite schematic for the TG express once and it worked pretty well. The symptoms I had was black and white video only. I gave up on trying to find the exact problem and just rebuilt the circuit using this. 

https://postimg.cc/image/4sqmybmbn/

[Shaggyneo]

Thanks very much for the link. When you did it did you lift the traces or leave them down and build the circuit?

[Keith Courage]

I pulled up the pins from the motherboard. Not sure if you can leave them down or not. so I figured I'd just lift them to be on the safe side. I then ran the final output from the circuit directly to the Composite Video pin of the AV port. I obviously severed the existing connection to the video pin on the AV port before hand.

[turbokon]

Yeah, you have to lift those pins and ground them to turns on those signals for composite in the TE/GT. You might check to see if those pins already grounded in the duo.

[Shaggyneo]

I tried the video mod and got the same result. I'm guessing the chip is bad. Time to call the Bones McCoy on it sadly. It's dead Jim. Thanks for the helpful suggestions.

[turbokon]

Before you give up, try the rgb to component video mod.

https://www.pcengine-fx.com/forums/index.php?topic=13231

Or you can just simply order the converter chip:)

https://www.pcengine-fx.com/forums/index.php?topic=14876

[Keith Courage]

yeah, I would 2nd trying the component video mod as well since it seems that the RGB signals are still good.

[Fidde_se]

The first pic looks like when sync is not working correctly in RGB, the same probably goes for any S-Video or Composite as it's blended in, it's not completely missing, as if it would it be more distorted, this is more how it looks like when the syncing signal is getting to low and just nearly syncs, happens on long cables, certain tvs or monitors, or when something in the console componentry is no correct, missing white I have never seen though.

Theory, white is all colour channels on max values, if something is to low maybe it can't be produced. Capacitors are not just used for charging and releasing energy they are used for their filtering side effect too, highpass in serial and lowpass in parallel, if a newly replaced cap is backwards weird stuff can happen, the fluid leaking from them are conductive meaning they can make invisible traces to other components building new circuits with new functions, the vias surrounding it can be totally corroded giving the circuits that's left new functions too, and a new function can be sending all frequencies over a certain value directly to ground, meaning it might be shorting something and the values don't add up and if the values are to low white can't be produced.

Doing the Component mod might solve it if all colour channels are correct, if however something is bad with the sync, who knows... it's needed, but it can be taken from both sync and composite...
they probably comes from the same source within the HU6260 though.

If that would be the issue, another wildcard, professional monitors uses sync signal generators to sync an array of monitors and equipment, more simpler circuits should or could be built or even stealed from other sources and be used instead. meaning you could try taking just the sync or composite (or cleaned composite) from a megadrive or snes too see if that fixes it.

The sync might just need a boost to get over the needed value, it's not overly talked about but the PVM and BVM monitor folks out there discusses it sometimes.

The little amp here can be built with ease and great success for that (ignore the colour amps and audio caps) and the keep in mind of the NPN symbol is EBC and C1815 is ECB, switch those legs (B&C).
http://www.gamesx.com/rgbadd/duorgb.php
http://www.gamesx.com/grafx/pce_rgb.jpg

[thesteve]

10uf cap open 2