Panel/Amp issue: Panel suddenly dead but blue LED still lights up

Hi All

I'm facing a problem with my Clarity's and need your help

I recently picked up a used Anthem MRX-700 to replace the Anthem MRX-300 I was using. Within the first few days of using it I noticed the music pulling to the left. I got out the SPL meter and found that the RIGHT Clarity panel output was suddenly lower by 3db. To test whether it was the speaker or the amp, I swapped speakers (R to L) and concluded it was a speaker issue.

Today, two weeks later, the panel of the swapped working speaker which is now on the RIGHT suddenly goes dead but the blue LED still comes on when the music starts. The woofer is working, but the panel is dead. When I pumped up the decibels and put my ear to the panel, I can hear very very faint highs from just one corner of the panel. Otherwise, the entire panel is just dead.

Could this be a speaker problem only or did the amplifier cause this? Two panels damaged on the same RIGHT channel of the amp (the first -3db and the second dead). Is there some current leakage or something else?

Oddly, in both cases the blue panel LED’s of both speakers light up when the music starts implying the HV boards work.

I’m confused as to what to do? If it is the MRX-700, can such a problem even exist? Or is it the speaker boards?

Just FYI, I re-Mylar’d and recoated the panels in Sep2015 using the ERAudio coating. The Clarity’s worked just fine till I got this Anthem MRX-700. I used the Anthem MRX-300 before this and never noticed any sound drop.

Tonight I will switch the -3db panel to the dead panel speaker to check if the boards are damaged. I will also switch the dead panel to the -3db speaker to check if it is a panel issue. I will report back once done.

neil5m said:

Tonight I will switch the -3db panel to the dead panel speaker to check if the boards are damaged. I will also switch the dead panel to the -3db speaker to check if it is a panel issue. I will report back once done.

Click to expand...

Yes, you need to do some elimination work.

Does the Clarity have external (brick) power supplies? If so, it could be that.

Hi amey01

I swapped the panels between the speakers and am relieved that the panels are fine. So it is one of the boards that has gone bad.

Now, on both speakers, the blue LED's come on when the music starts. Does this mean the HV boards are fine?

Is it the crossover boards that have gone bad? Would I need to wait for the HV and crossover boards to discharge before I can unscrew them to swap between and check?

Thanks
Neil




Sent from my iPhone using Tapatalk

Now's the time to contact ML

After understanding the info. presented my educated guess is problem is caused by the second hand Anthem MRX 700. The loudspeakers worked perfectly until you connected them to used Anthem.

Please borrow from a friend a suitable functional amplifier to see if the problem with the Clarity goes away, implying they are okay.

And the problem was caused by your amplifier.

Here is a typical ML high voltage board...the top left section is the music detect circuit, the input resistors and 4 diodes by the connector BB2 clamp the max music input voltage to IC1D to + or - .7 volts. IC1D amplifies the music signal and turns on Q2, discharging C6. Timing capacitors C5 and C6 give a turn-off delay, so it stays on for several minutes after the music stops, to keep the speakers charged between songs and album changes.
The high voltage section starts at the AC mains connector AC1, further down on the left, which feeds a step-up transformer, T1, then on to a voltage multiplier ladder circuit with diodes and capacitors around D15 to D20, on to four 15 meg current limiting resistors, and out to the speaker @ connector BB1.
When it detects music, C6 discharges, and the output of IC1C changes state, this puts voltage on connector BB3 to light the speaker LED, it also goes through an on-board LED D1, and turns on a triac TRIAC1. This enables the high voltage ladder circuit, and gives you the high voltage for the speaker.
Diodes D12, 13, 26, 27 form a bridge rectifier...that in conjunction with Zener diodes Z3 through Z13 clamps the maximum output voltage of the step-up transformer. By adjusting the number and voltages of the Zener diodes, you can adjust the high voltage that goes out to the speaker...(this board uses five 47 volt zeners [1N4756a], and five 12 volt zeners [1N4742a]...add them all up, and you get 295 volts...plus the two .7 volt drops of the bridge rectifier diodes) = 296.4 volts max output from the step-up transformer feeding the voltage multiplier ladder circuit...(this will likely vary depending on which speaker model that the PCB gets used with).
High voltage from the ladder multiplier circuit can be from 2500-5000 volts, and the capacitors (C13 to C22) will retain that voltage for quite some time, even after power is removed. Be VERY careful working on the PCB.
Other components on the board give you the low voltage DC to run the circuitry, etc.
If there was a problem in the high voltage section of the board, the music detect portion could still work, and light the LED OK, but not give the high voltage it should.

That's funny. Saving the world from crappy sound. I have a buddy that has Bose 901 I think. I brought over my m15 he laughed and said no way a speaker with two drivers will sound as good as his Bose. I did bring my balanced audio tech integrated with my resolution cantata used on Bose then switch to the Logan's he could not believe his ears. The look on his face was priceless.
Im referring to your friends don't let friends bye Bose.

M15 said:

After understanding the info. presented my educated guess is problem is caused by the second hand Anthem MRX 700. The loudspeakers worked perfectly until you connected them to used Anthem.

Please borrow from a friend a suitable functional amplifier to see if the problem with the Clarity goes away, implying they are okay.

And the problem was caused by your amplifier.

Click to expand...

Hi M15

I checked with both Martin Logan and the Anthem dealer and they believe it cannot be the Anthem. They haven't had any cases of the receiver outputting DC current. They aren't keen to service/check it either as they do not have a service set up here and it has to go all the way to China to check. Hence i'm assuming it is fine and is not the problem. After swapping parts, I've been running the working speaker on the "bad" channel and so far it seems ok.

Thank you Peter for the detailed explanation of the power supply board. I'm not well versed with boards and circuit diagrams, but will follow the path and try and understand the board from it. I followed the ML instructions and discharged it by shorting the blue/red wires. I did not realise it could still hold such a high charge even a day after disconnecting it. My two year old was fiddling around with the disconnected board, so I'll keep it locked away to prevent any mishap.

I spoke to Scott at ML and they are sending over a new Power supply. Thankfully it cost $95 (when compared to the larger models) so I ordered two to replace both speakers and will keep the current one as spare. The PS should arrive this week. I'll send a better picture of it before I make the connections.

M15 said:

After understanding the info. presented my educated guess is problem is caused by the second hand Anthem MRX 700. The loudspeakers worked perfectly until you connected them to used Anthem.

Please borrow from a friend a suitable functional amplifier to see if the problem with the Clarity goes away, implying they are okay.

And the problem was caused by your amplifier.

Click to expand...

M15, I've just dusted off an old tube amp lying at the back of my cupboard. I'm going to connect it as soon as the PS arrives and check if the Anthem is at fault.

Received the new power supply from ML. Plan to install it tonight

Peter Hogan said:

Here is a typical ML high voltage board...the top left section is the music detect circuit, the input resistors and 4 diodes by the connector BB2 clamp the max music input voltage to IC1D to + or - .7 volts. IC1D amplifies the music signal and turns on Q2, discharging C6. Timing capacitors C5 and C6 give a turn-off delay, so it stays on for several minutes after the music stops, to keep the speakers charged between songs and album changes.
The high voltage section starts at the AC mains connector AC1, further down on the left, which feeds a step-up transformer, T1, then on to a voltage multiplier ladder circuit with diodes and capacitors around D15 to D20, on to four 15 meg current limiting resistors, and out to the speaker @ connector BB1.
When it detects music, C6 discharges, and the output of IC1C changes state, this puts voltage on connector BB3 to light the speaker LED, it also goes through an on-board LED D1, and turns on a triac TRIAC1. This enables the high voltage ladder circuit, and gives you the high voltage for the speaker.
Diodes D12, 13, 26, 27 form a bridge rectifier...that in conjunction with Zener diodes Z3 through Z13 clamps the maximum output voltage of the step-up transformer. By adjusting the number and voltages of the Zener diodes, you can adjust the high voltage that goes out to the speaker...(this board uses five 47 volt zeners [1N4756a], and five 12 volt zeners [1N4742a]...add them all up, and you get 295 volts...plus the two .7 volt drops of the bridge rectifier diodes) = 296.4 volts max output from the step-up transformer feeding the voltage multiplier ladder circuit...(this will likely vary depending on which speaker model that the PCB gets used with).
High voltage from the ladder multiplier circuit can be from 2500-5000 volts, and the capacitors (C13 to C22) will retain that voltage for quite some time, even after power is removed. Be VERY careful working on the PCB.
Other components on the board give you the low voltage DC to run the circuitry, etc.
If there was a problem in the high voltage section of the board, the music detect portion could still work, and light the LED OK, but not give the high voltage it should.

Click to expand...

Hi Peter, a better view of the NEW Clarity PS board. The connections are:

CON6 (HV) = yellow wire
CON5 (GND) = thick red wire from transformer on base
CON8 (LED +) = thin red wire
CON7 (LED -) = thin black wire
CON3 = thick red wire from crossover
CON4 = black wire with red stripe
CON1 = black from ac low-voltage input
CON2 = red from ac low-voltage input

The OLD Clarity PS board....different from the new one. The old PS has 50V capacitors and two with yellow caps. The resistors on R1 onwards are different too. The new board has 100V capacitors and does not have the yellow capped pieces. It also has fewer resistors. Any idea why there is this difference?

Hi

I finally replaced both the internal power supply boards. I'm surprised by the difference to the music the new PS has made. Sound quality has noticeably improved. There is a punchiness to the music, the highs are a lot better and the soundstage is more expansive. Bass is slightly lower though.

After checking with an SPL meter, the earlier -3db difference in panels is now -1db. I'm happy and surprised!

Thank you all for your help