Beomaster 4400 restoration help

14 replies
filip_kbh
Offline
filip_kbh
Bronze
Posted February 3, 2022 at 18:11 GMT
#2213973

Hello fellow Bang&Olufsen enthusiasts,

I recently bought a used (well, they all are at this point) Beomaster 4400 that was in desperate need of a recapping. So, I have changed all the caps and also the light bulbs, and there is some good news:

1) The Beomaster turns on, the lights for ON and The S-meter as well as the stereo LED and the two stereo lamps are working. 

2) I have adjusted the no load current and the heat sink stays cool.

3) I have sound in the head phone jack :)

The bad news: When I check the 35v rail, I get nothing. So I am presuming the protection relay is active, though I hear no click when turning the BM on?

I have been measuring the transistors and TR11, 115, 120 and 217 look suspicious. Since I am not a radio technician, I humbly ask you if there is anything obvious I am overlooking.

/Filip

Location: Copenhagen

HC
Offline
hcraig244
Silver
Posted February 3, 2022 at 18:23 GMT
#2213974

hi.....does the overload lamp come on?

Craig

filip_kbh
Offline
filip_kbh
Bronze
Posted February 3, 2022 at 18:25 GMT
#2213975

No - the overload lamp is off

Location: Copenhagen

HC
Offline
hcraig244
Silver
Posted February 3, 2022 at 18:32 GMT
#2213976

If the lamp is good You should go back over all of the capacitors you have replaced and confirm you have installed them in the correct polarity, It's very easy to get one the wrong way around......

filip_kbh
Offline
filip_kbh
Bronze
Posted February 3, 2022 at 18:42 GMT
#2213977

The lamp is good. Alrighty - I will try to see if I have changed the polarity on them though I was very careful when replacing them.

Location: Copenhagen

filip_kbh
Offline
filip_kbh
Bronze
Posted February 3, 2022 at 19:01 GMT
#2213978

Well, well - C132 does indeed appear to be inserted with wrong polarity according to the board. I will switch polarity after my dinner and see how that goes.

Location: Copenhagen

filip_kbh
Offline
filip_kbh
Bronze
Posted February 3, 2022 at 19:36 GMT
#2213979

Changing the polarity of C132 made no difference

Location: Copenhagen

filip_kbh
Offline
filip_kbh
Bronze
Posted February 3, 2022 at 19:36 GMT
#2213980

So there is a discrepancy on the board vs. the schematics of C132. I think I trust the schematics more so will reverse it again.

Location: Copenhagen

S(
Offline
sonavor (archived2)
Bronze
Posted February 4, 2022 at 02:01 GMT
#2213981

Hi,

Do not interpret the polarity by the circuit board.  Sometimes the schematic can be wrong but sometimes the board indication (the white, circle) doesn't always mean the negative side of the capacitor goes there.  

Ideally the best scenario is you are recapping an original B&O board that hasn't been worked on.  In that case you can follow how the capacitors are installed and replace them one at a time, keeping the polarity as you found in the original.

If you no longer have that luxury then you will have to analyze the circuit and figure out how that is on the actual board and determine the correct polarity that way.  That can be kind of a pain but is a learning experience :-).

Another option is to take advantage of this Beoworld Forum and where you are in doubt about a certain capacitor - take a nice photo (maybe a couple) and post it here.  Some Beoworld workbench members will be able to look at it and tell you which way the polarity goes.

-sonavor

filip_kbh
Offline
filip_kbh
Bronze
Posted February 9, 2022 at 15:06 GMT
#2213982

Alrighty, if somebody could help with identifying if any caps have the wrong polarity, that would be great. 

Location: Copenhagen

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