So while still waiting for HBSound's Prototyping sponsor, PCBWay,  to finish up and ship off the prototypes for that project.  I did have some time to work on the ZX81 Restoration.   I am still working through the best way to clean up the corrosion without further damaging the silk screen, but I did have time to start thinking out  soldering the video modification.  Since the board came ceaseless,  and without a number of it's connectors and modulator can enclosure. This afforded me the opportunity to build out the existing board the way I want it.  And since I am building a custom wedge case enclosure to hold this thing;  that is the plan anyway.  I decided the best course of action was to solder two header pins in place of the can mounts and build up  Ziggurat communications video 555 Mod to add back the back porch that's missing from the video signal.  I cut a piece of perf board to fit across the two pins and went to work on modifying Ziggurat's strip board layout to work on perf board.  This also allowed for re-positioned  power and video connections.  As I am building a new enclosure I moved the connectors 90 degrees to the back of the case to clean up the wedge esthetic so it matches the rest of my micros.  If anybody has the slightest clue as to why Sir Clive decided to mount them on the side, instead of around the back shoot me a line, this has always mystified me.

The new layout:

As you can see I didn't picture wiring through the connectors on my layout.  I am still trying to figure out the best way to lay out the connections.  I will also most likely run a larger gauge wire down the side ground rail directly from the back side of the USB connector to one of the larger power traces on the PCB since back feeding the full current of the power supply from the can input is most likely not the best Idea. If there is any interest to the DIYLC files I can provide them at request, though the circuit and diagram are easy enough to follow from the pictures provided.  In keeping with the "volume of one" design rule I set for myself on this project, I will not likely do a layout for a PCB since I don't think its likely others will want my specific customization.  Perhaps if I get closer to the case build, if there is interest I would reconsider, for now we will see.

BOM:
I used the exact same BOM from the Ziggerat board which i will replicate here (the source document gives permission with accreditation to Ziggerat ind.):

Resistors
R1, R2 10 kΩ
R3 68 Ω
R4 56 Ω
All 0.25 W, 1% metal film.

Capacitors
C1 22 μF radial electrolytic, 16 V (or higher rating).
C2 10 nF ceramic disc.
C3 820 pF ceramic disc.
C4 82 pF ceramic disc.

Semiconductors
D1, D2 1N4148
Q1, Q2 PN2222
U1 NE555

My additions:

18x10 Perf Board

USB B type connector

2 conductor easy to mount Video connector of your choice

And while were at it the schematic:

(the source document gives permission with accreditation to Ziggerat Ind.)

The source document gives a very good description of the circuit function, so its not really needed to do a full work up here but if your are interested Oli's Old stuff does a fantastic job explaining the options, and Grant Serle has this resource on the ZX80, as well as this on the ZX81.  Ziggerat industries Web Site is the original source for the modification (under misc).

Up next:

Up next is building and testing the circuit, as well as fitting it.  I still have to do something about about the top board HASL; I may do some high resolution shots and ask around to see if it is problematic  For now I cleaned up the stuff under the can ground plane as the video mod will be soldered in place on top of it and accessing later will be a different kind of hassle ;-).

If you have liked this please feel free to share, comment and check out my other projects here on hackaday.io.  I usually have one major project going on and a few side things, most of which are related to retro or home brew computing.