VIC-20 Mod Identification Help

[rpiguy9907]

I have recently acquired a third VIC-20 and it has a mod I can’t identify. It looks like two audio jacks have been installed on the back. What could this be for?

Stereo sound? To use a regular cassette instead of a datasette?

[srowe]

Might be an S-Video mod but could be anything. Do you have a picture?

[rpiguy9907]

So there are actually THREE added line jacks on the back of the VIC.

https://imgur.com/gallery/DwqJfDI

Hopefully hose pics will help identify what they do.

[Floopy]

Banana plug? Guessing that the switch is for some kind of custom Memory add-on. Just a guess

[srowe]

Ow, someone's brutally widened that expansion port.

Could you open it up? I'd need to see what those sockets are connected to.

[rpiguy9907]

Wow it only gets weirder.

https://imgur.com/gallery/67O02D3

The line outs appear to be tied to the screw holes on th left and right side of the motherboard.

The red switch appears to be connected to a jumper on R9/UB6.

It looks like some of the SRAMs on the bottom row (not pictured) are 116 not 114, so it is possible it is some kind of RAM mod.

No idea about the through holes or all the copper conductive tape inside the case.

I bought a VIC from a madman, lol.

[rpiguy9907]

Having thought about it a bit, my only guess is that the copper conductive tape and line outs are actually just there for grounding and to reduce interference?

This is an earlier VIC-20 (under 100K) and they were known for generating interference. Maybe this guy just got tired of it messing up his TV, lol.

[Floopy]

No custom Rom, ignore my comment. The copper strip has to be a grounding device of some sort seeing that it is tied to the grounding plane. Why the 555 timer? I can't see the pins it is soldered to, or is it even soldered to it?

Just guesses,

[rpiguy9907]

Maybe the SRAM was replaced with DRAM? I have to go back and look. You would need a timer to refresh, but not just a timer so that is unlikely as well.

[Mike]

It looks like some of the SRAMs on the bottom row (not pictured) are 116 not 114,

There are no "116" SRAMs and, for that matter, no "114" SRAMs either.

Normally, 2-prong VIC-20s come equipped with eleven 2114 or 5514 1Kx4 SRAMs, of which ten realise the 5K main RAM (1K for the system, 0.5K for the standard text screen and 3.5K remain for BASIC programs and variables), and one provides the attribute data for the text screen (a.k.a. "Colour RAM").

In the CR variant of the mainboard, with DIN power jack, the 5K main RAM are provided with two 2Kx8 6116 SRAMs and a single pair of 2114 (or 5514) SRAMs.

If you suspect some form of RAM mod, your VIC-20 should display another number than 3583 BYTES FREE on power up (without any cartridges attached). You can safely assume, that there isn't some type of DRAM involved. And yes, a photo of the *entire* mainboard would be very helpful to sort this out.

Why the 555 timer?

Can't be anything else than a reset switch.