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A Beogram 4000

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Craig
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Craig posted on Sun, Nov 4 2018 4:22 PM

Drove down to Manchester yesterday to do some Christmas shopping, and picked this up while I was there...ebay again, need to get a handle on this ;¬)


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Craig
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Craig replied on Tue, Nov 13 2018 9:02 PM

Ok....checked to 6vdc at 2TR6 and its fairly stable at 6.8vdc...the Zener is set at this value, 2TR6 does indeed run quite hot however. Having done nothing more than confirm voltages around 3IC0, to see if it was switching, the pickup arm has mysteriously started to move across, this now occurs everytime I switch the unit on....it still starts at 45rpm but the pickup is now moving, it doesn't travel out when ES is reached...but that's a problem for tomorrow.....

Craig
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Craig replied on Wed, Nov 14 2018 8:52 AM

Having given this some thought and taking into consideration how flakey everything seems to be, One time on start up the machine set off at 33rpm, the pickup arm moved in and stopped at the first groove of a 33 album....but didnt drop, I havent been able to replicate this and it mostly starts as described above. So....in order to bring some order to the task I will dismantle all the mechanical switches....gold plate them and check the continuity from each one, this will give me the confidence to eliminate these signals from the fault finding process.

Dillen
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Dillen replied on Wed, Nov 14 2018 10:06 AM

And replace the regulator transistor. They go weak, allowing the voltage to jump up and down with varying loads.

I have no photos of the modification, but it's merely a matter of fitting a transistor to a small piece of board, fit a small cooling fin to
the transistor (I use the type found on Beomaster 3000/4000 driver transistors or voltage regulators) and secure it all to
the chassis bottom (insulated).
Two of the transistors connections (emitter and collector) are already found on the filter capacitors near by.
The remaining connection (base) is just made as a lead pulled with the other leads and fitted to the board where the transistor sat.
This takes a lot of heat away from the small board and also from the transistor itself, which has no effective cooling originally.

It clears many problems regarding instability.

Martin

Craig
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Craig replied on Wed, Nov 14 2018 12:11 PM

Martin

Thanks for that...I will replace the zener diode too while I'm in there ;¬)

Craig

Peter
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Peter replied on Wed, Nov 14 2018 7:16 PM

Would you like to borrow mine as a comparison?

Peter

Craig
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Craig replied on Wed, Nov 14 2018 8:19 PM

Peter

That would be very usefull…………..

 

Craig
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Made a start on the slider switches.....don't look too bad to be fair.


Craig
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Until I spotted this......looks like its been getting hot at some point, still measures up at 8.2 ohms however.  not a very clear pic I'm afraid......


Craig
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Scorched the board too...…..


Craig
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Need to order a new 1 watt 8.2ohm resistor. The contacts don't look bad, they where quite bent but did look like they where making contact. Before gold plating.


Craig
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And after.....


Peter
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Peter replied on Wed, Nov 14 2018 9:01 PM

I'll try and bring it down soon - I'll make sure it is working first!!

Peter

Craig
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finished with the carriage switch assemblies and need to set them up as per the service manual, something looks a little odd with the measurements shown against switch activation points.....but will need to give it a little more thought, meanwhile fitted a new voltage regulator off board in accordance with Martins advice.


Peter
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Peter replied on Sun, Nov 18 2018 4:39 PM

Having a clear out here - would you like a pair of Beovox 5000s - they are the correct speaker for your Beolab 5000 - they match well. Teak and legs all present and correct - were repaired professionally some time ago but not used except as a table since! Not that small....

Will accept a look at my BM8000 as payment!! Big Smile

Peter

Craig
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Craig replied on Sun, Nov 18 2018 5:27 PM

Sounds like a deal to me Peter ;¬)

 

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