Beomaster 2400 radio hum

7 replies
JA
Offline
jansjobe
Bronze
Posted August 19, 2023 at 02:31 GMT
#1642590
I am restoring/repairing a Bang&Olufsen Beomaster 2400.

After a minute or so, I get a hum from tuned station, no hum between stations. Hum is propably 50Hz.
I have recapped all electrolytes.

I suspect something wrong in the stereo decoder section. Could it be the IC itself?

Has anyone any ideas?

Best Regards,
Jan Sjöberg
Mark-sf
Offline
Mark-sf
Bronze
Posted August 19, 2023 at 17:09 GMT
#1658197
Do you get the hum when you turn off FM Stereo? How about any other inputs?
JA
Offline
jansjobe
Bronze
Posted August 19, 2023 at 19:42 GMT
#1658199
The hum is ONLY on FM radio.

At first the hum disappeared when switched to mono. Now it is still there, but slightly lower.
JA
Offline
jansjobe
Bronze
Posted August 19, 2023 at 19:42 GMT
Edited August 19, 2023 at 19:42 GMT
#1658200
SO
Offline
sonavor
Bronze
Posted August 20, 2023 at 07:06 GMT
#1658204
If you unbolted the main PCB from the cabinet for the capacitor replacement, did you keep the FM tuner (metal box) secure?  If the metal box was free to move while you were working it is possible a shield wire became disconnected...introducing the hum.

-sonavor
DI
Offline
Dillen
BronzeModeratorFounder
Posted August 20, 2023 at 07:14 GMT
#1658205
A bad rectifier D50 wouldn't be a first.
Also, check the solder joints around the standby relay.

Martin
JA
Offline
jansjobe
Bronze
Posted August 20, 2023 at 17:25 GMT
#1658214
It was in fact the bridge rectifier!

Thanks everyone for your time and effort!
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