amplified speakers

Good Day,

I accidently wrecked my amplified speakers by reversing the polarity from the battery. It is a fairly inexpensive set from radio shack with a sub woofer and two small "towers" . I still get a very quiet sound reproduction as well as a buzz from the speakers, but nothing from the sub woofer. I took it apart and it has a small circuit board with a bunch of capacitors, etc on it as well as two amplifier IC's. I read about someone fixing something like this by replacing the amplifier chip so I replaced them both........a learning experience. Anyhow, it made no difference. Now I noticed there is a zener diode in the circuit right where the power comes in. Could this get fried by giving it the opposite polarity? Any suggestions as to how to troubleshoot this would be greatly appreciated. I have already invested more time than the darn thing is worth, but I still want to try to repair it. Brett

First you need a circuit diagram.

Why? I almost never have them for things I repair.

Homer works on HVAC.

no way do you need a cct diag to fix a blown zener. Nor indeed for a large proportion of repairs.

NT

But you have to take into context the original poster and the question.

I read it to mean someone who isn't regularly repairing things, may not even have much knowledge of electronics. And that at the very least may require a schematic, if for no other reason than hand-holding.

Think of when you were young and first looked at circuit boards. How much of it was immdiately obvious?

Michael

Circuit boards ?

Graham

Now that is funny.

To be fair, I was thinking in terms of a beginner looking at circuit boards today (since they aren't likely to come across something else).

Nevertheless, it would apply to point to point wiring between tube sockets, though those had the slight advantage of being easier to trace.

Michael

So do I, and the same applies. Those are even simpler electrically, practically every system contains the same basic components wired in the same way.

I assume you have experience. You need one or the other and I doubt the OP has the experience.

That doesn't help a beginner. After 50 years you can figure out how 90% of things work. With 0 years you can figure out how 0% of things work.

Homer hangs around ABSE and other electronics news groups pretending that he knows something, but so far has never given anyone any useful answers. Then he brags that he can't be fired because he's a union HVAC man. he would need a schematic, because its out of his field.

Yes, but they had tubes on them. Nasty heat damage to those early phenolic PC boards by the heat conducted through the pins of the tube sockets, too.

A little snip from:

We, at American Circuits, are here to fulfill all your printed circuit board needs. Printed circuit boards were invented in the mid-1930's but it wasn't until the 1950's, when the auto-assembly process was developed by the U.S. Army, that printed circuit boards have been a part of consumer electronics. You can't even begin to imagine how our lives would be different without the convenience of printed circuit boards, and printed circuit design has progressed to the point that it makes them far different than their predecessors.

A cct diag wont help the OP find the zener, and wont help them replace it. Its not relevant here.

I remember trying to figure out where the voltage dropped :) Had me puzzled for ages that did, meters weren't given to kids like they are today.

But understanding the workings of the amp is not something the OP need get into. Anyway modern IC amps really dont explain themselves with cct diags, theyre just spider structures, a central blob with various support components hooked on, all of which do things that are well beyond the absolute beginner.

NT

It's highly unlikely there is a zener. Usually there's just a series diode.

That is, indeed, a 4.7V Zener diode. Power rating is a guess, but probably in the neighborhood of 0.5 to 1 watt. To test a zener, you need a power supply that can supply more voltage than the zener voltage, at about 10 to 50 ma (DC of course). Connect a voltmeter directly across the zener. Connect a 1K resistor between the power supply positive output lead and the zener cathode. Connect the power supply negative to the zener anode. Turn the power supply on and slowly turn the voltage control up. If the voltmeter reads zero or less than a volt, reverse the zener connections. If the voltmeter reads in accordance with the power supply's output as it is adjusted, continue adjusting the power supply voltage upwards until the voltmeter reads a constant voltage. That reading is the zener voltage. If the zener is shorted, the voltmeter will read zero or a very low voltage regardless of the direction in which it is connected. If it is open, the voltmeter will never stabilize on reading, meaning that the zener isn't regulating. Of course, this will also happen if the power supply voltage isn't high enough to make the zener conduct. In that case, get a power supply capable of higher voltage output.

Cheers!!!

C4V7 = 4.7 volts @ 500 milliwatts

O.K. Thanx for all the responses. The circuit board has a label " Z 1" where this small glass cylinder is and under it is what looks like a symbol for a zener diode. Now I am wondering two things - how do you test a zener diode and how can you tell what value it is for replacement. The board also has " 4V7" next to the diode symbol and with a magnifier I can see " C4V7" and "CH" on the diode itself. Also the glass cylinder sort of looks cracked, but it is hard to tell. Thanx again, Brett