Restored A Dropped And Neglected BANG & OLUFSEN Set Model BEOCENTER 7700
This is a sad story of a costly and lovely Bang & Olufsen Set, which many audio enthusiasts might crave to own. This had gone around many hands, tampered, dropped and then lying neglected for many years. This was finally brought by the last owner for a possible restoration. The set was totally dead. Well, I could not deny in spite of knowing its history, as the person who brought it was very close and intimate to me.
This set is very heavy and handling itself is very difficult especially for ‘youngsters’ like me! After allowing it to rest on top of an arm chair for a few weeks, waiting for its turn to come to my service table, I took it out one day, kept it on my car porch verandah, opened the set for a thorough cleaning by a powerful blower. I followed the instructions for dismantling, contained in the service manual downloaded from here:
I saw hundreds of lizard eggs in every part of the set, many of which were empty shells and a few unhatched. Evidently, the inside of the set was a cozy maternity hospital for the lizards! (LOL) Some were under the boards and revealed itself as I dismantled the whole set one by one. After all boards were removed, I used my blower and cleaned the inside using various suitable brushes.
Then brought it to my service table for an investigation, starting from the mains cord to power supply. I saw many dry solders and in one place, I was surprised to see that the collector and emitter of a transistor were almost short by an overlapping solder! As it did not look tampered, it was indeed an overlook at the manufacturing stage itself. The reason why it did not cause a problem is a mystery! My guess is that even though it looks shorted, it might not have been making a proper contact to cause a problem.
The amplifier-cum-power supply board was slightly bent, the bottom cover of which had suffered the impact when the set was dropped. (I had to provide plastic wedges while fixing the board back to avoid its touching the bottom metal cover) The drop had caused damages to the top cover of Gramophone Player and a few other parts. The tank capacitors in the power supply were found leaky. There was no visible breakage of PCBs, as the set had a sturdy body. But a few screw holding brackets were found broken. To tell you frankly, the condition inside was so bad that at one point of time I felt like giving it up and return the set as it was! Well, somehow, I overpowered this negative thrust.
I did a retouch of the boards one by one and ensured that there were no dry solders. Also replaced a few of the electrolytic capacitors wherever I found the need. Applied CRC 2-26 spray, wherever lubrication-cum-cleaning was found necessary.
I removed the uController from its socket, cleaned the contacts thoroughly and reinserted it. Every connector was removed, cleaned of fungus formations and reinserted. I also cleaned all the switches and controls located in various boards, and the input sockets. Fixed the broken parts with Superglue, reinforced by stapler pins inserted using soldering iron. Fixed the damaged lids and top covers using Fevibond, Superglue and double sided tapes. Cleaned and lubricated the hinges. The list of work done might be endless! I noticed that one long S shaped spring was missing in the cassette/Radio side lid, because of which the lid had to be lifted manually after pressing and releasing the lock. After I went through this marathon work, I assembled the boards back one by one and after checking and rechecking, I applied power. I had already replaced the belts in the cassette player when I dismantled it. Fumes emanated from the amplifier section, and I saw a couple of resistors burning. So, disconnected and once again removed the amplifier board for investigation. I checked the DC offset as mentioned in the service manual and found it to be very high. The adjusting pots were making erratic contacts. I replaced these and adjusted the voltage and current precisely as mentioned in the service manual. Then the set worked perfectly well. There was no damage to any transistors or other semiconductors. I was glad to see that the set came back to life and it responded to commands for a tape play. I loaded the cassette that came with the set and listened to the audio output in the headphone first (I had cleaned this also very well). Then connected external speakers and got a good audio output which is typical to Bang & Olufsen.
The gramophone (turntable) portion was left as it was, as advised by the customer. There was no cartridge and the motor was found disconnected. The top lid was pressed down and fixed with double sided tape as it was lifting up on its own because of breakage of the locks. That portion was permanently closed! What a sad thing to do! The radio did not respond to any of my trials in rectifying it and that was also was left as it was, as desired by the customer. He only wanted the cassette player to be ok. He had a dozen of turn tables and radios in his home. I fixed bushes at the bottom of the set as the exposed screws were scraping the table top while moving it.
Mission accomplished with aplomb though with perspiration and perseverance! Satisfaction with its maximum intensity jumped into the bag, and its comrades welcomed it providing accommodation.
This article was prepared for you by Parasuraman Subramanian from India. He is 72 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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