Lafayette CD4 demod

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aperh

New member
Joined
Sep 22, 2008
Messages
7
I have a lafayette cd4 demodulator and I need to know if it's functioning properly. The radar light never comes on while playing cd4 records, or the jvc setup disc. My question is, can I go into audacity and generate a 35khz tone and just run it into the demodulator. If the demod was working ok shouldn't this light the radar? I'm trying to figure out how I can tell if the demodulator is working properly or not because I need to know if it's the demodulator or something else in my setup.
 

Q-Eight

2K Club - QQ Super Nova
Since 2002/2003
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Sep 30, 2003
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Castlegar, BC, Canada
The bulb could be burnt out or wiring damaged. I've had to replace a light or two on many pieces of vintage equipment.

Does it SOUND like you're getting )) Separation (( ?
 

aperh

New member
Joined
Sep 22, 2008
Messages
7
The bulb looks ok and tests for conductivity so I'm assuming it's good. Also, it's not the original bulb, both the radar bulb and the power bulb were replaced sometime before I got the unit, the power bulb is ok and lights up. I tried 30khz, 35khz, and 40khz figuring anything above 30 would make the radar light up but I got nothing. I set the sampling rate to 96khz in audacity so it should be outputting fine. Is there any other way I can check if the demod is working or am I doing something wrong in generating the tone in audacity?
 

Doug G.

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Jul 8, 2007
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Austin, Minnesota
Ya, it doesn't look good. Usually the lamp is pretty easy to light up even with a stereo cartridge. So if you're using a quad cart. and it doesn't light and the bulb and wiring check good, that can only mean a circuit componant has flaked.

See any bad spots in there? There usually isn't any visible :^)

If you had a 'scope, you could trace where the signal's getting lost. Of course a schematic would really help there.

EDIT: I would find some way to make absolutely sure the bulb lights though, even though it has continuity.

Doug
 

aperh

New member
Joined
Sep 22, 2008
Messages
7
Well, I don't know if it's a dc or ac bulb and unless somebody can supply schematics I doubt I could figure it out, the bulb has no markings that I can see. Nothing looks bad, no leaky or bloated caps and no burnt circuit board. I'm using a grado g1+ cartridge with the original shibata stylus that should have about 20 hours on it so it should definitely be picking up the carrier signal. I guess the only way to really test the bulb would be to switch it with the power bulb and see if it lights, they look identical so I'm assuming they're both rated at the same voltage/current.
 

palmer

New member
Joined
Jul 23, 2010
Messages
4
I have a lafayette cd4 demodulator and I need to know if it's functioning properly. The radar light never comes on while playing cd4 records, or the jvc setup disc. My question is, can I go into audacity and generate a 35khz tone and just run it into the demodulator. If the demod was working ok shouldn't this light the radar? I'm trying to figure out how I can tell if the demodulator is working properly or not because I need to know if it's the demodulator or something else in my setup.
Did you ever get this resolved?
 
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