REPAIR SHOP 

Repair of  ALTO PS4HA  Bi Amplified - Powered Speaker

Fault: The speaker had a distorted sound.

This speaker has 2 amplifiers - a 350w class H for the 12" driver and a 100w class B for the tweeter, On inspection found the tweeter amplifier was giving a distorted waveform on the negative going part of the sine wave test signal, found the tweeter amplifier to be a TDA7294 100w integrated amplifier chip, which can be just seen middle top of photos bellow, suspected this to be the problem as a clean signal was going into the amplifier. 

The amplifier is mounted on a dedicated PCB board fed by the back ribbon cable

De-soldered the Amplifier chip

Installed a new TDA7294 Amplifier chip and refitted to the heatsink - see old chip lying next to it. 

Tested unit - now showing a good clean waveform all the way up to 20Khz

 Re-assembled the PCBs and covers

Tested speaker for 4 hours all ok.

Comments 

This unit is quite neat and easy to work on, the only thing I don't like is the input board that has a DSP, which is a bit over the top and would be quite expensive to replace.    

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