Schematic for a *working* PCE rgb amp with 7314?

Seems easy enough to me take the Digital Sync In, feed through A1, get out of Y1 and feed this to A2, A3, A4, A5 and A6. Tie any 4 of Y2, Y3, Y4, Y5 or Y6 together through a 620 ohm resistor and the out put of this should be pull down to ground via a 91 ohm resistor as well as being Csync Out. The remaining Y output you did not use is the digital Csync Out.

 

Yup.

You can probably get away with using just one inverter, but since they're there why not use them all? It's pretty safe to put HC inverters in parallel and in this application it will help distribute the current sourcing requirements. Sync is an 8 mA load, and while a gate may tolerate sourcing 8 mA, the gate's output voltage will drop. Distributing the current across 4 inverters means they each must source 2 mA--so there's less voltage drop and a more accurate signal at the TV. This circuit should give a good compromise of accuracy and ease to build, more accurate impedance matching (exactly 75 ohms instead of 80) would mean more resistors and would require analyzing physical chips instead of datasheets...

If you wanted to be really cheap you could use a single gate as a buffer (or 2 inverters), put the output through a 1k resistor and use that as CSYNC, it will be close enough to work and it will use half the current, but if you used it with a really long cable you might run into problems since there is no impedance matching.

 

@Calpis: Slightly off topic, but this could totally be part of your kickstarter idea. A device that plugs into a PC-Engine EXT port and provides *proper* RGB/S-Video out, could be 1 of the numerous features such an interface device might enable. That's in addition to other features it could provide, such as CD-ROM support (via solid-state emulation or USB). Because everyone focuses on NES/SNES/Genesis and other systems for flash cards, clones, and whatnot, you'd pretty much have the market to yourself in terms of unique devices that extend a console.

 

awesome, now to get the needed parts , sadly where I am I have to order them, I've given up on the local stores...
I assume I can use the c-sync signal from the EXP port? or I need to get it straight out of a chip or something?

 

www.ebay.co.uk/itm/150839685837

 

That's way more awesome than changing the inside of the PC-E. The only problem is that it costs so much
Anyway, very nice thanks for posting this up.

 

I wouldn't really agree. On my Core Graphics II I can make the mod look factory and not need some ugly box sticking out the back.

 

Wow, that's crazy! I had no idea someone made an EXT mod. Personally, I like the modular aspect of the EXT mod as you can swap consoles with it when one dies quite easily. But of course, since the PC-Engine has great composite video anyway, it's much more intresting talking about the CD-ROM adapter feature than video output in terms of an EXT device. But still, a cool link all the same!!!

 

I removed an smd 74HC04 from a dvd player that had a dead drive and soldered it on a SOP14 adapter :congratulatory:



I also found at mmmonkey's site that pin #44 of the Hu6260 is composite sync, straight from the source :tears_of_joy:

So basically before I continue with this, I need a little verification, does the following diagram look OK?

 

You can also get pure sync from C22.

http://www.gamesx.com/misctech/pcebp.php

 

C22 is what I use on my old amp but I don't know if it's a straight connection from the source or not...

 

May have some noise from the circuit or whatever. Would interested to see results.

My amp allows me to tap either, and I notice no difference between comp vid and comp sync from the ext connection.

 

are you using a LCD tv? tha's whrere you notice a difference... on crt it's fine
there is also the possibility that lcd is fine too due to image processing filters

 

Was on my PVM. Huge difference when using it with an LCD. Comp sync gave me no image while comp vid did.

 

Having all parts I started working on the amp

I used this diagram to make the RGB pull ups:



but the result was not very good as you can see :biggrin-new:



I triple-checked my connections, they all seem fine. Removing the pull ups part gives a nice image like the ones I posted before. I am now making the c-sync amp with a 74HCT04 , I'll report later


edit: tried the c-sync amp , it does not give any picture. Tried both pin44 and expansion points and also tried with both a 74HC04 and 74HCT04 . I have no picture with either. Using composite works. I have built the c-sync amps according to the diagram I posted above, unless I have it wrong then I don't think the amp is suitable for this situation.

 

Today I re-made the pullup part, apparently there was some sort of problem at my previous attempt (a bad cap? resistor?) and this time I used different components... here is the totally test pic LOL



with this I get this result (using composite for sync, there is a checkerboard pattern going on that the photo does not show clear enough...)



in my eyes it's the same as without the pull up... I also noticed that the reistors are not that great... R line measures 0.97v , G measures 1.17v and B 1.23v ... need to get some good 1% I think...
I also used the old tansistor-based amp only for the c-sync line... it works and gives out a great picture (7314 for the RGB lines, old amp for the sync)

 

So basically, nothing overly special needs doing with the amp to get it to work - it just has caps before the amp. Other than that, its identical as use in the N64.

Why did people have problems with this?

Also, did you try the other 4 channel amp again?

 

Maybe there was troubles with the input caps? 10mf worked for me, all my other previous 7374 attempts were a failure. I don't have those chips anymore, I returned them and got a refund. IMHO they were a bad batch.
There is also some discussion at nfggames , and there is a different schematic there posted for the 7314... I will also give it a shot since I believe I can get all parts locally this afternoon.
This amp will be great once a working c-sync amp is found , I have built 2 of them so far and none worked for me

 

I have some 7374 chips direct from TI

 

Then they are top notch like the 7314 ones you sent me
IIRC Calpis wrote that c-sync needs a different kind of amplification , wouldn't the extra channel be wasted on the pce?