Multistage coil gun modular

Not exactly a "repair" post.

Just presenting my modular multistage coil gun here.

Single LED replacement on LG TV LED strips

Applicable to all LED strips containing 6V LEDs and this lens:

Probably used in all these models:
42LF5800, 42LB5800, 49UH6030, 55LB6100, 55LF6090, 55LB5900, 55LB6500, 55LB5550, 55LB6300, 55LY340C, 39LN5300, 39LN5700, 42LF5600,
42LX330C, 42LB5500, 60LB6100, HC600DUF, 50LN5750, 50LN5400, 50LN5100, 50LN5200, 50LN5700, 50LN5600, 42LB5800, 42LB5600, 50LB6500, 47LB5800, 47LB5900, 47LB6100,
47LB6300, 60LF6090, 60LB6000, 32LY340C, 42LB6300, 39LB5800,
39LY560H, 32LB560B, 32LB561V, 42LY560M, 60LB7100, 49UF6400, 40LX560H, 65LB6300

Not following the recommendations here may result in this:

1.
Buy the correct LEDs. I got mine from eBay. These are 6V LEDs with the anode being the larger pad.
My very first attempt was to buy from digikey some "cool white" LED I thought could be working but they didn't have the same color temperature. You will find a better description of what to look for in the below video.

2.
The LED strip is glued with strong double sided tape to the back metal cover. I would not remove the strip to repair single LEDs in this case because by doing so the strip will be bend and the solder joints will be stressed and might break without noticing.
Use a hot air gun or two soldering irons to remove the defective LED.

3.
Clean the solder pads with solder wick.

4.
I prefer putting solder paste on the pads, that way I'm sure the new LED will be soldered underneath.
Press down the LED carefully then heat from the side with a soldering iron on both sides.

5.
Clean the lens. The faulty LEDs seem to overheat and cause some deposit to accumulate on the inner cone of the lens. This part of the lens must be absolutely clean. Do not use acetone (nail polish remover) , use non aggressive chemicals only, I used alcohol.

before

after   

6.
To correctly adjust the lens I recommend cutting out a piece of an old diffuser sheet from a TV and place it on top of the lens. Light up the new LED, put some glue on the protrusions underneath the lens and adjust the lens position to get a perfectly symmetric silhouette.

good  

BAD !

7.
Put the original diffuser sheet on the LEDs (with the little standoffs), and power up a whole LED string with an external power supply. Confirm that it looks good, The light/shadows from all replaced LEDs should look symmetric, original and new LEDs should be almost indistinguishable. Slight differences in brightness don't matter.

8. Put everything back together and enjoy your TV.

That's it good luck

Build an UHF 915MHz SMD spy bug

Features:

- 400m range

- can be powered from as low as 0.9V

- fits into a 6.5mm pen

- voice activation

How to harvest energy from an audio port of a cellphone for low power applications

Simplest most inexpensive way to extract power from a cellphone audio port for low-current sensor applications

Several methods exist to extract power from an audio port, many of which rely on boost converters with transformers and/or inductors. While these are more efficient I was looking for an inexpensive way to power a LED or a low power microprocessor with components readily available.

A voltage multiplier with schottky diodes does exactly this. For the following examples a quadrupler was used. It requires the use of a tone generator which can drive the left and right channel with an inverted signal. This increases output voltage.

Here is how to drive a LED

The AC voltage coming from the headphone jack is increased and rectified and then driving a LED.

The voltage drop over these diodes is slightly higher than 200mV, the open circuit DC output voltage goes up to 5V with the weakest phone (Xperia) tested.

The current through the LED varies between 1.5 to 2.5mA @ 1.6V depending on the Phone.

See it in action here:

Here is an example how to use that power to flash a LED

The increased voltage goes to a oscillator with a low voltage push-pull comparator. The flashing effect stems from the fact that 1uF capacitor charges slowly during the LED OFF period and discharges fast when the output of the comparator is low, i.e. when the LED is ON.

The 100uF helps to increase luminosity when the LED is on, the zener diode is there to protect the IC, just in case. Some cellphones have pretty powerful drivers.

See it working here:

Last but not least I'll show you a simple circuit to harvest a few mW out of the audio port at 3V. That voltage could be used to power sensors for example which typically operate in the tens of uA range. The sensor output could be transformed into a PWM or frequency signal and fed back into the microphone input.

Depending on the phone I used I got between 500uA to 3mA at 3VDC at the output, that  means up to almost 10mW.

Remember, the input is connected to the left and right channel and a sinewave 180 degrees shifted is fed to the audio output of the cellphone. This circuit obviously has no means to find the maximum power

point of  the cellphone driver, I found that it's in general between 10kHz and 15kHz.

LG PSU board EAY60968801 repair

This is a short tutorial on how to troubleshoot and test the LG PSU board EAY60968801.
There is also a Youtube video with the same content.

Let's first have a look at the schematic. There are some less important components missing but it will give you an overview. (it may also contain some errors)
You can download it from here: Schematic EAY60968801

It is used in several Plasma TVs like 50PK250-UA 50PK990-ZA 50PK950-UA 50PK750-UA 50PK590-ZE 50PK550C-UD 50PK550-UD 50PK540-UE 50PK350-ZB 50PX950-UA and probably others. The schematic is very similar also to the EAY60968701. which is used in the 50PJ340-UC 50PJ350-UB Z50PJ240-UB.
_________________________________________________________________________________

Refer to these pictures to find the components mentioned in the schematic:

If you prefer the trial and error approach you can also buy the repair kits available on the internet, they probably cover most of the problems. Usually included are the standby controller IC, a nearby diode, a shunt resistor, a fuse and some of the big white power resistors.

The big white resistors are 22Ohm on the EAY60968801, not 10Ohm like the ones shown here. 

Repair and troubleshooting tips:

1. Remove the board from the TV, it will be easier to work with.

2. connect a load (two 100W lightbulbs in series or an equivalent power resistor) from VS to Ground

3. Connect AUTO_GND to GND and two switches from RL_ON and M_ON to STBY.

4. Apply AC mains voltage to the input.

5. Measure the voltage at F302, should be around 166VDC for 120VAC input. 

6. Measure STBY at P813, may vary a bit but should be around 3.5V. The microcontroller should now be working. If the 3.5V is not present you most likely have a problem with the 3BR1565 and/or D304, R305, F302.

7. Switch on RL_ON, both relays should close. I can't say if the timing is fixed but I am assuming it can vary quite a bit depending on measurements taken with the circuit around PC102. The measurement here is taken at the relay contact that is sinked (it's ON when signal is LOW)

8. check the PFC output voltage, it should be 390V and stable, check at F302 and F801, if it's not you may have a problem with the PFC circuit

9. check AC_DET at P813, should be 4 to 5V. The training manual actually says 4.1V but in our case the uC output is not loaded and therefore the signal goes up to 5V. 

10. check 5.1V at P813

11. check 17V at P813

Leave RL_ON on.

12. connect 2x 100W light bulbs to VS/GND (or an equivalent resistor with >150W)

13. Switch on M_ON 

14. VS will be turned on

15. check VS, VA and M5V and adjust them if necessary according to the voltages indicated on the panel sticker

16. When turning off M_ON the circuit around Q906 will be activated and discharge VS capacitors

Have fun.