SINOTEC REMOTE CONTROL

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.  

As can be seen there is sufficient places for liquid to seep
into the remote control from either side.

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. 

ELECTRONIC COMPONENTS - LEARN ELECTRONICS

Capacitors continued. 

I intend to conclude with capacitors in this blog but also need to finish the general topic of electronics started in the previous blog, so here goes.

Fuses may be found in virtually all electronic equipment ranging from as low as a few milli-amps to hundreds of amps. The purpose of a fuse is to stop further destruction to an electronic device when some component had failed which caused the fuse to blow, limiting destruction to the device. Fuses mostly encountered in electronics are of the glass type though the SMD ceramic fuse is becoming popular. Earth leakage circuit breakers are used in larger equipment. Virtually every TV, video machine, CD Player, digital camera, photographic flash unit, ham radio, camcorder, Hi Fi, Inverter, Security Alarm, Power supply, Electric fences, Microwave oven, Computer, etc etc... has a fuse or fuses inside. Often positioned in a snap-in holder soldered on a PCB. Fuses are probably the most underrated electronic component but plays a vital role in human safety, so please don't go bypass them in any repair.

Wire is a conductor coated by an insulator. Wire can be found in various thicknesses inside equipment and the measure for wire is describe as standard wire gauge. Wire is predominantly made of copper since its a good conductor of electricity, sometimes its made of aluminum. Like that used for earthing aerials. Wires do have some resistance but of no concern at the moment. Wires are normally selected for its current carrying capabilities thus the thicker the conductor the more current it can deliver and the inverse is true for thinner wire. In electric fences, uninsulated stainless steel wire is used with insulated wire for underground cabling.

PCBs (printed circuit boards) are the forms or substrate used to manufacture electronic equipment from a meager "power supply" to a "computer" and forms the basis of most electronic gadgets. It essentially provides a connection capability between components predetermined by design. In the absence of a PCB, we would be compelled to connect components together with short lengths of wire which would be very cumbersome and messy and a nightmare to make sense of. PCBs are produced as a photo-litho process, etched in ferric chloride (or similar solvent) and drilled. Often different size holes are drilled dependent on the type or size of component it needs to support. PCBs come as single sided, double sided and multilayer boards application dependent. PCBs with edge connectors are commonly gold plated.

Switches are the devices we use to power electronic equipment on and off. Switches comes in various sizes and shapes, mostly with two contacts which are called SPST (single pole single throw) switch, meaning that the switch only has one contact and when the switch is operated, it either opens or closes.  Then there is SPDT (single pole double throw) meaning 2 SPST in the same switch. For example, if it is used to switch mains, there is a pole for both Live and Neutral each switched separately but simultaneously. Then there are DPST (double pole single throw) and DPDT (double pole double throw) and an assortment of other switches to many to cover right now. Switches are used less today than before because most equipment today function on low power and soft switching, meaning a solid state device is used to power up the equipment, like in an alarm system. Reset switches are also popular and come in two flavours PTM (push to make) and PTB (push to break) often found on the front panels of computers.

Lead, tin, silver, gold, tungten, nichrome, copper, brass, aluminium and iron plate are just some of the metals used in electronics.

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