Hello all,
state of the Orion XTR 275 is that it will power on fine without speakers attached, after a brief second of an current spike it will idle at 0.85A @ 13.6V
When powered on I'm able to attach speakers and it will work fine.
The problem is present when the speakers are attached and then yoi power on the amplifier... On power on the voltage of my bench power supply will drop to ~7V @ 10A and it will sit like that. The current will go to the speakers.
My speakers are two 2.2R load resistors.
To me it feels like on power on there should be a mute state, which does not happen, and the power amp. section is loading the power supply section (not waiting for the PS section to startup fully).
Kindly asking for repair advise.
Kind Regards Alex
state of the Orion XTR 275 is that it will power on fine without speakers attached, after a brief second of an current spike it will idle at 0.85A @ 13.6V
When powered on I'm able to attach speakers and it will work fine.
The problem is present when the speakers are attached and then yoi power on the amplifier... On power on the voltage of my bench power supply will drop to ~7V @ 10A and it will sit like that. The current will go to the speakers.
My speakers are two 2.2R load resistors.
To me it feels like on power on there should be a mute state, which does not happen, and the power amp. section is loading the power supply section (not waiting for the PS section to startup fully).
Kindly asking for repair advise.
Kind Regards Alex
If you connect the speakers after the amp is powered up, does it produce clean power up to clipping?
Is there DC offset on one or both channels when you power up the amp?
What do you mean:
The current will go to the speakers.
Is there DC offset on one or both channels when you power up the amp?
What do you mean:
The current will go to the speakers.
Thank you for the quick reply Perry! 🙂
I haven't checked till clipping, because my 10A bench supply will not allow it. But signal is fine with load.
Yes, when the speaker are connected on power up, I do have DC on both speakers. One channel is approx. +3.3V other channel is approx. -3.3V
I haven't checked till clipping, because my 10A bench supply will not allow it. But signal is fine with load.
Yes, when the speaker are connected on power up, I do have DC on both speakers. One channel is approx. +3.3V other channel is approx. -3.3V
Do you see -12v on the gates of the muting jfets when initially powering it up? I don't think this should be an issue but you need to check it.
The ±3.3v. Is that with no speakers/loads connected?
With no signal source plugged in?
The ±3.3v. Is that with no speakers/loads connected?
With no signal source plugged in?
Would need a boardlayout and schematic or your help to pinpoint the muting jfet, please.
The ±3.3V are with speakers attached. Correct, no source/signal plugged in.
The ±3.3V are with speakers attached. Correct, no source/signal plugged in.
I've f..ed it up - I tried to make one channel clip, seems I did not pay attention to the temps. because bottom 3 fets are getting hot loading the power supply to 10A (regarding remote on/off), but wanted to continue probing the muting jfets so I lifted the 3 source pins.
Power up (without speaker load) was fine again, but idle current was almost double ~1.8A - suspicious.
Gate of the muting jfet is slowly creeping up to -28V and staying there.
Not sure what happened, I did not short anything during measurements but the two resistors (below the 4 1000µF caps) are burnt now. Those are 75k right?
The single marked resistor is starting to get brown, but still fine.
I've read in other threads the metal bars (clamping down the mosfets) are hard to remove and will likely damage them when removed with force. Any advise removing the bars? Heat and pray?
Power up (without speaker load) was fine again, but idle current was almost double ~1.8A - suspicious.
Gate of the muting jfet is slowly creeping up to -28V and staying there.
Not sure what happened, I did not short anything during measurements but the two resistors (below the 4 1000µF caps) are burnt now. Those are 75k right?
The single marked resistor is starting to get brown, but still fine.
I've read in other threads the metal bars (clamping down the mosfets) are hard to remove and will likely damage them when removed with force. Any advise removing the bars? Heat and pray?
Attachments
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See attached.
75 ohms.
For mute, the gate voltage starts at 0v. As the gate drops towards -20 (I've never seen -28) the jfet releases the audio.
The 3 output transistors are bipolar transistors with a base, collector and emitter. It's likely only one of the 3 shorted. Remove it and reinstall the other two so you can continue testing.
75 ohms.
For mute, the gate voltage starts at 0v. As the gate drops towards -20 (I've never seen -28) the jfet releases the audio.
The 3 output transistors are bipolar transistors with a base, collector and emitter. It's likely only one of the 3 shorted. Remove it and reinstall the other two so you can continue testing.
Attachments
Thank you Perry, your technique to remove the bar worked just fine 🙂
I've removed the 3pcs 2N6488 and 3pcs 2N6491 and checked them, one of the 2N6491 was not good. That does not quite make sense, because in the thermal image the 3x 6488 heated up.
So I kept one of the 6491 out of circuit.
Replaced the burnt 75 Ohm resistors.
When applying remote the behavior is now different, speakers are not connected. All (both sides) the power supply fets NDP7060 are heating up. The amp. is drawing whatever the power supply will be able to supply (in my case 10A).
The 6488 which tested fine are getting mildly warm, so I'm not fully trusting them.
Probably lifting the 3 6488 emitter legs and powering on wasn't a smart move. Maybe the drive circuit got damaged.
To be sure I'm thinking of getting a new set of 6488 and 6491
I've removed the 3pcs 2N6488 and 3pcs 2N6491 and checked them, one of the 2N6491 was not good. That does not quite make sense, because in the thermal image the 3x 6488 heated up.
So I kept one of the 6491 out of circuit.
Replaced the burnt 75 Ohm resistors.
When applying remote the behavior is now different, speakers are not connected. All (both sides) the power supply fets NDP7060 are heating up. The amp. is drawing whatever the power supply will be able to supply (in my case 10A).
The 6488 which tested fine are getting mildly warm, so I'm not fully trusting them.
Probably lifting the 3 6488 emitter legs and powering on wasn't a smart move. Maybe the drive circuit got damaged.
To be sure I'm thinking of getting a new set of 6488 and 6491
The drive circuit may have been damaged when the outputs failed. There are only 2 drivers. Pull them to confirm that they're OK. Pull and check the protection circuit transistors as well.
Lifting the emitter of the transistors isn't generally a problem but pulling one terminal of the emitter resistors can damage the protection circuit transistors.
When you replace the tape, I'd recommend using high-temperature silicone tape.
In short power up/down cycles, measure the DCV across each of the emitter resistors. They should all read 0.000v DC. Do any read higher?
Lifting the emitter of the transistors isn't generally a problem but pulling one terminal of the emitter resistors can damage the protection circuit transistors.
When you replace the tape, I'd recommend using high-temperature silicone tape.
In short power up/down cycles, measure the DCV across each of the emitter resistors. They should all read 0.000v DC. Do any read higher?
Attachments
Thank you Perry, found two damaged drive transistors - one MPSA56 and one MPSA06
Pulled them, now power up is fine and the idle current draw is back to what it was before ~0.8A @ 13.6V
Will get the parts and go from there. I'm sure the power up issue with speakers attached will still be present.
Pulled the muting jfets and they confirmed okay in the tester. Still the gate of them drops to -28V during power up.
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The powered up amp. shows emitter resistors voltages of +34V or -34V depending on the transistor groups/types (NPN/PNP).
Pulled them, now power up is fine and the idle current draw is back to what it was before ~0.8A @ 13.6V
Will get the parts and go from there. I'm sure the power up issue with speakers attached will still be present.
Pulled the muting jfets and they confirmed okay in the tester. Still the gate of them drops to -28V during power up.
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The powered up amp. shows emitter resistors voltages of +34V or -34V depending on the transistor groups/types (NPN/PNP).
Okay we are back in business, I replaced the faulty drive transistors, resistors and new set of power transistors.
We are back to the state with the fault:
We are back to the state with the fault:
- The amp. will power up fine without speakers attached idling at 0.84A @ 13.6V
- The amp. will work fine when powered up, and in the powered on state both speakers are attached.
- The amp. will not power up fine when the speakers are attached prior to applying the remote signal. In this state the amp. will draw all 10A from my power supply (current limit and PS voltage drops to 7.2V), DC on both speakers present.
When you initially apply remote voltage, is the gate of the muting JFETs at 0v and then gradually goes negative?
Bridge the drain and source pads of the muting transistors to prevent the amp from releasing the muting. Does that allow the amp to start with speakers connected?
Do both the positive and negative regulated voltages come up quickly and at the same time/rate?
Do both the positive and negative regulated voltages come up quickly and at the same time/rate?
Bridging the drain and source pads of the muting transistors gives no different behavior in the startup. On top I've desoldered and tested them outside, they are fine.
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Pos/Neg rails are not able to come up to operating voltage when speakers are attached. They stop at +9V -9V
Without speakers attached the rails come up quickly to +33.6V -33.6V - yes at the same time/rate.
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Pos/Neg rails are not able to come up to operating voltage when speakers are attached. They stop at +9V -9V
Without speakers attached the rails come up quickly to +33.6V -33.6V - yes at the same time/rate.