Flashing OPC/DL light

Here's what I did to fix issues with my 37D5U - do at your own risk:

***Follow the instructions below to fix the same issue in your LC-37D5U tv***

Do this test first to confirm the failure:
(1) Connect the cable line to the tv.
(2) With the tv unplugged, hold down the Input and Volume-Down buttons simultaneously, then plug in the tv.

Expected result:
(a) You should hear the tv come on in the service mode; the OPC/DL and power lights on the front of the tv should turn green and blue, respectively.
(b) The broadcast sound should come through the speakers, but you will probably still have no picture or back light.

If your test yields the expected results, proceed to the fix.


Fix
===

Parts Needed
------------
(1) Part type: Fuse
Location on circuit board: F705
Official Part No: QFS-A1154SNEZ
Replacement Part No: BK/PCB-1-R (Mfg: Cooper Bussmann - about $2) or the original QFS-A1154SNEZ (Distributor: Sears Parts Direct - about $14)

(2) Part type: Mosfet (4 of them)
Location on circuit board: Q723, Q721, Q719, Q717
Official Part No: k3469
Replacement Part No: FQPF13N50C or FQPF13N50CF (Mfg: Fairchild Semiconductor - about $2 each)

Fuse F705 is part of the circuit on the power supply that powers the inverter circuit, and the inverter switches on the back light for the tv. The mosfet at location Q723 was suspect when I tested it, so I went ahead and replaced it and the other three mosfets "chained" to it as preventative maintenance. Parts can be bought from digikey.com - digikey is usually a same-day shipper with the best prices, so I use them. USPS Priority shipping is the best bang for your buck.

Tools Needed
------------
Philips screwdriver
Soldering iron
Desoldering braid or some other solder remover
Light bulb socket that has two wires running from it and a clear 100-watt light bulb - Home Depot sells the sockets. Alternatively, you can use a 2K ohm/10W resistor
Multimeter - not necessary, but helpful

Procedure
---------
(1) **Important: Make sure the tv is unplugged**

(2) Remove the back cover and stand - there are a bunch of screws holding the back cover on. You can either mark the screw locations and bag the screws or do what I did: Unscrew the screws, leaving them in their holes, then slowly lift the back cover off and carefully set it down with the screws intact.

(3) Set the tv on a flat surface with LCD panel facedown and remove the AC power cable.

(4) The board you want to work on is the power supply board (see pic below), which is the board where the AC power cable connects. Carefully detach the connectors that connect to the other boards in the tv from the power supply, then remove the screws that hold the power supply to the back of the tv and lift it off the tv by holding it by its edges.

(5) Locate the four large 450V capacitors at locations C734, C709, C710, and C852 without touching them (they look like soda cans). Flip over the power supply board. Touch each wire of the socketed light bulb or resistor for about 3 seconds to the negative and positive leads of each large capacitor, respectively; polarity is irrelevant. This discharges the high voltage from the capacitors so you don't get shocked while working on the power supply. The voltage usually slowly dissipates on its own, but it's better to be safe than sorry when you're talking about a potentially lethal 450V. Check the voltage with your multimeter in the appropriate DC mode to verify that the capacitor voltage has been drained; if you don't have a multimeter, just continue on.

(6) At this point, you can verify that the fuse at location F705 (looks like a small black box) has indeed failed by holding the multimeter's red and black probes on the fuse's leads with the multimeter in continuity mode. If you have no continuity, the fuse has internally failed; proceed to the next step.

(7) Desolder the fuse from location F705 and desolder the mosfets from locations Q723, Q721, Q719, and Q717 then replace with new components.

(8) Put the power supply board back in the tv, using just a couple screws to hold it in for now. Reattach the connectors to the power supply.

(9) Attach the broadcast cable line.

(10) Reconnect the AC power cable to the power supply (don't plug it into the wall socket). Hold down "Input" and "Volume-Down" simultaneously, then plug in the tv. The tv picture and sound should come on.

(11) With a small screwdriver or other probing device, depress the Reset button, not the System Reset button; it's the last recessed button below the cable jack on the back of the tv. The tv will reset, then you should get sound and a picture from channel 2.

(12) Reinstall the remaining power supply screws, back cover, and stand.