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I took a Lexicon NT 212 (re-branded Bryston 3B-ST) power amplifier out of storage for a secondary system. The NT 212 had been on the fritz, but still functioned.
Since buying the NT 212 years ago within the used marketplace, the first issue had been that the amplifier took longer than the normal 4 second delay for the soft start feature to power-on the amplifier, but without any issue once the amplifier powered-on. In every other respect, the amplifier had been stable and trouble-free.
Yesterday, the amplifier did not power-on at all, as dead as a doornail. So I checked the pair of fuses located in the IEC inlet fuse holder, and found that both fuses were blown. I then replaced the fuses with the proper 4A fuse value and plugged the NT 212 into a GFCI protected AC outlet to see if the device would power-on:
With the power switch in the off position, I plugged-in the power cord and immediately saw that the two LED indicator lights were illuminated. Pressing the switch to the on/off positions does not change the indicator lights. Even though not under load for the test to help discharge the power supply caps, when the switch stays in the off position for approx 2 hours, the pair of green indicator lights still remain illuminated. The enclosure is moderately warm to the touch, very typical of the NT 212 while in idle, so it seems to be powered-on. Note: The remote trigger switch is in the off position, so that aspect does not seem to be an issue.
I wish to avoid the next step of testing the NT 212 under load until I get an idea of what may have happened, or what might be happening at this time. If the amplifier remains powered-on 24/7 no matter the position of the power switch, that is no problem as long as the NT 212 remains stable and safe under load. Any thoughts? TIA
Edits: 07/12/17Follow Ups:
I would also check for dc offset at the speaker terminals. put your MM on dc and on the lowest range, let the amp warm up and then take a measurement at both terminals..
Should be less than say 20Mv this may be a dc offset problem certainly from the first episode it is suspicious. Other than that it could be anything like high ESR caps shorting the supply , failed rectifier or bad relay or latching cct for the relay soft start.
Needs a tech
Thank you, I appreciate all the helpful responses.
I tested the power amplifier with an expendable raw driver and found that the signal output was fine without damage to the voice coil, so I went ahead and connected the power amplifier to the loudspeakers in the second system. After connecting all of the audio cables, I plugged the power cord in, and after the proper 4 second soft start delay, the relay kicked-in and the power amplifier performs fine, with no sonic degradation as a result of the unknown issue in question.
At this point, I'm not concerned about the inability to power on/off the amplifier since I normally keep my solid state gear powered-on 24/7. The only concern I have at this point is the safety factor, and why the fuses blew in the first place. If I send the amplifier to Bryston's US repair facility for repair, the to/from shipping charges and Bryston's reboxing fee for return shipping are too costly for me to consider at this time for a second system application unless there is a significant safety issue.
Any further thoughts/insight are welcome. TIA
It sounds as though the amplifier was subjected to serious overvoltage or simply has a switch failure. The 3B-ST/NT-212 design is simple and fairly rugged, but even the newest of these are getting rather long in the tooth. Service and shipping heavy equipment to Canada can be expensive. If the problem is only the power switch, the repair should be simple and the part inexpensive. Testing with a dummy load and a multimeter (measure the voltage delivered to the load) should indicate if the output section is damaged. Using a loudspeaker to test the amplifier risks damage to the both, but is also a possibility.
This keeps the cross border stuff to a minimum.
If you want the am repaired by Bryston, I would suggest going over to Audio Circle, The Bryston circle and write a post to James Tanner asking about repairs if you need to get it repaired.
James Tanner is a big honcho at Bryston, and he is really helpful with questions and actual connections to Bryston.
The switch or relay has been over-voltaged into a welded state. Same time as the fuses were blown.
This would be my first guess.
I would certainly test the amp with some speakers etc, before doing the work to find out.. as more than just a switch/relay may be fried.
An extreme over voltage/power surge could have welded switch contacts together, although one would expect the fuses to blow first! Relay must be okay, because he says it clicks at proper time. Or maybe it's just a cheapo switch and the mechanism failed. After all, it's not a Bryston amp, and they must save money somewhere.
Probably needs a new switch. Duster, I bet you could replace that yourself, even if you do plan to leave it powered 24/7.
berate is 8 and benign is 9
From what I gather, the Lexicon NT Series is the same as the Bryston ST Series. The only differences are cosmetic, not the parts nor design. I'll consider replacing the switch, but for now I'm simply glad it's up and running again (knock on wood) in the second system.
red and green indicators status. Can you clarify?
berate is 8 and benign is 9
There are three colors involved with the 2-channel indicator lights:
Green, Amber, and Red.
Green lights for both channels are indicated at all times during the power-on process, and while idle, without load.
In a nutshell, the issue is the green indicator lights turn-on even when the power switch is in the off position. The power amplifier becomes warm to the touch in a normal way when idle, so it seems to be powered-on even when the power switch is in the off position. I'm hesitant to connect the power amplifier to loudspeakers until I get an idea of what's going on.
Is there a 20 year Bryston warrant on this? That may be your best bet
It's a Lexicon power amplifier made by Bryston, so the 20 year Bryston warranty does not apply to the product. The Lexicon NT amplifiers made by Bryston had a 5 year warranty.
Something to note is I can hear the soft start relay click a few seconds after plugging the power cord into an AC outlet, so it seems as though the power amplifier is actually powering-on, but the issue of the power switch not functioning as it should is a very odd thing.
I suppose I'll just have to test it under load. I'll use a raw driver that is expendable to find out if the power amplifier outputs are functioning properly. If the power amplifier simply won't power on/off via the power switch, but otherwise works fine, it will be an issue I can live with. I'll ask Bryston for their advice about the safety factor.
I know some equipment can have a big surge due to caps, huge transformer..
So a pulled out powercord could?? cause the fuses and switch to fry.
What do you think, Duster?
(or the swittch being broken.. The amp had to be on thus the unplugging surge and thus the blown fuses??)
The day before, the amp was turned-off via the power switch and the power cord remained plugged-in. The next day, the power cord was still plugged-in, and the power switch remained in the off position.
When the switch was pressed to the on position the green indicators lights did not illuminate, and the soft start relay did not kick-in. There was no indication of a sudden event; no popping sound nor smell involved. The first thing I checked was if the power cord was properly plugged-in at both ends of the power cord, and all was okay.
I then re-tried the power switch to see if the soft start function was taking far more time for the relay to kick-in, since on some occasions in the past the indicator lights would not illuminate nor the relay kick-in for up to 10 seconds or so. This issue might be a key factor regarding what could have been wrong to cause the event to happen. Perhaps something was on its way to failure. Maybe there was a problem with the switch that caused the fuses to blow and for the switch to perhaps be welded in the on position like you mentioned.
At this time, every time I plug-in the power cord, the green indicator lights immediately glow, and 4 seconds later the soft start relay kicks-in perfectly.
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