KFC monitor - speakers won't work

[SAZAR]

I have KFC monitor with speakers built in, which doesn't seem to work.

I opened my monitor and tried to figure out wheither speakers are dead for real or there's some other problem.

!!!As I suspected - speakers work!!! (when elcticity from weak battery was applied directly to the wires entering speaker (both worked) I heard clicking inside of speakers) - but what is the problem then(!?), and HOW TO SLOVE IT?

I had an idea (just guessing! my wild imagination) that maybe some transistors are "LOCKED" inside of the chip on the circuit to which speakers are conected (if something like that is possible, and I think it is - because it is known that there are types of transistors that can store an information even when they are not under vlotage). I don't know; just proposing some ideas to start you thinking. ...Maybe some stronger current was passed thorough the circuit, and the protective mechanism activated... How to "UNLOCK" it - if that's the case. How to reset the circuit, or maybe the circuit itself is dead?.. (gihly unprobable because it never was under such a huge stress!)

[DMR]

I have KFC monitor with speakers built in, which doesn't seem to work.

Before digging ino the fairly unlikely possibility that the audio electronics of your monitor aren't working because some overvoltage "crowbar" sort of protection circuitry has kicked in, can you give us more information regarding the whole problem:

- When did the speakers stop working, or have they never worked for you?

- What is the exact model # of the monitor?

- Have you tried the monitor on more than one computer, or have you tried to rule out software problems in any other way?

- If the monitor's speakers have a separate jack/wire for the audio, what happens if you power up the monitor and then plug the audio jack into the "line out" of some (low output wattage!) audio device other than the computer's audio card?

[SAZAR]

Before digging ino the fairly unlikely possibility that the audio electronics of your monitor aren't working because some overvoltage "crowbar" sort of protection circuitry has kicked in, can you give us more information regarding the whole problem:

That was just a thought motivated by the fact that it is quite imposible for me to imagine that some incignificant thing can damage the whole aparature so easy. (besides - when I went to service to repair something else on it some time ago, I mentioned this 'speaker problem' to the serviceman, and he told me that he can repair it and mentioned a price if I want that additional repair when I came back for a repaired monitor (not so big price, but one speaker worked so I didn't really needed a repair, besides I used headphones (I just mentioned this speaker problem to him by-the-way)), so I asked "Would it be stereo when you rapair it?", - he tried to avoid answering, so I asked him "Would you change a circuit?" - he still tried to avoid answering; so I "put 2 and 2 together" - it will be real stereo, and he won't change a circuit... possible logic...)

- When did the speakers stop working, or have they never worked for you?

They worked for a long time, then (quite a while ago) left speaker stopped working, and now right, so they both doesn't work now.

- What is the exact model # of the monitor?

I'm not currently looking at it, and I can't find my model on Net, but it's KFC 15'' monitor with stereo speakers (at the back of the monitor there is an input for speakers (from soundcard standard output), and output for microphone.

But, never mind the monitor, I know the model of the speakers circuit inside the monitors (it stands screwed-on on the right speaker (a small stuff)). The model of the circuit is:

PCBA REV:1.01

and the chip on it is:

Philips
TAIWAN
TDA7057AQ
N72AE2
HSH9740 2

- Have you tried the monitor on more than one computer, or have you tried to rule out software problems in any other way?

What do ou have on mind? Soundcard works. (I use headphones)

- If the monitor's speakers have a separate jack/wire for the audio, what happens if you power up the monitor and then plug the audio jack into the "line out" of some (low output wattage!) audio device other than the computer's audio card?

The same thing.

As I said - I speakers clicked when I applied battery current directly to speakers wires (avoiding circuit on which both of them are connected) thus - they work.

----------
Question: what are the conditions needed for that speaker electonics to fail or something?

[DMR]

What do ou have on mind? Soundcard works. (I use headphones)

In your first post you didn't indicate that you had verified the sound card (and associated software) were functioning correctly. That's all I was after.

speakers clicked when I applied battery current directly to speakers wires (avoiding circuit on which both of them are connected) thus - they work.

Yeah, I got that. My question was basically the flip-side of my question about the sound card. That is, I wasn't so concerned about the actual speakers, I was just trying to isolate the problem to either the sound card output or the amp that drives the speakers.

About the Phillips TDA7057AQ chip:

It's an integrated stereo amplifier chip, and it does actually have a built-in thermal/short-circuit protection circuit. Unfortunately, the chip has no external "reset" line; the protection circuitry, by the looks of it, should automatically reset itself once the thermal/short fault condition is no longer present. Aside from perhaps power-cycling the amp, there doesn't appear to be anything you can do reset-wise, so I believe the repairman you spoke with would have to replace something, although I'd think the parts cost and labor would be next to nothing.

The chip also seems to need very few external components- a few coupling/decoupling caps, a volume control pot, and a couple of resistors. That pretty much means that unless something like the coupling caps or volume pot have failed, the chip itself will need to be replaced. If you can get your hands on an oscilloscope you could apply an input signal to the beast and try to verify the exact point of failure from there, but otherwise...

what are the conditions needed for that speaker electonics to fail or something

Age, thermal degradation, excessive voltage applied to the chip, or a severe short-circuit condition would be primary causes for failure.

[SAZAR]

OK
Thank you for your atention.

(by the way - I've find out what model of monitor I have, it's: KFC MM6536SL (s/n: T17B52624))

[DMR]

OK
Thank you for your atention.

(by the way - I've find out what model of monitor I have, it's: KFC MM6536SL (s/n: T17B52624))

You're welcome :)

I Googled the model # of the monitor but didn't come up with anything more illuminating. If you want the monitor repaired, I'd suggest asking the repairman you spoke with to give you an estimate. Like I said, I don't think it should be terribly expensive.

[bynkxs]

hey guys. . . im just new here and i want to ask something . . .
my monitor (sharp) has its own speakers in it and it wont work . . . i dont
know why though. my cousin told me maybe my setup is wrong of something. i need some help too :(

Thanks:
bynkxs

[DMR]

Hi bynkxs,

First of all- welcome to TechTalk!

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Please start your own thread and post your question there. When you do, please try to give us as much specific info as possible regarding the problem (exact error messages, system specs, etc.).

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Thanks for understanding.