BEOMASTER 3400, help needed with repair

4 replies
M(
Offline
marcus_m (archived)
Bronze
Posted March 30, 2011 at 02:07 GMT
#1759479

Hello,

I've got a lovely BEOMASTER 3400 that had problems with the AFC section.

As the unit is some years old, I decided to change all electrolytic capacitors as well as the tatals. The AFC is now workling again and the overall perfformance is better (the little hum that was noticable before is now gone). But unfortunately the unit developed a new failure: after some minutes the left channel of the radio gets distorted - when connecting an external source to tape or phone all works well.

Where could the fault be located?

Thanks for your help and best regards

Marcus

YA
Offline
yachadm
Bronze
Posted April 10, 2011 at 09:48 GMT
#1759480

Look at 2IC4 MC1310. Pin 4 is AF left, Pin 5 is AF right. Scope the outputs.

Check that C41 - 2.2uF and C43 - 1uF are polarized correctly. Better to use Wima MKS2 bipolars here.

Scope TP10 (left) and TP11 (right) to compare.

Menahem Yachad

Location: Jerusalem

My B&O Icons:

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Electronics Technician in Jerusalem Israel. B&O fan for over 50 years.
DI
Offline
Dillen
BronzeModeratorFounder
Posted April 10, 2011 at 11:34 GMT
#1759481

Was this fault present before you began replacing capacitors ?
If so, replace the rectifier D8 as the first thing.
If not, check your work, capacitor values, capacitor types, polarities,  solder joints etc.

Martin

M(
Offline
marcus_m (archived)
Bronze
Posted April 13, 2011 at 01:42 GMT
#1759482

Thanks Menahem and Martin for your help.

As this fault was not present before the capacitor change, Martin was right to check the things I did. As I do not have a service manual for this Beomaster, I do not know the correct polarity of the caps. So I looked for the 2.2uF Menahem mentioned and decided to simply turn them around... Guess what - it works!!!

Thanks again and best regards

Marcus

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