Commodore 64 RF Modulator Replace with DIY board

Got an issue?
486junkie
Member
Member
Posts: 4
Joined: Mon Jan 29, 2018 9:41 pm
Location: SE Michigan, USA
Contact:

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

User avatar
eslapion
Member
Member
Posts: 763
Joined: Mon Jul 20, 2015 10:11 am
Location: Canada
Contact:

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
Member
Member
Posts: 4
Joined: Mon Jan 29, 2018 9:41 pm
Location: SE Michigan, USA
Contact:

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

dgc79
Member
Member
Posts: 3
Joined: Fri Jun 21, 2019 2:41 am
Contact:

Re: Commodore 64 RF Modulator Replace with DIY board

Post by dgc79 » Fri Jun 21, 2019 3:10 am

I had a similar issue with my 250469 rev4 board with the modulator no longer working.
Rather than have a go at repairing it I decided to build my own, the RF section was no longer required.

I found this schematic and set to work:

Image

Take note in that image the pinouts change between 6569 and 8565. I have the 8565 so I threw together this vero-layout:

Image

That red dot on the board is a cut track, there is another cut track underneath the diode.
The text labels on the left of the board are the pin headers. The audio pin can be skipped, in this case the cut track for the audio line is not required.
The pin headers I used were these:

Image

And this is how it ended up looking after I was finished:

Image

Note that I moved C4 so it didn't have to stretch so far.
This little mod works great as a replacement! I actually think the image on my 1084 is a little clearer now!
I hope this helps out someone.

User avatar
eslapion
Member
Member
Posts: 763
Joined: Mon Jul 20, 2015 10:11 am
Location: Canada
Contact:

Re: Commodore 64 RF Modulator Replace with DIY board

Post by eslapion » Fri Jun 21, 2019 3:53 am

dgc79 wrote:
Fri Jun 21, 2019 3:10 am
I had a similar issue with my 250469 rev4 board with the modulator no longer working.
Rather than have a go at repairing it I decided to build my own, the RF section was no longer required.
Great idea!

Personally, I would have done this board upside down (with the parts going down) and added a single side PCB on top (with the copper layer away from traces and solders) as grounded shield to prevent RF noise from getting in there.

Also, I would strongly suggest you check what comes out with an oscilloscope to ensure the signal's amplitude matches the requirements of RS-170A. The amplitude from sync to full white should be 1V peak to peak.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders

dgc79
Member
Member
Posts: 3
Joined: Fri Jun 21, 2019 2:41 am
Contact:

Re: Commodore 64 RF Modulator Replace with DIY board

Post by dgc79 » Fri Jun 21, 2019 10:59 am

I still have what's left of the old modulator. I was thinking of gutting it and soldering it over the top of the new board for shielding, just haven't got around to it yet. I wanted to see it work first!

User avatar
eslapion
Member
Member
Posts: 763
Joined: Mon Jul 20, 2015 10:11 am
Location: Canada
Contact:

Re: Commodore 64 RF Modulator Replace with DIY board

Post by eslapion » Fri Jun 21, 2019 11:19 am

dgc79 wrote:
Fri Jun 21, 2019 10:59 am
I was thinking of gutting it and soldering it over the top of the new board for shielding...
Just as good, I guess.

I remember back in December 2017, when I was at the World of Commodore, there was a guy selling little boards as replacement for the modulator and they had an S-Video output built-in.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders

dgc79
Member
Member
Posts: 3
Joined: Fri Jun 21, 2019 2:41 am
Contact:

Re: Commodore 64 RF Modulator Replace with DIY board

Post by dgc79 » Mon Jun 24, 2019 2:53 am

You aren't thinking of this one are you?

Image

The site where you purchase this: https://16xeight.de/ is not currently up.

"Diese Website ist zurzeit im Wartungsmodus.
Bitte später wiederkommen."

converts to:

"This site is currently in maintenance mode.
Please come back later."

So therefore I just went ahead and built a vero-board replacement.

User avatar
eslapion
Member
Member
Posts: 763
Joined: Mon Jul 20, 2015 10:11 am
Location: Canada
Contact:

Re: Commodore 64 RF Modulator Replace with DIY board

Post by eslapion » Mon Jun 24, 2019 10:14 am

The board you're showing is really from a German guy but Francis sells a similar design except there is no adjustment pot.

Francis was at the last World of Commodore in Toronto last December. He is listed here: http://c64os.com/post?p=75

If you click on the photo of his booth, you can see the C64 that's turned on has had its RF modul removed and replaced by a small yellow board.

You can also see both C64 are fitted with a PLAnkton!
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders

Post Reply Previous topicNext topic

Who is online

Users browsing this forum: No registered users and 2 guests