Black screen with RGB mod for PC Engine Duo RX?

[Piratero]

Hello everyone.

It looks like I'm having a string of bad luck. First my N64 and now my PC Engine.

Here are some images:
http://i.imgur.com/kHs0C.jpg
http://i.imgur.com/WHyXQ.jpg

That RGB amp is the same used on the N64. And all I get is a black screen. The resistor values are wrong in that image. I switched to 75ohms.



Why would the chip not even show at least a dark image? Is there anything I'm missing?


I'm very disappointed in the mod.

[viletim]

Is there anything I'm missing?

You are probably missing some coupling capacitors between the video chip and your amplifier board. Just a guess - I can't really tell what you've built here.

[Piratero]

Is there anything I'm missing?

You are probably missing some coupling capacitors between the video chip and your amplifier board. Just a guess - I can't really tell what you've built here.

Coupling capacitors? On each color line?

Here is some more information on the mod itself:
http://www.mmmonkey.co.uk/console/nintendo/ntsc_nintendo_64_rgb_new.htm

[Moosmann]

You are probably missing some coupling capacitors between the video chip and your amplifier board. Just a guess

I  have do this, but the THS OPV IC Mod don`t work (in the simple circuit design like here) on a PC Engine and NUS-CPU-04 N64.
Maybe it is a problem with input impedance or time constant... I own a oscilloscope since some months, but I still haven`t measured it but I will do it in the next time (because the high demand) and make an update on my webpage.


I modded a IFU with simply transistor mod yesterday to make it working with a XRGB-mini (chance the +5V point is very important) and the quality is great.

Greetings Markus

[Piratero]

You are probably missing some coupling capacitors between the video chip and your amplifier board. Just a guess

I  have do this, but the THS OPV IC Mod don`t work (in the simple circuit design like here) on a PC Engine and NUS-CPU-04 N64.
Maybe it is a problem with input impedance or time constant... I own a oscilloscope since some months, but I still haven`t measured it but I will do it in the next time.


I modded a IFU with simply transistor mod yesterday to make it working with a XRGB-mini (chance the +5V point is very important) and the quality is great.

Greetings Markus

Ah!!! That's why it wasn't working for me. I thought I had fried something!

What is an IFU?

Please do check the oscilloscope. I don't have one and can't afford one right now.


I thought I was going crazy! Thank you for this information.




What is the recommended RGB amp for PC Engine then?

[Moosmann]

IFU= Interface unit. I got some dropouts with RGB modded IFU`s on a XRGB-Mini but  not with the "nacked" PC Engine. I measured not exactly +5V on the same point from the 69-Pin Connector when it is connected (~5,1V) to a IFU, so that i have to change it.

Greetings Markus

[Moosmann]

What is the recommended RGB amp for PC Engine then?

In the comparison with RGB Mods for other systems, it is not much difference here.

Greeetings Markus

[Piratero]

What is the recommended RGB amp for PC Engine then?

In the comparison with RGB Mods for other systems, it is not much difference here.

Greeetings Markus

Comparison with other RGB mods? I don't know any RGB mods that work for the PC Engine...

[Dr.Wily]

RGB mod for Duo-R on mmmonkey website does not works as is, on gamesx too. You must build two amp because of very low voltage on RGB lines provided by hu6260 on Duo R(x) models. First take R, G and B signal from hu6260. Keep sync signal from AV connector.

To build the first amp you can use this schematic (sorry for "paint style"...  ). Hook up RGB lines directly from hu6260 to this amp. Then, at the output of your first amp use THS7314 for last video amplification. If you use scart you can take 5v from Duo-R av out for automatic AV switching.

[Piratero]

RGB mod for Duo-R on mmmonkey website does not works as is, on gamesx too. You must build two amp because of very low voltage on RGB lines provided by hu6260 on Duo R(x) models. First take R, G and B signal from hu6260. Keep sync signal from AV connector.

To build the first amp you can use this schematic (sorry for "paint style"...   ). Hook up RGB lines directly from hu6260 to this amp. Then, at the output of your first amp use THS7314 for last video amplification. If you use scart you can take 5v from Duo-R av out for automatic AV switching.

Thanks! How come I didn't see this information anywhere? I was going crazy!

Masse = Ground?

And you build one of these for every color?


What is the type of transistor that I need? Specific part name or #

[Dr.Wily]

How come I didn't see this information anywhere? I was going crazy!

Maybe nobody has performed a RGB mod on Duo-R. I personaly tested this mod and it works great. Sometime you must mod hu6260 with a multilayer capacitor if your image get instable, but it depend of your display...

Masse = Ground?

Yes, this is a french paint "art"  

And you build one of these for every color?

Ya, every colors. Fisrt amp look like this. closer view, underside.

What is the type of transistor that I need?

Take NPN transistor 1815 (collector DC 150ma, Vceo 50v, 80Mhz).

[Piratero]

Bad news!

I just finished building the mod and it doesn't work. I get a black screen. I connected the RGB amp straight through and nothing. I then connected it to the THS7314 and nothing.

I get a signal, but nothing shows up on the screen.

[Dr.Wily]

Which kind of TV did you use ? scart or others ?

[Piratero]

I'm using a Euro SCART (properly wired)

Scaler:
http://www.jammaboards.com/store/cga-ega-yuv-to-vga-arcade-hd-converter-pcb-gbs-8220-gbs-8220.html

As well as a sync stripper:
http://wp1114205.wp150.webpack.hosteurope.de/xtcmodified/product_info.php?products_id=15

I would think that the sync signal is too weak. Wouldn't I at least get a completely distorted picture if the sync signal was too weak?

[imparanoic]

have you tried this rgb modded pc engine on normal scart tv? without the sync stripper and scanline generator?

or your friends tv?

or even better, xrgb machine then to TV

[Piratero]

have you tried this rgb modded pc engine on normal scart tv? without the sync stripper and scanline generator?

or your friends tv?

or even better, xrgb machine then to TV

That's the biggest problem. I live in the US and no, I don't have anything else that I can test it with.

[imparanoic]

nearest hope is see if you can take you pc engine duo to some with an xrgb then ( which is quite hard), sadly, no choices

[BlueBMW]

I've done a PC Engine Duo R with that THS7315 chip.  At first I got a black screen too.   Here's what I've come up with as far approximately what you need to do it:

From the HuC chip pins...  500 to 1000 ohm resistor to ground on each color line. 
2k - 5k resistor inline on each color line headed towards the amp
between the 2k - 5k resistor and the amp inputs, put a 0.1uf cap inline on each line.
75 ohm resistor on each output.

I say 2k to 5k because I havent found the exact value that gets the right brightness just yet.  5.6k was too dim but close.  It'd be better run with a pot for fine adjustment.

I also put a 22uf and 0.1uf cap between vcc and ground for the amp.

Also, if you replace C961 with a larger cap (100uf+) you'll improve video output on both RGB and composite.