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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 Mon, Nov 5 2018 8:15 PM

Ok....powered up and was greeted with a platter that rotates but a pickup arm that remains stationary, the dial indicator lamps are glowing as is the 45rpm indicator lamp. The pickup arm can be driven forwards and backwards manually but that is the extent to the units function. Following the fault finding road map ON with no record turntable runs, does turntable run @ 33rpm No its running at 45rpm, suggests Q4=high yes or no, when I measure at this point in the logic I'm reading 0.4vdc or there abouts, to me this sounds like a low but I'm not sure what voltage level represents high. taking it as a low indicates a check for 24vdc at the collector of 1TR6 which is a No, I can hear the reed relay clicking when I operate the selector from 45 to 33, the platter speed reduces and the rpm indicator lamps change over to 33rpm, however when I let go of the 33rpm switch it reverts back to 45rpm and the 45rpm lamp is illuminated. This all suggests the relay is working, the road map says replace 1TR5, 1TR6...…...does this sound about right?

Craig

 

Peter
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Peter replied on Mon, Nov 5 2018 8:36 PM

When you get to it, I am sure I have a better cartridge you can have - I have never seen a cantilever look like that!!

Peter

Craig
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Craig replied on Mon, Nov 5 2018 8:47 PM

Pretty special eh! looks like it has been wrapped in some sort of insulation....or growth has started to take hold.....

Craig
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Ok.....been a little distracted painting the kitchen walls, little guidance required here, the road map leads me to suspect 3IC4....but for clarity I need to be sure that the High level im getting is really high. I'm measuring 4.8vdc as a high (however some of the measurements that may be high are only around 2.9vdc) and the low measurements are around 0.04vdc......

Also ann anyone confirm this odd symbol is 3IC6 output?


Craig
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This is what I think is the measuring point of the odd symbol, looks a bit like an inverted infinity symbol to me


RaMaBo
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RaMaBo replied on Fri, Nov 9 2018 10:15 PM

Hi Craig,

 

the symbol is probably the greek charachter for 'gamma', the third letter in the greek alphabet.

The used logic family in the Beogram 4000 is 'low-speed logic'. Those chips were produced by Siemens. They accept  < 1V as 'Low' and about  > 2V as 'High'.

I don't know the beogram 4000 but in the service manual there is a 'Auto speed sensing' mentioned. In the failure flow chart you added a comment about the speed switching from 45 -> 33 rpm and fallback if you release the button '33'. I would say that this is a correct function if i assume the mentioned 'Auto speed sensing' works as designed. Also if i assume that this function is correct and follow the failure flowchart it should give a way to the failing component because the speed  will be changed manual. So you should come directly to 'Y' branch of the decision ('Is SI missing Low IMP')  and not to the 'N' branch.

In every case should one of the chips be defect you can order all at 'little diode' Smile

Good luck with this nice icon from the seventies!

Ralph-Marcus

Craig
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Craig replied on Sun, Nov 11 2018 8:13 AM

Ralph....I'm tending to agree in so much as the speed will change when the 33rpm switch is made and returns to 45rpm when released, this does suggest that the logic gates are in fact flip flopping 😉  Just seems like it's starting out on the wrong foot. I have also noticed that before pressing ON  I can press the 45rpm switch and the platter spins at 45rpm, which is correct....however pressing the 33rpm switch does nothing...something fundamentally wrong with this 33rpm circuit, reed relay next under the spotlight..I have ordered some chips just in case.

 

Craig
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Took a look at the "SI missing low IMP" cause and measuring at 1TR20 found this pulse signal at the collector of TR20 which provides said signal to the logic gates.....looks fine to me, well its a pulse though not so sure its 10ms.


Craig
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Craig replied on Sun, Nov 11 2018 2:22 PM

still not convinced about the NAND gates but awaiting delivery of replacements so....had a look beyond the 33rpm issue. I have found that if I replace the platter and drop a 33 disc onto it and manually drive the tone arm into place I can manually pull in the solenoid and the tone arm drops nicely into the first grooves and the tone arm drive starts to jog along nicely, good to find something that works!

Craig
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After measuring the inputs to 3IC4 several times and confirming that all the inputs and outputs where as per the logic diagram still the flip flop refused to latch when 33rpm switch was made.....activating the 33rpm switch puts a "1" into the 45rpm gate which in turn puts a "0" into the 33rpm gate therefore holding it HIGH or latching it until the 45rpm switch is activated again reversing the outputs. My replacement IC's came today so I replaced 3IC4 and was rewarded with the ability to manually switch from 45rpm to 33rpm with the selection of 33 rpm latching.....


Craig
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Craig replied on Mon, Nov 12 2018 8:39 PM

I was expecting the platter to start up in 33rpm mode, that I can select 33rpm now is good but not what I was expecting. The tone arm still sits tight and refuses to move so there is still a long way to go,  the fault finding road map leads me to replacing 3IC0 or its capacitor 3C12....that's a task for tomorrow.

Dillen
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Dillen replied on Tue, Nov 13 2018 7:42 AM

Check the V6 supply.
A problem with the regulator or the zener can cause it to run high, and that typically causes problems in several circuits.
The regulator runs warm. I like to place it on a small cooling fin outside the board - near the two filter capacitors for ease of wiring.

Martin

Craig
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Craig replied on Tue, Nov 13 2018 12:26 PM

Keith :

Keith

Thanks for that info....dont know if a 4002 lid would be compatible with a 4000 unit ;¬)

Craig
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Craig replied on Tue, Nov 13 2018 12:30 PM

Martin

Thank you for the advice, will varify the voltage level is stable... though I suspect this is something I should be doing anyway, do you have a picture of this modification?

Craig

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