Hoping one of the lovely people on here can help me with some advice on this.
I bought a second hand PM66SE at the end of 2023, initially working fine then it packed up. Horrible sound issues from both speaker channels. I had a look at it and both filter caps had leaked. I got this repaired locally, the diagnosis from the repair was just replacement of the filter caps, but not sure that they did a full investigation. This did resolve the problem and it worked fine for a couple of months. However, it has recently developed an issue after being in use for a few hours with phono input. The sound quality suddenly starts to degrade, low volume and bad audio, from typically just one speaker but if I wiggle around the phono inputs it can resolve it. It is not always the same speaker but more often it is the right output. I have an aux plugged in and the sound quality remains fine from this at the time of issue with the phono. I think it is overheating and given the system operates as normal with aux, I think it must be either the phono input or in the pre-amp circuit. Does anyone have any experience with this or any recommendations for troubleshooting? Any help would be much appreciated. Thanks in advance!
I bought a second hand PM66SE at the end of 2023, initially working fine then it packed up. Horrible sound issues from both speaker channels. I had a look at it and both filter caps had leaked. I got this repaired locally, the diagnosis from the repair was just replacement of the filter caps, but not sure that they did a full investigation. This did resolve the problem and it worked fine for a couple of months. However, it has recently developed an issue after being in use for a few hours with phono input. The sound quality suddenly starts to degrade, low volume and bad audio, from typically just one speaker but if I wiggle around the phono inputs it can resolve it. It is not always the same speaker but more often it is the right output. I have an aux plugged in and the sound quality remains fine from this at the time of issue with the phono. I think it is overheating and given the system operates as normal with aux, I think it must be either the phono input or in the pre-amp circuit. Does anyone have any experience with this or any recommendations for troubleshooting? Any help would be much appreciated. Thanks in advance!
If wiggling around the phono socket on the amp alters the fault then it sounds like you might simply have a poor connection (dry joint) on the phono socket themselves. Generally a very common issue on many makes and models.
It can also be a problem elsewhere and its coincidence that wiggling that area seems to correct the issue but you should first just have a look at those sockets.
Speaker relays (if this model uses them) are also a common cause of low/distorted sound but a big clue there is that turning the amp up loud for a few moments often seems to fix it. The higher current 'punches' through any tarnish on the relay contacts.
If you suspect overheating then the one thing to do is to check the bias current in each output stage is set correctly.
It can also be a problem elsewhere and its coincidence that wiggling that area seems to correct the issue but you should first just have a look at those sockets.
Speaker relays (if this model uses them) are also a common cause of low/distorted sound but a big clue there is that turning the amp up loud for a few moments often seems to fix it. The higher current 'punches' through any tarnish on the relay contacts.
If you suspect overheating then the one thing to do is to check the bias current in each output stage is set correctly.
This shows exactly the issue on some sockets. The solder is cracked and the output intermittent. This was on a Sony CD player:
This is like meeting a celebrity! I've spent 2 hours this evening chasing a fault in a different Arcam Alpha 3 amp and following your excellent exchange on the subject in 2008 with wprice99. No luck on that one unfortunately, but thank you for your advice on this one. I'll investigate the dry solder later this week, hopefully it is that simple.
This stuff tends to cook naturally.
like Mooly, start by re-soldering the main PCB then download the SM and practice the basic controls.
Remember to note the voltages (all) at the secondary of the power transformer, this will be useful to you the day it gives up the ghost, it is another classic on this model.
like Mooly, start by re-soldering the main PCB then download the SM and practice the basic controls.
Remember to note the voltages (all) at the secondary of the power transformer, this will be useful to you the day it gives up the ghost, it is another classic on this model.
Update: took it apart and focussed on the phono pre amp board, most looked okay but as advised the phono input solders looked dry so gave them some love. All sounds much improved now, the issue has not resurfaced after some long tests. I intend to work through the components and replace some that are showing signs of age as I don't think it is yet as crisp as it could be. Just wanted to say a thank you to this community, I am a complete beginner (the amp is nearly as old as I am) but through this thread and other reading on this channel I was able to save some lovely equipment and learn a lot about the process. I think you all have a made another audiophile through your knowledge and passion, so thank you for your time put into this and hopefully one day I will be able to contribute as well as benefit!