Tube TV cuts out when cold


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Tube TV cuts out when cold

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LouF
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Apr 6, 2017, 5:58 PM

Post #1 of 16 (1621 views)
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Tube TV cuts out when cold	Can't Post

I have a older tube-type TV that I infrequently use and is on the fritz. I have recently de-shunned it as it has actually been a very good TV (1st anything in 15 years except for cleaning the remote control button contacts (and most everybody calls things like this a "little POS (that's not Point-Of-Sale)" TV Crazy

))

TV make and model: Emerson-TC1966D (a 19 inch tube TV). Problem: turns off (sound and picture) when initially turned on (cold); will eventually stay on. A 1/2 hour of warm-up time allows it to continually stay on.

No capacitors are bulged; no leaks on the board.

With this minimal diagnostic information, I am hoping that someone can suggest the probable cause. I am hoping it has to do with the power supply and is a capacitor(s). I have tried looking and reading, but it quickly turns into (for me) knowing about SMPS design, off-board component testing etc... all that I just can't do (plus, I have a brake line to urgently fix too) - but I don't want to just toss this away.

There is a bigger cap. (560 uF, 200V) near the line-voltage in that I want to first try. I would have, but as of last week the Radio Shacks have closed so I can't even easily try a remove-and-replace method; MicroCenter has even less basic-component stock. Then there are many, many other caps. that I don't believe are bad. All solder joints appear good (two a bit dull, but are not suspected); several browned areas, but nothing severe; I feel its a simple component degradation over time.

Credibility check: I'm a decent repair person, but the complexity that electronics has gone (although this is old , but still very complex) is beyond what my novice, fluent, electronics knowledge can keep on tap. I have successfully repaired a sub-woofer system, have installed car stereos, build my own computers, rebuilt solar stake lights ( lol) and other various other things - so the experience here would be appreciated to get to me pointed in the right direction.

The long post is, since I just signed up here, to introduce myself and not just blasting in as a complete know-nothing.

Thanks

jts1957
Veteran

Apr 6, 2017, 8:15 PM

Post #2 of 16 (1618 views)
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Re: [LouF] Tube TV cuts out when cold [In reply to]	Can't Post

If set uses a relay and it won't stay energized, there is likely a electrolytic responsible. 100 to 470ufd 25 to 35volt.

The big guy seldom fails and should be the raw B-plus filter.

-------------------------
Location: Far, Far Away

(This post was edited by jts1957 on Apr 6, 2017, 8:24 PM)

LouF
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Apr 6, 2017, 8:45 PM

Post #3 of 16 (1611 views)
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Re: [jts1957] Tube TV cuts out when cold [In reply to]	Can't Post

Thank you. That is usually how my remove and replace methods turn out and is why I was hesitant. You are correct, it is a soft power button, and it does silently shutdown. The relay sounding click still happens, but will not immediately turn back on; it is getting longer and longer too. I did also notice some sort of difference between off/on and unplug/on.

I did take a picture of the board.

If I don't hear back, I will have to order some caps. and will report back.

jts1957
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Apr 6, 2017, 10:37 PM

Post #4 of 16 (1605 views)
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Re: [LouF] Tube TV cuts out when cold [In reply to]	Can't Post

Also investigate the 6 volt supply.

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Location: Far, Far Away

LouF
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Apr 7, 2017, 12:33 AM

Post #5 of 16 (1597 views)
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Re: [jts1957] Tube TV cuts out when cold [In reply to]	Can't Post

To be clear, this is a CRT as opposed to a non-solid state.

jts1957
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Apr 7, 2017, 12:45 AM

Post #6 of 16 (1596 views)
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Re: [LouF] Tube TV cuts out when cold [In reply to]	Can't Post

https://www.flickr.com/...42267@N08/2204659455

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Location: Far, Far Away

LouF
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Apr 7, 2017, 12:57 AM

Post #7 of 16 (1591 views)
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Re: [jts1957] Tube TV cuts out when cold [In reply to]	Can't Post

LOL. I did see that during my searches. That's the one.

I assume they would be in similar shape, these repair attempts help me get my feet wet (or enough to be dangerous).

I ordered some capacitor kits; they'll take a week to get to me. (I am very disappointed of the recent closing of Radio Shack.). I just now am trying to see if they have that freeze spray. (I might have some automotive refrigerant (not R-12) also)

jts1957
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Apr 7, 2017, 1:08 AM

Post #8 of 16 (1590 views)
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Re: [LouF] Tube TV cuts out when cold [In reply to]	Can't Post

It IS a 'Solid State' TV.
Freeze spray (& various parts): https://www.digikey.com/...id=0&pageSize=25

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Location: Far, Far Away

LouF
New User

Apr 7, 2017, 1:21 AM

Post #9 of 16 (1585 views)
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Re: [jts1957] Tube TV cuts out when cold [In reply to]	Can't Post

Solid State: Yes, I wanted to be sure "tube" wasn't mistaken for a vacuum tube type television.

Digi-Key: Thanks. Do have an account there.

LouF
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Apr 10, 2017, 10:50 PM

Post #10 of 16 (1511 views)
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Re: [jts1957] Tube TV cuts out when cold [In reply to]	Can't Post

In Reply To

If set uses a relay and it won't stay energized, there is likely a electrolytic responsible. 100 to 470ufd 25 to 35volt.

The big guy seldom fails and should be the raw B-plus filter.

I seem to have it fixed after replacing one capacitor on the first try! It plays! One (C433) 470uF, 35V capacitor replaced w/ a 470/50. There is writing printed on the circuit board, and I followed the +B from the terminal on the flyback transformer to components. There were only two capacitors directly in line, and it would begin to get very indirect after that.

After reading through a lot of things about TVs, CRTs and SMPSs, I see that I am a know-nothing, and there is much more danger in this than I ever knew. Everything seems to discharge in this piece, although, as I never got any discharge from the CRT, and none of the capacitors I checked registered any voltage on a meter (I read that there is an reference of approximately one inch of "throwback" per volt. Laugh

-It does sound about right.)

I even found service manuals on E-Bay, and also see that I may not be so lucky the next time.

Again, thank you very much for taking the time to read and give your opinion/experience.

LouF
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Apr 12, 2017, 2:37 AM

Post #11 of 16 (1502 views)
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Re: [LouF] Tube TV cuts out when cold [In reply to]	Can't Post

Update: It is much better, but after a day of off, it takes two times before it will turn on.

jts1957
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Apr 12, 2017, 3:46 AM

Post #12 of 16 (1500 views)
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Re: [LouF] Tube TV cuts out when cold [In reply to]	Can't Post

On-Off relay 'coil' has 12V? If so one end or the other may have a 470ufd. 12V is also input for a 3-terminal regulator (5Volt output, if memory serves).

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Location: Far, Far Away

LouF
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Apr 13, 2017, 10:07 PM

Post #13 of 16 (1488 views)
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Re: [jts1957] Tube TV cuts out when cold [In reply to]	Can't Post

I tried another capacitor, and it didn't change. I am certain (99%) the coil stays energized as it's supposed to - I do hear the relay switch on with w/o any other abnormal sounds. Right now it takes a second try fire up after 24 hrs. (want to verify again that I let it try long enough) or a second off/on for it to fire up (this may be tricking me by allowing it enough time between attempts).

I've become wary of doing voltage measurements because of not knowing which ground to use. One thing I read said to use the main capacitor ground. I am also now noticing little test ports around the board (and QC stamps near them). I've been trying to stay around the line-in area, but am also seeing the capacitor sizes you suggested farther away from there.

I do have pictures of the of the board (top and bottom) which is very traceable: http://s328.photobucket.com/user/loufazio/library/Emerson%20TC1966D

I've been referencing a similar model's schematic, but the important page is blurry (PDF); I also know some values are different. I am also getting an original-print manual schematic in about a week.

(This post was edited by LouF on Apr 13, 2017, 10:31 PM)

jts1957
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Apr 14, 2017, 12:40 AM

Post #14 of 16 (1484 views)
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Re: [LouF] Tube TV cuts out when cold [In reply to]	Can't Post

If relay stays energized, unplugging the set should result in relay 'unclicking.'

According to your pix (can't quite make out location numbers), should be a single ground system. Tuner shield, main filter negative terminal, etc. should show continuity. It's wise to observe caution near that one.

ANY electrolytic near a high temperature source (high wattage resistors or flyback transformer as examples) should be shown special scrutiny.

TC1972

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Location: Far, Far Away

LouF
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Apr 15, 2017, 3:46 PM

Post #15 of 16 (1453 views)
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Re: [jts1957] Tube TV cuts out when cold [In reply to]	Can't Post

I don't know if there is inconsistency, a limit is approached, or I didn't wait that last second, but the picture DOES come up after 24 hrs.

The funny thing is, the cap. that I initially replaced is not on the B+ circuit that I thought it was. I can't tell what it is on, and I will be better able to try and look when I get the schematics. I want to understand these circuits better.

Pictures: Thanks for looking. Apparently they process the files; they WERE clearer.

Relay energized: Works correctly.

TC1972: Yes, this is the schematic I have been referencing; It is very similar to TC1966 (in the Power section by my limited recognitions).

Ground continuity check: Yes, I forgot about these practical methods of investigation/reasoning. I was being cautious with AC/DC and High Voltage/LV sides of transformation/circuits.

Your help is greatly recognized and appreciated. Thank you very, very much! You must have been a true professional. Your signature ("Location: far, far away") makes me laugh my -ss off. The comma makes it especially informative. Thanks again.

LouF
New User

Jul 12, 2017, 9:55 PM

Post #16 of 16 (1117 views)
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Re: [LouF] Tube TV cuts out when cold [In reply to]	Can't Post

Follow-up: TV still working - very happy. (came back looking for some reference).

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