LCD backlight problem? inverter problem? SHARP

[Nigel Goodwin]

Here's a technical bulletin for that set, don't know if it helps any?.

SYMPTOM Dead or stuck in standby.
All Sharp LCD TV sets have a Lamp Error detection circuit which will return the LCD
TV to stand-by if a fault is detected, the fault is logged by the lamp error counter which
will render the LCD TV inoperative if it the error count reaches 5.
To enable fault finding the lamp error detection circuit is ignored when service mode is
activated. Service mode activation is detailed in the relevant service manual.
After the fault has been diagnosed and repaired the lamp error counter must be reset
to “0” before normal functionality is restored, again this is detailed in the relevant
service manual.
CAUSE Possible causes of this symptom are:
· Inverter circuit failure (switching transistors)
· Lamp failure (no or low output)
· Poor or loose connectors, fuse holders (lamps or inverter board).
· Dry joints (power supply or inverter board).
· Trapped or chaffed cables to lamps.
· Power feed to lamp inverter circuit.
· Fault in error detection circuit
ACTION Repair the unit as necessary and reset the lamp counter.

 

[MikeM]

Thanks Nige,

an earlier post mentioned screwing down earth screws, which I did before going into the service mode. There were some loose earth screws but I will also check the other aspects mentioned in the service bulletin and at the same time keep an eye on that error code number.

May I say that as I have been in the business of servicing TV's since the mid seventies, this recent decade has not got any easier. With the advent of Plasma and LCD circuitry with which there seems to be a of lack technical information, sites like this have to be considered a blessing.

Best regards,

MikM

 

[unclejed613]

is this an LCD panel TV or an LCD projo TV? (sorry, didn't think to ask sooner).......

mike, where i work they're starting to see the new LED TV's....... a lot of failures because the thinner panels bend easily......

 

[Nigel Goodwin]

is this an LCD panel TV or an LCD projo TV? (sorry, didn't think to ask sooner).......

As the model numbe rincludes the size (37 inches) it's obviously a panel

mike, where i work they're starting to see the new LED TV's....... a lot of failures because the thinner panels bend easily......

You need to be more explicit - they aren't "LED TV's" they are "LCD TV's" but with LED backlights instead of CCFL ones.

 

[unclejed613]

no, they're LED tv's using RGB LEDs, no backlighting. very thin panels

 

[Nigel Goodwin]

no, they're LED tv's using RGB LEDs, no backlighting. very thin panels

Are they out now?, I wasn't aware they were - the LED backlight (and sidelit) ones are very thin as well.

What make are they?.

 

[Preher TV]

probably reffering to OLED TVs....which I've not seen one upclose yet, let alone had one in my shop for repair...hope to see some soon....

 

[Nigel Goodwin]

probably reffering to OLED TVs....which I've not seen one upclose yet let alone had one in my shop for repair...hope to see some soon....

Right, I understand that there are a few OLED ones around, but they have been promised for so many years now, and never delivered.

 

[GPTdave]

I've got a Sharp LC42PD7X, I have replaced the main board, and power board.
it will power-up, then after 5 -10 minutes shuts down, flashing power light, approx 1hz
The only rference I have indicates lamp/inverter failure. I am pretty much a total novice
when it comes to high voltage analog circuits. I am still waiting to hear back from sharp after 4 days, does anyone have any advice on how I should proceed?

Cheers,
GPTdave

 

[jokal]

Hi all,
i have the same problem with my LC-37hv4e, when i turn on, the power lamp does blink 2 times fast then in a cycle of 250 ms on 1 second off. i think, the lamp error is occured.
but at first time when i turn it on, it seams like the monitor power error, discribed on the service manuell.
when i press Vol- and input button at the same time, i turn the power on, the power led bright in Green? but i can't see any think in the pannel??
on the connector P7506, i mesured both on pins 2 and 3 (+15v). thoes any one have a idea to solve this problem please?
Many thanks.

 

[unclejed613]

jokal, did you look up the blink code in the service manual?

GPTdave, try replacing electrolytics on the inverter board. if those caps are dried out, the inverters won't start. the other place i'd look is along the high voltage wires from the inverter to the panel, make sure they're not pinched by sheet metal. bad backlight lamps are very common (even more common than bad caps, so i'd start there).

 

[jokal]

many thanks unclejed613 for your replay.
yes i have checked the Blink sequenz in the Service Manual, and i have remarked, that when i power the LCD, it blink 2x faste, then periodicly like the lamp error (250ms High, 1s low)??
Please remark that when i start the LCD in Process-Mode (Vol- & Input) then Power on, the LED light green, but no Backlight is on.
ok i try to check the Inverter Board, and all caps on this boards.
Many thanks one time more.

 

[jokal]

Hi,
so i have now checked all Capacitors on the Inverters Boards, but i can't localise any problems, but during my measurments, i have remarked, when i go with the Multimeter on Pins of the Transistor Q7704 or Q7705, the Backlights goes on ?? may be this Transistors are defect?
If you need the Service Manual, send me your mail addresse and i try to send it to you.
Many thanks to all they try to help.

 

[davids456]

i also have a fault with a sharp 17'' lcd. i sorted a 19'' cello lcd. there was a tiny white component on the inverter board that said 4a on it(a 4amp fuse). it should have measured 0 ohms but was measuring open circuit. i removed the part and soldered on a piece of 5 amp fuse wire and it has been working ever since. the inverter board causing about 95 % of lcd tv problems.

 

[A Man]

LC32SB21U inverter shut down

Hi Guys
I was recently given the same model of Sharp 37" LCD in wont fire up condition, and came across your posts during my searches for info. It has fired up in the service mode (Vol- and Input held down while turning on the power) a number of times, but it is very hit or miss and stubbernly refusing lately. I've had the power supply pcb and the video/logic board out checking for cracked solder joints and cleaned all the connectors with Deoxit, but none of that helped. I'm going to order a bunch of those PC123 optoisolators
Art

Exactly which PC123 is this referencing? The lamps do no power up but for a few seconds upon start-up. Where should I start checking?
Thank you!
A Man

 

[davids456]

hi

the inverter board is a small rectangular pcb which if you track wires coming from the main pcb should lead to the inverter board. check the small fuse on the board. its usually a surface mount component. it will say something like f1 next to it. measure the resistance across it. if its bust solder a piece of fuse wire across it.

 

[A Man]

Actually my power supply and inverter are all on one board with the PC123 optoisolators linking the two halves. I just wasn't sure exactly which variety they were. An actual wiring schematic and component list with be a really really really helpful thing right now.

 

[unclejed613]

actually, if the lamps come up then shut off it's also possible you have a bad lamp or a problem with one of the inverters or the lamp wires. do all of the lamps come on? or is one of them dim or dark? another problem i have seen with various models is the small capacitors on the high voltage side of the inverters (usually 10pf/6kv) being shorted, or a dried out electrolytic cap in one of the inverter driver circuits may be dried out. occasionally (this depends on the make and model) the lamp wires get pinched by the sheet metal and leak high voltage to ground.

 

[A Man]

Well, all of the lamps appeared to come on for a few seconds and the power LED stayed lit just no backlight. So I started checking voltages on the psu/inverter board and *POOF!* I accidentally shorted the MOSFET Drain & Gate and/or to ground on the heatsink that covered them when I was checking them. *goob noob* The zener(?)diodes that I blew & removed from D7115&D7116, D7117&D7119 had 24N written on them. The MOSFETs that I removed from Q7112 & Q7117 are R5007ANX. (Working on uploading pics) I need the schematic and component list so that I know what the diode values are. Or if anyone has any knowledge as to how to determine this in the absence of said schematic, that would be great!

Thanks!
Adrian

 

[unclejed613]

the MOSFETs are made by Rohm Semiconductor, and are 500V 7A MOSFETs that use a 10V drive voltage. as for the Zeners, i can only GUESS that they might be 24V zeners (you will need a schematic to know for sure). poking around on the primary side of the supply really wasn't necessary if you had a solid power LED. if you get it running again, stick to the secondary side of the supply. you should have connectors running to the main board, and they usually mark the voltages on the connector pinout. if they don't you'll need a schematic