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Beomaster 4000 Faint Stereo Light

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Keith
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Keith posted on Tue, Nov 7 2017 9:32 AM

The Stereo light on my Beomaster 4000 is quite faint.

If you move the tuner rail or adjust a preset,  the stereo light goes off and you loose stereo some times but not all the time. When the stereo light goes off if I turn the BM4000 on and off a few times the stereo will light up faint again.

The signal strength is very good and the stations very strong.

I have also done a full recap on the BM 4000.

Thanks for any help.

Keith

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Dillen
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Check that the lamp is correct voltage and wattage.

Martin

Keith
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Hi Martin 

yes the lamp is the right voltage and wattage, it came out of your kit.

The odd thing is, press Phono or tape 1/2 and the lamp glows bright.

 

Keith

Keith
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Just checked the voltage to the lamp and it’s 10.97volts

Dillen
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11 volts should make it glow fairly bright.
I take it that this voltage is measured in Tape or Phono mode?

Martin

Keith
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It’s the same  voltage for Phono, Tape and Fm, it only drops in FM as it looses the Stereo signal.

Keith
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Hi Martin 

Sorry, just rechecked 

The voltage from the FM is 1.3 volts on average lower than the Phono, Tape voltages.

when you move the FM slider, that’s when the stereo lamp voltage drops out. Turn the BM off and back on a few times and it will light up and run fine until you leave it off for a good number of hours.

Keith

Dillen
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Is FM drifting?
Did you replace the rectifier iwith the one from the service kit?
Did you perform any alignments to the tuner?
Does the voltage regulator transistor (at the right chassis side) get more than a pleasant hand-warm in FM?

Martin

Keith
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Hi Martin 

Thank’s for taking the time to reply.

No drifting, 

Yes I did. Took a bit to workout, should look more closely at your instructions.

only a small alteration of the IF as you suggested and it was only a small bit. But this problem persisted before this.

 I took off the heat sink and reapplied thermal paste, it now runs quite cool.

I have noticed that when it looses stereo, TR22 emitter drops to 0 volts.

Keith

Dillen
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Keith :

I have noticed that when it looses stereo, TR22 emitter drops to 0 volts.

Eh.. TR22 emitter is permanently tied to ground.

Martin

Keith
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Just me checking around, the collector side goes up in voltage when the emitter drops off.

Any ideas where to test next?

Keith

Dillen
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When TR22 closes, the collector voltage rises because no current flows through the lamp, so there will be no voltage drop across

the lamp. In other words, there will be the same voltage on both sides of the lamp. That's Ohms law.

Are you sure the emitter of TR22 is not permanently grounded?
If so, you have the problem right there.

Martin

Keith
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Thanks Martin, I will remove and re solder  and see if that resolves it. And let you know how it goes.

Keith

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