I own a ROM-0 that was part of a //e Upgrade Kit. Today, I saw photos of another ROM-0 board, and it has two slight differences that mine lacks.
There is an extra resistor on it, plus a little bodge board.
Do any of you know the purpose of these?
I cannot tell where this bodge board is wired other than to that 3340, so IDK what it is intended to remedy.
I don't recall ever seeing a board with that resistor in place, so again, IDK what purpose it serves, nor why it was removed in later revisions.
Just guessing, but being 75ohm I would say that R121 is part of the video out circuit. Maybe RS4 in the schematic which looks optional (feeds the modulator connector?)
::gs vid.png
Other board might be part of the audio out as well.
That is an interesting guess. I will look at the circuit paths and see if i can validate it. 75Ohms would indeed tend to be video, bt bear in mind that tose photos are the first time that I have seen this resistor wired, and I have had several Rom 0 boards. I was curious on the purpose of these mods/bodges because I am curious what they are intended to correct. That little sub-board is something that I have absolutely never seen before, although I have seen bodges on the back side of the PCB, so I might want to compare if any of those are to the same points.
To date, I hven't documented them, or tried to do a logic check on what they are doing. I wish that I knew where the other side of that sub-board was wired. (I can't logistically justify spending the money required to buy that specific eBay board, just to determine this.)
I suppose when I have anything to add, I will post it, in the event that it benefits anyone else.
P.S. Would it be typical for the component IDs not to align on these schematics? I would expect R121 to be identical on the schematic as it is marked on the PCB, as otherwise, the schematics are somewhat borqed.