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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
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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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Søren Mexico
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Welcome to the forum, get yourself a cap, lamp and trimmer kit from Martin (Dillen n the forum) and go from there, here is what I did https://forum.beoworld.org/forums/t/11085.aspx?PageIndex=2

Collecting Vintage B&O is not a hobby, its a lifestyle.

AntonvZ
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Hi Søren and thanks for the welcome.

I have indeed read and re-read your thread a couple of times as it is detailed and the closest model to mine. Thank you for that.

I hear you about the recap/trimmer kit and will have to do that in due course.

I know this is a big ask but do you by any chance have an image of the back of your 2317's PCB board, there is something I need to check with regards to the wiring on the back of the board in the area of the speaker output capacitors. I am hoping you took a shot when you had it open and were working on it.

Regards, Anton

Søren Mexico
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AntonvZ:
I know this is a big ask but do you by any chance have an image of the back of your 2317's PCB board,

Just checked nothing there Anton, sorry

Collecting Vintage B&O is not a hobby, its a lifestyle.

Dillen
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Dillen replied on Thu, Feb 20 2020 3:35 PM

Any chance of photos of the back, the dial and the serialnumber label?

Martin

AntonvZ
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Thanks for checking Søren

AntonvZ
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Thanks for checking Søren

AntonvZ
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Dillen:
Any chance of photos of the back, the dial and the serialnumber label?

Coming right up, but not sure which dial you are refering to.

 

AntonvZ
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Dillen:
the dial

Maybe this one?

Dillen
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Dillen replied on Thu, Feb 20 2020 9:47 PM

Thanks for the photos.
The dial is the tuning scale - the one with the frequency numbers etc. All in the photos.

The left channel emitter resistors look burned. This will be the reason for the warm underside, because the underside is used as a cooling surface for the output stages.
Too high idle current is my guess - probably caused by a bad idle current trimmer. Don't power up again until it has been fixed; Replace the trimmer, the emitter resistors and check the output stage transistors.

The right channel will need the same treatment more or less.
And new capacitors in general will solve many problems.

Martin 

AntonvZ
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Hi Martin, thanks so much for the advice, much appreciated.

And well noted to keep power off until changes you suggested are complete.

  • I still need to pick up some of the technical jargon, assuming the emitter resistors are the ones below numbered 680 & 678?
  • Is the whitish band in the middle an indication that they are toast?
  • Output stage transistors are the ones underneath on the chassis ie the 2N5034's ?

Thanks again

Anton

Dillen
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Dillen replied on Fri, Feb 21 2020 10:31 AM

Yes to all three bullets.

And the idle current trimmer (potentiometer) is the one in the center of the photo with yellow and orange pins (the new component will not have this).
Its correct setting is in the servicemanual. You can use the Type 2316/2317 servicemanual for this.

Martin

AntonvZ
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Dillen:

Too high idle current is my guess - probably caused by a bad idle current trimmer. Don't power up again until it has been fixed; Replace the trimmer, the emitter resistors and check the output stage transistors.

The right channel will need the same treatment more or less.
And new capacitors in general will solve many problems.

So I got busy over the weekend and replaced the output transmitters, trimmers and recapped most of the main board.

Results:

30V Stable voltage has dropped from 32V to 27.3V measured at point J (see pic below) - however adjusting new trimmer makes no difference.

Left channel still does nothing but hum - it is much softer though, barely audible. Hum does not get louder if you adjust volume.

Left idle current has come down a lot but still sitting at 295mV - adjusting new trimmer makes no difference.

Right channel has come back to life and is playing music (YES! Big Smile) and have managed to adjust idle current to 24mV.

Bottom of unit in area of output transistors and heatsink are running much cooler, at least you can touch it now without risking injury.

 

Dillen
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Dillen replied on Tue, Feb 25 2020 2:08 PM

Do you have a DC reading on the output rail (before the output series capacitor)?
Check the driver transistors and all resistors nearby,

Martin

AntonvZ
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AntonvZ replied on Wed, Feb 26 2020 12:38 PM

Dillen:
DC reading on the output rail

Copious amounts of googling left me with no idea where/what the output rail is - going to need a bit of help with finding that. For what its worth I am picking up DC readings in the 27-29V range on the output resistors on the left channel.

  • With regards to transistors, from my understanding they cannot be checked on the board, they have to be unsoldered and checked with a meter that that has a socket for transistors. Is this correct? No quick check?

Also picked up the following

  • There is a 15mV reading between chassis and power capacitor negative - is this leakage normal?
  • There is a 28V reading on the copper heatsinks for the left and right channel transistor, is that normal?

Thanks in advance

Anton

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