no picture or sound on JVC CRT 36"


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no picture or sound on JVC CRT 36"

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its TUCK3R
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Oct 22, 2008, 12:58 AM

Post #1 of 20 (19046 views)
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no picture or sound on JVC CRT 36"	Can't Post

Hey guys, i found a JVC 36" AV-36890 CRT Tv on the side of the road. I took the beast home, plugged it in, and turned it on. When I plugged the Tv in it made the normal sound when a Tv turns on, but there was no picture or no sound. I left the Tv on just in case the tube needed to warm up and when I returned, alas, nothing happened. I went to take off the coaxial cable and noticed that it was a little warm. I don't know if this normal or not. Also, I don't think the tube is bad because when I unplug it, the white line shows up for a split second when it powers down. Could it be a problem with and of the components? I have experience with circuity and am very capable of soldering components into a board, so no fix is too much. Also, could the tube be bad? I really want to get this working because this will be the first Tv I own that is over 25". Also, I would like it for games haha. So please, is there anything I can do?

dkdhas3
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Oct 22, 2008, 3:37 AM

Post #2 of 20 (19029 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

it sounds like it has a vertical collapse problem, if this line your speaking of is across the screen and not up and down.
at the back of the flyback(high voltage transformer)leading to the suction cup on the tube, there will be two adjustable pots. VERY slowly with the set on turn the bottom one clockwise and watch the pix. if a line from left to right appears you have vertical collapse and its going into a video blanking to protect the crt from this collapsed vertical burning the tube, when it shuts off this blanking can be lagged and you can see a flash of a line.
easy way to find the vertical section is to follow the yoke plug from the neck of the crt to the pcboard(generally its a red, blue, green, and yellow and it leads either to two plugs (then the smaller of the two usually green/yellow)if it leads to one the green and yellow or the two wires closest together follow that circut trace and it will lead there also. probably the ic an electrolitic or two a resistor and diode at the most.if the line is up and down its a whole diff ballgame. oh and for the tube, pretty rare for a tube to cause this symptom.
i tried to get a schematic at jvc and they do not have lit. on this available , others may be able to come up with it . but the vertl. output ic will be like a AN5515 or LA7838 between6 and 15 pin ic mounted to a heat sink i'm sure. find the 12 -24 volt supply that feeds it off the flyback more than likely, it hass been a while for a vert. repair but i'm sure it hasn't changed much.

good luck

its TUCK3R
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Oct 22, 2008, 7:06 AM

Post #3 of 20 (19027 views)
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Re: [dkdhas3] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

New Update...

I left the Tv plugged in and turned it on. There IS audio but still no video. Could this still be the same fix as you mentioned above?

dkdhas3
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Oct 22, 2008, 3:37 PM

Post #4 of 20 (19018 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

i was surprised that it didn't have it before. if it is not going into shutdown with no high voltage the audio will prob. be there. did you turn up the control i told you to? is the line left to right or up and down??

its TUCK3R
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Oct 22, 2008, 9:47 PM

Post #5 of 20 (19010 views)
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Re: [dkdhas3] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

When I took the back off the Tv I found the pots you were talking about. I turned the bottom one clockwise and got a light pink line across the screen horozontally. Is that good? What should I do next? Does this mean the CRT is still good? Also, thank you for your help!

I really hope the tube isn't bad because I checked JVC's website out and a replacement CRT was $600.00 and that's a bit much for my budget haha.

(This post was edited by its TUCK3R on Oct 22, 2008, 10:24 PM)

dkdhas3
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Oct 22, 2008, 11:15 PM

Post #6 of 20 (19004 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

all i said of the vertical collapse guess is exactly what is happening. the vertical(circuit that stretches the picture up and down)circuit has collapsed. yes your tube is still good. the ic, resistor,diode and elect. again i cannot look at a schematic so i'm not sure of the location # but look for the yoke plugs, adn follow the copper foil to the ic.

its TUCK3R
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Oct 22, 2008, 11:43 PM

Post #7 of 20 (19003 views)
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Re: [dkdhas3] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

All right, all it will take is some snooping around and some volt-ohm meter tests to see whats bothering the Tv. Thanks so much for your help, it was very much appreciated!

Also, is it ok if I take the suction cup off for the circuit repairs? Can I get it back on once I take it off?

(This post was edited by its TUCK3R on Oct 23, 2008, 12:04 AM)

dkdhas3
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Oct 23, 2008, 12:43 AM

Post #8 of 20 (18997 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

no it's not ok to take the suction cup off. if the set were to come on you would feel what 33 thousand volts or so to light up your world. the tank(crt) will hold a few thousand volts and if you go messing with the cup this is how it will bite you. your problem has nothing to do with the high voltage section. follow my instructions and if its not matching up dont fiddle, this is an easy repair, dont' make it a hard one. call a tv repair company and save yourself early-onset sterilization.if you can find someone who has a service manual (schematic) i will tell you exactly what to replace and check, but i am not able to find one.
you have a 15 dollar ic a 2 dollar resistor and a couple bucks in assorted other goodies. after determining exact problem find a tv shop tell them all the parts you need and i'm sure they would be willing to help you out, maybe even give you a squert of heat sink compound for the ic a little solder an solder wick to save from buying a lot of it. i would need to be there or have a schematic.

good luck

its TUCK3R
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Oct 23, 2008, 5:41 AM

Post #9 of 20 (18989 views)
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Re: [dkdhas3] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

I looked at the circuit board and there were very helpful printouts of the general circuitry for certain functions of the Tv (ex. Isolated, Tuner, V-Def, H-Def, Micom, Live, Power, and of course, HV DANGER!). They are printed directly onto the PCB and I'm guessing the problem will be somewhere in the V-Def territory? I can see the labels on the board too and I see resistors, diodes, capacitors, and that IC you were talking about attached to a long heatsink. Is this the right area where I can start my testing?

There is a picture of the location of the H-Def and V-Def I took a little earlier...sorry about the quality, my digital camera is a little on the cheap side...

http://i212.photobucket.com/...stuck3r/PICT0068.jpg

(This post was edited by its TUCK3R on Oct 23, 2008, 5:43 AM)

dkdhas3
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Oct 23, 2008, 4:15 PM

Post #10 of 20 (18973 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

SEE IF THE IC IN THE SHADOW IS IC421 OR SOMETHING LIKE THAT(WRITTEN NEXT OT THE PARTS ARE THE LOCATION #'S) I SEE IN THE PIXTURE C424 THAT IS A CAP IN THE VERTICAL SECTION. IF IT IS, IT IS PROBABLY SHORTEDIT MAY EVEN HAVE A HOLE IN THE MIDDLE OF IT. I WOULD CHECK AND SEE IF THERE IS ANOTHER ILECTRONLITIC AROUND THERE WITH A LOCATION OF C421 (100mf-35V CAPACITOR) I THINK ITS 35 VOLTS THAT NEEDS TO BE THERE AND THIS PROBL. COMES FROM THE FLYBACK AND HAS A RESISTOR AND DIODE OFF OF IT THAT MAY BE OPEN AND SHORTED RESPECTIVELY
YOU WILL NEED TO:

REPLACE CAPACITOR C-421 AND IC421 THE VERTICAL OUTPUT IC. YOU NEED TO SEE ITF THE 3O SOME ODD VOLTS IS SUPPLYING THE IC. I'M NOT SURE WHAT PIN ON THE FLYBACK BUT MAY BE T502 AND PIN 8 WILL LEAD TO A RESISTOR AND IF ITS OPEN IT IS BAD..THIS MAY BE VERT. OUTPUT PART #LA7832 BECAUSE THE VERT. CIR. IS MARKED WITH THE 400 LOCATION #S . ALL THE PARTS YOU WILL BE REPLACEING WILL BE IC421,D426,R421, C421 THIS I MADE UP SO DO NOT NESS. LOOK FOR THIS EXACT STUFF BUT THE RESISTOR BY THE FLYBACK WILL BE LIKE R421 AND WILL BE BURNED MORE THAN LIKELY IF IT IS BAD
GOOD LUCK

THIS IS ALL GUESSES BECAUSE I CANNOT GET A SERVICE MANUAL .

its TUCK3R
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Oct 24, 2008, 12:08 AM

Post #11 of 20 (18966 views)
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Re: [dkdhas3] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

There is a little burn mark under pin 4 of IC421. I did continuity tests on each of the pins and there is no continuity in the chip what so ever. I'm also doing capacitance tests and resistance checks. As I was going through I got a bogus reading on C425 Here's how it stands. I used a Capacitance Meter to do the measurements.

I got a weird reading at C425...
C425, 35V, 470 uF - measured at 1356 uF

I'm guessing this is called a bad capacitor? I'm JUST learning about capacitors in college so yeah...

(This post was edited by its TUCK3R on Oct 24, 2008, 12:34 AM)

dkdhas3
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Oct 24, 2008, 1:23 AM

Post #12 of 20 (18963 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

if you are checking this cap. in the circuit without taking it out you will be reading other things also. dont worry about that jsut replace it. there will only be the ic the diode the resistor and 2 or 3 caps in the vert. circuit just order the parts you could check caps all day but they are 1 buck and theres only 3 or so. is the resistor open?? if not the ic will probl. be the only problem but i would replace the caps also.

dkdhas3
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Oct 24, 2008, 1:35 AM

Post #13 of 20 (18962 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

when you say "under pin 4" do you meen above pin 4???
pin 4 and all the pins "are the under". everything else is above the pins. is the burn on the bottom side of the pcboard were they solder to the pcb pin 4 is burned.??

its TUCK3R
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Oct 24, 2008, 2:12 AM

Post #14 of 20 (18961 views)
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Re: [dkdhas3] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

The burn mark is on top of the PCB where the components are located. I replaced the capacitor and it still read 1342 but the old capacitor I took out still read around 700 uF, so it was still a little unusually high.

I checked R423 and it's open but R556 and R557 are good.

I still haven't gotten into how to test diodes, but I have a multimeter, so how would I go about testing the diodes and does it matter if some are Zener Diodes and Rectifier Diodes or are they both tested the same way?

its TUCK3R
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Oct 24, 2008, 3:31 AM

Post #15 of 20 (18957 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

I took the IC out, its a LA7832 chip with 7R underneath the LA and a 9 underneath the 2 like this...

LA7832
7R 9

I did some more continuity tests out and there is continuity from 1 to the other 6 but I don't know if the chip could still be bad?

dkdhas3
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Oct 24, 2008, 4:33 AM

Post #16 of 20 (18953 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

its bad.

its TUCK3R
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Oct 24, 2008, 6:30 AM

Post #17 of 20 (18946 views)
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Re: [dkdhas3] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

Haha, alrighty well I'll send in for a new one. It's only about $13. The resistor I'm looking at though I can't really tell what resistance value it should have. It has no color code, and only has a 1, a big dot then 2 and then the Ohms symbol...does this mean 1.2 ohms?

Here is a picture with the labeled components.

http://i212.photobucket.com/...stuck3r/PICT0080.jpg

Don't know if that'll help.

R423 (the light blue one) is measuring open from both sides...if that is a resistor at all. It has the Omega symbol on it for a resistor but has no color codes and a J...any hints?

dkdhas3
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Oct 24, 2008, 1:26 PM

Post #18 of 20 (18940 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

the ic, any open resistors, prob. nearer to the flyback for the feed resistor and yes that is a 1.2 ohm resistor and it looks good(did you say it was open, the blue one in thepictre.?) it should measure almost shorted(1.2 Ohms) if it is open this may be the resistor i was talking about i thought would be more near the flyback., and that 100uF @ 35volt electronlitic in this pix, prob. a pump up elec.t will correct any top line issues if it has it.with the ic out do you get any voltages on the traces of were the ic was like a 24 volt line or a 30 volt source or 12 volts or anything, if not the resistor is open and i would replace the diode in series with it,

its TUCK3R
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Oct 25, 2008, 8:16 AM

Post #19 of 20 (18936 views)
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Re: [dkdhas3] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

I plugged the Tv in and did the volt tests and no pin combination came out above 1 volt. Most were rather in the 750 mV range.

dkdhas3
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Oct 25, 2008, 1:30 PM

Post #20 of 20 (18932 views)
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Re: [its TUCK3R] no picture or sound on JVC CRT 36" [In reply to]	Can't Post

you went from the black probe on a ground and then all the pins. if that is the case and no voltages you need to trace back and find the resistor and diode off the flyback

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