This amp had blown outputs ..
I replaced the outputs and noticed Q404 and 405 getting hot within 5 secs and the amp draws excessive current ..
I removed both driver boards for the rear channels ..
With the driver boards removed Q404,405 still get hot within 4 secs and amp draws excessive current ..
Any ideas ?
I replaced the outputs and noticed Q404 and 405 getting hot within 5 secs and the amp draws excessive current ..
I removed both driver boards for the rear channels ..
With the driver boards removed Q404,405 still get hot within 4 secs and amp draws excessive current ..
Any ideas ?
JL
Check the bias pots make sure they are set for max resistance of 20K
You cannot remove the driver boards without adding gate-source resistors for each MOSFET.
Zed Audio
Check the bias pots make sure they are set for max resistance of 20K
You cannot remove the driver boards without adding gate-source resistors for each MOSFET.
Zed Audio
The gate source resistors are in place ..
I will check the bias circuit to make sure that it's working correctly ..
Thanks for the info
I will check the bias circuit to make sure that it's working correctly ..
Thanks for the info
I checked everything in that channel everything tests good..
With the bias pot fully counter clockwise and driver board out of circuit the outputs still get hot within 5 secs and amp draws excessive current ..
I noticed there is corrosion around the bus bars ..
Would that cause this issue or is there something else I should check ?
With the bias pot fully counter clockwise and driver board out of circuit the outputs still get hot within 5 secs and amp draws excessive current ..
I noticed there is corrosion around the bus bars ..
Would that cause this issue or is there something else I should check ?
I've replaced every part in that channel just to make sure something wasn't defective but still tested good..
With no driver board in that channel the outputs still get very hot within 3 secs ..
What am I missing ?
With no driver board in that channel the outputs still get very hot within 3 secs ..
What am I missing ?
As was previously stated, you need to install a pulldown resistor (value not critical) between leg 1 and leg 3 of each of the output transistors (one resistor per parallel group when there are parallel groups) for the channel without the driver board. Without a pulldown resistor on the gate, the gate can charge (simply by touching the gate with your fingers) and that will make the FET conduct (even after you're no longer touching the gate).
I had them in place I used 10 ohm resistors..
I removed the resistor and put the driver board from a working channel in the defective channel and the channel still blows outputs within 5 secs
I removed the resistor and put the driver board from a working channel in the defective channel and the channel still blows outputs within 5 secs
Checked all the vias .. I triple checked it and in getting connection from the top to the bottom of the board ..
The outputs still get hot and amp draws excessive current
The outputs still get hot and amp draws excessive current
How much current is it drawing?
To clarify, was it drawing excessive current with the resistors on the gate/source and no driver board?
To clarify, was it drawing excessive current with the resistors on the gate/source and no driver board?
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Its drawing 40 amps of current ..
I put everything back together and this is what I get ..
Q304,305 get hot within 2 secs ..
Q404 and 405'get hot also ..
I tried seeing if the bias pot in the channel that uses q404 and Q405 did anything and turning it up or down does nothing at all like it's not working ..
The channel that uses Q304,305 the bias pot also does nothing ..
With the resistors hooked up and driver board out the outputs still got hot
I put everything back together and this is what I get ..
Q304,305 get hot within 2 secs ..
Q404 and 405'get hot also ..
I tried seeing if the bias pot in the channel that uses q404 and Q405 did anything and turning it up or down does nothing at all like it's not working ..
The channel that uses Q304,305 the bias pot also does nothing ..
With the resistors hooked up and driver board out the outputs still got hot
No. Pull the gate resistors for the channels getting hot and install gate/source resistors for all FETs that you removed the gate resistors for.
If it will still draw excess current, power up through a limiter. The DC voltage across the gate and source for all FETs involved should be 0.000v. Are any higher? If so, which ones?
If it will still draw excess current, power up through a limiter. The DC voltage across the gate and source for all FETs involved should be 0.000v. Are any higher? If so, which ones?
I removed all the gate resistors in the defective channels ..
I used 100 ohm resistors from gate to source
Q304: 0.00
Q305: 0.00
In that channel the driver board gets hot
Q404: 0.00
Q405: 1.82
So Q405 across the resistor I get 1.82 volts
I used 100 ohm resistors from gate to source
Q304: 0.00
Q305: 0.00
In that channel the driver board gets hot
Q404: 0.00
Q405: 1.82
So Q405 across the resistor I get 1.82 volts
Meter set to ohms
Gate to drain:OL
Gate to source:OL
Drain to source: OL
Probes reversed
Gate to drain :OL
Gate to source :OL
Drain to source :11.67 M ohms
Gate to drain:OL
Gate to source:OL
Drain to source: OL
Probes reversed
Gate to drain :OL
Gate to source :OL
Drain to source :11.67 M ohms
As far as I know, with the gate resistors removed, there is nothing connected to the gates. Do you see any other components connected to the gates?
Does the board show signs of heat stress?
Pull the other FET for that channel and clean the pads. Does the amp still draw excess current?
Does the board show signs of heat stress?
Pull the other FET for that channel and clean the pads. Does the amp still draw excess current?
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