Sencor SCD 3554 MR - no backlight

[perseus142]

Hello guys,
I am experencing no backlight issue on detachable panel of my car stereo.
FM, CD works fine, information are sent and shown on the display however due to no backlight it is hardly readable. There is orange backlight for buttons - works fine and white backlight for display - currently off - dont know why.
It is not a menu settings - already checked.
Inspected board and no problem seen.
There are probably signs of glue ? Please see red arrows and advise. Anything to worry about ?
Also I replaced both capacitors 2200U and 470U however no luck - issue persists. Origin capacitors measured with low ESR.
I did measured voltage on the connector for detachable panel however I couldnt find service manual, neither schematic, so I cant compare. Do you you have an experience with the LCD panel ? What is your opinion about the values ?
I also inspected the detachable panel itself, please see attached picture. Do you know how the backlight works here ? There is no backlight LED as used by other car stereos. There is no dedicated backlight pin on ISO connector.

An idea/hint/direction will be very welcome. Thank you.

[perseus142]

Re: Sencor SCD 3554 MR - no backlight

Originally, it looked like

[sam_sam_sam]

Re: Sencor SCD 3554 MR - no backlight

The first thing that comes to mind is

Either one of two things

One either the LEDs are shorted or the driver for the LEDs is not working

Can you lift the display because I do not see the pins on the bottom of the display

If not

Do you have a Desoldiering Gun station that you can unsolder the display
Because if you do not see a white plastic defuseser for the LEDs then that means that it is part of the display which would mean that if the LEDs or open or shorted then there will be nothing that you can do for it

Or it is a VFD display which I do not know much about

[perseus142]

Re: Sencor SCD 3554 MR - no backlight

Under the display there is following:

- a thin white plastic foil/or tape with grey border. It is not connected to anywhere, it only sits under the display and it is partly glued on the clear panel underneath

- under the white foil sits a plastic clear panel or plate, about 2-3mm thick, it seems on side soldered to two pins, marked on bottom side. I dont see any LEDs under this clear panel.

I also checked all those SMD reistors - showing the value as per code, ZD and capacitor also tested good.

Do you know what is this and how works such type of display ?
Thank you

Pictures:

[R_J]

Re: Sencor SCD 3554 MR - no backlight

That white plate can contain one or two led's on the end where the wires attach, the rest is just the light pipe. What voltage do you have on the two wires going to it?
Could be similar to this http://www.globalsources.com/gsol/I/...htm#1139200430
Three also is EL (electroluminescent) panel, but they require high voltage at high freq. and require a driver circuit which I don't think applies here

[perseus142]

Re: Sencor SCD 3554 MR - no backlight

R_J you are right.
I desolder those 2 pin in order to remove the white plate (light pipe/difuser) and found a SMD LED.
I did measure 6,8V on the pins, so I need to find suitable LED.
I will replace is and post some pictures after the weekend.
Thank you for help.

[sam_sam_sam]

Re: Sencor SCD 3554 MR - no backlight

Chance are you could put some new LEDs on the same board if you have a tweeter soldering iron and replace them but I have not seen orange LEDs listed before

Or another option is to use some 3mm LEDs and carefully install them with some hot glue to keep them in place

I have a display on one of my Desoldiering Gun soldering station that LEDs when bad and this is what I am going to do to repair it

It might be a good idea to put a drop down resistor if the current is to high for your replacement LEDs

If the voltage is 6.8 volts then this might be cob LEDs which means that there is more than one LEDs in it

[Longbow]

Re: Sencor SCD 3554 MR - no backlight

The open circuit voltage across the faulty LED will not be the same as when that LED gets replaced. Order a few SMD parts of the proper size, and they will most likely work fine. There are already current limiting resistors in the LED circuit I will say 99% certain. This is a typical example of SMD led chips run near the limits, thus increasing heat and shortening the life of the part. Replace all the LED's in the string, not just the one that measures open.