Welp, after a long time, after I changed one 160uF electrolytic and a few others as well as some black beauties, I power on the chassis for the first time connected to a speaker from a 17" black and white RCA, I got static! Woohoo!, then I tune to channel 3 and I get some really clear audio!! I'm quite happy! :)

One thing I'm not happy about is that when you turn it on, there is a slight inrush and the chassis vibrates to the strong beat of 60Hz. Is this normal, drawing as much power as it does? It does say it draws 375W, but this'll cause the chassis to vibrate?

Then I turned it on again and I noticed a huge pop and a spark by the power transformer. After careful inspection, I saw that the inrush thermister was replaced by a component lead that heated up so much that it exploded! It was odd to see it, as a fusable link, be blown, but everything else is fine. By the looks of the wiring terminals, it was badly soldered on as a quick fix. This could be the reason of the chassis vibrating, but I'm not sure.

The Sams calls for an inrush thermister that is 79 ohms cold and .4 ohms hot. It's connected in between the AC line filter and the power transformer primary. It probably sees atleast 3 to 3.5A operating. Obviously, it NEEDS this inrush thermister for reliable and safe operation. When I was constructing an amplifier power supply, I had a 2kVA toroid made for use as a power transformer. It drew so much that it would pop the breaker instantly. I got it to work with a timed solid state 20A relay and a 20W resistor where it wouldn't blow anything.

In this case, what kind of inrush thermister should I use? I suppose an NTC would be the right choice (because a PTC would be low resistance cold and high resistance hot?), but should I use a 100 ohm NTC or string two 47 ohm NTC's together?

Thanks.

Jonathan

One thing I'm not happy about is that when you turn it on, there is a slight inrush and the chassis vibrates to the strong beat of 60Hz. Is this normal, drawing as much power as it does? It does say it draws 375W, but this'll cause the chassis to vibrate?


That's probably the degaussing coil doing its thing. As a set this old has more metal than modern Chinese sets, you'd hear it more.

In this case, what kind of inrush thermister should I use?

PC power supplies usually have thermisters in them. If you can't find an exact replacement you might be able to cobble something together with one or two thermisters taken from old PC power supplies.

I can't find any inrush thermisters that are close to what the Sams says. Can I use two 47 ohm inrush thermisters in series? The 47 ohm inrush thermister can handle 2A.

Thanks.

Jonathan

Unfortunately the ctc 9 was pre-built in degaussing coil.. I have two ctc9's

Unfortunately, I think you have a dead short somewhere. My 9 is buried, so I cant really look at what youre looking at, but I would bet something is shorted in the voltage doubler. I'll bet it was drawing too much current if it blew that fuse wire up.

If you have a variac I would use it now. If not I would make a dim bulb tester. The power supply is a voltage doubler. The other 160mf cap could be shorted or one of the diodes could be shorted. You could bring it up slow and see if both halves of the voltage doubler have equal voltage (measure across each 160mfd capacitor). If not you should figure out why. The doubler makes around 400 volts under full line voltage. So about 200 volts per side at full line . On the dim bulb it will be a lot less, but shouldnt be a bunch on one side and nothing on the other.

If you want to kill the high voltage so you can run it on the bench, just remove the horizontal oscillator and horizontal output tubes.

There have been old threads about the thermistor. Apparently the sets work fine without. I wonder though, if the thermistor is gone is there anything else to act as a fuse?

I suspect that fuse wire thing may have just saved your power transformer.

All the best,

John

If there was a dead short in the voltage doubler, would there be enough B+ for the sound section and tuner to work? It did turn on, mind you with a buzzing sound at first (the horizontal oscillator and output tubes were removed), and just kept on vibrating. The tuner and sound section did work, as I got clear sound from the speaker when I tuned to channel 3. None of the electrolytic capacitors got warm or hot. I only changed the 160uF electrolytic that connected to the rectifier and the B+ line that leads off to the filter inductor. It's definately the right polarity, as I made sure the polarity was right because I never never knew it was a voltage doubler until you told me. :) I replaced it with a fresh Mallory 160uF 350V from mouser. I checked the ceramic filter capacitors and no shorts, and I made sure the polarity of the rectifiers (I replaced those with fresh 1N4007s from mouser because they were rusted) And checked the B+ winding. Maybe I should check the 160uF capacitor in the multican and see if it has good ESR? It's not connected to the pucture tube, yolk, or convergence board. The seller did test it, and he did get sound, but he got an out of focus and dim picture, so maybe I should change that 160uF capacitor? Any other suggestions?

Thanks so much.

Jonathan

I would t least see if the voltages are somewhat equal. If half the voltage doubler is dead, you will have half b+.

I'm not sure how a ctc9 would behave with one side shorted, but there is a thread around here about a zenith that had a 160mf capacitor open. (it was the same basic voltage doubler circuit as an RCA.) It had a small dim raster with a bunch of 120hz in the raster. Anyway, if one diode or capacitor is open circuit, you will have half B+. Some things might partly work.

The buzzing chassis, while it might be normal, suggests probably a short somewhere. Your burned fuse wire kind of backs that up.

When one diode shorted in my ctc-15, it blew the breaker on the back of the chassis. I would check the power supply diodes for sure. I dont know, but I think its possible that if one diode or 160mf capacitor was shorted, you would have some b+ until the fuse blew. I dont think the power transformer would take this very long.

John

Oops, I missed some of the details in your post the first time I read it. Sorry about that. I would check that 160mf and I would recheck the diodes. I have had them bad out of the bag before.

If you look at the schematic, its not immediately obvious how it works. On one half cycle, current flows through one diode, and charges one capacitor. On the other half cycle it flows (the other way) through the other diode and charges the other capacitor. Since the capacitors are in series, you have double the voltage available.

Any problem with either half and you lose half the b+.

John

John,

Thats actually pretty darn interesting how it works, because I've wondered exactly how, and wondered exactly how you get such an odd waveform that the Sams lists. The way you describe how it operates corresponds to the waveform listed. I checked the old and new electrolytic for as well as both new diodes for polarity and opens/shorts. The capacitors charge like they should and the diodes are fine. Both are connected the way they should be in terms of polarity.

From looking at the schematic, if the B+ is cut in half, then the 270V and 140V used to supply the tuner, audio section, and video IF section. Infact the sound IF is taken from the 3rd video IF. Just by the sound working as well as it did, I really think the voltage doubler is ok. I'll measure the voltage and verify once I get the inrush thermister. I have checked for any B+ shorts and can't find any *crosses finger* (with most of the TVs I've worked on, I've always managed to cause a direct B+ to ground short, notibly the 630TS chassis) so I think I'm on the right track.


And I think I might have a good reason if anything isn't shorted that my chassis vibrates to 60Hz. The epoxy goop leaked out of the power transformer from the chassis being horizontal on top of the cabinet for a few months rather than being vertical when it's installed in the cabinet. A good amount leaked out (most of it, infact) and because there isn't a lot inside the power transformer, I believe the damping effect it had is no more since most of it is gone. I feel it more so than I hear it. I'm not sure what to make of that, but maybe that could be the reason?

Thanks.

Jonathan

I guess it could be. Its just that when you said it was humming loud, that sounded like a short. If the diodes and caps are ok, I guess its onward and upward :). After the voltage doubler, there is maybe 415 volts or so. coming off of the first filter, about 400v, ususally specified on schematics as somewhere between 395-405 volts depending what kind of set it is.

If you look on the schematic, there will be a string of resistors and filter caps breaking down the voltages for circuits that need lower voltages. Is this what you were talking about?

The first resistor is probably 1250 ohms at 18 watts or something to supply the 270v tap. After that will come other physically smaller resistors. If one is open, then all the voltage taps after it will be dead. You might as well check them with an ohmmeter while it is out on the bench.

John

in some of the older power transformers the thermistor was inside the casing of the transformer itself, usually stuck in between the windings either near the top or bottom of the transformer

I actually checked the B+ points in the sound section, and after I read your post I checked those two resistors and they are within range and no shorts. I certainly hope there is no short, because it is no where to be found. A good sign of a draw is decreased B+, so once I get the thermister and the AC line supression capacitor I'll measure and see if it's within range.

Thanks.

Jonathan

Ok, I have some good news. I got the AC line supression capacitor and the two 47 ohm inrush thermisters I connected in series to get 94 ohms. The set doesn't vibrate anymore or seem to draw insane amounts of current. I installed the .047uF 275V X2 AC line supression cap across the AC line like it said in the Sams/RCA service guide. I installed the two inrush thermisters in series across the AC line. They have a cold resistance of 47 ohm and a current capacity of 3A. That should give 94 ohms of cold resistance with plenty of current capacity at 3A.

The 160uF/50uF/50uF multicap gets warm and stays warm, but after being on about 15 minutes, it just warm. It's definately going to have to be changed, no? I'm just testing for sound, as it's not connected to the picture tube or yoke, and the horizontal oscillator and output tubes are removed. It's tuned to channel 3 and connected to the RF out of my tivo. I'm getting sound as clear as a whistle.

As for what was causing the vibration before, I have no idea. The AC line filter which includes the AC line supression cap connected across the AC line and the 820k resistors that are connected to ground and the two sides of AC, maybe that was causing it since the capacitor was removed? But with 820k on the 110V AC line, only microamps flowe from AC line to ground through the resistors. The thermisters? I have no idea if the absence of those was any big deal. As soon as I get some screws and nuts I'll install terminals and remove the multicap that gets warm. I'll install the new ones on the terminals. Then I'll connect it to the picture tube and see what happens.

Thanks guys.

Jonathan

My ctc 16 thermistor burned out.(R214) what is the RCA replacent part number? maybe a replacement could be available at radio shack?

I jumped the two wires, and the TV works, but is the Degaussing coil working? i am hoping am not burning the R2159 voltage variable resistance or the degauging coils. any Recommendations for alternative replacement? the schematic said 1200omhs cold, (workman part number 191)

needs help in NYC