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#1
06-25-2015, 12:07 PM
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CTC-7 Large spark no more HV
Hello all!
So today I was adjusting the horizontal centering control in my ctc-7 (this screw is located inside the HV cage with a hole cutout so you could stick a flathead in and make adjustments) As I was turning my screw driver the plastic screw popped off and there was a large spark between my screwdriver and the metal shaft that the knob was on and the HV immediately stopped working. Have I killed my flyback?! Or did I blow one of the HV fuses? Please help!!
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 Admiral C322C2 Regent (Restoring) RCA CTC-7 Pensbury (Restored) RCA CTC-5 Westcott (Restored) CRA CTC--4 Director 21 (Restoring) 
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#3
06-25-2015, 01:40 PM
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Quote:
I don't have my RCA schematics handy, so I'm not sure, the HV is fused. It's been ages since I worked on one. 
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#4
06-25-2015, 01:49 PM
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Quote:
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Admiral C322C2 Regent (Restoring) RCA CTC-7 Pensbury (Restored) RCA CTC-5 Westcott (Restored) CRA CTC--4 Director 21 (Restoring) Last edited by SwizzyMan; 06-25-2015 at 02:28 PM.
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#5
06-26-2015, 04:19 PM
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Ok so I put two new fuses in the high voltage fuse section but still no HV. All tubes light except for the high voltage rectifier shunt regulator and focus rectifier. I just noticed there is a blown power supply fuse... Could that be causing problems?
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Admiral C322C2 Regent (Restoring) RCA CTC-7 Pensbury (Restored) RCA CTC-5 Westcott (Restored) CRA CTC--4 Director 21 (Restoring)
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#6
07-05-2015, 07:28 PM
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You have to ask...?
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#7
07-06-2015, 10:24 AM
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Quote:
The OP has plenty of suggestions to work with now. 
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#8
07-06-2015, 03:24 PM
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I would replace the power supply fuse first. That may be why your 2nd anode voltage is missing, even if the fuse in the HV cage itself is OK. The spark may have been caused by a short circuit to ground, blowing the PS fuse. However, if the main power supply fuse (often called the line fuse) blows, the entire TV will be dead, since this fuse is on the primary side of the power transformer. If the HV fuse in the flyback cage blows, all you will lose will be the second-anode voltage to the CRT, while the rest of the set will continue to operate as normal. Do not keep replacing this fuse if it continues to blow every time you turn the set on, as this is an indication of a dangerous short somewhere in the HV plant. The same warning applies to the power-supply (line) fuse. Do not bypass either fuse with a length of solder or hookup wire, either. This may get the TV working for awhile, although if there is a short anywhere some components may burn or melt, and could start a fire.
The only way I know of to test the high-voltage rectifier tube is to replace it with a known good tube. It is impossible to tell just by looking at them if the filaments in these tubes are good, since they do not glow as most other vacuum tubes do. Be careful, though, as the CRT's second-anode voltage appears directly across the filament of the HV rectifier and will give you a good shock, to say nothing of even killing you, if you are not careful. Conventional wisdom says to keep one hand in your pocket while working anywhere under the chassis of a TV, radio or any AC-operated device. Even if the shock doesn't go across your heart, it can throw you clear across a room. Be sure to discharge the CRT by sliding an insulated screwdriver under the second-anode cap before doing anything around the HV cage. This is necessary since the aquadag coating (the gray coating on the bell of the tube) creates a huge capacitor, which can hold a charge for days or even weeks at a time.
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Jeff, WB8NHV Collecting, restoring and enjoying vintage Zenith radios since 2002 Zenith. Gone, but not forgotten. Last edited by Jeffhs; 07-06-2015 at 03:35 PM.
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