B&O BeoCenter 2100 Type 2442 - UK Vintage Radio Repair and Restoration Discussion Forum

SteveCG · 14th Aug 2018, 12:39 pm

This mid eighties unit has two problems: one occurring very recently and the other at an unknown date in the past.

The recent one is that the VHF/FM section has stopped working. If FM is selected then there is no sound - not even IF amplifier stage hiss (and this is with mono operation selected and no AFC where one did hear hiss if no aerial was connected). My thoughts were that a power supply line has gone down - but not having a circuit diagram and the complex multi-board nature of the beast where only the underside of the PCBs can been seen when the access plate on the underside is removed - does not help.

The second fault is that the phono stage is also silent. However for how long this has been the case is unknown as this input has not been used 'in living memory'. Likewise just where this stage is in the unit is not obvious.

I have wondered whether it shares a common power supply line with the FM stage.

Finally, the AM receiver works perfectly as do the audio power amps.

Anybody's experience with this Japanese manufactured era B&O unit please?

ukcol · 14th Aug 2018, 1:13 pm

Do you have the service manual Steve?

If not it can be downloaded free of charge here:

https://elektrotanya.com/bang-olufse.../download.html

SteveCG · 14th Aug 2018, 1:27 pm

Thanks for the link Colin - I had missed that one!

Now to go away and do some reading...

Edward Huggins · 14th Aug 2018, 4:55 pm

It's good that both amp channels are working. That's a head start. The phono fault could be the cartridge, oxidised connectors/connections/pins or the pre-amp section voltage rail.

SteveCG · 16th Aug 2018, 12:56 pm

Right, after an intensive day yesterday I've sorted out both faults.

First, I used the manual Colin suggested, courtesy of elektrotanya. The manual covered two main models and was partially tri-lingual (not everything was explained in English). I found a manual for the BeoCenter 2200 which is a related model and which I had downloaded from a B&O specialist site was quite helpful as it explained some of the dismantling which the first did not.

After I got my mind around B&O's way of doing things: modules described on Diagrams which in turn are carved up into boards...
I found that the supply lines were alright. I then checked the decoupled lines on the phono stage and found that the -12v line was fine but the +12v was 0v with some resistors getting rather warm. After powering off I then put an Avometer set to Ohms across the decoupling electrolytic and found a near short circuit. This did not make sense with the circuit so I eventually extracted it and found it was indeed short circuit. Temporarily powering up I had a working phono stage. I then replaced the capacitor (on the circuit diagram, capacitor C5 on Diagram B, Board 9) which was a 220uF, 16v working, Tk brand in green sleeving - made in Japan) with what I had to hand which was a 150uF, 16v working, made by Philips.

I then moved on to the FM tuner problem. Here the voltage lines were all alright. After following the audio path I came up against the IF IC with its multiple functions. I checked the voltages on the IC and found that some were as the manual stated but others were 0 where they should have been 6v. I first thought that the IC had failed then my eyes saw the decoupling capacitor (C54 on Diagram A, Board 2) to the tank circuit and they narrowed... Same value, same voltage, same make and guess what - short circuit as well. Removing it I was greeted with IF hiss (no aerial connected). I replaced it with another Philips 150 uF, 16v.

So I have a fully working 2100 again.

A few points: First, it was an absolute swine to service because of its compact, multi board nature. Second, there are other Tk capacitors in it which I did not have the will to change but at least I know what to look for in future. Third, I am impressed by its performance. Fourth, Japanese Hi-Fi of this era has had a good reputation for reliability, but I've realised/remembered that is the 4th bit of Japanese kit of that mid-eighties era that I have found that has short circuit decoupling capacitors. So is there a 'growing problem' for us restorers/repairers, c.f Transistor Tin Whiskers of the 1960s and oozing/split electrolytics of the mid nineties - early 2000s?

Neither of the faulty electrolytics showed any sign of problems - ie no top bulging, no top splitting, no oozing.

dave cox · 16th Aug 2018, 3:39 pm

Did you check the main smoothing caps ?
If the ripple is high it could put a lot of stress on the little ones further downstream.

dc

ukcol · 16th Aug 2018, 4:31 pm

Quote:

Originally Posted by SteveCG

So I have a fully working 2100 again.

Well done Steve.

SteveCG · 17th Aug 2018, 10:52 am

dave_cox,

No, I did not check the main smoothers other than I saw that, visually, they looked alright. I'm certainly not detecting any mains hum - or harmonics for that matter - it must be pushing BBC noise floor quieting when listening to the Radio 3 Proms, from the Wenvoe 92.1 Mc/s main transmitter about 60 air miles away, similarly playing an LP the background is very quiet, I'm well satisfied with its performance, but I understand your point.

14th Aug 2018, 12:39 pm	#1
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	B&O BeoCenter 2100 Type 2442 This mid eighties unit has two problems: one occurring very recently and the other at an unknown date in the past. The recent one is that the VHF/FM section has stopped working. If FM is selected then there is no sound - not even IF amplifier stage hiss (and this is with mono operation selected and no AFC where one did hear hiss if no aerial was connected). My thoughts were that a power supply line has gone down - but not having a circuit diagram and the complex multi-board nature of the beast where only the underside of the PCBs can been seen when the access plate on the underside is removed - does not help. The second fault is that the phono stage is also silent. However for how long this has been the case is unknown as this input has not been used 'in living memory'. Likewise just where this stage is in the unit is not obvious. I have wondered whether it shares a common power supply line with the FM stage. Finally, the AM receiver works perfectly as do the audio power amps. Anybody's experience with this Japanese manufactured era B&O unit please?

14th Aug 2018, 1:13 pm	#2
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: B&O BeoCenter 2100 Type 2442 Do you have the service manual Steve? If not it can be downloaded free of charge here: https://elektrotanya.com/bang-olufse.../download.html

14th Aug 2018, 1:27 pm	#3
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: B&O BeoCenter 2100 Type 2442 Thanks for the link Colin - I had missed that one! Now to go away and do some reading...

14th Aug 2018, 4:55 pm	#4
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,327	Re: B&O BeoCenter 2100 Type 2442 It's good that both amp channels are working. That's a head start. The phono fault could be the cartridge, oxidised connectors/connections/pins or the pre-amp section voltage rail. __________________ Edward.

16th Aug 2018, 12:56 pm	#5
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: B&O BeoCenter 2100 Type 2442 Right, after an intensive day yesterday I've sorted out both faults. First, I used the manual Colin suggested, courtesy of elektrotanya. The manual covered two main models and was partially tri-lingual (not everything was explained in English). I found a manual for the BeoCenter 2200 which is a related model and which I had downloaded from a B&O specialist site was quite helpful as it explained some of the dismantling which the first did not. After I got my mind around B&O's way of doing things: modules described on Diagrams which in turn are carved up into boards... I found that the supply lines were alright. I then checked the decoupled lines on the phono stage and found that the -12v line was fine but the +12v was 0v with some resistors getting rather warm. After powering off I then put an Avometer set to Ohms across the decoupling electrolytic and found a near short circuit. This did not make sense with the circuit so I eventually extracted it and found it was indeed short circuit. Temporarily powering up I had a working phono stage. I then replaced the capacitor (on the circuit diagram, capacitor C5 on Diagram B, Board 9) which was a 220uF, 16v working, Tk brand in green sleeving - made in Japan) with what I had to hand which was a 150uF, 16v working, made by Philips. I then moved on to the FM tuner problem. Here the voltage lines were all alright. After following the audio path I came up against the IF IC with its multiple functions. I checked the voltages on the IC and found that some were as the manual stated but others were 0 where they should have been 6v. I first thought that the IC had failed then my eyes saw the decoupling capacitor (C54 on Diagram A, Board 2) to the tank circuit and they narrowed... Same value, same voltage, same make and guess what - short circuit as well. Removing it I was greeted with IF hiss (no aerial connected). I replaced it with another Philips 150 uF, 16v. So I have a fully working 2100 again. A few points: First, it was an absolute swine to service because of its compact, multi board nature. Second, there are other Tk capacitors in it which I did not have the will to change but at least I know what to look for in future. Third, I am impressed by its performance. Fourth, Japanese Hi-Fi of this era has had a good reputation for reliability, but I've realised/remembered that is the 4th bit of Japanese kit of that mid-eighties era that I have found that has short circuit decoupling capacitors. So is there a 'growing problem' for us restorers/repairers, c.f Transistor Tin Whiskers of the 1960s and oozing/split electrolytics of the mid nineties - early 2000s? Neither of the faulty electrolytics showed any sign of problems - ie no top bulging, no top splitting, no oozing.

16th Aug 2018, 3:39 pm	#6
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,062	Re: B&O BeoCenter 2100 Type 2442 Did you check the main smoothing caps ? If the ripple is high it could put a lot of stress on the little ones further downstream. dc

17th Aug 2018, 10:52 am	#8
SteveCG Nonode Join Date: Jun 2009 Location: Herefordshire, UK. Posts: 2,495	Re: B&O BeoCenter 2100 Type 2442 dave_cox, No, I did not check the main smoothers other than I saw that, visually, they looked alright. I'm certainly not detecting any mains hum - or harmonics for that matter - it must be pushing BBC noise floor quieting when listening to the Radio 3 Proms, from the Wenvoe 92.1 Mc/s main transmitter about 60 air miles away, similarly playing an LP the background is very quiet, I'm well satisfied with its performance, but I understand your point.