Sunday, April 8, 2012

#fried remote control

i have a digital tv signal receiver, which comes with a remote control. the RC recently stopped working, so i've decided to check it out... obviously there isn't much sense into doing this, considering the price of it might be ~4$, but for the sake of not throwing a circuit board for something like a single electrolytic capacitor i gave this a quick check at least.

the board is named "KOR K4502A"

using an old russian multimeter "Gost 10374-74  USSR" = FTW

after checking the LED with a digital camera (without IR filtering) and it did not show any indication of emission, i've tried probing the board as much as possible...under the epoxy blob there is a integrated circuit, which i don't know the specification of, yet i don't really want to touch it (remove epoxy) - it is definitely a suspect. there is a tiny S8050 J3Y NPN transistor (marked in yellow above), the collector of which goes to the cathode of the RC LED. the other important/active element is a ceramic resonator (two legs in the bottom left corner on the photo), model ZTB455E, which provides a carrier of ~450KHz for the IR emission. i think the element is ok, but i might need to double check that. i don't have a scope which might have been very useful here.

after opening the RC, the first suspect was a 16V electrolytic capacitor, which is connected in parallel to the input voltage, but it seems to be working fine.

i'm able to force an emission if i shortcircuit the transistor B/C junction, but that obviously isn't a good solution and i'm not really certain what is the cause at this point. might as well replace the RC (throw away the board) :sadface:.

update: i was able to exchange the remote control for a used one that works (for free). overall i think the problem was due to the main IC chip (for the keyboard control) not working correctly.