Dear all,

My beloved Beocenter 9500 stopped working. It started with being in standby not reacting to any commands (like pushing a button) and resulted in not powering up after being disconnected and connected to mains.

When I connect it to main, it makes only one click instead of the two clicks by the relais that normally occure during "boot-up". The standby LED does not turn on.

I checked all fuses including on PCB 60 (all ok) and I also measured the voltages on PCB60 and PCB62 against chasses with the following results [in square brackets Voltages shown in Plug-Survey on Service Manual pages 2-1 if there was a deviation] - unfortunatly I get different results when unplug mains and reconnect - and/or wait some time. Sometimes all the pins with an “X” show no or only very low (1-2V) current, while the ones without an “X” are unaffected - but sometime the "X" pins show the voltage shown below:

For RL1 (PCB 66)

PCB60-P81-1 +7V
PCB60-P81-3 +7V X

For RL 1 (PCB 62)

PCB62-P94-3 +7V
PCB62-P94-2 +7V X

PCB60-P80-1 +14V X
PCB60-P80-2 +14V X

PCB60-P84-1 -12.4V [-12V]  X
PCB60-P84-2 -12.4V [-12V]  X
PCB60-P84-3 +7V
PCB60-P84-4 +7V

PCB60-P85-1 +29.6V [+28V] X
PCB60-P85-2 +29.6V [+28V] X
PCB60-P85-3 +29.6V [+28V] X
PCB60-P85-4 +12.1V [+12V] X
PCB60-P85-5 +12.1V [+12V] X
PCB60-P85-6 +12.1V [+12V] X
PCB60-P85-7 +25V [+22V] X

PCB60-P82 - 4.9 V on all pins [5V]

I also measured as signal on R2 (CD ON) and R6 (ST.BY) and sometimes not.

I assume that something is wrong with PCB60 and would really appreaciate a hint or feedback in regard to what to be checked next to find which part is at fault.

Thanks a lot and have a great weekend!
Patrick

 

Hi Patrick:

We still need to eliminate potential faults to isolate the problem. Try "unloading" the power supply. First remove power connections to the CD player, next remove power connections the casette, then radio (get it down to the bare logic). See if any of those individually has any effect on your voltage readings or if you will allow the system to come back on.

Derek

 

  

Hi Derek, Thanks a lot for your help! I measured today before disconnecting anything and the BC9500 showed no or only very little current on the pins marked above with an "X".

Then I disconnected CD, Tape, and Radio at the same time.

CD: disonnect P11 on PCB31.
Tape: diconnect P32 on PCB20 - that was difficult due to the much too short cables at the hinge!
Radio: disconnected P5 & P6 on PCB10.

Result: still no current on the X-Pins. I had the voltages reported above only a very few times yesterday and mostly no voltage at all.

 Should I try them seperately, too?

 Thanks again for your support!

 
Best, Patrick
 

 

 

Patrick:

If the voltages are goine today, it sounds like an intermittent power supply fault.

What I'd do is start with the windings of the power transformer. Do all the AC measurements to see that the the voltages are there.

Then trace the individual AC windings to the rectifier componenets (ie bridge rectifier, diodes and the check for the output on the filter caps).

Next check the voltage inputs going into the regulators and out. One or more of the DC power supplies are not working.

Double check the cannister fuses on PCB 60; I know you said you did (pull them out and do a continuity check). My beocenter 9500 was completely dead until I replaced the fuse on PCB 60.

B&O doesn't have the best quality circuit boards; look for cold solder joints or cracked traces.

Be patient...the 9500 is not an easy unit to fix....especially PCB 60... it is very cramped. Wasn't it was nice of the B&O engineers to put that little prop up rod though!

Derek

 

Start by resoldering the three main supply filter capacitors on the PCB next to the transformer. These often break their connections from thermal and mechanical stress in this model, and can cause many strange faults.