iPhoneSasuke
New Member
Hello everyone.
For a long time I've been happy with my Bang & Olufsen Beomaster 4400, but he's pretty old and now it asks for repair. When I touching any input, i.e. Tape 1 or 2, the red "ON" indicator is shining but I can hear the protective relay and there are no sound. Also sometimes during launching the "Overload" shines for 1 sec. It was very hard to understand something but I have some success.
1. When the power connectors P11, P12 are detached from PCB they are have +35, 0, -35v (both connectors) and relay closed.
2. When I connect ANY of connectors P11 or P12 - the relay opens (cuts off the power).
3. I've soldered the three 4.7R 2W resistors in series, 2 pcs (~15R, 6W, 1 pc for "+" and 1 pc for "-"), and wired 'em between main caps OC8, OC9 to the according poles of P11 or P12 connectors on main PCB and one wire between the mid point of main caps (- of OC8 or + of OC9) directly on according point of P11 or P12 connectors on main PCB. Than I've seen that the "+" having +33v and "-" having -4v. Voltage drop between outer leads of 15R resistor is 27 volts. It means that there is 2A leakage on "-" pole thac causes opening the protective relay.
4. I've desolder both L100 and L200 output coils and in these condition the relay is closed and voltages on both connectors are normal (+35, 0, -35). The zero level at the amplifier output is 1 millivolt.
It means that input, preamp, main amp are Ok and the trouble is after the coils... Speaker selector, headphones, acoustic terminals and ambio selector.
No matter if I select any speaker or doesn't select any at all. I don't use the headphones. Switching the ambio selector also doesn't affects.
Maybe somebody heard about these problem and can help?
I've replaced all elyt caps excluding OC8, OC9 and C3.
All voltages are in normal.
Also there's something strange at Input Selector: if the amp is OFF and I'll press Tape 1, it ON's; if after that i'll press Tape 2 - the Tape 1 will turn off - that's Ok; but if after that (when the Tape 2 in ON) i will press the Tape 1 - the Tape 2 will still stay in ON position... But I can press the Tape 2 with little strength and that the Tape 1 will turn off (mechanically). But... I can't turn off the Tape 2 by pressing on Tape 1... Is that normal?
P.S. Also if I will turn amp ON by pressing FM (no Tape 1,2), the relay will also open. If I will put the 6.3 jack and turn amp - the relay will also be open.
The only way for relay to be closed is to cut off the output coils. If the coils will be putted in their place, there will be some short on the body by "-".
P.P.S. The transformer with soldered coils is humming. With desoldered coils it works quietly.
P.P.P.S. With the thermal imager I saw that the resistors R4 150 Ohm and R5 100 Ohm (area 6) are getting very hot.
For a long time I've been happy with my Bang & Olufsen Beomaster 4400, but he's pretty old and now it asks for repair. When I touching any input, i.e. Tape 1 or 2, the red "ON" indicator is shining but I can hear the protective relay and there are no sound. Also sometimes during launching the "Overload" shines for 1 sec. It was very hard to understand something but I have some success.
1. When the power connectors P11, P12 are detached from PCB they are have +35, 0, -35v (both connectors) and relay closed.
2. When I connect ANY of connectors P11 or P12 - the relay opens (cuts off the power).
3. I've soldered the three 4.7R 2W resistors in series, 2 pcs (~15R, 6W, 1 pc for "+" and 1 pc for "-"), and wired 'em between main caps OC8, OC9 to the according poles of P11 or P12 connectors on main PCB and one wire between the mid point of main caps (- of OC8 or + of OC9) directly on according point of P11 or P12 connectors on main PCB. Than I've seen that the "+" having +33v and "-" having -4v. Voltage drop between outer leads of 15R resistor is 27 volts. It means that there is 2A leakage on "-" pole thac causes opening the protective relay.
4. I've desolder both L100 and L200 output coils and in these condition the relay is closed and voltages on both connectors are normal (+35, 0, -35). The zero level at the amplifier output is 1 millivolt.
It means that input, preamp, main amp are Ok and the trouble is after the coils... Speaker selector, headphones, acoustic terminals and ambio selector.
No matter if I select any speaker or doesn't select any at all. I don't use the headphones. Switching the ambio selector also doesn't affects.
Maybe somebody heard about these problem and can help?
I've replaced all elyt caps excluding OC8, OC9 and C3.
All voltages are in normal.
Also there's something strange at Input Selector: if the amp is OFF and I'll press Tape 1, it ON's; if after that i'll press Tape 2 - the Tape 1 will turn off - that's Ok; but if after that (when the Tape 2 in ON) i will press the Tape 1 - the Tape 2 will still stay in ON position... But I can press the Tape 2 with little strength and that the Tape 1 will turn off (mechanically). But... I can't turn off the Tape 2 by pressing on Tape 1... Is that normal?
P.S. Also if I will turn amp ON by pressing FM (no Tape 1,2), the relay will also open. If I will put the 6.3 jack and turn amp - the relay will also be open.
The only way for relay to be closed is to cut off the output coils. If the coils will be putted in their place, there will be some short on the body by "-".
P.P.S. The transformer with soldered coils is humming. With desoldered coils it works quietly.
P.P.P.S. With the thermal imager I saw that the resistors R4 150 Ohm and R5 100 Ohm (area 6) are getting very hot.
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