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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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Sonavor

Will look into that, I can now compare my machine against Dave's so will post the results, meanwhile I have hit the easy targets for now.....scale illumination and speed lamps now on LED's   


Craig
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Tracking sensor lamp replacement next, Rudi's work again....had to "borrow" Roasties cartridge again to set up the 4-5 turns before tracking commences....all is well.


Craig
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Craig replied on Tue, Jan 8 2019 11:18 AM

Ahhh......just when everything was looking good I have discovered that the tracking motor wont drive in reverse when the tone arm is moved backwards! I know it's very unlikely that this will ever be required....I dont know what the engineers at B&O where thinking of when they designed this feature into the tracking circuit...but it's there so I feel the need to bottom out the issue. This represents a fault in almost every aspect of this machine to date......it must have been saving them up over its lifetime, hopefully the photocell is good and the fault lies elsewhere. 

Craig
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Right.....measuring the voltage level at the photoresistor responsible for the return or reverse direction of travel (OR4) I found I was getting a voltage swing from 0 to 20vdc as I moved the tone arm in its direction and light fell on it....the measurement was taken at FC1 the extreme right solder connection below Rudi's lamp box.

Measuring the voltage at the same place on the photoresistor responsible for the forward direction (OR3) gives a much lower voltage level, around 5vdc, for the same movement of the tone arm in its direction.....open circuit somewhere.

 


Craig
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Measured the voltage at 1D13 on 1PC which feeds the Base of 1TR33 and was getting nothing.....traced the line back to 6PC and close inspection under my magnifier revealed this very odd break in the copper track, it's not a break in the board that has caused the copper to crack...its almost as though it has been cut through deliberately....but I have a hard time believing that, maybe a sharp blow...something dropped on it perhaps?

 


Craig
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Well...whatever the cause I filled it with a blob of solder and measured up once more......now the voltage level measured up very similar to the forward drive photoresistor....and on test the tracking motor now runs backwards and forwards depending on the position of the tone arm...fortunately an easy fix this time.


sonavor
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It looks like someone in the past had a slip of their flathead screwdriver (on that adjacent screw) and it ripped through the trace. 

-sonavor

Craig
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Craig replied on Wed, Jan 9 2019 9:42 AM

Sonavor

Yes....sounds a more likely explanation, I will press on with the replacement of the trimmers and I have ordered a new aluminium trim for the hood...It's a shame the platter is in such a poor state. I'm also awaiting a report on the condition of the cartridge and new belts will be required.....otherwise its actually starting to look good.

Craig
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Naturally I don't have the correct value trimmers to hand, ordered some up. Meanwhile I reset the tracking following the disturbance of finding the reversing fault...and as I had Daves cartridge fitted I couldn't resist a quick listen to dark side, played both sides faultlessly.....I'm impressed.


sonavor
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So a 47 year old analog control system design still holds up today Smile
Not bad at all.

-sonavor

Peter
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Peter replied on Wed, Jan 9 2019 8:32 PM

I probably have a spare cartridge you can have if you want one of your own. I must drop you off the Beovox 5000s as well and pick up the Beolab!

Peter

Craig
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Craig replied on Thu, Jan 10 2019 8:06 AM

Peter

Your a star.....the Beolab is working fine, has been in service for a couple of months without issue. I have no plans for the month end weekends and I'm home early Friday afternoons, I have an entire weekend to myself the 25th if your about?

Craig

Craig
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This rather gorgeous looking trim turned up yesterday...……..


sonavor
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That is very impressive. Can you post a picture of the other end? 
There is definitely a real need for that type of replacement part on our Beogram 400x projects.

-sonavor

Craig
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The other end......these are available with black or brown text, for no reason I chose brown.

Craig


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