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#1
03-10-2011, 09:31 PM
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Rca 9-t-246
Just got done recapping the ecaps on this set. Found 1 paper cap that was oviously bad, end fell out of it, replaced it. Crt checks ok, Got HV to the crt, no raster. All tubes check ok. If I have the lights off and twist the brightness control, I'll get a flash of light full raster on screen for a second, then nothing. I currently do not have a diagram. Any suggestions where to look next?
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#2
03-10-2011, 09:50 PM
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If you count the number of paper caps remaining in the TV, that tells you how many more caps to replace. Appearance is no guide. They can look brand new but still be junk inside.
You can usually read the values from the old caps. This article has more advice about identifying & replacing capacitors: http://antiqueradio.org/recap.htm Phil Nelson
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#3
03-10-2011, 10:23 PM
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The KCS28 to KCS40 RCA chassis' have a two stage DC coupled video amplifier from the second detector to the kinescope. This gets rid of the D.C. restorer diode from the earlier RCA designs. Note how the two stages are DC stacked. This means that the power supply voltages are more critical in these sets if you do not want bias the CRT on or off to heavily.
First check the bias on the kinescope: you'll likely find it biased off. Then next check the power supply voltages against the schematic. Note the resistive divider to provide the voltages. If you haven't gone through most of the decoupling capacitors yet, you'll likely find one pulling down one of the supply voltages in the chain.
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#4
03-10-2011, 10:47 PM
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I found your set in Riders Vol 4 and took photos of the schematics for chassis KCS28C and KCS38. Sorry, I don't have a scanner big enough to handle these big pages.
Let me know if there are areas you can't make out. http://www.bobandersen.com/images/schematics/RCA/
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#5
03-10-2011, 10:49 PM
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I took notice on the e can caps that they are not grounded to the chassis, how come?
So where do you put the negative wires from the new replacment electrolitic caps? The cans have carboard covers on them.
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| Audiokarma |
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#6
03-10-2011, 11:07 PM
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The negative side of the caps is at a lower potential than ground. You can solder the negative lead of the new caps to the can lugs of the old ones assuming you left them wired in. Disconnect the wires going to the positive lugs of the old caps and run them to the new ones.
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#7
03-10-2011, 11:10 PM
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Quote:
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#8
03-11-2011, 12:06 AM
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Quote:
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#10
03-11-2011, 08:06 AM
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Quote:
These sets have a somewhat complicated negative bias supply. All voltages are handled with the big power resistor on the back of the chassis. When working properly, these sets are tood performers, and, have very good contrast, and, decent brightness. Not really a bad little set. Bill Cahill
__________________
"Tubes are those little glass things that light up orange unless there is a short.. Then they light up all pretty colors..." Please join my forum. http://www.tuberadioforum.com/
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| Audiokarma |
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#11
03-11-2011, 02:02 PM
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I just got done replacing all the paper caps, "bumblebee" caps, and electrolitic caps. Got a raster now, and a nasty hum in the speaker. Brightness control not working correctly, goes from nothing to bright midway to nothing on the max end. Going to hook up the B&K later and see if I get anything on the screen.
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#13
03-12-2011, 12:12 AM
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Quote:
Also check the basic voltages coming out of your power supply. Those will be shown on the schematic. If your power supply is messed up, trying to troubleshoot other problems is just shooting in the dark. Phil Nelson
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Linear Mode
