MOD GUIDE - Universal RGB-to-YPbPr/Component Circuit & Mod [8/24/2014]

[Xenogears]

Well I also have a special bleeding problem. It´s white that goes out to the right. I did an RGB-Mod, using the THS 7314 Amp with 3,6M Ohm on +5Volt, 82nF CerCap to the Inputs and 330uF ElCap + 75 Ohm to the outputs of the IC.

To Sync I use C-Sync in line with a 220uF ElCap. On my 2nd Duo, this mod worked fine, I swapped the Mod and it also worked fine. So my conclusion - it´s from the Duo / 6260...

Any Idea where to look for ?

 

[thesteve]

are you saying your running as an RGB mod, or running an RGB amp into the component board?
it looks like you may just not be loading 1 (or more) of your signals causing an echo

[Xenogears]

Hello The Steve. Its like this:

I go from 6260 R / G / B to THS-7314 Chip. I use the circuit enclosed. It works in serveral Engines (I´m from Germay and RGB-Scart21 is common here). For some Reason this PC-Engine DUO has her own mind... could shadowing come from the IC-Circuit ?

P.S.: your Component Mod is great ! Especially used on LED-Flatscreens it looks superb ! Would it be okay to translate and post it into the german Forum Circuit-Board ? (www.circuit-board.de)

[thesteve]

yes, but i suspect thats not your issue
does the composite output have issues as well?

[Xenogears]

...yes. Let me check...

Just resoldered the Composite Video Connection - no bleeding. But still Bleeding if I use C-Video as Sync. I also tried to let the Kynar Wires go different paths - no change.... Also desoldered R, G, B and resoldered it, looked hard for solder blobs or bridges...nothing. 

The problem is, my Oszilloscope is 600 km far away - out of reach... :-(

[thesteve]

check your grounds and cables first
try a 1K resistor from the RGB inputs to ground

[Xenogears]

To be certain - 1K before THS to GND or 1K after THS (where the Signal goes to TV) ?

[thesteve]

should be before

[Xenogears]

Soldered in 1K to GND for each Color - no change, still "white bleeding" in RGB-Mode. If I connect to TV by Composite, the bleeding is gone. I never had this Issue before...

[thesteve]

and this amp/cable has been tested on another system?

[Xenogears]

For Certain. I swapped the Amp PCB with a working one into a 2nd PC-Engine Duo. The Test-System worked perfekt with the "bleeding Amp", the bleeding System was still blurring white with the "non bleeding Amp". I used the same RGB-Cable and also made a 2nd one with R/G/B to 75Ohm on GND. No reaction. What I might have found out - the Issue comes from the green line. If I swap colors the issue is still visible on the screen but not in white (...and not that strong). If I disconnect the green signal, it looks fine to me (but might depend on the missing color, dimming the brightness)

[thesteve]

the odd thing is your having an issue with white while using RGB
that means your getting the effect on all colors together

[crans]

I use this for my RGB only need's.

Some things changed from original is use of 5.1M resistors for each color input to ground.
Using 0.1uf on all inputs and one bridged power and ground rail's. For the output i use 75Ohm and 220uf.

Not sure what it will help just my use of this amp

[Xenogears]

I will try it out this week. But it must be something from the Engine, as thr 3.6 MOhm Amp works perfekt in other units. @thesteve: yes, this is really strange - bleeding / shadowing with white I had never before...

[thesteve]

its not bleed, its actually echo (bleed streaks decreasing from left to right, echo has more of a image copy shifted right overlayed on the pic)
is it possible you getting some composite crosstalk?