Beomaster 4500 – one channel only

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  • #6061
    BRONZE Member

      Hi everyone, good to see the new site is coming along nicely.
      Anyway, I recently aquired a Beomaster 4500 in very good cosmetic condition, but with one fault – I’m only getting sound from one channel only (it’s the same on speakers 1 & 2 regardless of input). Before I start troubleshooting, I’ve heard a story about these units having a EPROM/RAM. Basically, the question is, will I upset the EPROM/RAM if I start to dismantle the boards and/or components, to the point where I’ve lost the control functions of the EPROM/RAM ? (as I understand this will render the machine useless). I also understand that it has a lithium 3v battery speciically for this chip ?
      I’m guessing this may be the original battery and perhaps a new battery would be a good idea ? So, would I do any damage to the memory and/or settings by removing/replacing the battery ?
      And if anyone has any thoughts on the initial problem (loss of sound on one channel), I’d love to hear them. It’s a beautiful machine and deserves to be repaired.
      Oh and finally, the glass control panel had come adrift, I fixed this with (poor quality) double sided tape and has come loose again, any recommendations for a more permanant fix ?
      Any help or suggestions would be very welcome. Tim

      • This topic was modified 1 year, 3 months ago by Llurkio.
      BRONZE Member

        Hi Tim

        The problem should not relate to the EEprom or the CMOS battery, in my opinion, so better leave it as it is.

        When the Beomaster comes on with a “CODE” in the display, the FM stations and soundsettings are not stored anymore the battery has to be renewed.

        No sound on one channel on both speaker outlets is quiet uncommon, often the speaker relais fails. But the outlet “2” is connected directly to the poweramp section.

        The Headphone is connected to the poweramp section too.

        If you have a powerlink connected speaker you could check if these are running on both channels.

        Switch speakers to INPUT L and INPUT R

        If there is sound on both speakers (R&L) you have a problem behind the tonecontrol and preamp section in direction of the power amp section.

        If one speaker fails on the powerlink outputs too there is a error in the preamp section.

        Check this first and let us know what goes and what not.


        The panels can be cleaned with this stuff:

        I’ve made good experience and the old glue comes off in one go, please use only a creditcard or a spade of plastic, never use scraping metall spades or knifes, you will destroy the black coating.

        After use clean with a household windowcleaner, no acetone or thinner your coating will be lost ;-))


        For reglueing I use this double sided tape which is a little bit foamy but very sticky:


        Be careful if it sticks to the glass it’s hard to get it of again, so look twice which plastic frame belongs to it’s place and align the gaps of the middle part.

        I would never use 2 K Epoxy because you won’t get of the plastic frames from the glass even the glas is broken.



        I’m not familar with the offers I linked here and get no money for comercial !


        Kind regards




        The Glas

        BRONZE Member

          Thank you SO much Christian, it’s given me something to work on/look at, it’ll take me a few days to ‘get my head’ around this information and do anything practical (I’m not an electronics engineer – just a very careful amatuer), I don’t want to rush anything to make things worse ! (And I don’t have/use powerlink – yet, this is somethiing else I need to look into ).
          Oh, I initially cleaned the glass panel insides very carefully with minimal IPA (and a plastic scraper) – it seemed to work fine, and many thanks for the infomation regarding a suitable adhesive, I’ll definately get some of that (I wouldn’t have used epoxy anyway – I realised that’s not the best solution).
          Thanks again, I’ll keep you posted ! Tim

          BRONZE Member

            Well . . . . .

            So far I’ve managed to trace a stereo signal going into IC3 (STK4151V) on pins 1&18, but only one channel coming out on pin 13, nothing on pin 10!  So I think I’ve found the culprit.

            My concern now is, what could have caused this ? Do I look for other faults, or just replace STK4151V and hope that all will be OK ?


            BRONZE Member

              Hi Tim

              Well done so far that you could measure the signals ;-))

              As you wrote that signals comming in the Hybrid IC on PIN 1 & 18, for me, there is no other possibility that the IC is in heaven.

              I would buy a new one and try.

              It costs about 10 € so it’s not that big invest in renewing the IC.

              Thought about the muting PIN 6 but it mutes both channels (L&R) as far as I understand the Datasheet of the STK.

              The B&O Service manual shows that the Muting Switch is tied to GND, the Muting comes via the Preamp section.

              Hope you’re lucky!

              Kind Regards


              BRONZE Member

                Thanks Christian for those words of encouragement – it helps to know I’ve got people ‘looking over my shoulder’.

                Luckily I have a ‘scope so that made tracing the fault easier.
                The IC3 (STK4151V) replacement has already be ordered, as is the recommended (by Christian) tape, I’ve also ordered replacement transistors (BC546, BC547, BC557) bewteen IC3 and the speaker connectors (they only cost pennies !), but don’t know if I should replace these, I’m wondering if they were likely to be “spiked” and destroyed ? I could remove them for testing, but then I just as well put new ones back in !
                Glass control panel has already been cleaned up and ready for re-fixing, awaiting new tape !
                One final question regarding 4 x diodes which make up a bridge rectifier, (D10, D17, D19, D27), these have been running so hot, they’ve discoloured the PCB, my guess is that they might be a bit “tired”, I was thinking about replacing these with some higher rated diodes AND mounting them with longer ‘legs’ so the body of the diodes are away from the PCB for a bit of ‘air cooling’, – or is the PCB supposed to act as a heatsink ? I’ve got some UF5404 rectifier diodes (left over from a previous repair), would these be a suitable alternative, given that they’re rated at 3a and high(er) frequency, my logic is that these diodes wouldn’t have to work so hard?
                Any thoughts anyone ?

                BRONZE Member

                  Success !

                  The STK4151V power amp was replaced and also all the small transistors between the power amp and the speaker connections, one was found to be dud.

                  I have not yet replaced the bridge rectifier diodes, but will do so as soon as they arrive (I’ve ordered the same as is already in the machine (1N4002)), I will mount these with ‘long legs’ and try to find something to clip over them to act as a heatsink.

                  Although both channels are working now, I’ve found that after every time it’s put into ‘standby’, it comes back on at full BASS and minimum TREBLE which needs to be reset each time, is this something to do with the EEPROM memory ?

                  So my questions are:
                  Is it OK to replace the EEPROM battery without losing the basic functions, if so, should this be done with the machine on (to remember the settings) or to have the machine switched ‘off’ ?
                  Secondly, I bought this machine as used, and therefore do not have a comprehensive owners manual, so is it possible to do “facory reset” on the EEPROM ?

                  The word “CODE” does not appear.

                  Any thoughts or suggestions would be helpful.

                  BRONZE Member

                    Since the update I’ve realised my own stupidity ! (It must be an age thing – this is what I’ve got to look forward to in my retirement !)

                    I’ve been trying to “blame” the EEPROM/battery for not remembering the settings when being put into standby, I found out that these settings have to be stored manually ! Oops.

                    Anyway, that now done and a full test later revealed one remaining fault, the “Tape 2” function doesn’t work – I’ve tested this by using a hand held screwdriver and touching the solder post (on the control PCB – bypassing the sensi-touch panel) and still no luck.

                    (I’ve also confirmed this by using the panel from a good working machine, and all worked OK then)

                    This is going to be tricky as the components are tiny (I believe they are called “surface mounted”?  I’m thinking it’s TR24 (BF840), has anyone got any other ideas and/or thoughts about testing this theory ?

                    GOLD Member
                      • Near Munich



                      could be that the Beomaster 4500 is set to another option programming.

                      2022-07-05 12_36_15-Clipboard

                      Maybe this helps 🙂

                      BRONZE Member

                        Well . . Well. .  Well . . . !

                        Who’d have thought it from B&O !

                        In my last post, I was having concerns about “Tape 2” not responding, I was looking at the PCB with the intention of replacing TR24 (BF840) with some 8x magnifying spectacles but keeping the focus is difficult at times, so I took some photos to examine on the big screen, this is what I found !

                        Copy of IMG_0463


                        It was a dry joint in the most literal sense.

                        “Tape 2” was a little temperamental initially when only one channel was working, but this fault was low priority at that time. I’m guessing that the original owners may have had problems with this (?) and maybe this is why I was able to buy it at the low price I paid.
                        So some very careful soldering, then reassembly and hey presto ! Everything works perfectly !

                        The 4x diodes (bridge rectifier) were replaced with long legs and a small piece of brass glued to the bodies of the diodes (being careful NOT to touch the legs ) to act as a heatsink.

                        Many thanks to ‘RaMaBo’ for the info, but I couldn’t even get “Tape 2” to light up at that point, I knew the problem was not my ignorance ( for ignorance, read ‘stupidity’ !).

                        So now I have a beautiful Beomaster 4500 in very good condition with everything working.

                        One very pleased Tim

                        GOLD Member
                          • Netherlands

                          Congratulations Tim! I love my BM4500, very elegant and versatile. Mine was built from two donors (one with broken glass) and is actually my homage to the 1900 that my father in love gave me (and that I eventually sold as it is not M(C)L compatible). Same form factor though.


                          BRONZE Member

                            Hello – I have a Beocenter 4600 which has developed a similar problem – only one speaker channel functioning.

                            I’m guessing that the 4600 and 4500 are basically the same. Or not? There is no thread for the 4600. Both speakers work fine but neither Left channel works.

                            Is there a simple reason?

                            Thanks. Paul

                            BRONZE Member

                              Hi Paul,

                              Firstly I’m probably NOT the best person to ask for advise, I’m an amatuer that “dabbles”, I’ve had no formal training so I can’t really be of much help, but I usually start with a long good look at the boards, looking for anything that doesn’t seem quite right, discoloured boards, bulging caps, dry joints etc.

                              I do note that you mention “Beocenter”, mine was a “Beomaster”, two very different machines. I put as much information as I could in my write-up, beyond that, I cannot be of much help. However, I do have an old Beocenter 4600 that I was planning to attempt to repair, but I don’t think I’ll ever get around to it, so if you need a machine for spares (and you’re in the UK), this may be an available option for you.
                              In the meantime, good luck and don’t give up, it’s good to know these old machines are still being used.

                              BRONZE Member
                                • Denmark

                                Beomaster 4500 and Beocenter 4600 are different units from different year periods, so you cannot compare.
                                Beocenter 4600:
                                Beomaster 4500:


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