FAULTY SINOTEC REMOTE CONTROL
Last night after the late night movie, my TV remote control just wouldn't switch the telly off. So after contemplating whether or not I should leave it playing throughout the night or just get up a physically switch it off, I finally arose, tiptoes bare foot to the TV and fumbled in the dark to find the on-off switch and turned it off. So this morning I switched on the TV at its on-off switch and had another go it with the remote, to see if I could turn it off. I suspected the remote has none on the fritz.
It was time to dismantle the remote and see what the problem is. From past experience remote control problems more often than not turned out to be dry-joints caused from constantly dropping it. The main culprit being the Infrared LED that was loose or broken tracks at the battery contacts. But in this case it was neither the IR transmitter nor broken tracks but liquid spillage, because when I spit the top cover from the bottom that is held together by snap close hooks I could see a dried out brown substance in the grooves right around its edges. I suppose without my knowledge a family member, most probably my wife inadvertently, accidentally gave the remote control a sip of Coca Cola and omitted or forgot to tell me. Anyway and as I scraped the brown substance off, I just knew it was Coco Cola from previous experience.
The rubber switch contact mat was still wet but the coca cola had dried out into a sticky mess everywhere else. I then used a clean cloth dowsed with isopropyl alcohol to clean the Printed Circuit Board (PCB) and washed all the other plastic bits and the rubber mat in soapy water and scrubbed the holes in the top cover with an old tooth brush to remove all the brown gunk. After everything was completely dry, it was time to assemble the remote control.
Once assembled the remote still didn't work, so I replaced the batteries with a new pair but still no joy. I stripped the remote control again, whipped out my Fluke 77 and some dog clips and checked the voltage under load and whether or not the power reached the remote control chip via a series resistor. Funny enough all was well. I then used the rubber mat and shorted out the on-off contact and presto, the TV switched on. So once again I assembled the remote and once again it didn't work. It seemed as if their batteries weren't making contact.
So I took it apart once more and checked the battery contacts. Low and behold there was a small discoloured area on the PCB below and between the battery contacts and suspected is could be conducting the current flow. I measured for continuity between the Positive and Negative contacts and it measured 57 ohms. Surprise surprise, the PCB had gone conductive, so I used a jewelers screwdriver and scrapped the "carbonised" area clean. Thinking that should do the trick I reassembled the remote control but once again it didn't work. Turns out that when the two covers are snapped shut, the positive and negative spring contacts are hard press on the PCB, which then some how still conducts even after I cleaned away the conductive bits as can be sen the pictures below , besides there was now 3.9K ohms between them.
I needed to isolated contact between the two battery spring contacts and the PCB in the area that I scrapped clean because even though there was an acceptable resistance between them, it still prevented the remote control from operating properly. I then stuck a short piece of insulation tape beneath the spring contacts covering the "carbonised" area. After I reassembled the remote It finally worked. It's very surprising that "arching" actually occurred at 3 volts and at such low current, especially considering the remote control is powered by two AAA batteries.
Well that's electronics for you. Everything isn't always as straight forward as one would think. During my entire electronics career, I only encountered dielectrics that have conductive about a dozen times. The one I will never forget, is the High Voltage CRT plug on the tube base board of a television that went conductive, thereby dragging down the focus voltage so much so that it appeared as if the CRT was faulty. Well I actually bought and replaced the CRT, only to discover it wasn't the tube but that the dielectric CRT base adapter was in fact faulty. About two months ago, I also encountered the dielectric block that houses the two brushes on a Mercedes Benz alternator regulator that "arched", even "burning" between the brushes. It actually "carbonised" the dielectric which crumbled when I scrapped it off. It was safer and better for me to replace the alternator regulator than withstand the possibility that it would arch again after I cleaned it, seeing the dielectric has already broken down. Besides removing the alternator of a Mercedes Benz twice isn't fun at all.
Last night after the late night movie, my TV remote control just wouldn't switch the telly off. So after contemplating whether or not I should leave it playing throughout the night or just get up a physically switch it off, I finally arose, tiptoes bare foot to the TV and fumbled in the dark to find the on-off switch and turned it off. So this morning I switched on the TV at its on-off switch and had another go it with the remote, to see if I could turn it off. I suspected the remote has none on the fritz.
It was time to dismantle the remote and see what the problem is. From past experience remote control problems more often than not turned out to be dry-joints caused from constantly dropping it. The main culprit being the Infrared LED that was loose or broken tracks at the battery contacts. But in this case it was neither the IR transmitter nor broken tracks but liquid spillage, because when I spit the top cover from the bottom that is held together by snap close hooks I could see a dried out brown substance in the grooves right around its edges. I suppose without my knowledge a family member, most probably my wife inadvertently, accidentally gave the remote control a sip of Coca Cola and omitted or forgot to tell me. Anyway and as I scraped the brown substance off, I just knew it was Coco Cola from previous experience.
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| As can be seen there is sufficient places for liquid to seep into the remote control from either side. |
So I took it apart once more and checked the battery contacts. Low and behold there was a small discoloured area on the PCB below and between the battery contacts and suspected is could be conducting the current flow. I measured for continuity between the Positive and Negative contacts and it measured 57 ohms. Surprise surprise, the PCB had gone conductive, so I used a jewelers screwdriver and scrapped the "carbonised" area clean. Thinking that should do the trick I reassembled the remote control but once again it didn't work. Turns out that when the two covers are snapped shut, the positive and negative spring contacts are hard press on the PCB, which then some how still conducts even after I cleaned away the conductive bits as can be sen the pictures below , besides there was now 3.9K ohms between them.
I needed to isolated contact between the two battery spring contacts and the PCB in the area that I scrapped clean because even though there was an acceptable resistance between them, it still prevented the remote control from operating properly. I then stuck a short piece of insulation tape beneath the spring contacts covering the "carbonised" area. After I reassembled the remote It finally worked. It's very surprising that "arching" actually occurred at 3 volts and at such low current, especially considering the remote control is powered by two AAA batteries.
Well that's electronics for you. Everything isn't always as straight forward as one would think. During my entire electronics career, I only encountered dielectrics that have conductive about a dozen times. The one I will never forget, is the High Voltage CRT plug on the tube base board of a television that went conductive, thereby dragging down the focus voltage so much so that it appeared as if the CRT was faulty. Well I actually bought and replaced the CRT, only to discover it wasn't the tube but that the dielectric CRT base adapter was in fact faulty. About two months ago, I also encountered the dielectric block that houses the two brushes on a Mercedes Benz alternator regulator that "arched", even "burning" between the brushes. It actually "carbonised" the dielectric which crumbled when I scrapped it off. It was safer and better for me to replace the alternator regulator than withstand the possibility that it would arch again after I cleaned it, seeing the dielectric has already broken down. Besides removing the alternator of a Mercedes Benz twice isn't fun at all.
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