Eton PA 5402

[Achim1409]

Bought this burned amp. Railcaps are open, the inductor was burned and open. rewound the inductor with same size material from an crossover. Power supply is working. if i put the inductor inside, the power supply drops a few times until my fuse is burning. Seems its a tripple layer board. Should be a design from an old zapco. Maybe someone have diagramm. Also all tip35 and the other seems to be ok.

 

[Perry Babin]

If you power up through a current limiter, do you see any output transistors heating faster than others?

 

[Achim1409]

i havent checked yet, but i will do. Do you now, for what this inductor is?

 

[Achim1409]

I used the cables shown on the picture instead of the inductor. if i connect the left upper cable to the right lower solder, the amp turns green and the amplitude of the power supply drops. if i connect the other one, the amp switches to red and the power supply turn off. Nothing heats up at all. I dont now, for what this inductor is there. Maybe power supply, but if i measure the connections to the rail caps or to the audio out, there is high value measured. I have asked Eton for a diagram, but they dont replyed.

 

[Perry Babin]

It's most likely part of the filter for the secondary rails. When you would it, did you get the terminal windings in the correct locations? In the attached image, you can see how the positive and negative voltages have to go to the correct points on the board.

 

[Achim1409]

Thanks for the diagram, i have tried, if i connect wrong, it shorts directly, if i connect correct, at least sometimes the green led is flashing and directly the red turns on again.

 

[Achim1409]

ok, connected it now in the correct way. amps powers up and after a few seconds both red end green led´s flashing at the same time. No heating at any transistor. i will check for a manual.

 

[Achim1409]

nothing written in the manual about the leds....

 

[Perry Babin]

Do you see any DC on the output of either channel?

Are any of the outputs heating?

Are you testing with or without a limiter? Some amps have trouble powering up normally through a limiter.

 

[Achim1409]

amp is working with limiter, but powers up fine. Clipping and power flashing at the same time. No output is heating, but i can smell, that some of the smaller parts starts heating or burning. One output has 2VDC, the other 0,5VDC

 

[Perry Babin]

The channel with 2v of DC on its output terminals is likely triggering the DC offset protection.

 

[Achim1409]

ok, i will check tomorrow. thanks a lot.

 

[Achim1409]

Iam missing in your tutorial class A/B amps. Maybe an overview would be good.
Removed complete output stage. All transistors are ok. Cleaned the board from electrolytics.

Looks, that there is still a short somewhere in the output.

 

[Perry Babin]

Is there something amp still blowing the fuse?

For DC offset, read section 13 on the Beyond the Basics page (BTB in the shortcuts at the top of the directory).

 

[Achim1409]

Some MPS A 56 are short between base and emitter. can i use some A1275 instead? They have higher voltage.

 

[Perry Babin]

The pin configuration is different so you will have to twist and insulate the leads to use them. They may cause other problems so you may need to get the original before the amp is returned to use.

 

[Achim1409]

ok, thanks. i will look if i found in other amps some spare. I will go according your tutorial.
Thanks a lot

 

[Achim1409]

Put back one bank. Removed the four transistors from the differential amp and powered up without limiter. Drivers, voltage amplifier and tip 35c stay cool. Only Tip 36c heats up . After removing the diff amp, the voltage on the speaker out increases to 4-6V.

 

[Achim1409]

For testin my transistors and fets iam using a atlas dca pro. I think it would show me if a transistor is leaking.

 

[Perry Babin]

Work back from the outputs. Install outputs, remove driver stage, check for DC. Work back until you find the faulty stage.