Saturday, October 9, 2010


In the last article I described to those new to electronics or do it yourself on how to handle a case of electronics equipment using S.M.P.S. which has succumbed to power surge or high voltage.

In this article I encountered a real life situation from a customer who brought in his JVC TV for repairs.

The customer complains was that the TV was blown by high voltage from a generator.

I opened the set and scanned around the primary side of the power supply and found the main filter capacitor was bulging out.

I replaced it together with the control chip (str-G6653) which almost always goes when there is power surge.

After replacing the two components the set came up but no color (Picture was black and while) with some very thin lines across the screen.

I hit the set softly with my bare hands and the color came on but intermittent.

Then I concluded that the set has dry joints too. I soldered all the suspect areas starting from the RGB neck circuit board.

 and Component around the main ic (Jungle) and the color came back to normal.

Later I went to his house to check on the root cause of the problem which was the generator.

You know in electronics it is not wise to just replace the faulty components, always look for the root cause of the problem, it may be dry joints or Capacitors that have developed high ESR and therefore if you only replace the faulty component chances are high for call back.

This will affect your reputation and also waste more of your time, it is better to do your repair pretty well and that customer bring to you more customers by referrals than waiting for the same machine to come again after some time..It is simply not fair to your customers.

The generator was switched on and after measuring the output voltage was found to be at 330 Vac.

But why did the Main Capacitor which is rated 400Volts blow up? This is because you meter measure R.M.S (root mean Square) of the AC and not the peak.

To get the peak Voltage you have to multiply your meter reading (AC) by 1.414.( Therefore 330 X 1.414= 466 vdc)

Way above the maximum voltage rated for the main Capacitor.

So I adjusted the Generator Voltage to 220 Vac and went back to my workshop to serve other customers.

Thank you guys

Stay safe


    thanx for good article specialy with good ending
    you found the suspect of problem the generator .
    from where you got this no.1.414?!
    have nice day

  2. Good question, here we are talking about basic electricity Beh, an example is worth a thousand theories.
    Suppose you are buying electricity from two companies A and B.
    Company A says it will supply you with 100 Volts Direct current (DC)
    Company B says it will supply you with 100 Volts Alternating Current (AC)
    For me I will have no problem with company A because for direct current it is straight forward-he offers to provide 100 volts just like you would get from a Battery.
    But I will have some questions to ask company B, you know Alternating Current(AC) has a sinusoidal wave which moves from zero volts, up to positive peak(+) back to zero again, down to negative Peak(-) and the cycle continues. So it would be wise to ask if the 100Volts it is providing is peak or mean. ? If they are providing you with peak then it means you will be getting that 100Volts only briefly in every cycle.
    To get the equivalent of 100 Volts Dc (R.M.S) we multiply 0.707 X peak (Vac)
    R.M.S = 0.707 X Peak
    Make Peak the subject
    Therefore :-
    Peak= R.M.S/ 0.707
    Or Peak = R.M.S X 1/0.707
    But 1/0.707=1.414
    Therefore Peak = R.M.S X 1.414
    Oh! This figure 1.414 happens to be the square root of 2, hence the name root mean square….
    If you take your meter and measure the voltage at your power socket in your house you find it will around 110 volts AC in USA or 220 Vac in other countries like Kenya, Britain, and Australia etc.
    This voltage on your meter is in R.M.S (root mean square) or equivalent effective value
    The Voltage you get at the main Capacitor is actually the peak voltage of the supply outlet.
    So for countries using 110 Vac( rms) this will be 155 vac peak and for countries using 220 volts ac this will be around 311 vac.
    Hope I have answered your question Beh, you can also google basic electricity for more info.
    By the way Beh, in your country do you use 110 Vac or 240 vac?

    thank you so much for reply me .
    i fully understood that rms voltage means that:
    the ac voltage that has the same heating or working value as dc
    for getting the peak we have to multiply the amount of rms to 1.414 and this number is root of no 2 and this is mathematics and formula
    in Kabul the working voltage is 220

  4. Happy to hear that, otherwise don't hesitate to come back if you have any other question.


    Stay safe