Tuesday, November 23, 2010

Radio Dead on batteries (D.C) but work on 240 volts a.c)

This means there is something wrong on the dc line power supply. First I used my dc bench power supply and connected to the radio via ammeter (in series with the digital meter in amp range)

I noticed the meter has a high reading on ampere range. In fact it was 0.5 Ampere. (Normal current consumption of a radio should be between 0.06A and 0.08A)This is too high for a radio and therefore I suspected a heavy short inside the set on dc power line.

Usually when you find high current and nothing happens means that there is a short and the best way to know where the short is his to touch components on suspect areas and if any is getting hot then the problem is there.

After opening the set I followed the dc line and noticed the red positive wire joined together with the black wire negative. I confirmed there must have been a mistake there from the factory and fixed the wire to the right place and the set started working on the dc normally.


It is very important to measure current to the set because it can give a hint if the problem is short or open circuit even before you open the set.

If the current is zero expect an open circuit or component and if the current is high expect a shorted component.

First have a logical thinking to figure out what the problem is even before opening the set.

Also confirm the set is dead on both power sources (i.e. dc and ac power source) this can help you to know where the fault section is pretty first.

For example if a radio is hit by power surge in most cases only the transformer goes and this effectively cut off the power to the radio via the ac outlet but if you put batteries the radio will work and this is enough clue that the transformer has blown.

Repair tip

Before you open any equipment make sure you have gathered all the necessary information from observing the equipment and thinking logically where the problem is.

Then only open the equipment and go straight to the suspect circuit- do a thorough visual check for any suspect components-ie burnt components, visual check of all capacitors ie top swollen and also touching to feel any unusually hot components: this should be done even before doing any measurement.

Thank you guys

Let meet in the next class

No comments:

Post a Comment