Hafler 9290 blew line fuse

[tonyleeusa]

My Hafler 9290 power amp blew the 10A line fuse. I replaced with a new one and it blew again as soon as I turned on the power. All other fuses are ok. Any idea what could be wrong? I have schematics to help identify components.

[bob91343]

You will need to use normal troubleshooting techniques to discover the faulty components. Most often it's output transistors but you don't provide any information to guide us. Post the diagram and we can help.

[LAJ]

I've worked on a number of Haflers. They're fine amps. Most likely you've got a shorted FET or two in one or both channels. I'd remove both from one channel at a time and check if they're shorted. Keep track of where they came from. If you have only one channel blown, remove those outputs, and you should be able to bring it up.

[tonyleeusa]

It is the line fuse (10A, one and only) that was blown. There are 4 other fuses (2 each channel, 7A) that supplier power to the circuitry. 9290 has soft turn on feature. I do not think electric power ever got to pass the soft turn on stage. Attached are Hafler 9290 circuit diagram in two pages. Thanks for all experts help.

[tauro0221]

Hi,
I think the problem is in the bridge and the filter capacitors. Reason is that your are not blowing the fuse for the negative/positive voltages. Check for a short in the pins for the ac voltage at the bridge to ground and at the filter capacitor positive side of the bridge to ground. In the way you described the blow of the fuse look like a direct short to ground. Also check the capacitors in the AC side of the bridge.

[tonyleeusa]

It turned out just a defective bridge rectifier. Replaced and everything is back to normal.

[sakis]

well done ...small mistake though ...this line of haflers doesnt feature a soft start circuit as we all know it ( divsion that provides start power via a resistor or other method to the primary of the trafo to minimize inrush urrent while start up )

the specific amps feature a slow turn on on the audio circuit ....

Just repaired 9270 a few inutes ago ....tune it warm it up .... and didnt like it !!!!
next to my P3A was obviously more powerfull ... high was extremelly delicate and clean but more than obviously midle was thin and more than one step behind together with the bass though tight enough still under the impression that wasnt as low us is supposed to be ...

kind regards sakis