Friday, August 30, 2013

Visual inspection repair

This is short article about a low budget TV DVB decoder I just repaired today. An AXIL RT160.

AXIL RT160 Decoder

The decoder stopped working some days ago. As it didn't work at all a fail in the power supply was the expected problem.
After opening, the case, nothing was seen to be burnt on the switched mode power supply.

It could be the transformer, but I suspected of the electrolytic capacitors. It is a budget model and the manufacturer surely cut corners on the caps. Moreover, electrolytic capacitors are quite delicate devices and don't age well under stress.

Board View

There are a lot of capacitors on the board, but not so many on the power supply section. 
On a closer look it was evident that one capacitor was different that the others. You can see the difference between it an a normal one on the following photo:

Bad Capacitor on the right
The suspected bad capacitor is somewhat inflated. The top is bumped out. As in jam pots, a bumped out lid means it's bad. Something is probably wrong with the electrolyte inside the capacitor.

It was a 1000uF 16V cap. As I had no similar cap at hand, I replaced it with two parallel 470uF 16V caps. Quite close to the correct value.

Cap substitution
As you can see from the figure it's a quick and dirty solution as there was no place to put the two capacitors on the same place as it was the original.

After that the decoder is working as a charm.

It's interesting to see how a cheap capacitor can ruin the operation of the whole device.
It's also interesting to see how a bad cap can be located by visual inspection. It's not always so easy.