Edoardo kinmami
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Feb 02,2022
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Commodore 16 (C16) Plus 4 RF modulator replacement

Inspired by projects from c0pperdragon, mbarszcz-pcb, tebl and VGP. It fits the commodore 16, Plus 4 and replaces the RF modulator.
2745
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30
Published: Feb 02,2022
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Topic
DIY Electronics
Hardware
Computers & USB
Commodore Hardware video RF modulator 16 composite DIY C64 computer
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  • Tested with the A/V cable connected to the computer and monitor: LUMA OUT (pin 8) 0.912V, COMPOSITE OUT (pin 7) 1.063V, CHROMA OUT (pin 6) is 0.420V on my C= Plus/4. The video amp is supplied by 3.316V.

    Jun 03,20243 Comments
    cnehme 2024-06-03 21:25:03Reply

    on Mine. Video Amp = 3.288v, Pin 8 = .914v, Pin 7 = 2.106v, Pin 6 = .820v. I get the same reading from the board no matter if the video cable is plugged in or not. It seems something is causing Pin 7 to supply the wrong voltage. Could PCBWay have used the wrong value resister somewhere, if so, which would be the likely one?

    cnehme 2024-06-03 21:32:32Reply

    I just checked the resistors on the board, 4 of them are out of spec on the installed board. I had 10 of these built. I will check the others tomorrow.

    Edoardo kinmami 2024-06-04 06:53:39Reply
    Reply@ cnehme：

    Nominal resistors value is written on the top silk layer of the PCB.

    Reply

  • I have attached a photo of my board installed in the c116. I only connected 2 of the grounding points. Also I am using the standard c116 composite video connector I am not using s-video

    Jun 01,20244 Comments
    cnehme 2024-06-01 18:59:35Reply

    I have now solder all 3 point to ground, but makes no difference. The colour bleed occurs on both the CRT and LCD screens, also I tried two different cables and made no difference at all.

    Edoardo kinmami 2024-06-01 20:21:09Reply

    The components appear to be correct in value and position. C16 and Plus/4, C116 are electrically equivalent, then I suggest you check the voltage levels with a scope and multimeter. Verify if the 3.3V is steady at the video amp input and if the composite video level is between 1.0V to 1.1V (with the monitor connected). The blurry, yellow ghosting effect is likely caused by incorrect termination or improper voltage levels at the composite video.

    cnehme 2024-06-03 17:50:10Reply
    Reply@ Edoardo kinmami：

    Ok so I measured the voltage between Pin 7 on the Board and Ground on the board and I get 2v. I then measure the voltage directly on the RCA cable and I get 1.8v. I measure the RCA cable voltage with my unmodified c116 and Plus/4 and both read 1.5v. So your board is outputting an additional 300mv which I assume is significant? I don't know which chip is the video amp and which pins to measure for the 3.3v

    Edoardo kinmami 2024-06-03 18:52:18Reply
    Reply@ cnehme：

    I have posted several photos with actual voltage reading, FYR. Again be sure your cable has not an in-series resistor and/or your monitor is correctly 75ohm-terminating the COMPOSITE VIDEO to ground. The circuit is designed to work with standard spec.

    Reply

  • FYR

    Jun 03,20240 Comments
    Reply

  • Composite video output amplitude (termination 75 ohm to gnd @ monitor side and no in-series resistor across the A/V the cable)

    Jun 03,20240 Comments
    Reply

  • each video output is terminated by 75 ohm (to ground) when the A/V cable connects the computer to the monitor.

    Jun 03,20240 Comments
    Reply

  • Hi there I ordered a few of these already assembled by PCBWay. When installed in my C116, the picture (the words on the screen in attached below) has colour bleed which is non existent in the original modulator, any ideas why this might be the case?

    May 30,20245 Comments
    Edoardo kinmami 2024-05-30 12:31:11Reply

    I have tested the circuit on several PAL C16 and Plus/4. - Is the board properly connected to ground? There are 3 connection points on each side. - Is the solder jumper left OPEN? - Does your S-VIDEO cable have an in-series resistor on Luma or Chroma lines?

    Edoardo kinmami 2024-05-30 12:33:01Reply
    Reply@ Edoardo kinmami：

    I assume the video cable is 75 ohms and the termination at the CRT monitor (or video upscaler + LCD) is also 75 ohms. Pls be sure that your cable has not a series resistor anywhere from 300 to 2K ohms on CHROMA (some cables originally made for the C64 have a series resistor). If the resistor exists than it causes a very low CHROMA level.

    Edoardo kinmami 2024-05-31 21:10:25Reply
    Reply@ Edoardo kinmami：

    Ghosting occurs when impedance mismatches cause signals to be reflected

    cnehme 2024-06-01 18:58:05Reply
    Reply@ Edoardo kinmami：

    I am using an original cable I will try another one

    Edoardo kinmami 2024-06-01 20:22:11Reply
    Reply@ cnehme：

    no in series resistor?

    Reply

  • Any chances an audio jack can be added to the board? Something to like how the RF Modulator that The Retro Channel made for the Commodore 64 and 128

    Dec 11,20231 Comments
    Edoardo kinmami 2023-12-12 11:56:39Reply

    thanks for the interest. Noted well for a future V2.

    Reply

  • holes at the edge are NOT castellated

    Mar 22,20230 Comments
    Reply

  • THS7314 can be used as well if THS7316 is not available

    Feb 06,20230 Comments
    Reply

  • there's also a place for a component but no indication.

    Sep 06,20222 Comments
    Edoardo kinmami 2022-09-06 08:47:40Reply

    Hello, it is listed as L1 (ferrite bead) inside the BOM list. It is BLM18KG300TZ1D Murata Electronics 490-16498-1-ND. It must be mounted

    Marc Bronsard 2022-09-08 19:35:22Reply

    Hello, I installed L1 and everything is working perfectly ! Thanks a lot for your support.

    Reply

  • I tried to make this work, but I have no output at all. There's a pad just right of the 680 resistor, do I have to bridge it ? A schematic would help me diagnose the problem. thanks !

    Sep 06,20223 Comments
    Edoardo kinmami 2022-09-06 08:45:15Reply

    Hi that solder jumper is normally open

    Edoardo kinmami 2022-09-06 14:37:29Reply

    updated the silk screen layer to avoid mistakes

    Edoardo kinmami 2022-09-07 13:42:20Reply

    do not forget to connect the board to ground

    Reply

  • Hi Bronsard, pls find here the schematic for your ref. if L1 is not mounted then there is no power supply for the THS7316

    Sep 06,20220 Comments
    Reply
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