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Beomaster 1000 model 2318 repair project

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AntonvZ
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AntonvZ posted on Wed, Feb 19 2020 4:00 PM

Hi all, my first post on this forum.

You guys are doing a sterling job and thanks for all the wisdom shared, it has already helped me a lot.

The reason for me wanting to restore/repair the old lady is that it is of huge sentimental value, it was bought the year I was born and has been in my family ever since. It survived my student years (running a CD player through the tape input) but eventually got stored when the whole AV revolution started and has only been used sporadically over the last 15 years.

I have read most threads relating to BM 1000 but not finding anything that specifically relates to my issues.  The model 2318 seems a bit light on information - even my included circuit diagram is for a model 2316/2317.

I recently started venturing back into vinyl and thought that the BM 1000 with my (still working and recapped) Beovox 1200's would make records sound the way I remember them ie kinda warm and cozy. 

That is when the problems started. The BM 1000 would not switch on.  Opened it up and discovered the large 3000uF 50V cap had leaked out a copious amount of gunk, I replaced that and she lit up just fine and worked for a short while (couple of days) although the left channel for QII was dead.

At the time that issue was limited to the QII input only, QI and tape and FM worked fine so that is a preamp issue I will have to address eventually.

I also replaced the two 3000uF output caps because I had a lot of distortion on the left channel at medium volume and up.

Unfortunately the following issues have now appeared. They are different for each channel and will list accordingly. My electronic knowledge is limited and at this point my testing equipment is limited to a multimeter. However I can solder well enough.

Left channel only hums softly. Like a transformer hum. The hum is not affected by volume, when on a single speaker the hum continues even when the balance is switched completely to the right channel. Some basic investigation revealed the following : the voltage at point J over resistor 678 is measuring at 350mV iso 24mV.  Temperature after 5 minutes is 55C. Turning the potentiometer has no significant effect.

Right Channel very soft and tinny sound, no bass whatsover. The voltage at point J over resistor 754 is 681mV and that temperature jumps up to 122 C within 5 minutes.  Turning the potentiometer has no significant effect.

The 30V reading at point J measured chassis side of resistor 678 starts at about 32V and then slowly falls to 29.85V but is not stable at the point, it fluctuates all the time.

I desoldered the potentiometer for 30V adjustment, cleaned and replaced it - made no difference. I did test it before replacing and it did give me 0-1076 ohm.

I have checked all three fuses, they are fine.

After 5 minutes the bottom of the unit (where the transistors are) and the heat sink are hot enough to raise nasty blisters.

Some pointers as to where I need to start troubleshooting would be greatly appreciated - I really would love to restore the BM 1000 to working order.

Thanks in advance

Anton

 

 

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Dillen
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Answered (Verified) Dillen replied on Wed, Jul 29 2020 3:49 PM
Verified by Grissa

Grissa,

What are your concerns exactly?

One thing to keep in mind is, that Beomaster 1000 has positive ground.

Martin

Grissa
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Answered (Verified) Grissa RTFM [@Lee5] replied on Wed, Jul 29 2020 5:39 PM
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Thanks for your intervention.

If you can see on the photos ... The positive of the capacitor there is the black which comes out of 6.3v of transformers and orange, purple, 2 black, brown and a black white, gray ... They come from speaker and in capacitor negative a red that beeps if I touch the emitter of transistor 2n3205 next to it

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Grissa
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Grissa replied on Wed, Jul 29 2020 4:09 PM

The wires at my beomaster are soldered to the + capacitor and I'm not sure it's right ... Brown, black gray and orange .... it's anything and only photos on the 50v capacitor and the transistor side who can help me follow the wiring. Thank you

Grissa
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Answered (Verified) Grissa RTFM [@Lee5] replied on Wed, Jul 29 2020 5:39 PM
Verified by Grissa

Thanks for your intervention.

If you can see on the photos ... The positive of the capacitor there is the black which comes out of 6.3v of transformers and orange, purple, 2 black, brown and a black white, gray ... They come from speaker and in capacitor negative a red that beeps if I touch the emitter of transistor 2n3205 next to it

Grissa
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Grissa replied on Wed, Jul 29 2020 6:04 PM

How I can add some photos? 

Grissa
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Answered (Not Verified) Grissa replied on Wed, Jul 29 2020 6:05 PM
Suggested by Grissa

How I can add photos? 

filip_kbh
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You need to add the photo under your profile first. Then when writing a post, you can press the film strip symbol - it will take you to your photos. Beware that it does not work in Safari but if you use Chrome there should be no problems.

Grissa
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Grissa replied on Thu, Jul 30 2020 11:18 PM

Thanks for help 

Grissa
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Grissa replied on Thu, Jul 30 2020 11:18 PM

Thanks for help 

Grissa
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Grissa replied on Thu, Jul 30 2020 11:18 PM

Thanks for help 

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