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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hello,
Been lurking around for while, but now it's time to submit first post!
I have a beocenter 9500 that suffers from classic mute relay problem. At the moment both speaker sets (main and remote) are working even though mute is on (mute light is lit). There is no reaction in mute relay. I tried to measure the voltage over the coil in relay, but it shows 0V (when mute is on). I guess there should be something like 5-6V to "activate" the relay? What would be next step in troubleshooting, any suggestions?
Regards, Jyrki
Terve Jyrki
The other side of the relay should stay at +7V (in relation to ground) and the other end at the same voltage, or near zero depending whether the relay is "on" or not. It could be a few things in addition to the relay itself. The relay usually fails so that it doesn't make proper contact and the sound from the primary speakers will be weak or missing, not stuck on.
I'm not sure which way the muting relay & headphone socket contacts work in a BC9500 and the schematic is a bit ambiguous there, but have you tried what happens if you insert a headphone plug into the Beocenter? If nothing, the switch in the socket might be stuck. If the relay operates when you do that, probably the transistor controlling the relay (TR22, BC337) has failed.
--mika
Great tip Mika! When plugging in headphones the mute relay kicks in, so the relay itself seems to OK. So, it looks like next step is to locate the TR22 and verify / replace it.
Jyrki
If the transistor has failed, check also the diode (D6) that is connected across the relay coil. It is there to protect the transistor from reverse voltage spikes generated by the relay, so it's possible that the diode died first and the transistor later.
I'm not sure how much you need to disassemble to access these components, but be careful with the multiwire connectors. The wires easily break at the connectors and they are a pain to get back together in correct wiring order.
EDIT: Oh, and before you start taking things apart, confirm that the "electronic" way of muting is still broken! It may have been a stuck headphone socket that started working when you used it. Not that likely since it is the big type of socket and probably sturdier than the 3.5 mm sockets, but anyway...
I managed to locate the transistor on diode and measured the base, emitter and collector voltage (against ground) with mute activated and without mute.
- without mute: C=7,7V B=0,02V E=0,02V
- With mute: C=7,7V B=5,1V E=0,02V
So, with mute activated control signal is present at base (control circuits are working), but the transistor still has 7,7V voltage difference between collector and base, so transistor is not switching through the current i.e it's faulty. When short-circuiting the emitter and collector the relay pulls as expected.
One more relay related question to you guys, when connecting the mains plug to wall (or when switching off unit), should I hear some other relays to pull / release? Reason why I'm asking is that in my case the cassette player motor starts to run when I connect plug to wall (only the small standby led is lit). When touching the standby area of control panel (no light is lit) the cassette player motor stops. I have feeling that this behavior is not correct...
jlehtinen:So, with mute activated control signal is present at base (control circuits are working), but the transistor still has 7,7V voltage difference between collector and base, so transistor is not switching through the current i.e it's faulty. When short-circuiting the emitter and collector the relay pulls as expected.
Yes, time to get a new transistor (and perhaps the diode).
I just tested the plug-in behaviour on mine. When plugged in, the cassette capstans indeed start turning. Hard to say if there's a relay clicking from the other mechanical noise. But after four seconds or so, a relay clicks and it stops automatically. I don't get the standby button light at any time, though. Could be a software version difference (1.4 on mine according to the rear sticker).
Success! After changing the transistor (TR22) the mute is again working! Also checked the diode (D6) as suggested by Mika, but that was OK so I did not change it. While at it I also replaced the mute relay as preventive action. Could not find exactly same kind of relay, so used a Omron G2R-2 5VDC (https://www.elfa.se/elfa3~se_sv/elfa/init.do?item=37-152-16&toc=0) That relay has eight legs as it is "switching" type. I cut off two pins from relay base to make it fit the pcb (only needed ON/OFF type relay, so need for those extra pins). We´ll see if 5VDC rating will cause some durability issues on long run. Data sheet states that max coil voltage is 140% of rated voltage (5*1.4=7V).
Big thanks to Mika for pointing me to right direction with troubleshooting!
What comes my second question about plug-in behavior, my unit has sw version of 1.2. So maybe that is the reason for different behavior. The cassette deck motor stops after a wile (couple of minutes).
jlehtinen: What comes my second question about plug-in behavior, my unit has sw version of 1.2. So maybe that is the reason for different behavior. The cassette deck motor stops after a wile (couple of minutes). Jyrki
Regards Graham
Well done
I suppose your relay replacement will be fine, and much easier than wiring a relay with a non-compatible footprint somewhere off the PCB. The correct relay is probably available as a spare part from B&O, but at a completely different price.
Perhaps I should fix mine as well, it always needs some workout with the mute button after several days of non-use...
EDIT: the startup run of the cassette might be intentional to make sure that the mechanism is in a known state (heads retracted) after a power break that might have happened while the tape was playing.
There are similar oddities in for example Beocord 6500; once you operate a function, the motor & capstans never stop until you put the whole system into standby. Can't think of a sensible reason for that...
tournedos: Well done I suppose your relay replacement will be fine, and much easier than wiring a relay with a non-compatible footprint somewhere off the PCB. The correct relay is probably available as a spare part from B&O, but at a completely different price. Perhaps I should fix mine as well, it always needs some workout with the mute button after several days of non-use...
I now fit the 8 pin with 2 pins cut off type bought from Maplins for £2.29 in the UK here:-
http://www.maplin.co.uk/interface-relays-37523
Probably availabe cheaper elsewhere but no minimum order here.