Panasonic NVGS50 camcorder backlight issue

[Pierre95]

Hi,

I'm getting a backlight issue with the integrated LCD monitor. The LCD display itself is working well as the image can be seen when applying an external light source.

There is a hall sensor for detecting opening/closure of the display. When opened, voltage is supplied to IC908. However no oscillation occurs at none of the inverting gates within IC908. I assume IC908 is where the oscillations take place, then go to T901 through Q902, for finally driving T902.

But I don't know which component to check for the no-oscillation symptom. IC908 seems to be OK as each gate's output shows an inverted input.

Could you please help me understand what could be wrong

[R_J]

Re: Panasonic NVGS50 camcorder backlight issue

Check if you have backlight on signal, 0.8 volts on QR904 base
I am guessing it uses a ccfl for the backlight, are you sure it is good and not bad or broken?
You did check the menu setting under [LCD MODE] [DISPLAY SETUP] Sub-Menu [BRIGHT]

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

When the display is opened I have 1,2V between the base of QR904 and emitter (connected to ground). Firstly that seems a nonsense as the voltage between base and emitter cannot go beyond 0,7V-0,8V without destroying a transistor. However, according to a short description (don't have the datasheet), QR904 is a transistor-resistor, that means resistors are already serially connected to the base within the package.

You're right the inverter drives a CCFL, and I cannot claim for sure it is not broken, but I read 0V between TL901 ant TL902 terminals where the CCFL connects. As a consequence, I have 0V at the base of QR901, the voltage being fed through D906 from TL901 after being dropped through R973 and R974

Could there be an output voltage disabler if the CCFL is detected as broken (= an open circuit is measured)? Or 0V at the output terminals means some other component is defective/disoldered?

I also checked LCD brightness setting which is set to bright.

[R_J]

Re: Panasonic NVGS50 camcorder backlight issue

How are you measuring the voltage at tl901/tl902? this will be a high voltage at high frequency.
when the circuit works and lights the ccfl a a/c voltage will appear at tl902, if the lamp is open, no voltage will appear on d903 (3) and no dc will appear on d903 (1&2), this will likely shut off the circuit. This action happens within a couple cycles of the circuit

QR904 base is high but not concerning but is the collector at 0.1? if the collector is also high, qr904 could be open.

what is the number ON QR904? it may be a digital transistor

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

I am measuring the voltage at TL901/TL902 by the use of a digital multimeter set on 700V ACV. It displays 0V.

By open you mean the CCFL is broken? Is there a way I could simulate a CCFL by connecting a resistor at TL901/TL902 to see if this triggers the circuit?

Collector of QR904 is at 0V not 0,1V but this makes sense as the voltage issued through D906 is 0V.

The number on QR904 is 33 and according to the schematics its reference is B1GBBEMA0001 but no datasheet can be found.

Also assuming IC908 is a digital hex inverter, I don't understand the voltages labelled on the schematics. Depending on the duty ratios, if the indicated values are average voltages, that makes sense. However, how 1,3V at pin 5 could produce 0V at pin 6?

[R_J]

Re: Panasonic NVGS50 camcorder backlight issue

Most multimeters measure low frequency 50hz or 60hz, this circuit when working will likely run at over 25Khz.
The voltages on ic908 i suspect are when it is working (generating 25khz pulses)

What is the voltage on Q902 Drain? do you have 8 volts?
Do you have a scope to check if there are any pulses coming from ic908 pin 4?

If you can find a ccfl from a smaller computer montor (17 - 22 inch) or even one from a small lcd tv might work. I have a small inverter ment for 6inch ccfl's but it will light a 40inch ccfl but it is very dim

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

I checked the voltages with a scope: Q902 drain is only 4,4V. Pin 4 of IC908 output is 0V.

I tried on a 6 inch CCFL from a car display but it didn't light up.

[R_J]

Re: Panasonic NVGS50 camcorder backlight issue

Q902 should have 8 volts on the drain, Check the voltage on pin 4 of T901, Your M NOREG voltage from the power supply seems to be too low (missing), Check for open L901. then check page 74, You may have an open R1002 (0Ω)
You should have 8 volts from the battery test point CL1001, through IP1001 --> R1002 --> IP1003 --> (page77) M NOREG <to Monitor>

(page 32) I suspect you are reading phantom voltage on Q902 which is coming from the +5 volts back through R979 to L901 then to T901 and finally Q902 (D)

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

The 4,4V are also on pin 4 of T901 and on both sides of L901, I also checked L901 is not an open circuit. As per your suggestion, I have by now to check for low M NOREG on the other board (page 74), but I first need some further disassembly.

I had a look for disassembly instructions into the service manual, but it's more a schematics booklet than an service manual. So don't know where to start to avoid disassembling more than is actually required.

[R_J]

Re: Panasonic NVGS50 camcorder backlight issue

This manual might be similar and help with disassembly

I suspect there is NO M NOREG voltage at all, That 4.4v is showing up at that point from the 5 volt line through R979. since there is almost no current being drawn, there is no voltage drop across R979 so that's why you read the 4.4v

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

Thanks for this manual.

I succeeded in disassembling the camcorder.

Now I have to locate R1002 and LB1001 on the mainboard.

I agree with your analysis of the low voltage at Q902's drain, and as you mention the 4,4V is most likeky not coming from M NOREG at all but from M BL 5V, and as the current is close to 0A, there's close to 0V drop accross R979 and R953.

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

I have located R1002. I'm not completely sure about it as there are also components on the other side of the PCB. The component has a V label on it, and as you suggested, it's an open circuit. I read 7,7V on one side but 0V at the other which connects to the M NOREG pin.

I'm asking myself what could have destroyed R1002 to know if it could be simply replaced or if further investigations are required. In other words, is it a mechanical or an overcurrent breakage.

R1002 soldering seems to be OK.

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

Picture of what I think is R1002:

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

R_J, you are a master!

I just replaced the resistor that in opinion is R1002 and the backlight is working again!

Thank you so much for the help you provided to me.

I'm still guessing what could have broken the original resistor.

[R_J]

Re: Panasonic NVGS50 camcorder backlight issue

That smd marked "V" is likely a fuse 3.15 amp rating, I have no idea why it went, but sometimes they can just go open.
Glad to here its working.

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

IP1003 is also mentionned as a circuit protector fuse, but the component I replaced cannot be IP1003 which if opened will not affect M NOREG voltage.

Strange they labelled R1002 as being a resistor. Hope that a 0 ohm replacement resistor will not be risky as it can handle more than 3,15A.

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

After reassembly I'm getting an unexpected error. When a tape is inserted, the mechanism refuses to push the tape down. After a few seconds I get the error message "Please re-operate after pushing reset button". After pushing the reset button the message "To service" is displayed. If I reinsert the tape when the "Please re-operate after pushing reset button" gets displayed, the tape is properly loaded, however no recording nor playback is possible. If I switch OFF and ON again I can barely hear what seems to be the noise of rotating pinions, then again the error message.

Really don't know what could have gone wrong as the tape compartment was not disassembled at all...

[R_J]

Re: Panasonic NVGS50 camcorder backlight issue

Recheck any cables you removed during the disassembly and make sure they are seated properly, Does the mechanism open and close without a tape?
I don't know what you removed during the disassembly so I don't know what to suggest, If you removed any fpc flat cables, make sure they are in the correct way and none of the connections are damaged
For example: the video drum should spin up when a tape is being loaded, if it does not it likely won't load the tape and throw an error

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

OK, I will have a detailed inspection. The mechanism opens/closes normally without a tape, regardless of the ON/OFF status, and when turned ON, after the "Please re-operate after pushing reset button" gets displayed, the mechanism does finally close. When OFF, the mechanism never closes when a tape is inserted.

I only removed the front lens hood (which holds the microphone and its flexible), the LCD display and it's holding which also has VTR buttons. And finally, the little SUB CBA board and disconnected the flexible, but as per my unterstanding this board acts as a coprocessor for digital processing and is not involved in the tape mechanism.

I disassembled only what was required for accessing R1002, but I removed all screws from the outside of the case.

By video drum you mean the inclined 1 inch in diameter cylinder? As far as I can hear it does not spin up at all, it seems to me only a little pinion is rotating but I can be wrong as I cannot have a look inside when the tape mechanism is closed.

[Pierre95]

Re: Panasonic NVGS50 camcorder backlight issue

I reseated all 5 cables involved in the tape mechanism but unfortunately the result is the same. The loading motor is for sure operating as under some conditions the tape gets in. The capstan motor is also OK as I can see a pinion rotating.