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Old 2nd August 2012, 08:09 PM   #1
Mote is offline Mote  Estonia
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Default Hifonics Brutus BXi1600D excessive current draw

I have got another one of those BXi1600Ds.

Most of the power supply FETs were shorted, some of the outputs as well.
Removed all of the outputs and PS FETs, installed 2 new FETs in each bank in power supply.

Without output transistors amplifier draws more than 15 A of current and trips my power supply. Without rectifiers amp draws 1,3A, green Power LED lights up and relay clicks as if everything was fine.

I do not see any defective components in audio section, one Brutus which I fixed had a failed diode near HIP4080, on this amp they are fine.

Could it be shorted output filter inductor or transformer?
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Old 3rd August 2012, 01:26 AM   #2
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There is a small value resistor near the hip4080 as well, check that and pull the 4080 if you haven't yet.
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Old 3rd August 2012, 03:23 AM   #3
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Check the rectifiers for shorts, it's not common , but i've run across a few random ones here and there and since you have them out, it is an easy check.
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Old 3rd August 2012, 06:23 AM   #4
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There are 10 ( or 100 ohms, do not remember which) and 1 ohm resistors near HIP4080, none of those were shorted. Also I checked rectifiers for shorts while they were still on board, but will check them again out of the board.

I suspected PS FETs drivers and removed them to check. Interesting thing is that amp continued to pull current, produced rail voltage and blew one of the PS FETs. Is that normal? I thought that without drivers PS will not work.
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Old 3rd August 2012, 07:05 AM   #5
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In some amps, the PNP driver transistors are required to prevent the power supply FETs from switching on. Without the PNP driver transistor and without pull-down resistors, the gates of the FETs can charge which will make the FETs conduct. This can cause them to fail.

If the power supply driver IC is operating and the PNP driver transistors are out of the circuit, the voltage isn't pulled down enough to prevent cross-conduction and the FETs will fail.

In the future, if you need to remove the drivers with power applied (but no remote voltage), install a jumper from the collector to the emitter of the PNP driver transistor. If you need to check the operation of the driver IC (remote voltage applied) with the PNP drivers out of the circuit, remove NPN driver transistors as well and install the jumper as suggested above. If you only want to prevent the FETs from being driven, you can simply remove the NPN drivers (leaving the PNP drivers). This is for drive circuits that use both NPN and PNP drivers.
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Old 3rd August 2012, 02:07 PM   #6
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Thanks Perry, i did not know that.

Any ideas on the current draw?
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Old 3rd August 2012, 02:20 PM   #7
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What about the rail caps?

I'm assuming that you've double-checked the rectifiers and they are not shorted or leaky.
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Old 4th August 2012, 07:13 AM   #8
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Double checked the rectifiers, all 4 are OK. Pulled rail caps, none are shorted and my LC meter shows same number for all 4, although its max range is 200uF and these are 2200uF, but I get very similar numbers for each so I am assuming they are good.

Current draw is the same with or without HIP4080.
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Old 4th August 2012, 07:20 AM   #9
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With the secondary rail caps out of the circuit, does it still pull excessive current if you reinstall the rectifiers?
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Old 4th August 2012, 12:49 PM   #10
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Yes, with 4 2200uF caps out and rectifiers in, there is still current draw.
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