PC Engine Duo RGB video noise issue somehow related to power adapter

I'll try to keep this short.

I have two PC Engine Duos that I did a full recap and RGB mod on.

They both came without a power adapter so I bought one of those generic 9V 1500ma adapters on ebay.

Upon powering on each unit I noticed both were affected by very strong video noise that looks like a bunch of waves and dots that scroll across the screen at a slow pace.

This noise is only present when using RGB video, when switching to composite the picture is fine. In short the noise comes from the RGB lines.

I first tried to use a RGB amp that I built myself, and thought it was at fault. So I took out the amp and instead routed the HU6260 RGB signal directly to a SCART cable with a known good amp inside. The problem did not go away, so the problem is not related to the amp.

After switching the generic 9V adapter for an original PC Engine DUO adapter I noticed that the interference went away.

At this point I figured the problem was that 9V was insufficient for the Duo, since the original adapter is rated at 10V, and instead I purchased another generic adapter, this time 10V 1000ma. Unfortunately the interference persists even when using the 10V adapter.

Anyone know what could be causing such interference in RGB video when using the generic adapters?

Anyway to fix this problem? I really need to be able to use both these units with the generic adapters.

Oh, and by the way, other than the noise in RGB both units seem to otherwise function perfectly when used with the generic adapters, both the 9V and 10V.

 

Were the generic adaptors cheap ones off ebay? I have had these issues in the past on various consoles. Those adaptors are hit and miss quality wise....

 

Here are links to the two generic adapters in questions on ebay:

http://www.ebay.com/itm/200745491065?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

http://www.ebay.com/itm/251236850284?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

 

Never use generic power adapters, unless they conform with the specifications on the original power adapter.

 

Cheap switching power supplies could cause all sorts of noise and random issues.

 

In another Forum I was suggested to fit ferrit cores on the adapter cable to help reduce the noise. Are there any other tricks that can help in that regard?

I am comfortable with a soldering iron, so I can add parts to the adapter or inside the Duo if anyone has any suggestions.

There must be a way to filter out the noise since composite video is clean. I imagine getting RGB from the Hu6260 chip raw is part of the problem. Composite video is prolly processed by various components before reaching the video out port on the Duo.

I am shooting in the dark here, but could attaching some sort of capacitor to the RGB lines before they are fed into the amp help?

I see in some amp designs there are 10uF caps put there for reasons beyond me.

 

Just buy a psu that isnt a switching one. Id imagine that would sort it out.

 

For various reasons let us imagine that is not an option. I am interested in making RGB look good with these specific AC adapters. If anyone has suggestions I am all ears, or eyes.

 

What RGB amp are you using?

 

Waste of effort. If you can afford multiple PC Engine Duos, a better power supply is more than within budget.

 

I know it is a shitty amp that does not reduce voltage levels. But as I said I instead tried to use a professionally made boosted SCART cable from a reputable site which has worked perfectly in past and the noise was still there. So I doubt amp design could be the cause of the noise.

About the only thing the two different amps have in common is that they are both powered by the 5V pin of the AV out port. The thought that noisy 5V might be the cause has crossed my mind and today I will try to go home and grab 5V from a good shielded AC adaptor to power my subpar amp and see what difference it makes.

I imagine none as I suspect the noise is in the RGB lines somehow.

 

Of course I knew of that alternative from the get go. But, as I said, let us imagine that is not an option and instead focus on solving this issue, if possible, the hard way.

 

If the PSU is the cause, you will be doing damage to the system over time anyway with noisy/unclean power. So id suggest you take it as a warning sign and just buy a new one.

The issue that needs "fixing" is a shit power supply. Not the RGB. The reason you have this problem is likely because the amp is just forwarding the noisy power to the RGB of the tv. Solve the cause by replacing the power supply.

Even if the amp isnt the cause - the power supply IS.

 

Well, I do happen to know a trained electrician, I guess I'll shoot him an email.

 

Electricians generally don't know much about electronics - I started training to be one years ago and my uncle is one.

Id also put money on the cable you bought having exactly the same amp within it.

 

Nah, that guy knows his shit. He has been doing electronics repairs since before I was born.

Anywaste, that amp is legit, I've opened up and looked at the insides of that SCART, it is using an IC for the amplification. I am pretty sure that IC even does sync stripping to boot, so way, way better than my layman cobbled together abomination.

I've also measured the voltages coming out of that SCART and they are 0.7 as should be when my amp puts out a cool 3 volts, which is way over spec.

 

That is true about electricians, being a electrical fitter showed me that. I could wire up a vsd, battery chargers, make transformers etc but when it came to installing ceiling fans etc in my house i needed a sparky mate to lend a hand. Electrical/electronics is a vast field.

When i got any dodgy power supplies i put them where they belong, in the bin. If i found a good one i quickly ordered more. Whatever "fix" you do will be a bandaid fix.