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  • Re: Beogram 8000 main drive issues

    Hi ALF, That's a strange measurement. I presume the 15V is still present when you are reading the -0.8 to -1.1V? If so I'd suspect zener 1D26 and replace both it and 1TR26. Regards Lonnie
    Posted to BeoGram (Forum) by Lonnie on Thu, Jul 12 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, With "the base circuit" I mean any part of the circuit that is connected to the base of 1TR31. If there is a leak path that can generate approx 0.16mA of current flow then this would generate enough voltage drop in R109 to allow 1TR31 to be biased on. I think this is pretty unlikely to be happening now that you have confirmed that 1D35 is ok. To absolutely rule this out can you confirm that you can still get the TT operating clockwise at 33.3 or 45 rpm. If you can, is the voltage
    Posted to BeoGram (Forum) by Lonnie on Thu, Jul 12 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, The +&-15V supplies are controlled by 1TR21 which in turn is controlled by pin 38 on the uC Based on Martins explanation of startup I can think of two scenarios: 1. The brake is activated but the rotation is not sensed so the uC keeps powering the brake circuit. It was expecting to sense rotation, then stop the rotation and turn off the 15V PS via pin 38 but this never happens 2. The rotation is sensed but power is still supplied to the base of 1TR31 via an effective short in the base
    Posted to BeoGram (Forum) by Lonnie on Wed, Jul 11 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, If 1D35 has failed short (or has an intermittent short??) it could allow the base voltage on 1TR31 to remain biased on despite pin37 going high. I'd replace it and double check that the anode is closest to R91 and not the other way around. I'm thinking that if 1D35 has a short then the 5V which is supplying the base voltage to 1TR31 has access to the virtual earth at the op amp 1IC3. I calculate you'd have 1.1mA running through R7, 1.6mA running through R108 & R109 and 2.7mA
    Posted to BeoGram (Forum) by Lonnie on Wed, Jul 11 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, No problems, I hope I can be of some help. Your measurement at the collector indicates that 1TR27 is biased on. This makes it nearly a short to ground which is what R102 sees and therefore why the voltage becomes so low. If you want to further investigate the brake system you need to go further downstream as 1TR31 & 27 look to be operating correctly. You can't measure the reset voltage at P6-3 as this will just be seen as a step function after 1TR17 is biased on. You need to see if
    Posted to BeoGram (Forum) by Lonnie on Mon, Jul 9 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, The base of 1TR31 will not get down to 0.7V because it is isolated from the 0.7V by R7 (3k3) & R108 (18k). A really approximate way to think about it: When pin 37 is high you have a circuit with ~5V at Pin 37, then R7, then R108, then R109 and then the 5V power supply. Given that you have very little voltage difference at each end of the chain there is no motivation for electrons to flow so no current, so no voltage drop across the resistors. That means there will be 5V at the base of
    Posted to BeoGram (Forum) by Lonnie on Mon, Jul 9 2018
  • Re: Beogram 8000 automatic arm-drop issue

    Hi ALF, Looks like you’re on track to get this sorted. If you haven’t already removed the failed phototransistor it would be worth taking some in circuit measurements to confirm the failure mode. If you measure the voltage drop across R2 (the good phototransistor) you can see what the correct voltage drop and hence current drawn on the working circuit is and compare it to the voltage drop across R3. I can think of three scenarios on the failed circuit: 1. Voltage drop on R3 of ~15V (
    Posted to The Workbench (Forum) by Lonnie on Thu, Nov 16 2017
  • Re: Beogram 8000 automatic arm-drop issue

    Hi ALF, In addition to John’s suggestions I’d check the Detector Arm Circuit. A simple test to do is with a record on and press Play, watch the speed of the arm as it moves towards the set down point. Does the arm slow down as it approaches the set down point or does it travel at the same speed? If it doesn’t slow down then the detector arm circuit is not working properly to control 2IC1 pin 33. Pin 33 should be low when there is no record on and go high when a record is detected
    Posted to The Workbench (Forum) by Lonnie on Wed, Nov 15 2017
  • Re: Preamplifier for beolab8000

    Hi Christian, Have you thought about Tim De Paravicini's mid priced tube phonostage - EAR 834P? It does have a version with a volume control. I've been using one for about 10 years, but mine has no volume control. Not sure if it is high end but I like the design and enjoy the sound it makes. Regards Lonnie
    Posted to General Discussion & Questions (Forum) by Lonnie on Fri, Nov 3 2017
  • Re: BG8000 fuse issues

    Hi ALF, If you look at the function table for the Microcomputer: When you activate pin 2 by pressing play the arm should move across to the record with pin 24 in the low state so that it won't lower. In the Playing state pin 24 has gone high which turns on TR8 as described in the Technical Product information. 1TR8 is a standard NPN transistor with a grounded emitter and the high state needs to be high enough with some margin to turn it on and keep it on while playing. You should have the understanding
    Posted to BeoGram (Forum) by Lonnie on Fri, Jul 14 2017
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