Bemoaster 1200, 3000uf Capacitor Polarity

6 replies
J(
Offline
Jamian (archived2)
Bronze
Posted January 27, 2016 at 06:12 GMT
#2057914

Hi

Almost finished the re-cap of my BM1200.  Only thing is I am totally unsure of the correct connection of the 2 3000uf caps.  One had clearly marked polarity, but the other was an old original Wicon.  I can not decipher its polarity marking.  I attached the multimeter to determine polarity but do not trust the outcome.  Rather than run the risk of blowing up my hard work, I am posting to see if some one can tell me which wires (yellow, green; orange, blue) go to positive and negative (obviously the new caps are clearly marked).  Here is the story so far- 

Original BM1200 caps.  The right hand cap is clearly marked, so I copied that for the new cap.  The left cap is not clearly marked so I measured the DC across the connectors.  That suggested the right connector is +ve.  This is the initial information I followed when connecting the new caps...

1200 initial connection based on multimeter reading of DC across old Wicon cap (which I do not trust).  yellow-, green+; orange+, blue-.  This did not feel right, so I also measured the DC across the clearly marked old cap.  I got a -ve reading when red was connected to + and black to the black connection; strange. Danger, danger!!!  Time to reference my working BM1001...

My BM1001, which I just opened up for reference.  The polarity of these according to my multimeter (DC reading) is yellow+, green-; orange+, blue-  That would seem to be logical.  Is this correct?

Thanks for the advise!

OR
Offline
orava
Bronze
Posted January 27, 2016 at 07:34 GMT
#2057915

Hi

I have same operation ahead. Do yuo happend to have list of caps neede?

 

 

DI
Offline
Dillen
BronzeModeratorFounder
Posted January 27, 2016 at 15:54 GMT
#2057916

Usually, the square (and triangular in double caps) marked pins are positives.
Doesn't it say "Plain Neg." on the old cap ?

Martin

J(
Offline
Jamian (archived2)
Bronze
Posted January 27, 2016 at 20:26 GMT
#2057917

The cap does read 'plain negative.' I looked that up on line and found a guy who had the same challenge as me on a different amp.  He concluded the flatter/simpler pin was +ve.  that contradicts my DC reading on my working BM1001.  What does 'plain negative' mean?

There is a slight difference between the pins in the BM1001 (Last image above).  The left looks like a slightly smaller diameter and has an impression in it.  The right is slightly flatter.

J(
Offline
Jamian (archived2)
Bronze
Posted January 27, 2016 at 20:28 GMT
#2057918

Hi Orava - I simply got my cap kit from Dillen (he has posted below.  You could PM him).  Comes with simple visual instruction.

I also referred to the user manual to help locate pins on the back of the PCBs and will use in a while to adjust the trimmers.

J(
Offline
Jamian (archived2)
Bronze
Posted January 29, 2016 at 05:44 GMT
#2057919

OK, sat down with the service manual this evening -

Using the PCB diagram (and looking at the actual PCB), I can see that the yellow wire goes to TR36 and the orange to TR38:

Then looking at the circuit diagram I could see that T38 goes to the Left Speaker cap +ve and T36 goes to the Right Speaker cap +ve.  So, orange and yellow will connect to the cap +ve pins.  Using the PCB diagram (above) and following from the speaker connections back to the caps confirms the blue and green wire connections:

So I will be switching my yellow and green wires around; which matches my readings off my working BM1001.

Eureka?

or
BeoWorld Gold Membership card
Join BeoWorld

Register to access the forums, reference material, and exclusive member benefits — including our monthly prize draw.

Become a Member

December 2026 Prize Draw

Gold Members Only

As a Gold member you're automatically entered into our exclusive prize draw — your chance to win iconic Bang & Olufsen products. A unique benefit of BeoWorld Gold membership, every draw brings a new opportunity to win something special.

View Prize Go For Gold