HELP! I Short circuited a IRF9610, now what? - diyAudio
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Old 16th June 2002, 06:35 PM   #1
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Default HELP! I Short circuited a IRF9610, now what?

Help!

While fooling around with my Aleph 4, I touched resistor R38 with the cooling element fixed on Q1A1 which gave a big bang... R38 his leg has been blasted in half :-((((

I have changed R38, Q1A2 and Q1A1 and Q2 and Q3 with a new fresh versions, but the amp is still dead. I have no bias whatsoever...

What did I fry? Hopefully not the IRFP240's ...

Enlighted me???

Edwin
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Old 16th June 2002, 08:51 PM   #2
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Default Re: HELP! I Short circuited a IRF9610, now what?

I just tested 4 IRFP240's. One random one of first six, one random one of the second six, and the two which had the sense wire fixed to it. All seem to give a good Vgs reading when I test them with the 'matching' method.

Any help is appriciated...

Edwin
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Old 16th June 2002, 09:27 PM   #3
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Default Re: Re: HELP! I Short circuited a IRF9610, now what?

Is it very likely for a passive component to blow up? Because I checked a few IRFP240's, changed the IRF9610 and ZTX's for new ones, and still no sign of a bias running through the fet's...

I have the 22ma through the frontend fets, however I do not see 4-5V across the 392 ohm resistor. Also I only have about 2.5V across the Q3 instead of 4-5V .

What can it be?

Edwin
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Old 16th June 2002, 11:15 PM   #4
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I am sorry, to hear your misfortune.
You should test, / swap the zeners. Specially the one on the current source near Q3.
Try and measure the 9..9,2V. If this is not OK swap the zener for a new one. Check the resistors in this CS as well.

Hope this helps a little
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Old 16th June 2002, 11:40 PM   #5
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Quote:
Originally posted by rtirion
I am sorry, to hear your misfortune.
You should test, / swap the zeners. Specially the one on the current source near Q3.
Try and measure the 9..9,2V. If this is not OK swap the zener for a new one. Check the resistors in this CS as well.

Hope this helps a little
Protection zener Z1 and Z7 were blown. I changed them, however still no go. No bias whatsoever... What can be blown also when Z1 and Z7 were blown?

I checked the 220uf's they seem to 'load up' when I solder them out and place them between the ohm meter.

Edwin
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Old 17th June 2002, 12:09 PM   #6
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Hello edwin,

since there are not too many parts in the amp I would check every resistor.
If there´s no current going through the 392 ohm resistor maybe it´s broke or a pcb track has been blown, or the value has changed. If you´ve got 22/2mA this always gives 4volt across this resistor!

william
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Old 17th June 2002, 05:59 PM   #7
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Default How to test the mosfet's?

When I run the Vgs match testing way, and I get a normal Vgs of about 4.20V going down when it heats up.

Can I than safely conclude that this mosfet is ok? Or need I an other test to make sure they are ok?

Also, when one mosfet is broken on the current source side what will happen?

And when one mosfet is broken at the amplifier side what will happen?

I swapped boards between my channels, and the working board of the other channel does not give any bias. So it must be the IRFP240's...?

oh, lots of questions...

Edwin
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Old 17th June 2002, 09:31 PM   #8
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Hello Edwin,

when you test the fet and it has a normal Vgs at a given current it works!
Did you test all the gate resistors?
Does the other main board work on the other side?

Check all the connections (drive in to each gate resistor, +, - etc.) if the fets and all of the parts are allright either your pcb or some connection must be wrong.

if one mosfet is broken on the current source side it either has 0 ohm or infinite. The first case didn´t happen cause you would have noticed, when the second happens I think you´ll get 2/3 of the current (same for the amplifier side)

william
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Old 17th June 2002, 11:27 PM   #9
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Quote:
Originally posted by wuffwaff
Hello Edwin,

when you test the fet and it has a normal Vgs at a given current it works!
Did you test all the gate resistors?
Does the other main board work on the other side?

Check all the connections (drive in to each gate resistor, +, - etc.) if the fets and all of the parts are allright either your pcb or some connection must be wrong.

if one mosfet is broken on the current source side it either has 0 ohm or infinite. The first case didn´t happen cause you would have noticed, when the second happens I think you´ll get 2/3 of the current (same for the amplifier side)

william
I did a quick on circuit test of all gate resistors and the 1.5 ohm resistors. They all seemed ok.

The 'other' board works perfectly on the 'other side'. As both amps did run perfectly before the disaster.

I will desolder all fets to test them all and I am going to breath in and out and then put the 'broken-and-fixed' board in the working side...

I am going to sweat a bit... first of to bed and then tomorrow with a fresh look!

Edwin
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Old 18th June 2002, 12:34 PM   #10
nar is offline nar
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If you are not able to locate the error in the amp,then you should repopulate the input board completely.Check out all power mos are OK,and so for the power resistors.Should not be so long,neither high cost problem.
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