Tuesday, July 28, 2015

LG W2243T-PF Monitor (NOT) Fixed

Position of capacitors on the power board
From this ebay listing
This was going to be a success story.  My monitor went dark (well, it just flashes the LG logo, then the display, then goes dark--it does with 2 computers).  This was actually a refurbished model that LG sent me to replace another (different model) that went dark about 3 years ago.  This one was originally manufactured in 2009, according to the sticker on the device.

This repair is something I never would have considered until I began my electronics hobby at Christmas 2013.  I didn't even know how to solder until a few months after that. Now, after numerous blinking light and other educational projects (see the rest of this blog), I had the opportunity to do something useful.

Unfortunately, this repair did not do the trick--so either something else is wrong. or I did not fix it properly (I think the former, because there is no change in the monitor's behavior, but I'm perfectly willing to accept blame.  But this was educational, and only cost me about 50 cents US in parts to apply.

I was aware that faulty capacitors were probably the cause, so I found the ebay listing above, for a "repair kit" and a couple of YouTube videos.  The ones where it all goes smoothly are not very useful, because things rarely go smoothly.  I found one where the author struggled to get the case open and that's the real challenge. Find it here. I killed my fingers, as the author indicated, and the final push required the gentle insertion and twisting of a screwdriver, but I got it open.

Note: the author of that video only wanted to remove the stand.  To someone remove the capacitors after having an easier time opening then monitor, try this one.

Once it was open, the rest was fairly straightforward.  I marked the location of the wires I disconnected, and removed the housing, which was taped on. I was then able to remove the circuit board for the power supply (4 screws), turn it over, and see that some of the capacitors were bulging, showing signs of stress. Since I had appropriate replacement capacitors in the 125 assortment in  this kit on ebay, which cost about the same as the repair it, which only had 6 capacitors (so I still have some subset of the 119 remaining capacitors).
Open, turned over, housing marked to id wires for replacement
Housing opened and turned over
Circuit board removed. Note bulges on some capacitors

The capacitors on the board were 1000uf 16V and 470uf 35V, all 105 degrees C.  Mine were the same, except that the 470ufs were 50V.

Capacitors removed

Desoldered Board

New Capacitors in place

Thursday, July 9, 2015

@SciToys Steam Experiment

Soda Can crushed after driving the air out by steam and dunking the open end in water

I get weekly science experiments from +Simon Field. I saved this on until my 5-year old granddaughter was here.  We did it today, and she was fascinated (so I am very happy)

video from scitoys

@MAKE #Electronics Experiment 30: Fuzz

From Make: Electronics, by Charles Platt. Sebastopol, CA: Maker Media, Inc, 2009, p 259.

In Experiment 30, we are creating distortion rather than filtering.  It's really an extension of Experiment 29, using a schematic similar to part 2. The differences are:
  1. The 10K and 33K resistors on TEA2025B IN1 pin 10 are replaced by an 820 Ohm resistor. The audio input still comes in at this point.
  2. There are no filters. The speaker connections go directly to OUT1 (pin 2) and OUT2 (pin 15) of the amp. 
  3. The 680K resistor on 555 and 500Ohm Pot on output pin 3 of the 555 are replaced by a .1uf cap, going to the base pin of a 2N2222 transistor (Q1). The rest of the 555 connections are unchanged. The 100K Pot still adjusts frequency.
  4.  The big difference is the addtion of the transistors.  The collector of Q1 is connected to power through a 33K resistor. The emitter of Q1 is connected to a 1K resistor and 1uf capacitor, which are also connected to the emitter of Q2.  Q2's base pin is connected to the 33K resistor, power, and Q1's collector. Q2's emitter is connected to a 100K pot through an 8K2 and 390 Ohm resistor and .22uf cap, with the other side of the pot connected to the audio input.
The transistors amplify the waveform coming from the 555, as adjusted by Pot1.  This signal overwhelms the amp, causing distortion to a degree determined by Pot2, which Charles calls the "fuzz adjuster."

I spent some time with the datasheet for the TEA2025B.  It's a stereo amp that we used in "bridge mode" for these Experiments 29 and 30.  The leads to the single speaker are connected to OUT1 and OUT2 (pins 2 and 15), and the audio input goes to IN1 (pin 10). In stereo mode, each speaker would have one lead connected to an output and the other to GND, and the additional audio input would connect to IN2 (Pin 7), which would have the same .22uf cap + resistor combination as IN1,

Another interesting experiment.  I plan to fuss around more with the TEA2025 and associated resistor and capacitor values, just for grins.

One curiosity: as reported here and by +Eric Buijs, the TEA2025 overheats, and overheats a lot at 9V.  I was having trouble getting go0d results from this experiment, so I decided to swap out the chip. It hat melted the breadboard under it, and the new chip gave me what I expected (including overheating).  The datasheet says it will take up to 15V, but at least 2 of us have experienced overheating.

Wednesday, July 1, 2015

@MAKE #Electronics Experiment 29: Filtering Frequencies Part II

Note: first, apologies to +Eric Buijs who noted that the TEA2025B runs hot at 9V.  I either did not notice or did not perceive that in part 1. However, in part 2 I experienced the same thing. Using an adjustable wall wart, I was able to apply different voltages.  9V works best, but it runs at safer temps at 7,5V and 6V. Besides the heat, the biggest difference is the volume coming out of the speaker (see video at link below).

Part 2 of this experiment involves adding a 555 timer in astable mode (with resistors and capacitors) and two pots: a 500 Ohm for volume control (between output pin 3 of the 555 and the input of the TEA2025B) and a 100K to manipulate the waveform (between 555 discharge pin 7 and threshold pin 6). I skipped the buttons for this exercise, and connected it with each filter and with no filter at all. The differences are discernible.

I did not have a 500Ohm pot, so I used a 1K.  It really only worked as a volume control at 9V.

Charles says to disconnect the audio source and use the timer as input to the amp.  I also added my cell phone playing Pandora back in.  It works for that, too.

A very worthwhile experiment. I'm looking forward to doing more with audio.

Here's the video.