Announcement

Collapse
No announcement yet.

Cambridge Audio azur 540r volume control problem

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Cambridge Audio azur 540r volume control problem

    Hi everyone.

    I have a Cambridge Audio azur 540r and face the following problem - from time to time the volume can be set only to VOL MIN and VOL MAX ( from both the volume knob and the remote ).

    The volume control IC is BD3816K1 and it is controlled by the CPU M5964C40J.
    The volume knob VOL_A and VOL_B signal enters the CPU and is processed to VOL_DATA and VOL_CLK which go straight to the volume control IC ( I believe the remote control signal also goes the same way ).
    The CPU is powered by a stand-by transformer with constant +5V ( 7805 ).
    The VOL IC is powered from the +/- 12V ( 7X12 ) rail which is converted to +/- 7.
    After I replaced U2 ( 7812 ), C143 and C144. I got the following V:
    U2 (7812) - IN 19.3, out 11.92
    U4 (7912) - IN -20.1 out -12.11
    +7 ( measured at R171 ) 6.29
    -7 ( measured at R172 ) -6.64
    The +/- 7V rail is little low, but still within the volume control IC limits.
    I checked the rails with a DIY oscilloscope kit ( DSO138 ) and did not notice any ripples on any of the V rails ( which probably can not be really trusted ).
    C139 measured around 3100uF ( should be 3300 ), but did not have at the moment something similar to replace it with ( I have stocked up now, and on the next run I'm replacing C140, C139 and C138 even for just being right next to the voltage regulator heatsink ). I'm also going to replace the C106 and C102 on the mainboard ( they are part of the +5V stand-by rail ).


    And here is the interesting part - can a bad filtered power supply cause the described volume control problem? I'm not familiar with how that volume control ICs are controlled. I know that they use some kind of serial interface, but that's all.
    Attached Files
    Last edited by madan1; 11-01-2018, 01:13 AM.

    #2
    Re: Cambridge Audio volume control problem

    So I guess, no one has worked on a similar issue .

    I found this on a forum
    "The information was that the error was in the eprom (24c01), where the microcontroller writes the confi (volume, selected inputs, etc.). The firmware writes the volume value over each click when the volume button is clicked and the tile tolerance of the million typing was just full. RIP" ( auto-translated ).

    It sounds logical, so once I'm sure that the problem is not power-supply related, I will look for someone to copy the data from the above eeprom to a new one ( if I'm able to find one ).

    Comment


      #3
      Re: Cambridge Audio volume control problem

      And looks like we have a winner .
      The EEPROM ( IC12 ) in my case is an ATMEL552 24C02BN ( instead of 24c01 as stated in the SM and the above forum quote ).
      So I changed and the rest of the +/-12 rail caps and there was a slight improvement in the measured V values, but did not affect the main problem.
      I removed the EEPROM chip and fired up the amp. For 20+ power cycles ( in several hours ) there were no volume issues.
      I guess the guy who pointed out the eeprom is right on the money. From what I've tested, looks like that eeprom keeps all user settings including the most recent volume value. Next week I will look for a new chip and will solder it as is, without copying the content from the old one, and see what will happen.

      Comment


        #4
        Re: Cambridge Audio volume control problem

        If you have a programer you could copy the contents then clear the contents of the eeprom and try it, but it is likely just easier to replace it with a blank ic. if it works without it thats likley all thats wrong.
        the 24c02 is 2k storage but they may not even use all of it
        Last edited by R_J; 11-03-2018, 10:42 AM.

        Comment


          #5
          Re: Cambridge Audio volume control problem

          Unfortunately I do not have a programmer.
          The original IC was 24c02bn. I swapped it with a blank 24c02w6 ( ~0.30 EU, ~0.40 USD in the local electronics shop ) and for now everything seems to be working fine.
          From what I have seen in the internet, the same problem affects almost all Cambridge Audio av receivers from that period - Azur 340R, Azur 351R, Azur 540R, Azur 551R, Azur 640R, Azur 650R, Azur 651R, Azur 751R ( listed for indexing purposes ).

          And while I had the board on the desk, I changed the filter caps of the eeprom, the CPU, the crystal and the voltage regulators input and output caps. To my surprise all old caps measured within 10% of their original value.

          Comment


            #6
            Re: Cambridge Audio volume control problem

            Congrats on the repair and thanks for taking the time to post it here!

            Every time I see an amplifier with a microcontroller of some sort, I just cringe (especially early-mid 90's "home theater" amps with more silicone used for the logic/processing chips than the output transistor section).

            I'm also surprised your original caps appear to be good - or at least the Samxon general purpose (GP) caps. Last time I had a run in with an amplifier with Samxon GS, about half of them were bad. Same deal inside an early 2000's LCD monitor. Seems these caps just don't like any heat at all.

            Comment


              #7
              Re: Cambridge Audio volume control problem

              Thanks for the posts above, My Azur 650R had the problem where remote volume worked OK but front panel knob didn't. I took the encoder out completely and opened it up. Looked 100% inside but cleaned it anyway with some contact cleaner and a cotton bud. Now working perfectly. In my case it was a dead simple repair but had it been anything else I would have been left floundering.

              Comment


                #8
                Re: Cambridge Audio volume control problem

                HI. My Azur 651A volume does not work with remote. All the function of the remote is working fine. I checked the IR for volome buttons and it looks OK. My Marantz CD5005 CD player also picks up the IR from 651A remote. What might be wrond with my amp?

                Comment


                  #9
                  Re: Cambridge Audio volume control problem

                  Originally posted by madan1 View Post
                  And looks like we have a winner .
                  The EEPROM ( IC12 ) in my case is an ATMEL552 24C02BN ( instead of 24c01 as stated in the SM and the above forum quote ).
                  So I changed and the rest of the +/-12 rail caps and there was a slight improvement in the measured V values, but did not affect the main problem.
                  I removed the EEPROM chip and fired up the amp. For 20+ power cycles ( in several hours ) there were no volume issues.
                  I guess the guy who pointed out the eeprom is right on the money. From what I've tested, looks like that eeprom keeps all user settings including the most recent volume value. Next week I will look for a new chip and will solder it as is, without copying the content from the old one, and see what will happen.

                  Hi madan1, I realize this is a very old thread but I have the same volume issue with my 540R. I'm a reasonably handy novice and have worked on my Azur 651R without destroying it, and this 540R is a paperweight as is so I'd like to at least make it usable again.

                  In short, as per your post can I theoretically just remove the EEPROM (IC12) to resolve the max/min volume issue, but lose the volume “recall” memory on power up?

                  Thank you in advance for your help!

                  Justin

                  Comment


                    #10
                    Re: Cambridge Audio volume control problem

                    Originally posted by Justin4053 View Post
                    Hi madan1, I realize this is a very old thread but I have the same volume issue with my 540R. I'm a reasonably handy novice and have worked on my Azur 651R without destroying it, and this 540R is a paperweight as is so I'd like to at least make it usable again.

                    In short, as per your post can I theoretically just remove the EEPROM (IC12) to resolve the max/min volume issue, but lose the volume “recall” memory on power up?

                    Thank you in advance for your help!

                    Justin
                    Hi Justin and Thank you Madan1,
                    Indeed an old post but useful for me today in 2022

                    Comment


                      #11
                      Re: Cambridge Audio azur 540r volume control problem

                      A late addition to this thread, just in case it saves someone else the time it took me. Our community hall owns one of these amps where it is used for sound by the monthly "film club", in conjunction with a decent Blu-Ray player and projector. It was bought 2nd hand and whist the volume setting by remote has always worked fine, the control knob has been increasingly intermittent in its behaviour, sometimes working, sometimes not, sometimes making large jumps before refusing to respond (by Sod's law, usually when it's either gone silent or become deafeningly loud!)

                      From the Googling I've done it seems this is a common problem, and it's likely caused by the manufacturer's unfortunate use of a cheap (and inappropriately named) "Everbest" rotary encoder for the manual volume control interface. (If the remote volume setting doesn't work - and the remote's otherwise good - then it's more likely to be the EEPROM, as has been well explained in earlier postings here.)

                      The good news is that the Evercrap (sorry, Everbest) encoder is directly and easily replaceable with a decent Bourns equivalent - in fact the encoder is a standard frame 16 incremental device with 24 steps / rev. The correct Bourns part number is PEC16-4220F-N0024. This is physically and electrically identical to the original, but stands a chance of lasting rather longer! Be sure to get the exact part number, or you may end up with a physically incompatible part - the PEC16 range are made with both horizontal and vertical PCB mounting arrangements, with different numbers of steps per revolution, with and without mechanical detents ("clicks"), with different shaft lengths and with/without an inbuilt switch. Lots of permutations all of which need to be correct! The part I've specified is readily available from Mouser as 652-PEC16-4220FN0024 (all of £1.29 each + VAT!), from RS Components in the UK (order code 181-4479 at £1.10 each in a pack of five) and also from Farnell. Hardly an expensive repair!

                      In case useful, the encoder is easily accessed but requires removal of both the lid (via 8 x M2.5 security screws) and the volume knob, which simply pulls off the encoder shaft (this may be a tight fit but should respond to a good firm pull!) Take care when removing the lid screws - they can be a tight fit due to passing through two lots of metalwork, and the security heads can easily get chewed up making their removal difficult. a touch of WD40 in advance isn't a bad idea. I recommend discarding these screws entirely and replacing them with some decent conventional hex-socket, slotted or even (if you must) Pozidriv screws, M2.5 x 8mm countersunk head is correct.

                      Once the lid's off and the encoder knob has been removed, you can access the little PCB on which the volume encoder is mounted. This is held in place both by two Pozidriv screws, one either side of the control's shaft, plus the larger diameter nut around the central threaded bushing of the encoder. First remove this nut (preferably with a 12mm nut driver, pliers only if you must) and then remove the two screws either side. These are screwed into a pair of nylon pillars which are a simple press-fit into the PCB, and arguably you could now leave the pillars in place and carefully pull the board off them. My sample however had the pillars glued in place as well as their locking press-fit mechanism, and I doubt they'd have survived the process. Undoing the screws from the front is much easier and unlikely to be destructive, but may require you to grip the nylon pillars from the back of the panel to stop them rotating. I was able to do this by hand but a gentle grip of some long-nosed pliers may help.

                      Once the PCB's free, gently lift it up to allow desoldering of the duff encoder. Note that the three-wire cable is CAPTIVE to the board (that little white thing is a soldered-in cable-to-PCB interface, NOT a plug-and-socket pair. Don't try to separate them! Use a solder sucker or some desoldering wick to remove the old encoder, and take care not to drop blobs of solder onto the signal processing PCB behind. The new encoder is a direct drop-in replacement; give the PCB a bit of a clean with a brush and some alcohol once the soldering is done. Refitting is a reversal of the above (as the old car manuals used to say). Finally whilst the lid's off, take the opportunity to lightly brush and vacuum out dust that's probably accumulated over the PCB's and heatsink. A purloined (or safer, purpose-bought!) ladies' soft make-up brush is ideal for this - use it in conjunction with a plastic nozzle of the vacuum cleaner, much as the dental hygienist does!

                      Hope this helps someone else out there. The above all refers to the Cambridge Azur 540R but likely applies to other similar models in this range. Take care and good luck!

                      Comment


                        #12
                        Re: Cambridge Audio azur 540r volume control problem

                        Hi Majkic, welcome to BCN Forums!
                        Thanks for posting your repair - that was a delight to read through, even though I don't have this set.

                        Comment

                        Working...
                        X