Saturday, October 8, 2011

Customer support-via email between me and a customer from Belize

One of my latest customer Mr. Jorge from Belize send an email to me with an issue which he wanted me to explain a little, let hear what he is saying.

Hello Mr. Humphrey,

Please just one question on the CRT course that I am not sure about. 

1.   I reached chapter 9 “on how to find a shorted components using series bulb on the primary power supply fast!”… Where it says you remove a pin of some components. When I do this, do I re-solder back a component if it is ok and go to another or do I leave the pin out and go take out the pin of another?   

Humphrey: The reason I introduced this method is to assist technicians to be able to catch those hard to find components which present a short under load and if there is no load the meter will not detect them.

Please note that the component which present short (bulb lights with high intensity) are component placed in parallel with the power line (by this I mean one pin is touching on the power line and the other leg on the ground. Good examples are the components I have highlighted on chapter 9 of your book. So if any of those components present a short it is like you have placed a jumper wire between the live and ground and hence short circuit.

Now coming to your question I will say you are right(just lift up only one leg of the component) with the power off and equipment disconnected from the outlet , apply power again via series bulb and if the bulb is still bright then it means that component is ok and should be re-soldered back and continue with the rest.

2.     Also is there a possibility that a component will blow up by doing this?

Humphrey: When you dis-connect one leg of a component placed in parallel it means that component is now open circuit….open circuit does not make any harm to the circuit…the greatest harm is done by a short circuit and this is the biggest killer of electronics equipment.

A word of advice though is when you are troubleshooting the secondary side of the power supply and  decide to dis-connect the B+ load ,it is always advisable to use a dummy load on the B+ line, if not the B+ voltage may increase a lot and blow some capacitors a long that line. See details of making one in Chapter 4 of your book.

All the best Jorge

Regards Humphrey


  1. Ok, I have the understanding of this. So now because I have told my friends that I am starting to do the practical he brings me a TV as a gift. So I try to get as much information as possible, and he says that its good, but just that it doesn't work. And nobody has touched it.

    The first thing I do is check the TV Model and notice that it is the first time I hear this brand name. It's a Skyworth. So I plug it in and there is no noise. I open the set and notice the chassis number it is TH2105F Model STV-2105.

    I l look around and all wired to CRT Board and speakers are disconnected. Now immediately I go to my computer and download the schematic, behold, the Ac wire in is connected where the degaussing coil is and the other way around. I check the capacitor just in case after 5 minutes the voltage is 45 volts.

    Now i believe the live stops because the PTC stop current flowing. However I will keep you update after I put all wires in their proper place and diagnose.

  2. Hi JGManza

    That sounds interesting, but in electronics expect even more interesting scenarios, having said that it is important to listen to the owner first, hear his story then power on the equipment and confirm his story.
    Waiting for your success report on this assignment and more POWER.

    Regards Humphrey

  3. I have discovered that this, TV also has missing a capacitor C305, It was taken out but was not replaced, And there is also a capacitor that contains 250W 10UF close to the flyback, but it is set up wrong because it is backward. Because I only noticed when I went in to check the ESR. Because I have no schematic, and this TV was given to me free, I will put it aside and maybe use for parts. So I will turn my attention to the next one given to me by my cousin for practice.