Cambridge Audio Azur 550A Repair help required

[MALE20]

Hi,

I would like to share with you my latest extreme repair and ask for some help as the unit does have some temperamental issues that I am struggling to diagnose.

I purchased the unit as not working for an occasional price with a view of restoring it. Unit was activating protection mode just after start. I found some corroded resistors and links that were in contact with adhesive. I replaced them and cleaned the PCB. I inspected transistors and found no issues with them. Once I started checking further I found that there was no voltage from the toroidal transformer.  I measured the primary winding and confirmed that the thermal fuse was blown. Finding another one was quite hard and not worth spending the money. At that stage I decided to take a risk and carefully unwind the transformer and replace the fuse. Nothing to lose.

I carefully marked everything and coiled each winding. I removed as much as necessary, and I cut through insulation to get to the fuse. After soldering new fuse in place I pushed it back in and injected epoxy resin with syringe. Kapton tape was used to encapsulate resin. Once cured, I used few layers of Kapton tape for extra protection.  At that stage in was time for tedious task of rewinding everything. I tried my best to straighten the wire ensuring it is not damaged at any stage and keep everything tight at the same time. To be on the safe side, I used a multimeter to check from time to time. Final result was satisfactory. I carefully installed it back in place and measured output voltage before connecting it to preamp board. All readings been fine and I felt comfortable to connect it fully. Unit at this stage was alive. I left the unit up and running for a few hours and the transformer held up nicely.


At this moment I am struggling with some temperamental issue as occasionally the right channel fades out or is not playing at all. I suspected potentiometer as changing sound level can cure the problem. I measured resistance and couldn't find any issue. I opened it and the condition was almost like new. I can't find any dry joints and moving components/cables does not have any effect. At this stage I am a bit puzzled. Any ideas are more than welcome. Service manual in the attachment.

[wasedadoc]

Are there relays between the power amp outputs and the speakers? If yes, check if the signal from the amp into the relay is OK. It is possible that a poor relay contact gives low or no volume until a high volume (=high current) temporarily improves matters.

[MALE20]

 I haven't thought about them and yes you are correct 200hz signal IN but no OUT on one relay. I had turn unit on and off and sometimes it works sometimes not. Looks like quality of the contacts isn't that great. I am going to look for a replacement. Thx a lot wasedadoc!

[wasedadoc]

I haven't thought about them and yes you are correct 200hz signal IN but no OUT on one relay. I had turn unit on and off and sometimes it works sometimes not. Looks like quality of the contacts isn't that great. I am going to look for a replacement. Thx a lot wasedadoc!

Check that all is well at the input side of the relay contacts before condemning it.

[MALE20]

All seems to be good up to that point. When looking for a replacement I found a nice article about modification to similar model 651. In this article they question quality of relays used. Both relays are less then £7 so I will give it a try. I will let you know once replaced.

http://audiopurist.pl/en/mods-en/cambridge-audio-azur-651a-modification-eng/

[GLouie]

Many of those relays can be opened and contacts cleaned with some stiff paper and Deoxit. Sometimes you can get a bit more life out of them, but the best solution is to replace them if you can. Don't use an abrasive paper, the contacts are often plated. This is a common problem with older power amplifiers.

[David_AVD]

Bad speaker relays can also cause the audio to be distorted or intermittent, especially at lower levels.

It may be ok when testing with headphones (due to the much higher impedance) and only be noticeable when used with speakers.

[MALE20]

I just removed a pair and unfortunately this relays are not serviceable. Sealed design MASSUSE ME-11-012-2Z4. Replacement on order RELPOL RM84-2012-35-1012. Out of curiosity I will get my Dremel out later this week to see the contact condition.


Success!!!

Unit is now working correctly. Tested for few days no issues. In the future I am planning to look into replacing caps to improve sound quality.

Thank you for all the help.