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 Post subject: RCA-8-PT-7030 Double Image
PostPosted: Jun Thu 20, 2019 2:26 am 
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Joined: Dec Tue 23, 2014 4:12 am
Posts: 52
Location: Belleville, Ar 72824
I have checked the resistors around the horizontal oscillator and they are all within 10%. I have also replaced the paper capacitors. I have also tried adjusting the horizontal frequency along with the horizontal drive.

Any idea what could be causing this double image?

Thanks,
Cody


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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jun Thu 20, 2019 3:28 pm 
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Joined: Nov Thu 11, 2010 6:03 pm
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Location: Pewaukee, WI
Your horizontal frequency is some multiple of correct.

Get an oscilloscope, connect the scope to a composite video line and adjust it until 2-3 sync pulses are on screen, measure the horizontal divisions between leading edges of peaks, leave the horizontal time base of the scope untouched for the remainder of this procedure. Now hook the scope to the horizontal of the TV and center the H hold control, and then adjust the horizontal frequency and stability slugs of the osc coil to get the peAks of the waveform the same number of divisions apart as the sync pulses you measured earlier. Make sure you maintain the spike and hump wave form with the spike and hump equal or the spike a pinch higher. If you can't get the frequency into adjustment check every cap resistors tube etc In the circuit.


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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jun Thu 20, 2019 5:35 pm 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
You should leave the horizontal drive alone. The problem is with the frequency or sync.
I think there is a horizontal sinewave coil that is adjustable. I'll see if I can find the proper way to adjust it.
Double check that you installed the correct values for the caps.

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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jun Thu 20, 2019 5:45 pm 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
You will need an oscilloscope.
You can download the manual from Phil Nelson's site.
https://www.antiqueradio.org/rca16.htm

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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jun Thu 20, 2019 9:25 pm 
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Location: Redlands CA
The horizontal Hold control on these is also the frequency coil, did you try turning it past the point of sync and see if it will come around again to the correct frequency? Other than that possibly a wrong value capacitor in the circuit?


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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jun Fri 21, 2019 2:31 pm 
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Joined: Dec Tue 23, 2014 4:12 am
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Location: Belleville, Ar 72824
Thanks guys for the suggestions! I do have an older oscilloscope, but haven't had a lot of time to dedicate.

I am wondering if the The 390pf capacitor could make a difference. It come from the frequency coil to the grid pin 7 of the 6CG7. The parts list says it should be a 330pf but the schematic shows a 390pf. There was an obvious replacement of that capacitor with the value of 390pf and I am wondering if it should be 330pf.

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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jun Fri 21, 2019 3:03 pm 
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Location: Dallas, TX
cparsons2391 wrote:
I am wondering if the The 390pf capacitor could make a difference. It come from the frequency coil to the grid pin 7 of the 6CG7. The parts list says it should be a 330pf but the schematic shows a 390pf. There was an obvious replacement of that capacitor with the value of 390pf and I am wondering if it should be 330pf.


That could be a factor. I also notice that there is a 0.01 uf cap across the sinewave coil. You would have replaced that when you recapped. Since with the tolerance of the caps might not be very tight, the replacement cap's actual value might be different enough to make re-adjustment necessary. That sort of thing is why replacing mica and ceramic caps in the RF sections is not recommended unless you plan to do alignment.

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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jun Fri 21, 2019 7:06 pm 
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Joined: Jan Sat 16, 2016 10:03 pm
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I've had two sets with the exact double image problem and on both sets it was a bad resistor in the horizontal section. I would recheck each resistor with one leg isolated. Maybe you missed one.

One of the resistors (I think it was the maggy set) tested good but had carbon streaks from one lead to the other which under higher voltage would perform with lower resistance but still test good, I forgot what this is called, maybe somebody with more knowledge can chime in.

I hope this helps friend.


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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jun Fri 21, 2019 7:18 pm 
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Location: Albion, CA, USA, 95410
clsoca wrote:
One of the resistors (I think it was the maggy set) tested good but had carbon streaks from one lead to the other which under higher voltage would perform with lower resistance but still test good, I forgot what this is called


Carbon tracking.


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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jun Fri 28, 2019 4:58 am 
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Location: Ann Arbor, MI
There is a method for adjusting the horizontal oscillator that does not need a scope.
Short out the sinewave coil with a clip lead or some such.
Adjust the frequency coil to sync the picture.
Remove the clip lead.
Adjust the sinewave coil to again sync the picture.

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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jun Fri 28, 2019 6:49 pm 
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Joined: May Thu 14, 2015 4:15 pm
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Location: Dallas, TX
Tom Schulz wrote:
There is a method for adjusting the horizontal oscillator that does not need a scope.
Short out the sinewave coil with a clip lead or some such.
Adjust the frequency coil to sync the picture.
Remove the clip lead.
Adjust the sinewave coil to again sync the picture.


I have heard of doing it that way. This is a synchroguide circuit. Works great when it works but just about any
component being off or leakage can mess up the operation.

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 Post subject: Re: RCA-8-PT-7030 Double Image
PostPosted: Jul Mon 08, 2019 7:41 pm 
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Joined: Dec Tue 23, 2014 4:12 am
Posts: 52
Location: Belleville, Ar 72824
Hey guys!

I appreciate everyone's help and willingness to give me some guidance. I finally resolved the issue!

I checked and rechecked all resistors around the horizontal oscillator and made sure they were all in speck. I also changed C166 from 390pF to 330pF. Finally, I substituted the horizontal oscillator tube. After all of that, I went ahead and shorted the sign wave coil and was finally able to get a decent picture. I used the below method to align the sinewave coil.

Quote:
There is a method for adjusting the horizontal oscillator that does not need a scope.
Short out the sinewave coil with a clip lead or some such.
Adjust the frequency coil to sync the picture.
Remove the clip lead.
Adjust the sinewave coil to again sync the picture.


This method is mentioned in the RCA service data.

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