Reply To: Beomaster 6500 & 7000 improvement of pre-amp circuit

[Die_Bogener]

Open the BM6500. 2 screws on the rear, 2 in the preamp plug section.

Remove the black lower plate, 4 + 3 screws.

Then you have access to the boards. There is no need to remove the boards out of the cabinet. Just unplug the tuner board, the hinge can be removed or unpluged from the cabinet.

Warning!

The boards are made of pertinax, not epoxy. Any overheeting of the solder will destroy them. Do not exceed 320 degrees of solder temperature or the board will seperate the copper layer! There is NO REPAIR!

B&O used a special method to place the parts on the boards before soldering. The part is plugged into the holes, and the wires are angled outwards, fixing the parts for the soldering process. If you just pull the part during the desoldering work then the pad will break off from the board. It will be very hard work to fix this pad again… and the board will not look good any more.

Heat up the pin, use a small screwdriver to straighten the wire in the hot solder and then unsolder/remove it. Any force on the pads will destroy the board.

Clean the board will Isopropanol after your work and during resoldering/replacing parts.

Chapter 1: Parts you do not need.

In the preamp of the BM6500/7000 are some filter caps that do change the sound to dull. The sound will be much clearer without them. Just remove them, they do not need any replacement…

… and removing is simple.

C10, C11, C12, C14, C15, C16,  C17, C18, C22, C23, C24, C27, C30, C31, C32, C33, C45, C46, C67, C68, C69, C70

All are small ceramic caps.