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Old 08-18-2018, 04:47 PM
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Ctc 16ex sos

Hi friends
Ctc16 xe was working fine with stable and bright picture, and decent colors. Last time it trip the circuit breaker. There was no smoke nor burning odors. I removed the back cover reset the breaker and it trip the breaker again. The thermister was arcing badly. The B+ circuit was out so was the 6volts for the tubes. Nothing, no juice in the set. second attempt was to disable flyback but it trip again.

During visual inspection there was nothing burn under the chassis. Power diodes checked OK

My rational points to the main transformer, because the lack of 6 volts that is independent of the B+.(thermister) set is not use on regular basis.

open to any suggestion that could help me out
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Old 08-18-2018, 05:37 PM
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I think you have a shorted electrolytic in the B+ system and that it was the start of the problem...I hope the transformer did not die while you were trying to diagnose.

According to the CTC-16 schematics here ( http://www.earlytelevision.org/tv_sc...ams_color.html ) the breaker only protects the B+ windings so there almost has to be a short in the B+. I've never seen the H output blow the breaker (I suppose stranger things have happened) usually the flyback or output tube are smoking/redplating and there is no picture long before the breaker's trip point is reached (part of the reason these had a reputation for fly failure). The first couple of times your breaker tripped the power trans was fine...Now you need to check and hope for the best.

How I (strongly) recommend you proceed: 1). Remove the chassis from the cabinet. Disconnect one of the wires from the breaker and cover the end with electrical tape (this disconnects the B+ winding from any short that might be loading it...It would be dangerous to apply power into a short). Power up the chassis with the B+ winding disconnected as described and look for tube heaters to light...If they do skip to #2, if not check AC voltage across the primary (the one the power cord connects to) winding of the power transformer. If the primary has 120V power set off and check the resistance of the primary if open it's dead. If the primary is not getting 120V troubleshoot the wiring between the plug and the primary and fix the open.
2.) remove electrical tape you added at the beginning of #1 but do not reconnect the wire yet. Check AC voltage on the B+ winding of the power trans...it should be normal to high (if more than %30 lower than normal the transformer is bad)...Okay at this point you will have verified a good power transformer and have lit heaters...Now to fix the B+ short.

There are a few ways to find a B+ short. Really bad ones can be found with the ohms mode of a DMM, but the most common source of B+ shorts, capacitors, only short with voltages several times higher than a DMM can apply to them.
If lytics C1 and C2 (or any sections of them) are the original chassis mount can style I would not bother to troubleshoot, but just replace those damn timebombs and be done with it (I'd probably replace every lytic over 15 years old with new while it was on my bench).

If it had new lytics fairly recently then you can troubleshoot it. If you have a tester that can apply full rated voltage to the caps and check for leakage current (you have to disconnect one leg of 2 lead cap for the test to work) that is the safest route. If you don't have a tester you can reconnect the B+ winding to the rectifiers and power the TV up on a variac (probably only need ~30V from the variac). Take voltage measurements from the first lytic off the rectifier and the first 4-5 highest B+ rails. usually a voltage will jump out as being too low...Don't crank the variac beyond 50% till you fix the short.

Two additional things to watch out for: Your thermistor may have gone open as a result of the overload. Your rectifires may have shorted (or less likely opened) from the overload. The first will cause no B+ the second could burn up your transformer.
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Last edited by Electronic M; 08-22-2018 at 11:35 PM.
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Old 08-18-2018, 09:59 PM
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Quote:
Originally Posted by bluenorm View Post
During visual inspection there was nothing burn under the chassis. Power diodes checked OK

open to any suggestion that could help me out
Did you check each diode both forward and reverse? If using a digital ohmmeter, you should disconnect one end of each diode for a reliable test.

As a side note, an analog meter can test each diode for short/no short without disconnecting anything. Gawd, I would never think of being without at least a cheap analog meter with an RX1 scale for situations such as this.

Last edited by old_coot88; 08-18-2018 at 11:26 PM.
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Old 08-19-2018, 07:47 AM
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thank you Electronic M
this morning chassis was removed and a circuit breaker point was removed. and there is electricity through the tube heaters.(tube are on) So in the next hour will follow up with step 2.
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Old 08-19-2018, 08:48 AM
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step 2 there is 330 voltage coming out of the transformer at circuit breaker. looking good so far. to old coot88 thank you. I checked the diodes they appear to be ok. with my tester at the diode selection it shows .70, however my test is coming to an end here. so I might jump in to the F train ( F train is not currently running on weekends due to repairs to the tunnel) tomorrow and go harbor freight and get a decent volt meter. I did change some electrolytic about 10 years ago but not all of them. (my mistake)

Last edited by bluenorm; 08-19-2018 at 08:58 AM.
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Old 08-19-2018, 03:59 PM
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If the thermistor is bad, you may be able to use one out of an old PC power supply. It sees similar voltages and currents as that seen in the TV set.
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Old 08-20-2018, 12:28 AM
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the thermistor burned to pieces. thanks for the tip. in nyc you see lost of old tower comp. during recycling day.
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Old 08-20-2018, 01:23 PM
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When you check the caps, do so with a dedicated cap tester that tests voltage breakdown, with an eye tube. I had a few CTC16's and when caps began to go bad, it was just one is a 4-section can. I f you are going with more power-up testing, change out that first cap anyway, it gets nailed with 420v of DC, buffered only by that thermistor on the AC side, every time its turned on.

Check then 420 volts on load side of the power supply choke disconnected, it looks like a vertical output transformer with two terminals. One terminal can be disconnected to isolate all downstream caps. Try a slow power up too, say 75-80 volts it may lead you right to the shorted cap via a hot can.
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Last edited by DavGoodlin; 08-20-2018 at 01:28 PM.
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Old 08-20-2018, 03:18 PM
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If that first lytic after the rectifiers has been changed (I'd recommend the one on the other side of the choke be changed too) you can short the two thermistor terminals together until you find another thermistor...You loose degaussing and the transformer has less of a cushion if one cap is still shorted, but it is a valid workaround (in sets where all is good but the thermistor techs would often short a dead thermistor as a temp workaround).
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Old 08-21-2018, 06:21 PM
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hi guys
I just order the thermistor, diodes, capacitors and an couple of resistors for that area. checked the big resistor such as 1400ohm @18 watts (r212) 3500 @ 3watt(213) and 1200 @ 4watts. (r210). parenthesis states numbers according to sam folder 818. will replace 1400ohmdue values are way off. now am looking for was reasonable variac to bring the set up nice and gentle. all parts appears to be original excepts two caps that I change 15 years ago.
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Old 08-21-2018, 06:40 PM
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hi
a brief story of this tv. 15 years ago I place an ad in one of local byline magazine ( for queens nyc area). the ad stated, wanted color tv from the 50' or 60' non working or working. two years later I was contacted by the original owner and a hard core Yankee fan. the tv was found dead. no nothing, with cataracts and the price was about $200.00. he did not want to go down with the price so I walk away.

a few week later he contacted me again and this time his grandkids were there and they said to him that I was the only one interested, so my offer was 40.00 he said no and finally we agreed on 60.00.

the damage was dead circuit breaker. broker burst phase transformer and non functional 3.8 crystal. two electrolytic capacitors were replaced. Picture tube red and blue very weak, and tube was rebuild in texas.
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Old 08-22-2018, 02:44 PM
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I bet it ran as long as it did because it was indoors all its life. My blond CTC11 (like yours) was the same way, then I moved to a space that was not so conditioned and got near freezing, still using it gently and at least monthly, but the caps finally started to go open and it was obvious in the raster. I have not turned it on since, knowing I have to do the full-monty on it.

I usually found the first PS cap C1A, 80 uf @ 450 volts, was the only one leaky. Often too, a can with three 450v sections and one section at 25v, such as the 50 uf at the contrast control, only that one section goes open. Its really a crap-shoot so I change them all.
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Last edited by DavGoodlin; 08-22-2018 at 02:58 PM.
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Old 08-22-2018, 09:26 PM
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hi guys.

I followed the recommendation of electronic m and replaced all electrolytic. One of them C2 under sams and 124 under rca and it did not have marking of what and where. I took one hour to find out what and where. Replaced all the rectifiers. jump the thermistor and it trip the breaker again. the hum is not as severe as before but it comes from the transformer.

I have a spare chassis, for parts, but changing the main transformer knowing that this one pushes about 330 volts with thermistor disconnected is like going fishing. schematic states 320vac and 7.7 ohms. there is another winding (255v) that goes to the sweep board. tomorrow I will check voltage in that area.
I guess from here if to get a variac and see where that take me.

any other part of the chassis that could trip the breaker, such as the other transformers.
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Old 08-23-2018, 12:13 AM
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Not having a variac here is what I'd do.
Resistance tests:
With the set unplugged (wait at least 15 min for lytics to discharge), and the positive end of the bridge rectifiers disconnected from the B+ system try measuring the resistance between the chassis and the 5 highest (by listing on the schematic) voltage B+ rails (do them in order from highest to lowest). The resistance of the 400V rail should be higher than 250 ohms (number obtained by applying ohms law with the breaker current and high B+ rail voltage as inputs). It should be MUCH higher than 250 ohms (at least once your meter charges the caps) since the tubes aren't acting as loads since the heaters are out.
If the resistance is lower than 250 ohms start unhooking wires from that point and check the resistance of each separate wire...Follow the path of least resistance to find the short.

Another troubleshooting option is to do 'unloading' tests (keep the H and V output tubes removed during these tests). For example (using sams 818 for reference) Disconnect L45 from where it connects to C1A/the rectifiers (disabling power to the choke and all but the 400V rail) then power the set up. If the breaker does not trip the C1A and everything on the 400V rail are working okay. Now power down, reconnect the choke to 400V and disconnect Resistors R112, R213, and R214 from the choke. If you power it up like this and no trip then 390V is fine too. You can reconnect a resistor, power up then reconnect another resistor and power up, and so on.
The first rail that when reconnected causes a trip is the source of the problem*.
*If there are lower voltage rails derived from the culprit rail disconnect those from it and check for a trip again to incriminate or clear the derived rails of suspicion.

There are many possibilities what could be wrong. A lytic installed with reverse polarity could do it (double check your work, I've made that mistake more times than I care to admit), a winding to frame short in the 400V rail choke (L45 sams 818) could do it, a wire with damaged insulation rubbing on something could do it, a conductive spec fallen in exactly the wrong place could do it...The trick is finding it.
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Old 08-23-2018, 09:51 AM
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hi guys

thank you electronic. m I will follow your second paragraph to the letter, because I checked those resistors and I know the location. and I replaced r212. will to locate L 45 today and follow up from there. I got your point which is to isolate different voltage points. disconnecting L45 will tell me if the will power supply section is ok and that will be a good start. will u keep inform.
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