Reddit reviews Svideo to HDMI Adapter Converter RCA AV CVBS Composite S-Video R/L Audio to HDMI Upscaler CoolDigital Support 720p/1080p with 3RCA Svideo Cable for DVD VCR PS2 HDTV

Get a converter box https://www.amazon.com/Converter-CoolDigital-Composite-S-Video-Upscaler/dp/B01CY34ZQA this box will take in SD analog video and convert it to HDMI, then HDMI just goes into the receiver.

To get an 80-col image out of your C128, you need to handle the following things:

1. the C128's VDC outputs a digital RGBIHV (R-G-B-Intensity-Hsync-VSync) image, while VGA needs an RGBaHV or RGBaC input (R-G-B analog-HSync-VSync, or in some cases R-G-B analog - CSync) so you need a digital-to-analog converter of some kind
   

• The VDC outputs its signals at 5V (TTL levels) on all pins, while VGA works with 5V HSync/VSync and 0.7V signals for each of the primary colors, so you also need to have a level-shifter of some kind
  
• the VDC outputs its signals at 15.625 kHz HSync, whereas most modern monitors won't even sniff at a signal that's not at 31.25 - I just checked and your monitor needs a minimum scan rate of 30 kHz, so you need either a VGA scan converter, or you need to ditch VGA entirely.
  
  The first two things can be handled in one go - take a look at the C128 RGBI to VGA Ultimate. There aren't many components to it and it's relatively easy to understand:
  
  
• the diode ladder (six of them) around the middle of the image acts like a rudimentary ADC (Analog-to-Digital Converter) for each colour channel:
  
  • if the input colour pin for a pixel is low, the output colour is low (close to 0 V) - it ignores the intensity pin
    
  • if the input colour pin for a pixel is high, but the intensity pin is low, the output colour gets to halfway the maximum voltage (about 0.35 V) - it's a regular-intensity colour pixel
    
  • if the input colour pin for a pixel is high and the intensity pin is high, the output colour is set to the full voltage (0.7 V) - it's a high-intensity (bright) colour pixel
    
• the 2 kΩ trimpots near the diode ladder can help fine-tune the colour levels
  
• the bottom glue logic chips (7486, TTL XOR logic gates) combine the positive-level (a value of "high" is active) HSync and VSync into a negative-level ("low" is active) CSync (composite sync) that VGA can work with
  
  • some converters need positive sync, some need negative - best to build them in at first and bypass them later if they're not necessary
    
• the big 74LS138 chip performs a special "brown correction"
  
  • normally, Commodore 80-column and CGA monitors would make the colour palette a bit more versatile
    
  • any "dark yellow" (R-G-B-I 1-1-0-0) pixel would be corrected by halving the analog level of "green" by dropping the voltage through an extra diode
    
    At the output of that, you have a fairly standard RGBa VGA-like signal at a low (15.625 kHz) scan rate.
    
    To handle point 3. from my list above you need a frequency doubler - if you want to just be done with it, get a GBS8200 board and a good power-supply for it, plug your circuit's RGBa output into it and get a nice, clean VGA signal out of the other side. If you want to DIY it, read how an AD724 RGBa-to-S-Video chip works, make a mini board for that, then finally get an S-Video to HDMI converter which will give you an even cleaner HDMI out.
    
    EDIT: Almost forgot. Since the C128 has dual video outputs, you might also want to make an A/V to S-Video cable. If you go the full DIY route, you'll now have two S-Video outputs, so if you also get a cheap S-Video switchbox with two inputs and one output into an S-Video to HDMI converter, you can swap between 40/80 modes at the push of a button.
    
    EDIT EDIT: There's actually a circuit board that does all that and gives you a switch to flip the outputs through a single S-Video made by Pyrofer and Appy Paul, but they haven't made one in a while, we're still waiting for them to continue production.

For power supplies, I've had good luck with Commodore4Ever (https://commodore4ever.net/collections/power-supplies/products/commodore-64-vic-20-power-supply-atom-retro?variant=29735132725312).

For video cables, provided your monitor/tv has RCA or SVideo, you can try 8bitclassics.com (https://www.8bitclassics.com/product/c64-svideo/). Getting those attached to HDMI is a bit more challenging (and expensive). It looks like the RetroTink (http://retrotink.com), or the OSSC (https://www.videogameperfection.com/products/open-source-converter/) are the "Cadillac" options. I opted for a "cheap" SVideo to HDMI converter (https://www.amazon.com/dp/B01CY34ZQA/ref=cm_sw_em_r_mt_dp_U_QGeuDbCFBY6VF), which is servicable, but there is a slight video lag that I find annoying.

If you don't have your original drive or floppy disks (or if your floppy disks have degraded over time like some of mine), you might also explore some drive emulation options. The more affordable approach is an SD2IE device (https://www.c64-wiki.com/wiki/SD2IEC). If you're a bit of a tinkerer, you could look at the Pi1541 (https://cbm-pi1541.firebaseapp.com). And the Cadillac solution is the Ultimate2+ Cartridge (https://ultimate64.com/Ultimate2Plus_Red_Tape). I don't have any experience with the SD2IE or Pi1541 options, but I do have the Ultimate2+ cartridge, and can't recommend it highly enough if you have the budget (and it is spendy).

Alternatively, if you have the budget, and are looking for a non-purist, but convenient solution, you could look at the Ultimate 64 (https://ultimate64.com/Ultimate-64). It's an FPGA implementation of the C=64 using all modern components, and has native HDMI out, support for the original peripherals, as well as implementing all the niceties of the Ultimate2+ cartridge -- it's made by the same folks. I also have one of these, and can also not recommend it highly enough. You could drop it into your original case, or put it into a brand-new case from PixelWizard (https://shop.pixelwizard.eu/en/commodore-c64/36/c64c-case-breadbin-gray).

I put my U64 into a new PixelWizard case, but used an original C=64 breadbin keyboard for EBay. Using vintage parts for this purpose does give me the heebie-jeebies a bit... but at least *I* didn't pull it from a system. LOL

https://www.amazon.com/Converter-CoolDigital-Composite-S-Video-Upscaler/dp/B01CY34ZQA
Mono price.com sells the also but it is more expensive (personally I would buy the Monoprice. Their equipment is very good)-https://www.monoprice.com/product?p_id=9994