Gray screen on RF output from C64C.

[tcv]

I bought a C64c. It has a power supply, but there are only four pins on it which may or may not be suspect. The computer LED comes on. I connected it to a TV with an RF modulator. It's an Atari modulator, but I guessed it might be okay to use. The output, however, is a solid gray screen. (I don't have a monitor, otherwise I'd try that!)

I don't mind if I bought a project. I'd like to try to troubleshoot the problem.

I have a logic probe, a multimeter, and have some soldering and desoldering experience.

Can anyone give some tips on what to check?

[7800fan]

4 pins are normal. 2 are 5v and ground and other 2 are 9v AC.

 

First, I would check the power supply. Stock power supply are garbage and they usually fail. If you don't have 5v DC on the 2 pins furthest away from the top (notched shield), it's dead.

 

9 out of 10 times C64 has a blown chip when the PSU goes bad. Fortunately they are easy to troubleshoot and fix.

 

http://personalpages.tds.net/~rcarlsen/cbm/c64/ has LOTS of useful into on C64, repairing and troubleshooting guide, etc.

[tcv]

4 pins are normal. 2 are 5v and ground and other 2 are 9v AC.

 

First, I would check the power supply. Stock power supply are garbage and they usually fail. If you don't have 5v DC on the 2 pins furthest away from the top (notched shield), it's dead.

 

9 out of 10 times C64 has a blown chip when the PSU goes bad. Fortunately they are easy to troubleshoot and fix.

 

http://personalpages.tds.net/~rcarlsen/cbm/c64/ has LOTS of useful into on C64, repairing and troubleshooting guide, etc.

 

Thanks a bunch.

[carlsson]

The C64C has built-in RF modulator, that is the phono jack. Thus you don't need an external modulator, just plug the cable straight into the antenna input on the TV.

[tcv]

The C64C has built-in RF modulator, that is the phono jack. Thus you don't need an external modulator, just plug the cable straight into the antenna input on the TV.

What kind of cable can I use, though? Just RCA? I don't have an antenna input on my TV but I do have an RF-2-Coax converter.

 

Thanks for replying.

[carlsson]

What kind of cable does the Atari modulator end with? RF 2 Coax sounds like some sort of F-type adapter for the signal.

 

If you would have a composite video cable suitable for e.g. an Atari 800XL, it would be usable on the C64 too. Or if you're handy, you can solder up one yourself if you have spare parts and don't want to pay for a cable just in case. What you'd need is a 5-pin DIN, some cable and suitable connectors in the TV end, usually RCA/phono plugs but I suppose it depends on your TV. Ground is on pin 2 (middle), video is on pin 4 and audio on pin 3. You can search for a more visual guide elsewhere on the net.

[tcv]

What kind of cable does the Atari modulator end with? RF 2 Coax sounds like some sort of F-type adapter for the signal.

 

If you would have a composite video cable suitable for e.g. an Atari 800XL, it would be usable on the C64 too. Or if you're handy, you can solder up one yourself if you have spare parts and don't want to pay for a cable just in case. What you'd need is a 5-pin DIN, some cable and suitable connectors in the TV end, usually RCA/phono plugs but I suppose it depends on your TV. Ground is on pin 2 (middle), video is on pin 4 and audio on pin 3. You can search for a more visual guide elsewhere on the net.

 

Here's an image:

http://i.imgur.com/2NfLwMr.jpg

 

This cable and box is the one that connects to the RF output of an Atari 800XL to a TV. The coax adapter I mentioned plugs into the coax input on a TV. The other end accepts an RF signal from a cable like this. I know the cable works with the Atari 800XL to this same TV. The 800XL also has an internal RF modulator.

 

Does that help?

[carlsson]

Ok. Isn't that an automatic computer/TV switch, rather than a RF modulator per se? I would assume it can be made to work with the C64 too, so there is a risk yours has gone bad after all.

[tcv]

Ok. Isn't that an automatic computer/TV switch, rather than a RF modulator per se? I would assume it can be made to work with the C64 too, so there is a risk yours has gone bad after all.

 

Correct. It's not an RF modulator. Even though there's a suspicious black box along the cable, I believe it's just a cable. Since it works with the Atari (which also has an in-built RF modulator), I imagine it would work the a C64.

 

I've got a few things on the way to help test it. I have a replacement PLA on the way, better video options, among other things. We'll see. I verified the voltages today and did some probing with a logic probe and it's making all the right voltages and sounds so far. I'm hopeful.

 

Thanks for replying again!