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VIC-20 No Signal yet the system is working.

V

VirusVox

Member
Joined
May 5, 2020
Messages
45
Location
New Brunswick, Canada
Good afternoon everyone!

Over the weekend I acquired a VIC-20 minus the power brick from a flea market and after acquiring a few cable pieces I've got all of the necessary items to test the system. Powering on the system turns on the power LED, but I'm getting no signal from my RF modulator. I can see the static patterns in the TV change, but no signal ever comes in. My cable setup is the RF modulator into a single yellow RCA cable, running into an RCA to Coax adapter, screwed into the coax jack of my tv.

After doing some troubleshooting I've determined the actual system appears to be working fine - Pressing Run + Shift will start the Datassette drive spinning and reading a cassette, so the system is able to accept and interpret commands.

As another troubleshooting step I inspected the RF modulator and as far as I can tell all wires and whatnot are connected correctly, and nothing appears broken or burnt.

I have partially opened the system (clips are unbroken but extremely brittle) and the internals looked almost spotless, less some minor dust which I carefully blew out.

For a power brick I am using the power supply I had used on my Commodore 64 (after I had learned they were backwards compatible with this type of VIC-20) when I got it a few years back - though it doesn't look standard. It is an official Commodore power supply and was given to me as a PSU for the main system, but it only has 4 pins and not in the same orientation as the floppy power supply. It bears a part number I couldn't find an exact match for - 251053-10. I do know this brick fully powers a Commodore 64. I intend to replace it with a modern one as soon as I can confirm the system fully works.

Where should I go next?

Thank you!
 
I am a little confused regarding what is an RF signal (from the RF modulator) and what is a video signal in your description.

Can you explain a bit further please as to how your signal is connected please?

Dave
 
The exact cable setup in this instance is: The VIC-20 runs to the RF modulator through a 5-pin DIN plug. This outputs to a standard RCA jack on the modulator box itself, which is connected to an RCA to Coax coupler through a standard one-cable RCA cable, which is then screwed onto the antenna jack of the TV.
 
How hard would it be to buy/borrow/build the cable that would let you go straight to composite in on the TV side instead of messing with RF? Maybe the modulator bought the farm, or your TV just doesn’t like the output.
 
In practice it'd be quite difficult right now as I don't have any of the supplies to build said cable. I'll be ruling out the TV tonight, as I'll have a different, much older TV available to test on, just in case!
 
VirusVox said:
In practice it'd be quite difficult right now as I don't have any of the supplies to build said cable. I'll be ruling out the TV tonight, as I'll have a different, much older TV available to test on, just in case!
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Of course you have! Just cut the cable from the RF box and resolder it for composite. You have at least one RCA jack, don't you? That's enough for the video signal.
 
Timo W. said:
Of course you have! Just cut the cable from the RF box and resolder it for composite. You have at least one RCA jack, don't you? That's enough for the video signal.
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Ahhh I see! That's true, the issue is I don't have like a soldering iron or anything, though I was planning to pick one up within the next couple weeks. I've hooked the VIC-20 to an Emerson CRT TV manufactured in 1993 and now I can more clearly point the finger towards the RF Modulator. When powered on, depending on the switch setting, I can see the static in the TV shift from a normal 'flat' pattern to a much more shapely and angled one; it's very clearly affecting the TV itself, it's just not outputting proper video. If I flick the switch on the modulator, this changes which channel the VIC-20 effects static on. The TV also emits a relatively high pitched sound from the speakers.
 
For testing, you can also just splice the wires without soldering. At least you will know then if the RF box is really the issue - but it seems so.
 
I'd second just buying one. The 5 pin DIN connector is a very common/cheap part and it's not "hard" to just take an existing AV cable you might have lying around and just cut off one end of it and solder the ends to the appropriate pins but... actually, soldering to the pins in those things is kind of a POS to do without melting the plastic in the connector if you're a novice, and at $6 for the assembled cable you won't really save any money.
 
Yes, buy a cable once you know that the RF box is bad and not the VIC-20. But why spend money beforehand if you can cobble together a cable quickly to verify that the VIC-20 is indeed working? Either way, you don't need the RF box after that anymore anyway.

Also note that the RF box takes the composite signal as an input already, so you don't even need to mess with the pins on the DIN connector. It takes maybe 2 minutes to make and all you need is a sharp knife.
 
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Timo W. said:
Also note that the RF box takes the composite signal as an input already, so you don't even need to mess with the pins on the DIN connector. It takes maybe 2 minutes to make and all you need is a sharp knife.
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Not that I'm expressing an opinion one way or the other here, but one could point out that they're not making any more (now 40 year old) VIC-20 RF modulators and it's an "original" accessory so, sure, I can get why the OP might not want to butcher it without knowing for sure it's the problem. And it might not be, the VIC certainly *could* have a bad 6560 video chip/output transistor/whatever.

Frankly if you're really that concerned about spending any money you don't have to another option is just cut the end off an AV cable, strip off a little extra length of wire, fold it back on itself and twist it up to make it fatter/stiffer, and insert the bare ends into the DIN connector on the VIC itself. Boom, same test and you don't need to cut up the RF modulator. Don't bother with sound right now, just cut a simple RCA cable in half, figure out which wire is the "shield" and which is the "tip", and stick the shield wire in pin socket 2 (the one directly across from the alignment notch) and the "tip" wire in pin socket 4. (The one to the immediate right of pin 2 if the diagrams on this page are from the point of view looking into the socket from the back.)
 
And it might not be, the VIC certainly *could* have a bad 6560 video chip/output transistor/whatever.
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That's what I'm saying.

I can get why the OP might not want to butcher it without knowing for sure it's the problem.
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He never said anything like this. He would have done it already had he access to a soldering iron (see above - that's what he said).

another option is just cut the end off an AV cable, strip off a little extra length of wire, fold it back on itself and twist it up to make it fatter/stiffer, and insert the bare ends into the DIN connector on the VIC itself. Boom, same test and you don't need to cut up the RF modulator.
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That's not an option when it comes to testing. Using a flaky video connection like this on a system that is in unknown condition just adds another possible error cause and may even lead you into the wrong direction. You need to use the correct plugs for a proper connection.
 
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Timo W. said:
That’s not an option when it comes to testing. Using a flaky video connection like this on a system that is in unknown condition just adds another possible error cause and may even lead you into the wrong direction. You need to use the correct plugs for a proper connection.
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Hogwash. I’m not saying it’s going to work that well or be a great idea for long term use, but I’ve shoved wires into socket connectors for a quick test plenty of times. For a more solid connection look for some needles or unbend and bisect a paper clip with wire slightly smaller in diameter than the DIN plug pins and insert them along with the stripped wire ends. Seriously all we’re looking for here is if fiddling with this gives at least a flash of a full display on a composite monitor input, you need a clean connection for all of ten seconds.
 
I agree. Poke the wires in for a test...

If it works (even briefly) you can then do the job properly.

If it doesn't work - you are correct, it could be the VIC-20 or it could be an incorrect connection. You just try something else instead.

Obviously, the best solution is to stick a ‘scope probe on the video output and look for a clearly-defined video signal. But I guess that is not an option by the OP.

Dave
 
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