Commodore 64 RF Modulator Replace with DIY board

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486junkie
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Commodore 64 RF Modulator Replace with DIY board

Post by 486junkie » Mon Jan 29, 2018 10:27 pm

Hello everyone:

First time on this forum and first time Commodore 64 owner. I have a Commodore 64 that I got off of eBay after winning it on an auction, which came with a dead PSU (9VAC lines were at 0.63V). I recently got a new PSU off of eBay, plugged in the C64 using an RCA cable and an RCA to RF, and it fired up. However, when I moved or accidentally bump the RCA cable, the picture goes out, is garbled, etc. The next day, there was an RF noise on the screen (horizontal vertical hold line), and after a reset, there was no video.

After doing some diagnostics, I found out that 2 or more capacitors leaked big time that destroyed the circuits on the C64's RF Modulator. I successfully removed the damaged RF modulator in question, tested two of the electrolytic capacitors, and they were flat. The Tantalum (tantrum) capacitors saw better days as well, and the markings were hard to read.

So my question is this: can someone provide to me a schematic for the A/V port by using the pinout of the old RF modulator (2x 4-pin jumpers) for the A/V port?

The motherboard is a 250407 Rev. B with the following pinout:

RF:
1 - +B*
2 - Sync + Luma In
3 - Color (Chrominance) In
4 - Audio
5 - Composite
6 - Luma Out
7 - Color (Chrominance) Out
8 - M1*
9 - PF. Out (RF)*

* Not sure if these are needed, but I don't need the RF as it's more of a suggestion

A/V port:
1 - Luma
2 - Gnd
3 - Audio Out
4 - Composite
5 - Audio In
6 - Chrominance (Color)
7 - N/C
8 - N/C (or +5VDC on some models)

Also, would it be a good idea to add the 330ohm resistor for the chrominanace (color) on the PCB board I'm planning on making?


10 PRINT "HELLO WORLD"
20 GOTO 10
RUN

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eslapion
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Re: Commodore 64 RF Modulator Replace with DIY board

Post by eslapion » Mon Jan 29, 2018 10:31 pm

Francis Bernier makes small replacement boards for the RF modulator which provide better image display but no more RF.

Contact: fb@3dpxl.com
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders

486junkie
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Joined: Mon Jan 29, 2018 9:41 pm
Location: SE Michigan, USA

Re: Commodore 64 RF Modulator Replace with DIY board

Post by 486junkie » Tue Jan 30, 2018 9:25 pm

Figured out what Pins 1 and 8 are for on the RF Modulator. Pin 1 is the voltage (+5VDC or something thereof from the VIC-II chip on pin 40), and pin 8 is the ground. Those are important, right?
10 PRINT "HELLO WORLD"
20 GOTO 10
RUN

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