The title almost says it all - I'm looking for a Cambridge Audio 640A v2.0 Service Manual - I've got the 640A SM dated 2003 revised 2008 (SERVICE MANUAL – AP14676/1) but I've yet to be able to find a v2.0 - is there one out there. There seem o be others that have looked for it but none seem to have found it yet Please 🙂
I think I may have found an answer to my question: whilst scanning down through the component details I saw that two sets of 8 caps were listed..... 2200uF 50V - Screened for CA/63V for 540A (540A only) and, 2200uF 63V - Screened for CA/63V for 640A (640A only). It rather seems to me that the 540A v2.0 is schematically the same as the 640A v2.0 and that probably explains the lack of a SM for the 640A v2.0
This problem has been raised before, as you found. See this old thread, reading from post #117: http://www.diyaudio.com/forums/solid-state/54329-modding-azur-640a-12.html
Yes, as they are fairly similar, the 540A V2 manual should meet your needs, noting the differences listed in posts and of course, by looking at the components and layout itself.
https://www.manualslib.com/manual/813039/Cambridge-Audio-Azur-540a-V2-0.html The main differences for the power amplifiers, are the power transformer and rail voltages, separate headphone amplifier and the MCU type and firmware which is integrated with the protection circuits.
Note that the power amplifiers themselves, used the obsolete Sanken SAP15 Darlington output transistors and any existing problems there, may not be simple to resolve as it will now require a modification to fit the STD02 replacement types along with additional, external emitter resistors. Don't take chances with alleged NOS Sanken parts - even these are faked, as I found in a 640A that came to me for a second repair, some years ago.
Yes, as they are fairly similar, the 540A V2 manual should meet your needs, noting the differences listed in posts and of course, by looking at the components and layout itself.
https://www.manualslib.com/manual/813039/Cambridge-Audio-Azur-540a-V2-0.html The main differences for the power amplifiers, are the power transformer and rail voltages, separate headphone amplifier and the MCU type and firmware which is integrated with the protection circuits.
Note that the power amplifiers themselves, used the obsolete Sanken SAP15 Darlington output transistors and any existing problems there, may not be simple to resolve as it will now require a modification to fit the STD02 replacement types along with additional, external emitter resistors. Don't take chances with alleged NOS Sanken parts - even these are faked, as I found in a 640A that came to me for a second repair, some years ago.
Thanks Ian. I'd got the 540A, 540Av2 and 640A SMs and I was initially trying to discern where you need to stick a probe into the board (single regular flash - 'DC out' I believe) but when I got the torch out to start reading the actual cable connector numbers etc I spotted leakage at the base of several large caps (8 x 2200uf 63V ) so I'm tempted to put my meter away and go straight to swapping them out which kinda obviates a service manual). Interesting thread link though - thanks.
Are you sure that the "leakage" isn't just the adhesive gunk used to mount larger items that have a relatively small footprint? The caps shouldn't be leaking at this stage of their life but probe the gunk with a screwdriver blade - if its tough and rubbery, its most likely adhesive and that's fine. Electrolyte is a viscous substance that darkens to a sticky mess as it dries out, more like foodstuff.
Good call, though this looked like it's spread out from one or two of the caps and has gone hard on the board (and looked mildly corrosive in it's actions) - that said, the goo was in equal quantities in the are of the two sets of 4 caps so glue does sound right. However, when I was peering at the board and cleaning up the mess I did spot that R42 (100K) was heavily discoloured and open cct and that another, R48, was also looking (at least to me) that it was showing signs of stress (it was partially discoloured in the same was as R42). There is a YT video from some chap who had commented on R42 and he too reckons it's glue and suspects that the glue has had an effect on R42. Sounds like I might be able to get it working again without too much effort.
R48 is part of a zener dropper regulator circuit, as is its counterpart R56. They are known to overheat. Simply use a higher wattage resistor there.
Likewise R42 on the amplifier PCB is a 1/8th watt part, replace it with a 0.6W metal film type.
The stuff you mention around the capacitors is indeed glue, ive never had any problems with it on these amps... usually the problem is the SAP transistors failed because someone had a party and cranked the volume too far!
Likewise R42 on the amplifier PCB is a 1/8th watt part, replace it with a 0.6W metal film type.
The stuff you mention around the capacitors is indeed glue, ive never had any problems with it on these amps... usually the problem is the SAP transistors failed because someone had a party and cranked the volume too far!
My 640A v2 is up and running again after 2 years collecting dust. The R42 was obviously the culprit - I dropped a 1/4W one in (cost, less than 10 pence), though as I'd ordered 8 new Panny caps, and as I'd removed the existing ones as part of my ham-fisted fault-finding, I decided to go with the new caps (cost, a little more...). I can't believe just how many screws I had to re-fit just for what was effectively a single resistor! Anyway, sounding good so far (this does make the need/desire to upgrade to a PureSound valve amp less pressing/justifiable!). Thanks to all your guidance.
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R48 and R56 scorched
I have a Cambridge Audio Azur 540A Amplifier (recently bought), I'm not sure what version it is, but it has a fault. Where is the version written?
From what I can recall there's hardly any output through the speakers, whichever input is being used. More importantly R48 and R56 get "very hot", and are cooked - I think they may even smoke a bit. See attached picture.
I can't see what value they are, so if anyone knows I'd be grateful. I see further up this post it's recommended to get a higher wattage metal film replacements, so I'll make sure they are. Is it worth replacing anything else at the same time? I see other contributors have said it's a lot of work to get the board out, so would be good to do it in one hit 🙂
I'll try and download the manual too - hopefully the correct one.
Thanks, Rob
I have a Cambridge Audio Azur 540A Amplifier (recently bought), I'm not sure what version it is, but it has a fault. Where is the version written?
From what I can recall there's hardly any output through the speakers, whichever input is being used. More importantly R48 and R56 get "very hot", and are cooked - I think they may even smoke a bit. See attached picture.
I can't see what value they are, so if anyone knows I'd be grateful. I see further up this post it's recommended to get a higher wattage metal film replacements, so I'll make sure they are. Is it worth replacing anything else at the same time? I see other contributors have said it's a lot of work to get the board out, so would be good to do it in one hit 🙂
I'll try and download the manual too - hopefully the correct one.
Thanks, Rob
Attachments
I've downloaded the manual on the link on this post and have the Cambridge Audio 540A V2 (31st March 2006) Service Manual.
If this manual is correct for the version of 540A that I have, then I think R56 should be 4.7K, and R56 560. Can anyone confirm this for me, before I order some and fit them. I've attached some pictures, to see if that helps identify that those values should be correct.
Thanks, Rob
If this manual is correct for the version of 540A that I have, then I think R56 should be 4.7K, and R56 560. Can anyone confirm this for me, before I order some and fit them. I've attached some pictures, to see if that helps identify that those values should be correct.
Thanks, Rob
Attachments
The burnt out resistors are both 100 ohm 1/4 watt metal film.
The version of Amplifier you have is V1.
You will also need to replace the input selection IC NJU7313.
Before installing the new IC and after replacing the resistors check you have the plus and minus 12 volt supply rails for the IC.
Connect the negative probe of your multimeter to any of the black speaker terminals and then measure the voltage on each end of the R56 and R48, the other end of the resistors you should read plus and minus 15 volts.
The version of Amplifier you have is V1.
You will also need to replace the input selection IC NJU7313.
Before installing the new IC and after replacing the resistors check you have the plus and minus 12 volt supply rails for the IC.
Connect the negative probe of your multimeter to any of the black speaker terminals and then measure the voltage on each end of the R56 and R48, the other end of the resistors you should read plus and minus 15 volts.
Many thanks.
Should I upgrade the power of the 1/4 watt resistors, or would this not be necessary?
Thanks, Rob
Should I upgrade the power of the 1/4 watt resistors, or would this not be necessary?
Thanks, Rob
No there is no need to up rate the wattage of the resistors, they burnt out because the input selection IC has gone short circuit.
This typically happens when input leads are switched around when the Amplifier is still powered up.
This typically happens when input leads are switched around when the Amplifier is still powered up.
640A V2 blinking protection light (2)
Hi All,
I also have a 640A V2 that immedietly goes into protection after power up cycle, the protection light blinks twice.
Is it the same R42 issue as mentioned before? Any idea/suggestions?
I noticed that in the 540A V2 service manual R42 appear twice in the parts list, once as a 100K ohm resistor(page 30) and as 560ohm resistor (page 12) so which one is the correct one?
Thanks
Hi All,
I also have a 640A V2 that immedietly goes into protection after power up cycle, the protection light blinks twice.
Is it the same R42 issue as mentioned before? Any idea/suggestions?
I noticed that in the 540A V2 service manual R42 appear twice in the parts list, once as a 100K ohm resistor(page 30) and as 560ohm resistor (page 12) so which one is the correct one?
Thanks
It's had an overheating issue for sure.
Have you opened the lid and done a visual check?
Of course unplug the kettle lead from the unit first.
Careful with the star screws too as they round off easily
Have you opened the lid and done a visual check?
Of course unplug the kettle lead from the unit first.
Careful with the star screws too as they round off easily
The user manual for the Amplifier provides the following information.
Protection LED constantly double Flashes
The internal temperature of the output transistors has reached the over temperature limit. The unit is not damaged although it should be left for 15 minutes to cool down before being switched out of standby.
But if the protection system is operating randomly and the Amplifier is not over heating then the following should be checked.
With power and top cover removed first make a visual inspection of the Amplifier main board the one with the heat sink.
Look for brown glue which may be covering multiple components, the glue will be near to the power supply smoothing capacitors.
There are also links near to the capacitors all the brown glue covering any components or links needs to be removed.
The glue becomes corrosive and conductive and can result in spurious operation of the protection system.
Also check the bias for each channel disconnect the speakers set the volume control
to minimum and the balance treble / Bass to mid point.
Next with a multimeter set to millivolts and power up the Amplifier measure across R113 and then R78 they are raised up from the circuit board near to the output transistors.
Your meter should read 13 millivolts if it high or low adjust the respective Bias trimmer PR1 / PR2 until correct.
After initial adjustment wait 15 minutes and repeat.
Protection LED constantly double Flashes
The internal temperature of the output transistors has reached the over temperature limit. The unit is not damaged although it should be left for 15 minutes to cool down before being switched out of standby.
But if the protection system is operating randomly and the Amplifier is not over heating then the following should be checked.
With power and top cover removed first make a visual inspection of the Amplifier main board the one with the heat sink.
Look for brown glue which may be covering multiple components, the glue will be near to the power supply smoothing capacitors.
There are also links near to the capacitors all the brown glue covering any components or links needs to be removed.
The glue becomes corrosive and conductive and can result in spurious operation of the protection system.
Also check the bias for each channel disconnect the speakers set the volume control
to minimum and the balance treble / Bass to mid point.
Next with a multimeter set to millivolts and power up the Amplifier measure across R113 and then R78 they are raised up from the circuit board near to the output transistors.
Your meter should read 13 millivolts if it high or low adjust the respective Bias trimmer PR1 / PR2 until correct.
After initial adjustment wait 15 minutes and repeat.
In my case (a 640A v2) R42 was a 100K. Looking at a resistor chart will help confirm - Resistor color code | Resistor standards and codes | Resistor Guide
Did as above (on my Version 1, 540A), and happy days, all is well again. Just love this forum. Also when you've fixed something, firstly it feels like you've done magic, and then it gives you a real buzz - or is that just me?
Anyway, many thanks. Rob