Home Device Repair

Hello again, it has been a little bit. College has picked up, and as I am moving in a little over a week, most of my projects have been packed. However, I’ve worked on a few things in the past little while.

Remember my half-repaired LCD monitor? Well recently I obtained yet another defective LCD monitor. Symptoms: no power, no lights, no noise. I may or may not post photos about this one, because I did all repairs without taking photos, and it was a pain to take it apart, and I wish not to do so again, hehe. Basically, the cause was 4 blown caps in on the circuit board, which I’ve replaced and it now functions fully, aside from a little squealing when in stand-by or turned off (I believe due to a capacitor that started blowing but that I measured to be within proper values.)

LG LCD

A few months ago, however, I did document a repair project I undertook. I have two home theatre amps at home that I’ve had problems with. At one point, both had stopped functioning properly. So, naturally, I decided to set to fixing them.

The first one shown, the problem was the right channel would cut out intermittently, and had gotten worse to the point where it was almost constant. I noticed that, by setting the balance to full right, and maxing the volume, I was able to “pop” the sound back into coming out. I realized that the issue was likely due to dirty contacts on the relay.

Amp Dissassembly

1) First step is to remove all the screws around the amp. The back, the bottom, the sides. Then, piece by piece, remove parts.

Amp Cover Removed

This is with the cover removed, we can see the relay (center, bottom).

Front Panel

More screws, this time allowing us to remove the bottom tray.

Bottom of Motherboard

2) Now, the goal is to get access to the bottom of the motherboard, so that we can de-solder the defective/malfunctioning component. The two red circles, erm, encircle the 6 pins that need to be de-soldered.

Relay "Cleaning"

3) This is where ingenuity kicked in. In order to clean the relays, I can’t really simply open them up, and scrub/use contact cleaner to clean the contacts. So, using the correct input voltage (24v), and some alligator clips, I repeatedly closed and opened the relay, for about a minute. I did it quickly, in the hopes that the movement and friction would cause whatever dust/dirt was causing the problem to rub off.

Well, I was right. That’s all it took, and the amp works like new again!

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Sunday, February 14th, 2010 electronics, projects


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