Wel-come to the wonder ful world of ELECTRONICS Repair articles.Once you know the basic in an electronic every thing is possible.let me take you today in repairing PA Sounds.AHUJA Amplifer PA SYSTEMS.Below is the one came to repair in my service center.
Came to repair with AUX Picking compliant
Amp Inside look
Ahuja is one of the Indian brand having its name in quality.Many people trust & prefer this in Temples,schools,collages & even orchestra team own this brand.Since from my child wood i have seen many models starting from in-built casset player like single wheel machenisum to latest USB player model.I have repaired many models since from those days.
Simply speaking amplifiers are simple circuits. I think you are studied in your basic diploma or engineering course. Same circuit is commercially applied here in this model. Any how once if you receive this kind of equipment's for repair one can charge more depending up on the the wattage. Now let us discuss how I repair this model and what was the complaint. When I received amp with new costumer he told me that he is having aux compliant I mean it's not picking aux input I think every one understood that what was the complaint no further explanation. When I removed the front panel I noticed it is having one-one input composed with NPN C1815 transistor works as a pre-amplifier which is used to boost the incoming signals.
Since this amplifier related aux complaint my concentration is on aux related circuits only. Before touching active component I checked the aux control knob for its working found OK. Now I checked the transistor found OK. Also checked preamp vcc found normal. Now myself totally fed up when every thing is OK then what could be the problem??. I need to know what is happening to this signal feeding to aux input. Finally I pulled up my oscilloscope to see the the conditions. When I placed the probe to test point to my surprise signal is dropping low at the preamp input due to transistor leaky. As I discussed in my earlier articles defective or leaky transistors are looking good even when tested on good meters.
Based on this concept directly replaced aux preamp transistor NPN C1815 . Again when I tested it was success. I got good visual signals in my scope. Re-assembled the panel and turned on the equipment. Very happy to listen the melody song when I played via my mobile. This is how I repaired AHUJA amplifier. That's an end of the story. Let us meet in the next session.
Regards
Basavaraj BM
basavarajradiotech @gmail. Com
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