PC Engine THS AMP based RGB schematics

[kamiboy]

By the by, it seems the mobius AMP has two 100nF decoupling capacitors. I suppose those two can be omitted since my design already had another set of two decoupling caps, a 22uF and a 100nF.

I decided to keep them, just in case, but in the interest of space, complexity and cost I suppose they could just be nixed from the board altogether.

[Syntax]

Copy Mobius design to a T, he spent a long time on the scope (as did Voultar) ensuring all components and outputs were correct.


Move your wire vias forward as far as you can and make 2 holes for a cable tie to hold down your scart cable.

[skum]

Actually, after posting that screenshot I redesigned the board to increase the SMD size of the 10uF, 22uF and 47uF capacitors to 0603. I am planning on buying only tantalum capacitors. I checked on Mouser, and while 0402 sized tants can be found for 10uF and 22uF, I think there were no 47uF caps of that size. The 220uF caps are 0805 sized.

Remember then that tantalums are polarized yet your board seemingly doesn't reflect that.

[kamiboy]

Copy Mobius design to a T, he spent a long time on the scope (as did Voultar) ensuring all components and outputs were correct.


Move your wire vias forward as far as you can and make 2 holes for a cable tie to hold down your scart cable.

The enclosure I am using already has a spot for holding down the cable, so no need to put one on the PCB.

Remember then that tantalums are polarized yet your board seemingly doesn't reflect that.

Damn, you are right about tants being polarized. I picked generic SMD components in the PCB designer, based on case size, and those are unpolarized.

Well, too late to do anything about it, I already ordered a batch of them for manufacturing. In a week they’ll be in my hand for fit testing.

If anything needs changing I’ll add custom polarity markings to the PCB of the second revision.

I’ll also prolly have to move to a bigger package size for the 220uF caps as well.

I was putting together a project BOM for this board on mouser and noticed the 0805 220uF tants are actually on back order until February 2021.

Same thing at other suppliers, seems like AVX is the only ones making a cap of such a large capacity with such a small footprint.

[skum]

Handsoldering 0402... That's gonna be interesting I hope you got the proper tools Otherwise looks nice!

[kamiboy]

Funny thing is that I think I could have easily gone up a size on all those 0402 components. Seems there is plenty of room on the PCB still. But that is prolly just a trick of seeing it on a big monitor, when I look at the room inside the enclosure I see that I have my work cut out for me.

I think the manufacturer of these PCB’s does offer actually placing components as well. Hmmmm...

[skum]

0603 is usually the smallest I'm comfortable doing. If you're using paste and reflow/hotair it's of course another thing, but if you don't have tweezers, I hope you got some pointy chisel and narrow solder . Looking forward to see an assembled prototype.

[kamiboy]

Actually I ordered an SMD tweezer set on ebay right after I ordered the PCB, as I had a feeling it would come in very handy. I also feel this would be lot easier if I had a PCB oven or hot air station, but I am just going to have give it a go with the equipment I already have.

Unless I find a replacement for the 220uF 0805 cap you might have to wait a long while for that assembled prototype.

[kamiboy]

Well it took a while but the first manufactured PCBs turned out to contain a few measuring mistakes that prevented the PCB from fitting inside the enclosure, so I made adjustment and got a second batch made. Then I ordered the components on mouser and boy, you guys were not kidding about the puny size of the 0402 smd components, and my final design had a ton of them!

Luckily I have steady hands and by some miracle I managed to solder them all on without dropping any as finding them again would have been impossible and I had no spares. Barring a single smd which was not soldered on properly on one end everything worked during testing with a crisp RGB picture and clear sound though the SCART cable I used.

However, the trouble reared its head when I fitted the enclosure on and did a final test, it seems the two protrusions on the top and bottom of the enclosure prevent the cable from inserting fully into the PC-Engine EXT port. So I'll have to somehow remove the plastic using pliers and ruin the aesthetics of the unit, ugh.

The second problem is that even without the enclosure the PCB makes a flimsy connection with the PCE EXT port. I think the problem is lack of support making it easy to rock the PCB up and down, and causing connections to be lost.

Hopefully that is where the thingiverse 3D printed bracket that was posted comes in. Trouble is I don't have a 3D printer and have no experience with soliciting 3D printer services. Can anyone recommend me a service I can utilise to print a copy of the bracket?

I am located in Denmark so it would be good to find a service located here, or perhaps a Chinese one would be cheaper overall, since their shipping costs are always suspiciously lower than anything in the west. Advice is appreciated.

In hindsight if I were to make one final revision I would change all 0402 components to 0603 and move the port pin holes further forward to avoid the necessity having to remove plastic from the enclosure.

If I were really ambitious I would learn 3D modelling and build a custom perfect fit bracket to fit around the head of the enclosure that screws into the two holes the enclosure has on the side to help provide support when inserting into the EXT port. That would result in the, in my opinion, perfect PC Engine EXT RGB SCART cable.

What I have now isn't half bad, it just needs the extra step to achieve perfection.

[BuffaloWing]

You can order 3D printing service from Sculpteo. Base on your location, your order will likely come from the France factory. If you post the dimension of of your board, such as the distance of two diameter and there relationship to the connector, the diameter of your cable, I could model it for you so you get it professionally printed with high-end 3D printing service (in resin or SLS).

Well it took a while but the first manufactured PCBs turned out to contain a few measuring mistakes that prevented the PCB from fitting inside the enclosure, so I made adjustment and got a second batch made. Then I ordered the components on mouser and boy, you guys were not kidding about the puny size of the 0402 smd components, and my final design had a ton of them!

Luckily I have steady hands and by some miracle I managed to solder them all on without dropping any as finding them again would have been impossible and I had no spares. Barring a single smd which was not soldered on properly on one end everything worked during testing with a crisp RGB picture and clear sound though the SCART cable I used.

However, the trouble reared its head when I fitted the enclosure on and did a final test, it seems the two protrusions on the top and bottom of the enclosure prevent the cable from inserting fully into the PC-Engine EXT port. So I'll have to somehow remove the plastic using pliers and ruin the aesthetics of the unit, ugh.

The second problem is that even without the enclosure the PCB makes a flimsy connection with the PCE EXT port. I think the problem is lack of support making it easy to rock the PCB up and down, and causing connections to be lost.

Hopefully that is where the thingiverse 3D printed bracket that was posted comes in. Trouble is I don't have a 3D printer and have no experience with soliciting 3D printer services. Can anyone recommend me a service I can utilise to print a copy of the bracket?

I am located in Denmark so it would be good to find a service located here, or perhaps a Chinese one would be cheaper overall, since their shipping costs are always suspiciously lower than anything in the west. Advice is appreciated.

In hindsight if I were to make one final revision I would change all 0402 components to 0603 and move the port pin holes further forward to avoid the necessity having to remove plastic from the enclosure.

If I were really ambitious I would learn 3D modelling and build a custom perfect fit bracket to fit around the head of the enclosure that screws into the two holes the enclosure has on the side to help provide support when inserting into the EXT port. That would result in the, in my opinion, perfect PC Engine EXT RGB SCART cable.

What I have now isn't half bad, it just needs the extra step to achieve perfection.

[kamiboy]

Cheers for the reply, that service seems to do the trick.

As for modelling it for me, thanks for your offer, but I think it will be difficult to design such a thing without having all the parts on hand, along with a 3D printer to experiment with.

I had a look at the 3D print files for the bracket on thingiverse and it would serve as a good template to work with. The bracket would have to extend back a bit further though, and have two holes added, with a slot of sort or something similar to incorporate a bolt or something that the screws can screw into, to secure it to the extension cable enclosure. I think getting this thing right will undoubtedly take quite a few iterations and experimentation. In addition, the thingiverse files has screen shots demonstrating that the EXT portion of the OG and later revision PC Engines have slight differences which prolly should be incorporated in the design, or would at worst case require different designs for each, yikes!

I can share with you the PCB design files if you are planning on making a cable for your own PC Engine. But the PCB would be better serves with a final revision with the updates I suggested. However, I already have my cable so I don't see a reason to spend more time on revisions. I think I'll just order a resin print of the bracket for my own machine and end this project. It would be worth going the extra step if I or some other prospective entrepreneur was planning on mass producing this cable.

Alas, the margins on such after market solutions are so low that I don't think it would be worth anyones time.

[Konsolkongen]

That cable is a really neat design. Well done!

[kamiboy]

Cheers, 'twas a labour of love reflecting my fondness for that underrated gem of a platform.

[gorgyrip]

Yeah, I copied the mobius audio AMP. There was no schematics, just a PCB, so I hope I didn't make any mistakes copying it.

And, yes, the cable I am planning to solder to the end of that board has no components in it. It is an ultra high quality premium SCART cable that I bought for way cheap a few years back on clearance, I just chopped off one end of it.

This is going to be one helluva cable when it is done.

The circuit is the same for csync or is it only for composite?

[kamiboy]

The circuit uses and amplifies the c-sync signal from the EXT port.

[CZroe]

Wish I saw this thread a long time ago because this would’ve been a HUGE shortcut:
https://imgur.com/a/uVhjGKU

Made that post May 5th last year. It’s the Hyperkin Adapter for PC Engine and the first thing I thought of was that it needs a custom PCB for an RGB amp. I mean, it isn’t good for much else since both of the Hyperkin products it’s intended for are garbage. I got it specifically to explore making it into an RGB mod but lost interest when I heard about the RGB vs YUV colors thing.

For whatever reason Hyperkin’s partner designed their NEC composite video adapter and HDMI converters without a universal fit. They only fit US consoles without this adapter. Not that a physical lock-out would really stop us, right? I laugh at their nerve when they add $10 to those crappy $20 generic RGB2HDMI converters to make their less flexible console-specific “HD Link” cables, then they have the nerve to charge another $10 more for the TurboGrafx one, and THEN they have the nerve to charge another $10 for the PC Engine Adapter that could’ve been made to fit one of their cheaper cables instead.

They are $10 most places and even Console5 carries it. You get an enclosure and two fully-pinned connectors. I was also curious to know what kind of issues you might have if you severed the traces and jumpered the pins straight across so that you could connect a TG16 to a Super CD-ROM² or something else ridiculous. For an RGB mod a QSB could fit between and interface directly with the back row of pins from both connectors. The other two rows can have the necessary signals jumpered... or maybe the entire QSB can fit on the bottom.

[kamiboy]

Yikes, what an ugly monstrosity hyperkin has wrought. The design disaster that is the TurboGrafx is not worth that sort of effort. Better just throw that money after a PC Engine revision.

The YUV vs RGB PC Engine thing has recently entered my periphery as well. I haven't read up on it much, but from what I understand the jist of it is that the YUV derived composite colour space differs from the RGB derive one that all RGB mods rely on. I think I heard someone is working on a board that uses the YUV signals to deliver an S-video out with more accurate colours than RGB. If that circuit is ever built, and released for general use, I could have made an S-Video EXT cable, but I am afraid the video signal pins necessary for constructing color accurate S-Video are not among the EXT pins, so a no-mod cable is prolly not going to be possible. Such a shame, it would have been a fun spin on this project.