CRT TV no picture, no sound only high pitching noice


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CRT TV no picture, no sound only high pitching noice

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madhushankaroxi
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Oct 2, 2015, 4:44 PM

Post #1 of 48 (11487 views)
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CRT TV no picture, no sound only high pitching noice	Can't Post

Hi everyone, I'm trying to fix an old TOSHIBA CRT TV.

After I turn it ON and press the channel button it starting to output a high pitch noise from the transformer. There is no sound or picture.

Horizontal transistor and the vertical IC seems OK.

Any thoughts?

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(This post was edited by madhushankaroxi on Oct 2, 2015, 4:45 PM)

jts1957
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Oct 2, 2015, 6:27 PM

Post #2 of 48 (11476 views)
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Re: [madhushankaroxi] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Which Toshiba CRT TV? I can't seem to make it out from Far, Far Away.

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Location: Far, Far Away

(This post was edited by jts1957 on Oct 2, 2015, 6:31 PM)

madhushankaroxi
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Oct 3, 2015, 12:45 PM

Post #3 of 48 (11463 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

It's a very old CRT Color TV. Model is Toshiba 2020QM. I'm trying to repair this because I would like to learn more about these stuffs :)

When its on standby mode, everything works fine (Red LED lights up, no any noise from the transformer).

After hitting the channel button (When turning on), transformer emitting a noise (like a mosquito) continuously. RED LED brightness reduces, flyback transformer powers up (can feel the static electricity), electron gun glows.

No sounds from the speaker or pictures.

@ Horizontal transistor (2SD1555) seems okay.
@ ~300VDC across main capacitor.
@ ~124VDC after lifting the middle pin of the horizontal transistor and probe the middle pin solder joint.

@ ~112V seems okay according to the following diagram (It measures about ~120V).

# I'm not sure about the vertical IC (AN5515).

Hints:
$ Looked for dry solder joints and re-soldered.
$ This TV was having color issues previously. Pictures was red, however it worked.

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jts1957
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Oct 3, 2015, 1:03 PM

Post #4 of 48 (11457 views)
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Re: [madhushankaroxi] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Mark G2/Screen control shaft so it can be returned to its initial setting, rotate shaft clockwise slowly while watching CRT face.

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Location: Far, Far Away

madhushankaroxi
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Oct 3, 2015, 1:14 PM

Post #5 of 48 (11455 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Okay I will give a try and update you. Do you know the reason for this noise? A short or something?

Also what will be causing the audio issue? It does not output any sound.

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(This post was edited by madhushankaroxi on Oct 3, 2015, 1:18 PM)

jts1957
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Oct 3, 2015, 1:32 PM

Post #6 of 48 (11449 views)
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Re: [madhushankaroxi] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Need to see all of schematic.

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Location: Far, Far Away

madhushankaroxi
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Oct 3, 2015, 1:33 PM

Post #7 of 48 (11445 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

I don't have any. Still looking Frown

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madhushankaroxi
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Oct 3, 2015, 2:52 PM

Post #8 of 48 (11439 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Exactly like this.

https://www.youtube.com/watch?v=dx2G-JmI1qs

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jts1957
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Oct 3, 2015, 8:26 PM

Post #9 of 48 (11434 views)
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Re: [madhushankaroxi] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

http://www.telespares.com.au/...p;products_id=304821

How EXACT?
In THAT set in YT video, appears to protect tuner voltage.

You Tube set uses 2SD2499 H. Output
You Tube set uses LA7837 Vert Output
C805 ? 47ufd 35V
C825 ? 47ufd 50V

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Location: Far, Far Away

(This post was edited by jts1957 on Oct 3, 2015, 8:36 PM)

madhushankaroxi
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Oct 4, 2015, 12:12 AM

Post #10 of 48 (11424 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Noise is exactly like that one. Not the TV. Sorry for the confusion. Unsure

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jts1957
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Oct 4, 2015, 12:25 AM

Post #11 of 48 (11423 views)
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Re: [madhushankaroxi] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Components may NOT have SAME location numbers, ratings may be different.
Caps would still be in SMPS primary, diode in secondary. They may be protecting a totally different supply line.

Does your set show a chassis number? Family number?

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Location: Far, Far Away

(This post was edited by jts1957 on Oct 4, 2015, 12:25 AM)

madhushankaroxi
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Oct 4, 2015, 3:28 AM

Post #12 of 48 (11418 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Some photos of the PCB. (Album: http://s1101.photobucket.com/user/madhushankarox1/library/Toshiba%202020QM)

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jts1957
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Oct 4, 2015, 5:16 AM

Post #13 of 48 (11415 views)
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Re: [madhushankaroxi] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

1997 vintage. Pix of Label on back of set or possibly tuner with Model/date/other info.
IC303 on vacation?

Quote

~124VDC after lifting the middle pin of the horizontal transistor and probe the middle pin solder joint.

IF NO voltage when middle pin attached, remove HO transistor.

with DVM on diode test put meter red lead on pin 2 and record reading when you put black meter lead on pin 1 and then pin 3 (C-B & C-E) - now reverse the test leads.
with DVM on diode test put meter BLACK lead on pin 2 and record reading when you put RED meter lead on pin 1 and then pin 3 (B-C & E-C)
with DVM on diode test put meter red lead on pin 1 and record reading when you put black lead on pin 3 (B-E) - now reverse the test leads.
with DVM on diode test put meter BLACK lead on pin 1 and record reading when you put RED lead on pin 3 (E-B)
SIX reading in TOTAL.

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Location: Far, Far Away

(This post was edited by jts1957 on Oct 4, 2015, 5:37 AM)

madhushankaroxi
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Oct 4, 2015, 5:42 PM

Post #14 of 48 (11410 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

It's late night for me. I was away today. I will look for the model/info and let you know. I have tested HOT before not sure exact readings. But, seems it's good.

red lead on pin 2 and black meter lead on pin 1 = no reading
red lead on pin 2 and black meter lead on pin 3 = no reading

BLACK lead on pin 2 and RED meter lead on pin 1 = ~0.4xx
BLACK lead on pin 2 and RED meter lead on pin 3 = ~0.4xx

red lead on pin 1 and black lead on pin 3 = ~0.1xx
BLACK lead on pin 1 and RED lead on pin 3 = ~0.1xx

edit: IC303 (AN5515, Vertical IC) and its heat sink de-soldered. Can't power up TV without the IC303? It still emitting that transformer noise.

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(This post was edited by madhushankaroxi on Oct 4, 2015, 5:46 PM)

jts1957
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Oct 4, 2015, 7:14 PM

Post #15 of 48 (11404 views)
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Re: [madhushankaroxi] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Quote

~124VDC after lifting the middle pin of the horizontal transistor and probe the middle pin solder joint.

IF NO voltage when middle pin attached, remove HO transistor. So that answer would be: voltage IS present at solder joint whether the middle pin of horizontal transistor is lifted or not!

You really shouldn't be letting me answer my questions to you.

Would that be power supply or Flyback 'transformer' noise?

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Location: Far, Far Away

(This post was edited by jts1957 on Oct 4, 2015, 7:21 PM)

madhushankaroxi
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Oct 4, 2015, 7:19 PM

Post #16 of 48 (11398 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Coming from the power supply transformer (T802) under load. When it's on standby no sounds and the LED lights up.

As soon as I press the channel button, transformer noise starts, electron gun glows. 120V on HOT middle pin. LED stays on.

No sound no picture. Sort in a secondary section?

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jts1957
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Oct 4, 2015, 7:27 PM

Post #17 of 48 (11395 views)
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Re: [madhushankaroxi] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

First off, Is the schematic above accurate (location numbers, values, etc.) to your set? (Any schematic that shows 112V source connected to '-' negative terminal of the bridge rectifier, I am rather dubious about).

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Location: Far, Far Away

(This post was edited by jts1957 on Oct 4, 2015, 7:30 PM)

madhushankaroxi
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Oct 5, 2015, 2:24 AM

Post #18 of 48 (11384 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Sorry for the delayed answer. I just re-soldered the middle pin of the HOT and checked voltages.

Before solder, it was 124VDC and now it's 0VDC ~ 1.4XXmV. My meter keep showing 0V and 1.4mV again 0V and 1.4mV like that.

After re soldering HOT's middle pin, wired noise from the TWP disappeared. Normal flyback noise started to come up Smile

So I re soldered the AN5515 IC back and attached a speaker. But I can't hear any sound from the speaker.

Separated, all the PCBs from the TV set (from the tube, yoke) unable to test for pictures at the moment.

Yes. given schematic is similar to the one I have here. 112V is across D823 and L813

Checked L78MR05 's voltages too seems OK (5.1V)

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(This post was edited by madhushankaroxi on Oct 5, 2015, 2:37 AM)

jts1957
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Oct 5, 2015, 3:24 AM

Post #19 of 48 (11375 views)
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Re: [madhushankaroxi] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

http://imgur.com/XZDcoUe

Try turning up G2 for 30 - 45 seconds while its cycling on/off.

'TWP number' in your photo does NOT match schematic.
Chassis number would help. I can find schematics for all areas except power supply.

Resistance from HO xstr collector to ground?

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Location: Far, Far Away

(This post was edited by jts1957 on Oct 5, 2015, 3:25 AM)

madhushankaroxi
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Oct 5, 2015, 6:40 AM

Post #20 of 48 (11369 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

G2 turning does nothing Frown

voltage is still like before.
However, when it's on standby, HOT 's collector voltage is stable (~54VDC).

HOT's collector resistance to ground is OL (open).

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madhushankaroxi
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Oct 5, 2015, 7:13 AM

Post #21 of 48 (11365 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Sorry.. HOT's collector voltage is not mVDC. It's switches between 0v and 145vDC.

When it's on standby, the voltage is about 60vDC stable. While on standby and hit Chanel up down or volume up down buttons, set powers up. No sound from speakers. TWP noise disappeared.

When hitting channel up down buttons, flyback noise changes. like a normal TV

What the heck happening here.. ? Gosh

TDA2611A voltages: 20.09, 9.95, 1.50 to 0 switch, 0, 1.31, 0, 1.30, 10.01, 130.0mV

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(This post was edited by madhushankaroxi on Oct 5, 2015, 7:33 AM)

jts1957
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Oct 5, 2015, 10:45 AM

Post #22 of 48 (11349 views)
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Re: [madhushankaroxi] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Still no pix of model label?

Fuse still being jumpered. What parts were replaced due to blown fuse?
Better watch - solder frays and wire clips can and do move & short. (IC801 & IC805 areas in particular.)

Some sets mute audio without signal source connected. BM on tuner 12V?

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Location: Far, Far Away

madhushankaroxi
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Oct 5, 2015, 11:27 AM

Post #23 of 48 (11347 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Found a fried resistor closer to the flyback. I can't find the value of it. Some parts of it are not clear 7.xx something and OHM sign is visible (and a J sign). Measures 20Mohm.

I didn't clean up the board and solder all the joints properly yet. This soldering wire is used to make that jumper. Fuse blew due to a wrong main capacitor replacement Mad

(voltage).

Voltages on Tuner:

BM: 11.93V
BL: 11.37V
AGC: 7.22V
BT: 4.22V

Only labels I found are:

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(This post was edited by madhushankaroxi on Oct 5, 2015, 11:28 AM)

jts1957
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Oct 5, 2015, 12:30 PM

Post #24 of 48 (11338 views)
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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Approximately 5 ohms is likely.

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Location: Far, Far Away

(This post was edited by jts1957 on Oct 5, 2015, 12:33 PM)

madhushankaroxi
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Oct 5, 2015, 12:43 PM

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Re: [jts1957] CRT TV no picture, no sound only high pitching noice [In reply to]	Can't Post

Reason to get this brunt? Any thoughts?

I soldered a 10ohm resister and same thing happened to it too. De-soldered AN5155 's 3rd and 7th pins and the resistor isn't getting hot / burned any more.

Bad vertical IC?

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(This post was edited by madhushankaroxi on Oct 5, 2015, 12:44 PM)

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