diyAudio

diyAudio (http://www.diyaudio.com/forums/)
-   Solid State (http://www.diyaudio.com/forums/solid-state/)
-   -   output transistors are dead? (http://www.diyaudio.com/forums/solid-state/172565-output-transistors-dead.html)

mdm102 26th August 2010 10:06 AM

output transistors are dead?
 
Hi,

Could you help me to understand, I tried to bias amplifier module, but overturned VR at some moment, it is single turn VR, and seems that I burned output transistors. I measured 42-50 DC voltage on the speaker terminals. Is this mean that output mosfets 2xIRFP240 and 2xIRFP9240 are dead?

Thank you!

MD

Mooly 26th August 2010 11:19 AM

Do they read short circuit Drain to Source ? and what's the amp ?

east electronics 26th August 2010 01:21 PM

yeap .... post a circuit ...that behaviour rings a bell ...that could be fun to see !!!

mdm102 26th August 2010 04:09 PM

Thank you for reply, guys! Drain to Source opened in both directions. The model of the module is HPA-nxV300se by Anthony :)

AndrewT 26th August 2010 04:25 PM

what does "opened" mean.

Open to the free flow of test current?
or
Open circuit when tested?

nigelwright7557 26th August 2010 04:59 PM

If the bias became too great you would turn on both sets of transistors at the same time and short out the power supply.

Thye usualy go short Drain to Source although i have sometimes seen MOSFETs go int all sorts of weird states. I even had one with a partial short from gate to drain.

To be safe I would replace all the MOSFET's not forgetting to wind the bias back to zero before you power up again.

mdm102 26th August 2010 05:28 PM

Quote:

Originally Posted by AndrewT (Post 2284400)
what does "opened" mean.

Open to the free flow of test current?
or
Open circuit when tested?

I meant current can flow in both directions, seems diode between Drain and Source allow to flow current in both directions. http://www.vishay.com/docs/91210/91210.pdf

mdm102 26th August 2010 05:34 PM

Quote:

Originally Posted by nigelwright7557 (Post 2284428)
If the bias became too great you would turn on both sets of transistors at the same time and short out the power supply.

Thye usualy go short Drain to Source although i have sometimes seen MOSFETs go int all sorts of weird states. I even had one with a partial short from gate to drain.

To be safe I would replace all the MOSFET's not forgetting to wind the bias back to zero before you power up again.

Yes, I measured all 4 power transistors, they allow to flow current from Drain to Source in both directions, seems they all are dead. I don't know should I change also small biasing bipolar transistor MJE340, could you advice how to check it? Thank you!

Mooly 26th August 2010 06:12 PM

If they are short they will read 0.00 on DVM on diode check.

The MJE340 needs to be tested out of circuit to fully check. If you are unsure how to interpret readings then it might be wiser to replace it... that said a FET amp shouldn't do much damage to drivers etc when the FET's fail.

When you power up use a 100 watt bulb in series with the mains supply until you are sure the amp is OK.

mdm102 26th August 2010 08:16 PM

Quote:

Originally Posted by nigelwright7557 (Post 2284428)
To be safe I would replace all the MOSFET's not forgetting to wind the bias back to zero before you power up again.

Anthony said in his manual to set VR to 450-500ohm (VR is 0-500ohm single turn), strange:confused:

I just desoldered all mosfets and checked these with DMM, 1 of 9240s is dead for sure, the second 9240 is alive, 240s are alive also.


All times are GMT. The time now is 12:52 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio


Content Relevant URLs by vBSEO 3.3.2