NAD C 520

Description: The LCD display on the NAD C520 compact disc player has become unreadable. The audio and CD deck are functioning properly, but operating the unit without a legible display is challenging. When viewed under the right lighting, the basic LCD display appears to be working, indicating that the backlight has failed. This device is more complex than a toaster, so the first step is to locate a schematic diagram and service information to avoid spending excessive time tracing the backlight circuit manually. An internet search revealed that the backlight is an electroluminescent (EL) panel, which has a limited service life of approximately 3,500 hours. Many users have experienced similar issues. A copy of the service manual was found, which includes a schematic, a fault diagram (not useful for this problem), board layouts, and component identification. The EL backlight power supply was checked, starting from the AC fuse and working through the rectifier and regulator to the EL high voltage AC test socket. These checks can be performed with a multimeter, ensuring safety from the mains supply on the AC power board. The service manual does not specify the EL output voltage; however, the inverter switches regulated 9 V DC through a transformer with a 5:85 turns ratio, suggesting an output of about 150 V AC under no load, adjustable via a variable current-limiting potentiometer. This estimated drive voltage is typical for EL panels, operating at around 400 Hz. If the potentiometer (R708) needs adjustment, it should be returned to its factory setting due to insufficient information for a proper reset. The EL backlight power supply was confirmed to be functional, producing approximately 180 V under no load and 100 V with the EL backlight connected, indicating that the EL backlight panel has failed. The next step was to contact the local NAD service agent for a replacement LCD board. Disassembling the LCD module to replace the bonded backlight involves significant desoldering risk, potentially damaging the display. The technician advised that the EL backlight could be replaced without removing the LCD display from the board. The backlight terminations should be desoldered carefully with minimal heat, allowing the replacement to slide under the LCD display module. A replacement EL backlight was ordered for around $30, available for pickup in two days. NAD and the service agent received commendation for their helpfulness and spare parts availability. While the EL backlight's failure is a limitation of the technology, they provided guidance for repair and accessible parts at a reasonable cost. Warnings: If uncomfortable with the potential for damaging the CD player, soldering, or delicate manipulation, it is advisable to take the unit to a certified NAD repair agency. For those opting to undertake the repair, it is important to keep tools and hands clean (or wear disposable medical gloves), protect the LCD display with a sponge sheet, and avoid impacting the LCD with tools. Damage to the LCD may necessitate obtaining a replacement LCD board. Disconnect the three LCD plugs from the main printed circuit board by carefully prying at the connectors with a fine wide-bladed screwdriver, avoiding pulling on the cables to prevent additional repairs.

The NAD C520 compact disc player utilizes an electroluminescent (EL) panel for its display backlighting, which is known to have a limited lifespan. The failure of the backlight results in an unreadable display, complicating the operation of the device despite its audio and CD functionalities. The troubleshooting process begins with obtaining a schematic diagram and service manual, which provide essential information for diagnosing and repairing the backlight circuit. The power supply for the EL backlight is critical to its functionality, and testing should commence at the AC fuse, progressing through the rectifier and voltage regulator to the EL high voltage AC test socket. A multimeter is adequate for these checks, but safety precautions must be observed to avoid electrical hazards.

The inverter circuit, which converts regulated DC voltage to the high AC voltage necessary for the EL panel, operates at a specific frequency and voltage output. The EL panel's typical operating conditions, including voltage and frequency, should be adhered to in order to prevent further damage. It is essential to maintain the potentiometer at its factory setting unless sufficient information is available to adjust it accurately.

Replacing the EL backlight necessitates careful handling to avoid damaging the LCD itself. The process involves desoldering the old backlight and installing a new one without removing the LCD from the board, thereby minimizing the risk of damage. Proper tools and techniques should be employed to ensure a successful replacement. If the repair is beyond the user’s capability, professional assistance is recommended to preserve the integrity of the device.The LCD display on my NAD C520 compact disk player has become unreadable. The audio and CD deck are operating fine but operating the unit without a legible displayis difficult. If you look at the LCD under the right external lighting you can see that the basic LCD displayis still functioning so the backlighthas died for some reason.

This machine is somewhat more complicated than a toaster so the the first thing to do is try and find a schematic diagram and some service information - otherwise you will spend an age tracing out the schematic for the backlight circuit by hand. The first thing I discovered from an Internet search was that the backlight is an electroluminescent (EL) panel and that these have a limited service life of perhaps 3, 500 hours.

It appears that many folk have had similar problems. I also found a copy of the service manual with a schematic, a fault diagram (which won`t help with this particular problem), board layouts and component identification. Then I checked the EL backlight power supply starting at the AC fuse and progressively working through the rectifier and regulator to the EL high voltage AC test socket.

You can do these checks with a simple multimeter (just keep yourself physically well-away from the mains supply on the AC power board). The actual EL output voltage isn`t specified in the service manual but the inverter is switching regulated 9 V DC through a 5:85 turns ratio transformer so under no load we should see about 150 V AC at the output terminal, adjustable through a variable current-limiting potentiometer.

This estimate of the drive voltage seems typical of EL panels, with a frequency of around 400 Hz. If you must tweak the potentiometer (R708) then tweak it right back to its factory set position because we have insufficient information to reset it. I figure that the factory setting is better than my guessing at the correct drive voltage for the EL backlight.

Okay the EL backlight power supply was fine with a voltage of around 180 V under no-load and 100 V with the EL backlight connected. The EL backlight panel has clearly died. Mynext mission was to contact the local NAD service agent and inquire about a replacement LCD board. Pulling an LCD module to bits to replace a bonded backlight involves a lot of desoldering with significant risk of damaging the display.

The technician I spoke to was exceptionally helpful and advised that it was possible to replace the EL backlight without removing the LCD display from the board. The backlight termination`s should be de-soldered very carefullywith minimal heat and the replacement should simply slide under the LCD display module.

I ordered a replacement EL backlight at a cost of about $30 which was available for pickup in just two days! NAD and my service agent should receive full credit for this helpful response and the availability of spares.

Sure the EL backlight has died due to a limitation of the technology in the design but they told me how to fix it and they have spares readily available at a reasonable price. Warnings. If you are uncomfortable with the prospect of damaging your CD player, soldering, or delicate manipulation then take you unit in to a bona fide NAD repair agency for service.

If you decide to complete the repair yourself then keep your tools and hands clean (or wear disposable medical gloves), protect the LCD display from hard surfaces with a sheet of sponge and avoid any impacting the LCD with your tools. If you chip, crack or impact the LCD you will probably need to get a replacement LCD board. Disconnect the three LCD plugs from the main printed circuit board by carefully prying at the connectors with a fine wide-bladed screwdriver.

Don`t pull on the cables or you`ll be trying to fix these too. Note the plug orientation for correct reassembly. Remove the LCD display board by unscr