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 Post subject: Re: Crosley 9-403M Restoration
PostPosted: Feb Tue 06, 2018 2:58 am 
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Joined: Jan Sun 18, 2015 5:01 am
Posts: 1215
Location: Waxahachie Texas
irob2345 wrote:
Before you go to all that trouble, what's the AGC voltage? Your IFs might be cut off.

I don't think this chassis uses AGC.

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 Post subject: Re: Crosley 9-403M Restoration
PostPosted: Feb Tue 06, 2018 3:47 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 441
Oh yes it does. All TVs do. Pretty much essential.

Look for a negative voltage on G1 of the 1st vision IF amplifier. With no signal, it should be zero volts or thereabouts.

The circuit you've posted doesn't have enough resolution to read it properly but it looks like the set uses simple AGC and that the TV-Radio changeover switch switches the AGC somehow - maybe to cut off the IFs when the radio is on?? There seems to be some kind of back-bias arrangement to generate the required negative voltage.


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 Post subject: Re: Crosley 9-403M Restoration
PostPosted: Feb Tue 06, 2018 3:57 am 
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Joined: Jan Sun 18, 2015 5:01 am
Posts: 1215
Location: Waxahachie Texas
What does AGC have to do with my question on how to hook up my Eico to do the last sound alignment?

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 Post subject: Re: Crosley 9-403M Restoration
PostPosted: Feb Tue 06, 2018 4:08 am 
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Joined: May Sun 07, 2017 11:35 am
Posts: 441
I thought you were trying to get a picture through the front end. I was wondering why you would need to check the alignment ???

In any case, when you are sweeping an IF you often need to apply external bias so the stages aren't driven into clipping, distorting your response. Alignment instructions often recommend a battery (typically 9 volts) and a pot to create the external bias.

BTW that set has separate sound and vision IFs, typical of very early designs. A bit unusual and more complicated. The sound IF alignment is more critical than later sets that use the intercarrier system.


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 Post subject: Re: Crosley 9-403M Restoration
PostPosted: Feb Tue 06, 2018 4:31 am 
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Joined: Mar Sun 01, 2009 10:27 pm
Posts: 4671
Location: Ann Arbor, MI
Crist Rigotti wrote:
I need a little clarification on the alignment instructions.
I don't really understand what or how to hook up my test equipment. Maybe I'm a little tired.
The Sams instructions are below. What I don't quite understand is how do I continue to use my Eico 369 sweep generator to produce the 21.9MC signal and my demod cable? IT seemed to work for steps 6 and 7. But when I move the RF out cable and the Demod cable as in step 8, I still get the same waveform as in fig 3 and not fig. 4.

I don't think that you are supposed to be using a Demod cable, a straight probe is probably what is intended. But that may not matter. You may have discovered a fault in the FM detector. First double check that the center frequency of your sweep is really what you think it is. Then try adjusting the detector transformer over a wider range than you have been doing. If nothing produces anything like the proper waveform, do resistance checks on the transformer to make sure that no part of the windings are open. If the windings seem OK, try replacing those two 47 pf caps.

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