generally speaking - yes, they are. especially for a product that is not really so old.
mlloyd1
mlloyd1
Hi there,
so, another year passed by and I was still not able to find a circuit diagram for the ML 431; I took both power amps out and after some solid resoldering (I did not see one suspicious solder joint) the scratching noise in the left channel is now on a very low level. The right channel is now completely scratch- and hiss free.
Does anybody got in between a circuit diagram of this ML431? Just in case when there may be a bigger problem??
best regards
Dieter
so, another year passed by and I was still not able to find a circuit diagram for the ML 431; I took both power amps out and after some solid resoldering (I did not see one suspicious solder joint) the scratching noise in the left channel is now on a very low level. The right channel is now completely scratch- and hiss free.
Does anybody got in between a circuit diagram of this ML431? Just in case when there may be a bigger problem??
best regards
Dieter
I just stumbled across this thread, and the problem sounds a lot like what I had back in 2011. The following is the description of the problem I sent to Harmon international.
“For the past 3 or 4 months I have experienced an intermittent and random distortion in the form of snap-crackle-and-pop from the left channel of my system. I have cleaned both male and female parts of all cables in my system. I have exchanged and swapped cables. I have replaced tubes in my preamp. I have exchanged speakers. Only to finally conclude that my problem is with the newest and, what I thought, was the least likely component, my six-year old Model 431 power amp (Serial No. 1454). I confirmed this by removing all input connections, powering up the unit and simply waiting. Sure enough, after a few minutes, about 3-5, there would be a few crackles, or maybe a second or two of “static.” Sometimes it would take 10-15 minutes, or maybe even an hour before the burst of static. This would continue for as long as the unit was powered up. I usually leave the amplifier in standby mode when I am not actively using my system.”
It was repaired under warranty, but it took two trips to Pyramid Audio Service in Austin TX. I asked repeatedly for a description of the fix, but no luck, just, “we replaced some noisy boards.”
Cheers,
ceulrich
“For the past 3 or 4 months I have experienced an intermittent and random distortion in the form of snap-crackle-and-pop from the left channel of my system. I have cleaned both male and female parts of all cables in my system. I have exchanged and swapped cables. I have replaced tubes in my preamp. I have exchanged speakers. Only to finally conclude that my problem is with the newest and, what I thought, was the least likely component, my six-year old Model 431 power amp (Serial No. 1454). I confirmed this by removing all input connections, powering up the unit and simply waiting. Sure enough, after a few minutes, about 3-5, there would be a few crackles, or maybe a second or two of “static.” Sometimes it would take 10-15 minutes, or maybe even an hour before the burst of static. This would continue for as long as the unit was powered up. I usually leave the amplifier in standby mode when I am not actively using my system.”
It was repaired under warranty, but it took two trips to Pyramid Audio Service in Austin TX. I asked repeatedly for a description of the fix, but no luck, just, “we replaced some noisy boards.”
Cheers,
ceulrich
The circuit schematic diagram of NO.431 current gain board is missing. Are there any? Can you provide it?
Hi LJYS,
just stumbled over the thread and found the circuit diagram for the ML431 - THANK YOU VERY MUCH !!!!
My 431 is still running since I resoldered the pcb´s and turned the trimpots a bit; one question still arises as the 431 have "only" 5 pairs of power transistors but the 432 have 7 pairs, but this is not so important.
best regards
Dieter
just stumbled over the thread and found the circuit diagram for the ML431 - THANK YOU VERY MUCH !!!!
My 431 is still running since I resoldered the pcb´s and turned the trimpots a bit; one question still arises as the 431 have "only" 5 pairs of power transistors but the 432 have 7 pairs, but this is not so important.
best regards
Dieter
Dear,
I have a problem with my Proceed HPA-3 / HPA-2. I can't find the schematics anywhere. Would you have these?
I have read that it could be the same as some Levison model.
Thank you very much for your time!
Rolando
Hi Symphony,
it looks similar, but I dont have any info about this amp - sorry!
Dieter
Hi Symphony,
the heatsinks look similar to the 431, but the pcB is different, but I have no clue about the details - sorry!
I am currently trying to fix my 432. It worked faultlessly all theses years of light use, but sadly the 432 has now developed a fault. During the weeks leading up to the fault I had the occasional crackling noise through the speaker, not sure if one channel or both channels. Then from one day to the next it had developed the following fault all of the sudden: When I take the amp out of standby it switches itself off almost immediately after being taken out of standby. The red led flashes fast and the led is on half of the time and off half of the time.
In order to get a better understanding what the problem is I started to take the unit apart, because I would like to find out more about the cause of the problem to see if this is something I can get fixed locally or maybe even fix myself or if I have to freight ship the 432 to an expensive repair shop. Anyway, on visible inspection I could not find any obvious signs for a leaking capacitor or anything the likes.
I am now trying to narrow down the fault by following the schematics, many thanks to LJYS !!!
So far I haven't been able to locate the cause of the problem and therefore I wonder if I simply need to adjust the trimpots, because it seems in 2007 and 2008 Mark Levinson had released a technical bulletin "ML431_432_010408" on the topic of adjusting these trimpots to avoid crackling noise as well as avoiding a loud thump when switching on the unit. Both of which I had experienced prior to the fault. Does anyone of you know how to adjust the trimpots, Habadudl/Dieter can you help with information on how this is done? I understand you have done this with your 431.
Or does anyone like to share the technical bulletins which were released for the 431/432 in the year 2007/2008?
The technical bulletins I am looking for are "ML431_432_010408" and "ML4312_112107".
Many thanks in advance,
Mischa
In order to get a better understanding what the problem is I started to take the unit apart, because I would like to find out more about the cause of the problem to see if this is something I can get fixed locally or maybe even fix myself or if I have to freight ship the 432 to an expensive repair shop. Anyway, on visible inspection I could not find any obvious signs for a leaking capacitor or anything the likes.
I am now trying to narrow down the fault by following the schematics, many thanks to LJYS !!!
So far I haven't been able to locate the cause of the problem and therefore I wonder if I simply need to adjust the trimpots, because it seems in 2007 and 2008 Mark Levinson had released a technical bulletin "ML431_432_010408" on the topic of adjusting these trimpots to avoid crackling noise as well as avoiding a loud thump when switching on the unit. Both of which I had experienced prior to the fault. Does anyone of you know how to adjust the trimpots, Habadudl/Dieter can you help with information on how this is done? I understand you have done this with your 431.
Or does anyone like to share the technical bulletins which were released for the 431/432 in the year 2007/2008?
The technical bulletins I am looking for are "ML431_432_010408" and "ML4312_112107".
Many thanks in advance,
Mischa
Hi Mischa,
first of all, fortunately I don't had this immediately switch off of the amp almost immediately after being taken out of standby. Neither the red led flashes fast and the led is on half of the time and off half of the time. I also don't have any info about a technical bulletin "ML431_432_010408". There is at least one additional sheet missing showing the power supply and the logic and RJ45 communication board.
The loud thump the amp is doing since I have it - the reason is that there is no output relay - ML says that this will deteriorate the sound due to nonlinearities of the relay contact material over time.
In my case crackling noise had been due to bad solder joints which became old - I took out the PCB's and resoldered the whole power amps and slightly turned the trimpots. After that action the crackling disappeared. Especially look at the semiconductors with heatsinks (Q119 - 122) because they are becoming pretty hot
The two schematics does not inform us about the voltages and currents which have to be adjusted - the four trimpots are doing the following:
R2 and R5 are adjusting the prestage voltage POS_REG and NEG_REG, but I don't know the necessary voltage here (should be only a bit less than the UNREG)
R133 is for adjusting the symmetry - should be zero volt DC on the output at warm up and power on.
R213 is for adjusting the quiescent current of the power stage, probably measured between TP9 and TP10 (in case of a 432, the 431 does have two pairs of power transistors less); also here I don't know the value - maybe LJYS knows?
In your case I doubt that only the adjustment of the pots will heal the amp - maybe the optocoupler U3 is faulty???
Thats my suggestions - sorry for not being able to provide more info!
best regards
Dieter
first of all, fortunately I don't had this immediately switch off of the amp almost immediately after being taken out of standby. Neither the red led flashes fast and the led is on half of the time and off half of the time. I also don't have any info about a technical bulletin "ML431_432_010408". There is at least one additional sheet missing showing the power supply and the logic and RJ45 communication board.
The loud thump the amp is doing since I have it - the reason is that there is no output relay - ML says that this will deteriorate the sound due to nonlinearities of the relay contact material over time.
In my case crackling noise had been due to bad solder joints which became old - I took out the PCB's and resoldered the whole power amps and slightly turned the trimpots. After that action the crackling disappeared. Especially look at the semiconductors with heatsinks (Q119 - 122) because they are becoming pretty hot
The two schematics does not inform us about the voltages and currents which have to be adjusted - the four trimpots are doing the following:
R2 and R5 are adjusting the prestage voltage POS_REG and NEG_REG, but I don't know the necessary voltage here (should be only a bit less than the UNREG)
R133 is for adjusting the symmetry - should be zero volt DC on the output at warm up and power on.
R213 is for adjusting the quiescent current of the power stage, probably measured between TP9 and TP10 (in case of a 432, the 431 does have two pairs of power transistors less); also here I don't know the value - maybe LJYS knows?
In your case I doubt that only the adjustment of the pots will heal the amp - maybe the optocoupler U3 is faulty???
Thats my suggestions - sorry for not being able to provide more info!
best regards
Dieter