View Full Version : JVC 56P575 no power


pac.attack76
07-16-2015, 10:53 PM
JVC 56" rear projection 1080i set plugged in and nothing happening when i push power or attempt to use remote. Can someone point me in the right direction for repair? Not sure if its caps or what. Fuses seem ok.

rca2000
07-16-2015, 11:20 PM
You get no "click" or attempt at power on?

JVC sets were mainly known for losing the convergence amps...not too much more in my experience. This can shut down the set. but you WILL get an attempt at power on.

pac.attack76
07-17-2015, 08:46 AM
You get no "click" or attempt at power on?

JVC sets were mainly known for losing the convergence amps...not too much more in my experience. This can shut down the set. but you WILL get an attempt at power on.

Not hearing anything at all. Just a quick spark at plug in.

kf4rca
07-17-2015, 09:20 AM
Sounds like you don't have your +5V standby supply. This supply is on all the time as long as its plugged in. Diode could be blown as a result of a lightning surge. Or open primary or secondary of the standby supply transformer.
But the last time I saw this it was due to a cracked circuit board interrupting the AC from the standby supply's transformer.

pac.attack76
07-18-2015, 08:30 AM
Sounds like you don't have your +5V standby supply. This supply is on all the time as long as its plugged in. Diode could be blown as a result of a lightning surge. Or open primary or secondary of the standby supply transformer.
But the last time I saw this it was due to a cracked circuit board interrupting the AC from the standby supply's transformer.

Sounds like a start. is there a number on this diode? where do i start testing?

kf4rca
07-18-2015, 09:59 AM
I would look for a terminal on the PS board that says 5VSBY and see if you have it.
Also remove the PS board (might be difficult) and inspect all the connections. Does the board look like its been hot? Then check for bad caps.
Have you looked around (on this here web) for a pdf schematic?

pac.attack76
07-18-2015, 08:10 PM
I would look for a terminal on the PS board that says 5VSBY and see if you have it.
Also remove the PS board (might be difficult) and inspect all the connections. Does the board look like its been hot? Then check for bad caps.
Have you looked around (on this here web) for a pdf schematic?

No sign of overheating. Actually very clean. No bulging caps. Cant find the 5VSBY. Nothing out of the ordinary. I'm lost:sigh:

kf4rca
07-19-2015, 08:44 AM
Put the PS board back in, turn it on, and probe around with a DVM to see if you have ANY voltages on it.
Be careful cause an inadvertant short can send the whole thing up in smoke.
Might be conv board but you would most likely get a distorted picture first.
I'd also sniff around for any unusual burnt smell.

rca2000
07-19-2015, 09:07 AM
Get a couple of GOOD pictures of the boards...good enough for me to be able to follow things and I will try and tell you what to look for .

pac.attack76
07-19-2015, 09:13 AM
Get a couple of GOOD pictures of the boards...good enough for me to be able to follow things and I will try and tell you what to look for .

Will do. Just gonna take me awhile.

kf4rca
07-20-2015, 08:07 AM
Whats the power LED doing? Is it on, off, or blinking (count the blinks).
It could actually be working. Try feeding an external audio signal into it. Do you get sound on the speakers?
A possibility exists that the CRT is in "protect" due to scan failure (either H or V).
My guess is the vertical has died. Pull the deflection board and sniff for burnt smell. The vertical chip might have a TDAxxxx number on it. I always thought they had inadequate heat sinking on these.

pac.attack76
07-20-2015, 08:50 AM
Whats the power LED doing? Is it on, off, or blinking (count the blinks).
It could actually be working. Try feeding an external audio signal into it. Do you get sound on the speakers?
A possibility exists that the CRT is in "protect" due to scan failure (either H or V).
My guess is the vertical has died. Pull the deflection board and sniff for burnt smell. The vertical chip might have a TDAxxxx number on it. I always thought they had inadequate heat sinking on these.

No led, no sounds. Its as if it was not even plugged in. I dont even know where the led is on this set.

kf4rca
07-20-2015, 09:16 AM
You have a power problem! Check continuity of the line cord. This might be an easier fix than I thought!

pac.attack76
07-20-2015, 09:40 AM
You have a power problem! Check continuity of the line cord. This might be an easier fix than I thought!

I'll test and let you know. Could possibly be a break somewhere in the line.

pac.attack76
07-20-2015, 08:33 PM
Tested and getting 119.1 where the cord hits the board.

kf4rca
07-21-2015, 08:59 AM
Just for kicks remove the conv board. (Make sure its been off for a while-like overnight) and power it up.
There are a number of posts regarding the conv board and even a repair kit is available.

pac.attack76
07-22-2015, 09:05 AM
Not sure where the conv board is. The tdks are mounted on the same board as the fly back. I'll have to check it out later.

pac.attack76
07-22-2015, 09:38 AM
Not sure where the conv board is. The tdks are mounted on the same board as the fly back. I'll have to check it out later.

kf4rca
07-23-2015, 08:22 AM
187522

pac.attack76
07-23-2015, 02:09 PM
187522

Ah gotcha. Ok, I'll check it out later today and disconnect.

pac.attack76
07-24-2015, 08:39 AM
Nope, looked everywhere. It seems the convergeance and deflection or whatever along with the flyback is all the same board. The two black STK chips and heat sinks are on the same large board lying down with the flyback. Board is labeled Conv/Def or something like that. Would a chassis number help? Is it possible for a fuse to be bad even if the element inside still seems intact? You would swear the fuse is blown on this because there is no power at all. Nothing.

kf4rca
07-24-2015, 08:57 AM
Does anything look burnt? Pretty much out of ideas now. Were you able to check the PS board for ANY voltages? Not sure if its in shutdown or if the PS board has a problem. A schematic sure would be helpful. Fuses are probably OK if they look OK, but you can check them anyway.

pac.attack76
07-25-2015, 10:00 AM
Does anything look burnt? Pretty much out of ideas now. Were you able to check the PS board for ANY voltages? Not sure if its in shutdown or if the PS board has a problem. A schematic sure would be helpful. Fuses are probably OK if they look OK, but you can check them anyway.

Not sure what to do now. Can check some caps, etc. and see what i get. Not sure where to get a schematic. I can get the chassis number. Maybe that would provide something.

rca2000
07-25-2015, 10:08 AM
I STILL need some good pictures...of both of the large boards on the bottom of the set. The deflection board and the sigal board. I need to be able to see different connectors and such and i CAN then help you "figure it out. This has been my thing for many years....I weas out of the "scene" for a couple of years due to illnerss...but am getting "back in the saddle a little now.

pac.attack76
07-28-2015, 09:03 PM
Hope these help.

http://i800.photobucket.com/albums/yy287/OlderIsBetter/WP_20150728_005_zpsnmydfjsl.jpg (http://s800.photobucket.com/user/OlderIsBetter/media/WP_20150728_005_zpsnmydfjsl.jpg.html)

http://i800.photobucket.com/albums/yy287/OlderIsBetter/WP_20150728_004_zpsaojwzmas.jpg (http://s800.photobucket.com/user/OlderIsBetter/media/WP_20150728_004_zpsaojwzmas.jpg.html)

http://i800.photobucket.com/albums/yy287/OlderIsBetter/WP_20150728_003_zps9fcn9k9v.jpg (http://s800.photobucket.com/user/OlderIsBetter/media/WP_20150728_003_zps9fcn9k9v.jpg.html)

http://i800.photobucket.com/albums/yy287/OlderIsBetter/WP_20150728_002_zpsmmnhyhf6.jpg (http://s800.photobucket.com/user/OlderIsBetter/media/WP_20150728_002_zpsmmnhyhf6.jpg.html)

http://i800.photobucket.com/albums/yy287/OlderIsBetter/WP_20150728_001_zpsbv1ijhyy.jpg (http://s800.photobucket.com/user/OlderIsBetter/media/WP_20150728_001_zpsbv1ijhyy.jpg.html)

rca2000
07-28-2015, 10:38 PM
They WILL work...GOOD pictures BTW.,..

You need to check that "whatcamacallit"..next to the "whatchmagieer" connected to the "thing a mig."!!

Ok SERIOUSLY now...

It looks as if you do NOT have a seperate standby power supply here ...so this means that the main SMPS runs at ALL times...or at least it is SUPPOSED to.

I see a relay on the COLD side--this is likely to switch off the B+ to the Horiz ckt--in standby. Also what looks like an "SE" voltage reference chip" this is for regulation..it is in front of the relay--looks lke a TO-220 transistor. But in standby...it MAY not have voltage on it--if it is switched through that relay..but likely the relay is AFTER that reference chip.

that large transformer is the SMPS power transformer. It powwrs the set. the VERY first thing you need to determine is...if it is even running at ALL.

If you can...turn over the chassis and get a voltage reading on that large capacitor behind the SMPS tranny. You need to see if there is at least 150 volts DC on it..ACROSS it's terminals. If it DOES have that on it..(and since you say you see a spark when you plug the set in---it likely DOES)...then you need to see if you are getting ANY voltages out of the power supply.

In front of the SMPS tranny...there are several capacitors with diodes near them. ALL of these diodes should have some sort of DC voltage on one side of them...as measured to chassis ground. LIkely 12 volts, maybe 24 volts, 18 volts and perhaps a 9 volt or 5 volt or so supply. A couple will likely shgow a negative voltage to ground--like -18 or maybe -24..

if you see voltages there....move over to the connectors that go over to the signal board (the green one on the left side of the power supply board)..and see how the voltages look on thaty connector. there MUST be at least a couple of voltages there in standby...a 12 volt or maybe a 5 volt supply. These power the MPU and remote ckts...to keep the set "alive". Ground the black probe and check and see what those connectors have on them. with the set off but plugged in...there likely will not be too many with voltages...but a FEW should have some voltages.

Your convergence chips are up front on the deflection board..STK 394-250..and do NOT go bad as often as others but they CAN go bad. But it is NOT likely they will totally kill the set. They likely are powered by an +18 or +24 and - source--from the SMPS supply. Just for "kicks"..unplug those three 4 wire connectors in fornt of STK chips...those are the convergence lines...(be SURE to label them in some way...to get them back to the RIGHT connecors..otherwise...when you DO get the set to run...the convergence will be WAY off. )

So....check this out...and we will go from there !!

pac.attack76
07-29-2015, 09:02 AM
large cap was 171 dc. i put the black on chassis ground and most diodes seem to be .000. i had a couple that had something on them as you can see in the pic. Connectors were varying, .002 .001 .005 .43 .349 .003. These are all with the meter set at VDC. NOT VAC. Unplugging the 3 lines from the convergeance did nothing.

http://i800.photobucket.com/albums/yy287/OlderIsBetter/WP_20150728_004%20label_zpspkhsbttg.jpg (http://s800.photobucket.com/user/OlderIsBetter/media/WP_20150728_004%20label_zpspkhsbttg.jpg.html)

rca2000
07-29-2015, 09:42 PM
171 volts DC on that big cap-with no load...sounds about right. This sounds like your power supply is NOT running at all. If you did not see some appricable voltage on those diodes--"the side connected to those capacitors--NOT the transformer side..cathode of most..anode of a few--),with the black probe to cold ground...this means the SMPS is not runni9ng at all--since if it was in overcurrent mode...from a shorted load...it would either be squealing or chirping..but with NO noise...it is just DEAD.

SO...NOW.. I need a better look behind the transformer-- that big heat sink...to see what sort of switch mode driver you have...whether it is a chip or a MOSFET driven by a small chip off of it. I THINK I see an optocoupler--those OFTEN go bad--and stop all oscillation of the SMPS... I ALSO... need to see the BOTTOM of this board...especially the area near that transfoemer...

pac.attack76
07-30-2015, 09:47 AM
Let me know if these work.

rca2000
07-30-2015, 12:24 PM
They help SOME.

I see you have an "STR"-type SMPS chip. IC -911. Can't see the number--but i KINOW it is one.

Go to the negative side of that big cap you got 171 volts on...and take the positive lead...on IC -911. See if those 2 larger pins have that voltage on them. If they do...then check the smaller pins to the same ground. If all show zero or so..the IC is NOT running and is likely BAD. But before you replace it... BTW__get the # of IC-911 for me.

ALso check ALL diodes near that IC..ESPECIALLY any glass ones. And check that "optocouler"..that little black thing with 2 leads on each side. On the side near IC-911...check it with the probe on hot ground--that big cap. There should be a BIT of voltage on it--it is is working and IC-911 is good. There is a small transistor in front of the optocouple--check it also.

if you do NOT have the 171 volts or near it on IC-911..but you DO have it on that cap...it is likely SHORTED. Take your postiive lead and put the meter on OHMS..and check those 2 larger pins on IC-911...to hot GROUND. It should NOT show low ohms...it should show at lEAST 10K ohms or higher. if it shows an ohm or less or so...the IC is SHORTED. If do...then the two pink-looking resistors beside the sink ar elikelyt OPEN...because of the shorted IC.

You notice the "line" around the transformer and IC..it says "live" on one side and 'isolated" on the other. This means that EVERYTHING inside that "box" the line contins is "HOT" with respect to the AC line...and all OUTSIDE Of the line is COLD...with respect to the AC Line. This is why you have to emasuse stuff on the HOT side--with respect to the HOT ground--that big cap and ALL outside of the line to CHASSIS ground..COLD ground. You are mainly concerned with the HOT area right now--since your SMPS is NOT running at ALL. But it IS possible--a fault on the COLD side--is stopping oscillaton.

pac.attack76
08-02-2015, 02:27 PM
STR
X6737

I'll get some more readings soon as i can.

rca2000
08-02-2015, 05:11 PM
Ok. I took a look at this chip. I have a "typical application" diagram to go by. Yours MAY be a bit different...BUT the functions WILL be the same.

pin 1==should have full hot B+ on it--as it is the drain pin--the one going to the transformer. Measure to HOT gorund.

Pin 4--the chip B+ line.If it is Near 0--measured to HOT ground (as are ALL voltages on this IC.). either the chip or something erxternal is loading it--likely that optocoupler. It should measure at least a few volts to hot ground--when the chip is running. There does appear to be a "start up" resistor on it. if it was OPEN...NO start and no power up. The strat resistor will be a high-value one--100K or higher--and come off of the HOT B+ from that cap in some way--to pin 4. If it DOES show 0..unsloder that pin and re-check. If it THEN shows a decent voltage...the chip IS VERY likely bad. If it does NOT come up when unloaded...a diode or that optocouplwr is loading the line down. After the chip is up and running...a diode form the feedback line THEN supplies the chip with this voltage and the "start voltage" is bypassed.

Pin 2.. Source... goes to hot ground through a current sense resistor. if the chip was in over current mode..it will mute oscillation to prevent damage. But since you have nO power or squealing or chirping noise..likely NOT the issue. Just measure it to hot ground with an ohm meter and see if it is very close to zero ohom to ground.

Pin 3--Ground. Should also be zero ohms to hot ground.

Pin 7--over current protection. Shares part of feedback ckt and voltage developed from pin 2. . Likely will NOT show any voltage--since the chip is not running.

Pin 5..feedback pin. This is used by the chip to know if it is producing enbough output. it will be connectoed ot the HOT side of that optocoupler. WHen running...there should be a few volts on it--but with it dead...likely NONE

Pin 6..soft start.. Likely will not show anything with the chip not running. It goes through a cap to ground to allow the SMPS to start "gently".

THIS should give you an idea. I would bet..either your chip is bad..or that optocupller is bad (amybe BOTH of them), or a zener diode in the ckt is shorted. Check around the optocoupler and feedback pins for any diodes there and see if any are bad.

CHip is NOT overly expensive on Ebay--new. $16 INCLUDING ship..from FL.

pac.attack76
08-03-2015, 08:23 AM
Sounds good. I'll try and get on this later today and see whats there.

pac.attack76
08-05-2015, 08:38 AM
Looking on the board, im having trouble identifying these "pins" you refer to. If i had a pic marking what i need and where to test, it would be easier for me. I can barely even get in there so i had to unhook everything and bring out that board. Labeled "POWER & LF PWB LCB90284 -001C. would another pic of this area help especially now that its out where it can be seen better? maybe you can circle or mar where to check. placement of the red lead and black.

pac.attack76
08-05-2015, 08:54 AM
here's some new ones:

pac.attack76
08-08-2015, 08:44 AM
Should i just go ahead and change both the chip and the optocoupler?

pac.attack76
08-09-2015, 09:17 AM
Where did everybody go? I really need to get this thing running since its sitting in the middle of my living room. I'll make it a point to get those numbers today and see whats going on. Anyone know the part number of the optocoupler?

andy
08-09-2015, 11:18 AM
If you don't have the service manual, it's available here for free:

http://elektrotanya.com/jvc_av-48p575_av-56p575_av-56p585_ch_rp.pdf/download.html

The schematic is confusing because it shows a lot of parts that aren't used on this model. Ignore everything labeled "OPEN".

rca2000
08-09-2015, 03:42 PM
Sorry--I have been busy for the last few days--with the 127 corridor sale and such.

ANYWAY...before you order ANY parts... what did you measure on the STR IC--to hot ground ? :Pins 1, 4 and 5...in particular. If 4 or 5 is off by much...that optocoupler is likiely loading things down.

pac.attack76
08-09-2015, 07:05 PM
Thanks Andy for the service manual. Very handy. I'm having trouble fiuring out which pins are which and if the board needs to be installed in the set when i test. Where is "hot ground"?

rca2000
08-09-2015, 07:38 PM
Hot ground is ther negative lead of that big capacitor you measured 171 volts on. This is the reference point for ALL voltages on that IC.

Looking at the IC from the front...see where the pins all go into it. From left to tight--pin 1 should be on the left and in order from there. I KNOW they are "staggered" in the way they end up on the PC board..But if you look at how they enter the IC--you should be able to figure out which pin is which.


I tried to dowlaod that manual myself...but was NOT able to do so for some reason.

andy
08-09-2015, 09:46 PM
Thanks Andy for the service manual. Very handy. I'm having trouble fiuring out which pins are which and if the board needs to be installed in the set when i test. Where is "hot ground"?

The hot ground would be the negative side of the large can cap on the primary side. If you're not using an isolation transformer, use caution since even the negative side of the cap has voltage compared to earth ground. It's best to only power it when it's installed in the set.

pac.attack76
08-10-2015, 09:12 AM
Ok, guys, looking at the board where the words "live" and "isolated" read upright, the pins are like this:

. .
. . . With the cap out to the left. Now, going from left to right, left to right, i got: -.033, -14.06, -.003, -1.26, .000

Not sure if i did this right. Red on right side of cap since the other side has a plus mark. Set to VDC.

pac.attack76
08-13-2015, 08:46 AM
Did i do this right. If not, i can hit it again.

rca2000
08-13-2015, 10:55 AM
You did it BACKWARDS. Put the black probe lea don the hot ground. Use ther red or positive one---for all of the other readings.

BUT...i did NOT see any 171 volts on ANY pins of that chip. Are you SURE_-you got all of the pins? 2 of them are scattered from the otherrs--remember. if you did NOT...then check those 2 large resistoirs beside of that chip...and see if they are OPEN. They likely read LESS than one ohm. If OPEN--that ahip IS shorted.

pac.attack76
08-13-2015, 03:08 PM
You did it BACKWARDS. Put the black probe lea don the hot ground. Use ther red or positive one---for all of the other readings.

BUT...i did NOT see any 171 volts on ANY pins of that chip. Are you SURE_-you got all of the pins? 2 of them are scattered from the otherrs--remember. if you did NOT...then check those 2 large resistoirs beside of that chip...and see if they are OPEN. They likely read LESS than one ohm. If OPEN--that ahip IS shorted.

Ok, i figured as much. I'll hit it again tonight or no later than tomorrow. I'll need to get this part, whatever it ends up being, ordered so i can get it in soon.

pac.attack76
08-13-2015, 03:42 PM
Yeah, i missed two pins. Layout is actually:

. . .
. . .
.

Now from left to right with black on cap neg. i get:
169.8, 13.73, .017,
.000, 1.309, .004,
.000
Note these are taken with board out of set but still plugged to ac.

rca2000
08-13-2015, 06:39 PM
At this point...I would re-check ALL diodes and any transistors near that IC..on th HOT side of it (within that white drawn area surrounding HALF of the transformer and optocoupler.) be SURE to check any diodes and make sure none are shorted.


If you do NOT find anthing...that i would order than IC and the optocoupler--as a "just in case". Your voltages indicate the IC is NOT shorted and is getting full voltage from the big cap and it ALSO looks to be geting its "start voltage" too. I would gues it is just bad.

pac.attack76
08-15-2015, 07:20 PM
I have a guy in the area that looked at the board the other day and he thinks the optocoupler is bad. Probably $1 or $2. Hes wondering what the readings should be if it were good. Getting voltages on the large cap and STK.

pac.attack76
08-18-2015, 08:22 AM
If the optocoupler is good, what should the reading be?

Zenith26kc20
08-18-2015, 03:52 PM
I'm sure you did this but the picture of the PC side shows a solder connection blown loose with the number 912 going to it. Did you check the resistor and resolder that connection? Just curious.

rca2000
08-18-2015, 04:08 PM
C912 is likely some sort of "snubber cap" for the primary of the SMT transformer.. Somehow I missed seeing that. R912 is on the supply line to the chip...if it was open...you would NOT see 171 volts on the chip...but check the connections anyway..

And YES...IF that cap is not connected...the PS may NOT run at ALL.

Not sure EXACTLY what the voltage on the hot-side of the opto should be.... withoust seing a manual...BUT it WILL NOT be high...likely 12 volts or LESS...on BOTH pins..

pac.attack76
08-21-2015, 08:29 AM
checked both c912 and r912. both connected well. not sure how to test them. i'm assuming the board would need to be powered but not sure what meter setting to use. still trying to get used to this whole meter thing. the solder on r912 just has two different appearances. shiny and dull surface, im guessing made it look like it had lifted. any ideas?

rca2000, i have the pdf service manual if you want me to email it to you.

pac.attack76
08-28-2015, 05:07 PM
I guess i'll just order the chip and optcoupler. Chip is $16 shipped. How do i look up the optocoupler? I'm 3 days away from ordering so i just have to figure out what to do. If this doesnt fix the no power issue, then i dont know.

pac.attack76
09-01-2015, 06:24 PM
Well, off to the storage building she goes. Not sure what i need still so i didn't order anything. Probably sit in storage till i finally decide to toss it.