Beomaster 1900 (2904) weird voltages on the 15V supply and the 31V amp section.

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quattttro Posted: Mon, Apr 5 2021 11:20 PM

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Hello. New here, great forum, would greatly appreciate some help.

The voltages on my 1900 all appear to be too high in both the 15V and the +31V sections. In the 15V supply section, even with R151 turned all the way down, I'm reading 16.8 volts on TP16 and TP10. The big C92 capacitor tests ok, I even tried replacing it with no change. Tested C96 and C95, they were in spec. I get 25V across C92, 28V in standby. 20.73V AC coming out of the transformer. The only place the voltage is low is at the bass/treble/balance indicator lamps, I'm only getting 11V there. 

I replaced the rectifier (D50) with one I had in-stock, perhaps that's the problem. The original one was burnt. New one is  a D3SB60 (4.0 Amp. Single Phase In Line Bridge Rectifier). I tested T27, seems to be fine.

Radio works fine, sounds good. Adequate volume. Tape and Phone inputs are extremely quiet, even on max volume. Getting 38V on the big reservoir caps (0C7 and 0C8).  Any suggestions on how to proceed? Thanks.

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Dillen replied on Tue, Apr 6 2021 5:31 AM

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Check ground connections from the rectifier to the regulator circuit etc.
Check the two zener diodes.

Martin

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quattttro replied on Tue, Apr 6 2021 5:18 PM

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Appreciate your suggestions, Martin.

I have continuity from the rectifier ground all the way across the board and down to the chassis screw ground point.

For D52 I have a 0.83V drop across it.

For D51 0.85V drop. 

I'm not equipped to test the reverse voltage drop, but on the diode function they both read 0L on the reverse.

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quattttro replied on Tue, Apr 6 2021 7:26 PM

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Update: I feel like an idiot. It turns out my multimeter was reading too high. All voltages are spot-on now that I changed it for a new one. Live and learn

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quattttro replied on Tue, Apr 6 2021 8:45 PM

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So now my question is, what would cause the radio to work perfectly, sounds great out of the speakers, but the tape and phono input both are are very quiet, can only be heard at max volume (very quiet and distorted). Muting circuit not disengaging? 

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quattttro replied on Tue, Apr 6 2021 8:45 PM

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So now my question is, what would cause the radio to work perfectly, sounds great out of the speakers, but the tape and phono input both are are very quiet, can only be heard at max volume (very quiet and distorted). Muting circuit not disengaging? 

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Dillen replied on Tue, Apr 6 2021 9:13 PM

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Bad C90?

Martin

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quattttro replied on Wed, Apr 7 2021 2:40 AM

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The C90 is new, but perhaps i need to check it again. Will update tomorrow, thanks.

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Dillen replied on Wed, Apr 7 2021 7:25 AM

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What is the voltage across it?

Martin

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quattttro replied on Wed, Apr 7 2021 5:27 PM

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I've got 13.94V across C90.