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I have an old Beomaster 900 K, which is in an overall pretty good shape but I would like to have it technical again in good working condition. Today, it has 2 major problems : when switching on there is large background noise and the FM reception is extremely bad (same storie for AM, but I never use AM). Right after switching on, it's very hard to find a signal. When I turn the volume very loud, I sometimes hear a little bit music through the noise/hum. After leaving the radio on for a couple of hours, it's getting better. After a couple of hours, the background noise is going down and it's easier (not yet very good, but easier) to find a couple of good frequencies without turning the volume knob to the right.
Furthermore, there is no music from the internal speakers. Not that big of an issue, since I have a couple of type S speakers, in good condition.
Can anyone help me to fix the problems?
thanks!
Bad IF-stage transistors (partly same circuit used for AM and FM).Noisy germanium transistor in the output amplifier.
And check the connector inside for the internal speakers. Perhaps it hasn't been fitted last time the Beomaster was closed.
Martin
Thanks for your reply Martin! What type of transistors should I use to replace?
Danny
For the IF stages, you can fit any good AF-substitute, f.e AF109r (or AF179 but they seem to have
become expensive for whatever reason), then check the biasing and adjust the resistors if needed.
AF109r fits nicely into the board if mounted upside down. Pins upwards, bent into arches and down. Just make sure no
pins short to the housing.
For the preamp transistors, you can use AC126/AC151. I've also found the russian MP26B quite good and often easier obtainable, though its housing is a bit different.
My BM900 provided only A buzzing sound when I bought it. I could improve this by trimming the potmeters on FM unit. I did this only by hearing; thus whithout any oscilloscope.. Nevertheless the buzzing appears when the volume knob is at 10’o clock. In case I put the bass on 12 ‘o clock. The buzzing appears allready by moving the volume at 8 o’clock. What could be the cause of this and how to get ris of this? BTW the stereo sound is pretty well even before the buzzing starts. Nevertheless the stereo indicator lamp does not light up in FM anyway. I Will try to upload the video to make clear what is happening. Appreciate you suggestions to fix this.
Middelfart,
Does your Beomaster 900K have the optional stereo-decoder installed?If not, please don't expect stereo reception.
The buzzing sound could be caused by several things.Are the speakers in god condition?Is the filter capacitor good?
Yes the gear do have an stereo decoder installed.
The speakers are in good condition. I am not sure how to check the filter capacitor. I. Would appreciate to learn about that!😃
Which "potentiometers on FM unit" did you adjust?
If I rememer correctly, the Ant.sp-coil and the Ant. tr.🤔
I tried to load up a video regarding this case. Unfortunately this was not accepted. I could send it to you by messager or any other media..