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Old 5th April 2003, 06:09 AM   #1
shyfx is offline shyfx  Australia
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Default Amplifier repair.

A long while ago I blew up my Technics SU-Z780 amplifier while connecting it to a power generator at a farm party. Don't ask!

So yes, it is busted and I want to know where I should start looking for problems and what to check etc. The amplification part is a big "STEREO AMPLIFIER" IC, probably about 3/4 the size of a playing card with a damn lotof pins coming in and out (I didn't bother to count them).

When you power up the unit, all the lights come on (for the source selector) and the electronics for it are obivously working. However the LED VU meters don't show any signs of signal, there is no output via the headphone jacks or out of the speaker terminals. I am guessing the output stage is maybe knackered which basically means the whole amplifier IC is cactus?

Any ideas/help would be greatly appreciated.
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Old 5th April 2003, 11:45 PM   #2
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If your not comfortable working around or havenít before worked around hazardous voltages, find and read some of the safety precautions that abound out there. NEVER WORK ALONE. Everyone makes mistakes, no matter how experienced and should have someone how can call 911 or drive them to the emergency room. CPR certification is also useful.

First step is always to check the outputs of the power supply with a multi-meter.

*Make sure that all of the transformers AC taps have AC. Make sure that there is DC on the output of the rectifiers.

*Make sure that there is no AC on the DC.

*Look for any voltage regulators and make sure they have output levels less than their inputs.

*By now you'll likely have found all of the fuses in the power supply and verified their continuity too.

*still not working? try chasing the signal path next.

* Play a CD through one of the inputs. Use an oscilloscope or an other amplifier to trace the signal threw the chassis.

*Those big Stereo amplifier chips can be purchased from MCM electronics for not too much money. Could also be some of the logic or compneoents used to select the souce inputs

Clear as mud?
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