Problem with one Aleph 2 monoblock

[KatieandDad]

The Aleph 4 uses the same front end.

This diagram gives you the volages around the input pair.

It is possible that one of the Q1A1 or/and Q1A2 have failed as they do run rather hot, possibly even taking out the third IRF9610

[KatieandDad]

Q1A5 is a 20mA Constant Current Sourse for the input pair Q1A1 and Q1A2.

It should be impossible to blow this up as the CCS by its own nature will only deliver 20mA even if you short the output to GND. Therefore you should see about 4V at the Sources of Q1A1 / Q1A2.

I've just confirmed, the IRF9610 is a 200V device so even shorting Q1A1 or Q1A2 to the -ve rail shouldn't cause the demise of Q1A5.

Does the mono-block blow its fuses if you put a shorting plug at its input ?

Best way to confirm that CCS is working is to measure 4.5V across R3 (in the Aleph 4 diagram), if that's wrong then one of the actives around the input stage has failed.

I think the 4V at the sources of Q1A1 / Q1A2 must be relative to PWR GND.

[generg]

Originally Posted by Lucas_G

Dear KatieandDad,

thanks for your suggestion.

What partnumbers should I start looking at? I have got the schematics here, but I don't know what parts might be the the most likely culprits.
Is it around Q3?

Best wishes,

Lucas

Hi Lucas,

do you refer to the manual of Aleph2 or Aleph 4 because in both manuals Q3 means a different Semiconductor....

when the IRF are o.k. I would look next for the Q5 the MPSA18 (nomenclatura of Aleph2 manual)


you see we are all eager to help you.....

not building myself anything at the moment...

[KatieandDad]

You need to compare your diagram with the one that I posted at Post 11.

If anything is wrong around the outputs I would expect it to blow fuses all the time, not just with an input.

The IRFP9610s are easy to spot on the PCB, they are the TO220 devices as opposed to the TO92 MPSA or ZTX devices that control the ouputs.

Q1A1 and Q1A2 will be very close to each other.

The part numbers that I am referring to are for the Aleph 4 at Post 11.

[KatieandDad]

If you could post your schematics it would save an awful lot of confusion.

[KatieandDad]

Originally Posted by generg

Hi Lucas,

do you refer to the manual of Aleph2 or Aleph 4 because in both manuals Q3 means a different Semiconductor....

when the IRF are o.k. I would look next for the Q5 the MPSA18 (nomenclatura of Aleph2 manual)


you see we are all eager to help you.....

not building myself anything at the moment...

I might be wrong, but dont the two MPSA's just control the quiescent currents by measuring the voltage across the Source resistors ?

I would have thought a failure here would cause fuses to blow at power on ?

[Lucas_G]

Thanks a lot to all of you!

I will look into it tomorrow morning, when I 'll be back home, and I will also post the schematic...

[generg]

Originally Posted by KatieandDad

I might be wrong, but dont the two MPSA's just control the quiescent currents by measuring the voltage across the Source resistors ?

I would have thought a failure here would cause fuses to blow at power on ?

Yes KatieandDad you are right, I did not reflect that a damage in this place would cause more visible mess...
I was inspired by his comment of oscillation and because the caps stopping oscillation are in this area I was so free to suggest to look for this place in second order....

[Lucas_G]

This is the original scheme of the Aleph2:

[Lucas_G]

Here are some pictures of the monoblock...