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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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Peter
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Peter replied on Sun, Nov 18 2018 6:39 PM

I'll have to work out when I can get down - will be a weekend as working flat out at present!

Peter

Craig
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Martins mod complete im back to this......on startup the platter runs at 45rpm, 45rpm lamp glows and the platter moves towards the centre, the logic looks like this which seems fine to me..


Craig
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However when I press the 33rpm switch the logic flips over fine, the platter runs at 33rpm, the 33rpm lamp glows...the logic looks just as I would expect


Craig
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And thats great...what I dont understand is when i release the 33rpm switch the whole thing flips back to 45rpm.....surely this shouldnt happen as it must latch? I have tried replacing the chip to no avail......am i missing a trick here?


sonavor
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Perhaps there is a pulse on one of the NAND gate inputs that is flipping the latch back.

-sonavor

Dillen
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Dillen replied on Wed, Nov 21 2018 4:59 PM

Shorted 45 contact on the frontpanel?

Martin

Craig
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Just for the hell of it I have had a look inside these NAND gates, I always thought that the outputs from these chips where driven from there own internal 6vdc supply but I didn't realise they also provide the voltage at the inputs too. So having sorted that out I can see the required configuration for 45rpm operation.....the yellow highlight represents a high state or something above 0,5v


Craig
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Operating the 33rpm switch drags down the high input which flips the gate over to drive the 33rpm lamp and motor speed.....


Craig
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Craig replied on Thu, Nov 22 2018 7:28 PM

All that said it looks to me like inputs 2 & 9 provide the latching when the gate flips over......I'm not getting this latching

Craig
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Craig replied on Fri, Nov 23 2018 7:55 AM

Pondering this in the shower this morning, when selecting 33rpm the 45rpm output from the logic gate goes low which de energises the speed control relay, I hear it click out and the speed changes to 33rpm....the output from the logic when 33rpm is selected only switches the 33rpm indicator lamp on via 1TR1 and runs to ground via resistor 1R2.....i'm now suspecting insufficiand load on this output? will check the resistor out this evening

Piaf
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Piaf replied on Fri, Nov 23 2018 5:41 PM

Peter,

Frede doesn't have any of those trim pieces anymore. I JUST asked him. I "may" have a new source, but I need to see the product before commenting. The trim piece on my Beogram 4000 is adhesive tape, and now looking something less than pristine. I ordered a new trim piece and it is being manufactured, as I type this.

Your advice, as always is spot-on vis-a-vis cleaning a stylus. You guys got me to use the Magic Eraser on my "collection" and it works. However I prefer, when needed, to use alcohol with an artist paint brush.

Much as been said about how these B&O cartridges age, and of course they do. The dreaded flat spots and the hardened suspensions.

I really don't know what makes one cartridge fail/wear-out, and another continue. However, offered only as a hopeful comment, my BEST cartridge is a MMC20CL that is 43 years old. And my daily use cartridge a MMC6000 sounds almost as good.

Jeff

Beogram 4000, Beogram 4002, Beogram 4004, Beogram 8000, Beogram 8002, Beogram 1602. Beogram 4500 CD player, B&O CDX player, Beocord 4500, Beocord 5000 T4716, Beocord 5000 T4716, Beocord 5000 T4716, Beocord 8004, Beocord 9000, Beomaster 1000, Beomaster 1600, Beomaster 2400.2, Beomaster 2400.2, Beomaster 4400, Beomaster 4500, Beolab 5000, Beomaster 5000, BeoCenter 9000. BeoSound Century,  S-45.2, S-45.2, S-75, S-75, M-75, M-100, MC 120.2 speakers; B&O Illuminated Sign (with crown & red logo). B&O grey & black Illuminated Sign, B&O black Plexiglas dealer sign, B&O ash tray, B&O (Orrefors) dealer award vase,  B&O Beotime Clock. Navy blue B&O baseball cap, B&O T-shirt X2, B&O black ball point pen, B&O Retail Management Binder

 

Craig
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Craig replied on Mon, Nov 26 2018 8:33 PM

Still working away at this......I have discovered that when switching on the 6vdc drops to around 4.6vdc, smoothing capacitor may be responsible for this, I'm of the opinion that the logic gates are working as designed but I'm still chasing the latching at 33rpm issue.

Dillen
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Dillen replied on Mon, Nov 26 2018 9:54 PM

Did you replace the regulator transistor 2TR6 or just move it away from the board? if you just moved it, I suggest you replace it (BC141).
Also check the zener 2D4.
And rectifier 2D5 is known to become weak.

To me it still sounds as if the 33 button is held constantly, only interrupted when - and as long as - 45 is pressed.
Have you checked the signal from the 33 button?

Martin

Craig
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Craig replied on Tue, Nov 27 2018 7:57 AM

Martin

Yes I did replace 2TR6 with a new device, BC119 however not  BC141. I have a new zener for 2D4 and I also have a couple of 2000uf caps I can use to replace the existing dodgy looking pair. I will see if I have a rectifier too when I get home this evening. As for the 33 switch I'm thinking its fine...bear in mind the machine is starting up at 45rpm with the corresponding lamp illuminating and not as it should in 33rpm mode, operating the 33 switch flips the 45rpm lamp off and the 33rpm lamp illuminates.....the turntable drive motor drops to 33rpm too, however releasing the 33rpm switch flips everything back to 45rpm mode....I can see from the circuit that the 33 switch actually de energises the reed relay 2MS2 by diverting its coil voltage to ground and thus drawing the logic input 33' to ground to (via 4D3) which is responsible for flipping from 45 to 33....so everything seems to be working as it I think it should, but it just isnt ;¬)

All the mechanical switches are working fine too.....so I'm hoping re establishing 6vdc across the board will improve things.......

Craig

Dillen
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Dillen replied on Tue, Nov 27 2018 8:44 AM

I meant the 45 switch...
I'm getting old.

Martin

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