Hello Bang and Olufsen friends,

after a break due to the two business trips to China, I started repairing my Beomaster 5500 (I already managed to repair the Beogram CD5500 with the powerfull help from this forum->thanks again).

The problem with my Beomaster is, that it will not start into standby when the power plug is connected. Nothing is displayed, I hear only the clicks from the relays. If the power plug is disconnected and connected again and again some times, the Beomaster starts and shows standby point on the display. Then it can be operated normally with the remote. All functions works (CD,Radio,Tape,Volume,Treble,Bass etc.). Switch to stand by works too.

If the system was on, I managed to test RAM and processor as described in SM. Both are OK.

As soon as it is disconnected from the main and connected again the same situation: no display, only clicks of relays. But after same tries, stand by light goes on and operation with the remote is possible. Then when I switch from standby to radio and again to standby more then ca. 5-8 times, the display goes off and no remote operation is possible.

Do someone has an idea? 

Thanks in adwance for any hints.

Regards

satmonster321

edited by: satmonster321 at 6:53 PM (GMT -5) on Thu, Jun 2 2011]

I am not sure whether I successfully finished my repair today, but the system worked OK for last 3 hour and at the moment I'am happy. It switches on and off without any problems.

The whole hi(story):

The Beomaster 5500 was broken as described above. I managed to start it (after lot of tries) and left it working.

After 40-60 minutes I recognized that the two resistors R53 and R54 on the radio board (Nr 1) were burnt. The source of this was a short circuit of the C45 capacitor. 

This causes very high current, so high, that the Zener diode D5 (3V3) on the power supply board (Nr 2) was broken. This anyway caused that instead of 5V the whole 13V was provided to the processor board (Nr 4). 

13V on the processor board caused blowing up the fuse (flink, 1A) and (maybe) the processor. 

After replacement of the Zener diode, fuse, nearly all electrolytic capacitors and the battery, the machine started with problems as before, that means first after second or third connection to the mains. I tested it as described in the SM and processor and RAM were OK. But the Beomaster didn't start normal way. 2 Days ago it stopped working and it was not possible to start it anymore.

I removed the processor board, provided 5V (power supply from my Iphone) to it and wondered why the processor is warm and the voltage goes down to 4,71V. Voltages of the processor were not OK (according to the SM), so I decided to replace the processor. I had an old Skymaster CX11 analogue SAT-Receiver with the DIP40 socket and processor in it. I desoldered the old Siemens 8031 SAB from Beomaster and the socket from SAT-Receiver with the Atmel80C52X2 MC processor. I checked the pinout of both processors: it was the SAME !

I decided to use the Atmel processor in Beomaster. First I tested it with the 5V power supply as before. Now the voltage was ideal (5,01V) and the processor was not warm. I assembled the board and put it into Beomaster. 

After switch it to mains it worked !  I did a check of the processor and RAM->all were OK.

Today evening I enjoyed my CDs on my new/old Beosystem 5500.

I hope this description can help someone find a fault in the system.

Regards

satmonster321

It looks like a problem with the RESET function of the 8031 cpu. It could be a problem with the power supply of the cpu board, like bad caps or even a defect processor.

Measure the voltage over C1 47uf, it should be 5V. Replace C1. This is the power supply function.

There is also a cap C10 33uf responsible for the "Reset Power up" function. Replace the cap.

Martin

Hello Martin,

thanks for the tip with the power supply. I replaced C1 and C10 on the processor board, but no change. Measuring shows 5V and other voltages were also correct. Then I decided to temporary replace the 4700uF in the power supply with 3x2200uF cheap capacitors (I have only those 3 at the moment). And ? The machine starts much better, after second or third time I switch mains.

Now I have to order new caps including those big 2x10.000uF and check all again. I hope this will help. Really exciting hobby

Regards

satmonster321

I had a similar problem and replaced the memory battery, I could not realy find anything wrong with the battery I removed but the machine worked fine after I replaced it

Stuart

Thank you Stuart (3400SJ) !

your tip was my hope. I replaced the battery (by the way I soldered the battery holder like in the PC on the motherboard) and all capacitors on the board 3. The system worked fine but only for the short period of time. In this time I could hear music, switch the sources (CD, AUX, Radio etc.) using remote. I was happy that I repaired this receiver. I checked for example processor and display and they were OK. The receiver didn't started by the first time the power was on, but after the second or third time.

Now it doesn't start anymore. I tried lot of different things, but no success. It only switches both relays, but no display. No reaction to remote. All three voltages are OK, 4,99V or 12,37V or 41V. The fuse on the processor board is OK, the capacitors are new (Panasonic FC series).

Does anybody has a tip? Thank you in advance !

It has to be a bad solder joint somewhere... Sometimes you think it's a component change that cured the problem when it is in fact the new solder that did the trick (which you will never know of course)!

I suggest you get your magnifying glass and inspect! I 'repaired' countless DOA units that way, even a TV set!

satmonster321:

I had an old Skymaster CX11 analogue SAT-Receiver with the DIP40 socket and processor in it. I desoldered the old Siemens 8031 SAB from Beomaster and the socket from SAT-Receiver with the Atmel80C52X2 MC processor. I checked the pinout of both processors: it was the SAME !

Yes, they are both descendants of Intel's MCS-51 family of microcontrollers. There are some differences (the latter one is based on CMOS technology and has more internal peripherals), but basically they are compatible in that direction.

One problem might be that the Atmel X2 is capable of executing all instructions in half the clock cycles needed by the original 80xx. This might create timing problems if the B&O program code takes any shortcuts in initializing the hardware or writes into some register locations that were unused in 8031. If you find problems in any remote control or Datalink functions, this might be suspect and you might need to find an original 8031.

Anyway, if everything works - don't worry, and congratulations on good work

If it was a BM6500 or 7000 the 8032x2 will definitly fail. IR commands will not work correct, the distance is short and will fail again and again. And sometimes it will work like new for some hours.

The status register is written wrong and the clock will run x2. B&O did not set bits, there were status bytes written... what can be wrong when you use a different cpu.

The BM5500 uses a lot of code sequences identical... because it is almost identical to the BM6500 cpu board.

Hello Marin,

hmm... is still working. I checked it with Beo 4 and MCP6500 remote. Using Beo 4 there was no problem with distance up to 7-8 meter. MCP6500 distance approx. 5-6 meter. The receiver works now since 6 hours (playing CD). The radio works too. Searching stations, displaying the frequency on the MCP etc. The distances are ok for me, I don't go outside my living room to control the system, even it will work from my terrace.

The issue with the X2 processor clock: does it have to be activated by the software? I think when the firmware of B&O doesn't activate it extra it should work with the "normal" frequency?

Another question: I got the idea to replace LF353 and the 4558 Opamp with the OPA2134 or OPA2604. What do you think about it? In the other thread it will be done for the CD player and should give the improvement.

Regards

satmonster321

Hi,

you can replace the lf353 and 4558 opamps of the BM5500 by the compatible BurrBrown OPA's, it works perfekt. But also replace the power filtercaps too... the OPA needs a little bit more power. Use a good low ESR type... and the BM5500 sound really nice :)

The x2 function of the cpu is sometimes activated, sometimes it works a very long time. I had several BM6500 and 7000 here for repair, the x2 cpu did not work and had problems with ir function. And it took weeks to find out, that it was this function...  

You can use the 8032x2 cpu, it's fully compatible, but if the x2 is activated there will be problems. Maybe you are lucky and it doesn't  matter with your firmware...

satmonster321:

The issue with the X2 processor clock: does it have to be activated by the software? I think when the firmware of B&O doesn't activate it extra it should work with the "normal" frequency?

The CPU starts in normal mode, and the X2 mode is activated by writing a 1 into a single bit in a certain control register (which is unused in the basic 8051 architecture). It disables an internal :2 divider, and everything will behave as if the processor was driven at a double clock rate. The mode can be deactivated and reactivated by software at will.

The firmware (which is prepared for a normal 8051) should not write into these register locations - they are all marked as "reserved" in processor models that don't use them -  but it can happen due to a bug, or via some side effect if the programmer has done something overly clever to conserver memory or code space or to speed something up.