Hi all,
I'm trying to repair a power supply PCB from a 10" powered PA speaker. Both input fuses on the PCB have blown. The power supply is linear and the PCB is fed from a toroidal transformer. The power supply PCB components consist of two T3.15A fuses from both AC legs of the transformer fed to an RS 808 bridge rectifier and small bypass capacitor. The supply is smoothed with two large 3300µF capacitors on both DC rails.
I have tested the forward voltages of all the diodes in the bridge rectifier and all seem to be OK. I have also tested the 3300µF capacitors out of circuit with an ESR meter - they check out OK. The power supply amplifier IC is a TDA 7293.
On the rest of the board are filter components for the HF and LF speaker drivers and a couple of zener diodes from the main supply to feed the signal PCB on another board.
I can't figure out what would have caused the fuses to blow? The only thing I have noted is that the resistance between the positive and negative TDA 7293 supply pins (+Vs & -Vs) is around 3 Ohms. I'm not sure if this is normal? Resistance from each of those pins to ground is high.
Below is a photo of the power supply/amplifier board.
Any suggestions would be appreciated.
Thanks.
I'm trying to repair a power supply PCB from a 10" powered PA speaker. Both input fuses on the PCB have blown. The power supply is linear and the PCB is fed from a toroidal transformer. The power supply PCB components consist of two T3.15A fuses from both AC legs of the transformer fed to an RS 808 bridge rectifier and small bypass capacitor. The supply is smoothed with two large 3300µF capacitors on both DC rails.
I have tested the forward voltages of all the diodes in the bridge rectifier and all seem to be OK. I have also tested the 3300µF capacitors out of circuit with an ESR meter - they check out OK. The power supply amplifier IC is a TDA 7293.
On the rest of the board are filter components for the HF and LF speaker drivers and a couple of zener diodes from the main supply to feed the signal PCB on another board.
I can't figure out what would have caused the fuses to blow? The only thing I have noted is that the resistance between the positive and negative TDA 7293 supply pins (+Vs & -Vs) is around 3 Ohms. I'm not sure if this is normal? Resistance from each of those pins to ground is high.
Below is a photo of the power supply/amplifier board.
Any suggestions would be appreciated.
Thanks.
Last edited: