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Re: power out blown
I'm not sure if I follow this question but, let me try.
The "power out" is blown? Do you mean this unit has no sound but, works with headphones or do you mean the "power out" socket has no output? What exactly did the tech unplug? Was it the output jack socket or the dead speaker, does the speaker work? I need more information and a clear explanation to help with this problem, please.
Speakers blow in 2 ways leaving an open circuit or a short circuit.
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The power amplifier is the UPC1188H It will be attached to the heat sink with thermal grease on the back side of it.
Before you change it, Make sure to clean the contacts in the headphone and speaker plug as there are several interupts that may be dirty or corroded and may be preventing your music signal from getting through.
If the headphones work fine- that amp chip is driving them, the fault if the main speaker does not work will be one of those interupts. Contact cleaner should take care of the issue on the headphone jack- just spray the contacts down from the open side of the chassis and plug and unplug a number of times to clean up the contacts. Do the same for the external speaker jack
Check to make sure the problem is not with the headphone jack or the external speaker jack as these are in the circuit between the power amp chip and the built in speaker.
You can also trace through the circuit with a music source on the amp input and with simple headphones check the signal path through the circuit until the music disappears. To do this, take a headphone and set it up with 2 test leads on the ends- attach one to ground.
Now your TL072 op amps have 2 outputs, pin1 and pin 7. The inputs for pin 1 are pins 2 and 3, and the inputs for the amp section outputing on pin 7 are pin 5 and pin 6. If you get sound at pin 1 or pin 7, you move forward to the next TL072. Check for output. Then move to the power amp chip on the heat sink. Pin 1 should be the output and will be wired to the headphone jack first. The external speaker jack second and the built in speaker third. The input for that power amplifier chip is pin 7 or pin 8 depending how it is wired.
If the amp chip is blown, make sure to put an adequate amount of thermal grease on the back side of the IC in contact with the heat sink so it can operate as cool as possible.
The power amp chip has probably blown. It is a TDA2050 cost about $3. They don't even use thermal grease on these to help conduction to heat sink. Make sure you do use thermal grease when replacing. Also be careful of pluggin anything OTHER than headphones in the headphone jack. It can result in blowing the amp chip.
The power amp section has blown parts. You will likely find they use a chip like the TDA7293 as the power amp output and it will be blown, shorted causing the fuse to blow. These cost $6 from Digikey.com. Find a competent tech to replace it and use heat sink compound. Verify the part before ordering one. They come with leads bent either way so make sure you get the one with a matching suffix letter. When firing up after repair, put a 60 watt light bulb in series with the hot power lead to act as a current limiter... saves blowing fuses if there is another problem.
The headphones socket is on the preamp stage - it works so the problem must be after the pre-amp.
Do you get any sound at all from the speakers (hiss or perhaps a click) when you turn it on?
If yes it is an amplifier problem.
Here are some possible causes
A wire has come off the loudspeaker - easy to fix
Speaker protection fuse has blown - small glass fuse mounted on main amplifier chassis - replace with correct rated and type of fuse (note some of these are 'slow' blow type - important that you get the right one)
faulty component in the main amplifier stage - requires attention from qualified repairer
Loudspeaker burnt out - this can be tested by connecting another speaker across the terminals of the built in speaker.
The headphone jack socket automatically disconnects the loudspeaker when phones are plugged in - it could be that the contact in the headphone jack socket is bent and not re-making contact when the headphones are unplugged.
It is likely the amps have been blown. Take for repair as further use may cause further damage.
Test the mixer by plugging headphones into the main L and R outputs. Note you will hear only one side of the headphone being these are mono outputs. The level will be low, but will check that the rest of the mixer is working.
ALSO please read my tip on here regarding a hazard of speaker polarity.
There are some possibilities. One, your speaker may be blown or disconnected. Make sure the wiring is still connected to the speaker and if you have one, try measuring the resistance(impedance) of the speaker with a volt ohm meter.Do this unplugged from current and disconnect one of the wires from the speaker or you will get a reading from the output stage. Two if there is a heaphone or line out jack it may have become faulty. If you have sound with the headphones plugged in your amp is still producing sound. Some jacks are designed to interrupt the signal to the speakers allowing you to practice without bothering anyone. If your amp has that feature and you still have sound with the headphones and your speaker tests OK then your problem is the jack. Hope this helps.
it could have blown the speaker, a regular guitar amp is not meant to handle a bass, you should be able to look into the back of the amp and see if any of the speaker is damaged, or there may be a blown fuse inside the amp, if you check for this please MAKE SURE TO UNPLUG THE AMP FROM THE POWER SOURCE FIRST, and if needed replace the fuse with the exact same type