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  • Re: Beogram 8000 main drive issues

    Hi ALF, I would've been very surprised if you did have a current probe. It's still an interesting measurement. I presume the light blue trace is P4-2, anyway it shows that the brake is being activated. Regards Lonnie
    Posted to BeoGram (Forum) by Lonnie on Wed, Jul 18 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, The current will under go the phase change not the voltage so unless you have a current probe for your oscilloscope you won't be able to measure the phase change. Regards Lonnie
    Posted to BeoGram (Forum) by Lonnie on Tue, Jul 17 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, Before you move on from the electronic switch that manages the power supply I'd verify it's working properly by manipulating it without the uC. I'd lift the base of 1TR21 from the PCB and hook up a small circuit with a 1.5V battery and a 2k, 1.8k & 200 ohm resistor and tap voltage at 0.75V and 0.0075V and use a switch to bias 1TR21 on and off and confirm that the +15V & -15V supplies go off and on. Looking back a few pages ago John asked you to measure the voltage at P6
    Posted to BeoGram (Forum) by Lonnie on Mon, Jul 16 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, How can the emitter of 1TR21 be at -15.9V in Play mode. It is supposed to be grounded? Is there a ground problem at the emitter? Regards Lonnie
    Posted to BeoGram (Forum) by Lonnie on Sun, Jul 15 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, I'm not giving up on the uC just yet. If you notice the difference in the voltage output between Standby and Play it is the same difference as mine just offset by about 4.8V. Did you put new parts in or just measure the old parts and put them back in? If you put new parts in did you remeasure the voltages around 1TR19, 20 & 21 and did they change at all? Regards Lonnie
    Posted to BeoGram (Forum) by Lonnie on Sat, Jul 14 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, You need to replace 1TR20 (PNP) and I think you should also replace 1TR21 (NPN) at the same time. Regards Lonnie
    Posted to BeoGram (Forum) by Lonnie on Sat, Jul 14 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, The emitter voltage at 1TR18 is correct and 0TR1 will only "close" when 1TR18 is biased off which means the emitter voltage at 1TR18 goes above -0.63V. This will only happen when the -ve 15V supply is turned off. Things to measure and check: Examine solder of pins P6 - 3,4,5 to confirm there are no solder bridges Double check that 1TR21 has been replaced with NPN and is not in backwards. Measure the CBE voltages of 1TR20 & 1TR19 during standby and play. If you don't find
    Posted to BeoGram (Forum) by Lonnie on Sat, Jul 14 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, I opened up my BG 8000 to take some measurements: At P6-4 on Standby = 0.76V, during Play = 0.076V Collector 1TR21 on Standby = 0.067V, during Play 0.58V So during standby 1TR21 is biased on and during Play it is biased off. A little different to how I thought it worked. Your measurements of -ve voltage at P6-4 are an issue that we need to understand.
    Posted to BeoGram (Forum) by Lonnie on Fri, Jul 13 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, Rather than just replacing it again why don't you measure the voltages around 0TR1 to see if it is operating properly. It is biased on by 1TR18, so you want to measure the voltages around both. Since the base of 1T18 is grounded then for it to be forward biased the emitter needs to be at least -0.7V. If this is the case it will draw current through R78 & R77 which will cause a voltage drop on the base of 0TR1 which will forward bias it and you will have your 15V power supply. If 1T18
    Posted to BeoGram (Forum) by Lonnie on Fri, Jul 13 2018
  • Re: Beogram 8000 main drive issues

    Hi ALF, And while your working on it I'd check/replace 1TR20. Regards Lonnie
    Posted to BeoGram (Forum) by Lonnie on Thu, Jul 12 2018
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