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  • Re: Beomaster 1500 - DC offset problem

    [quote user="krais"] Thanks Martin. Yes, C110/210, C111/211, C117/217, C120/220, C121/221, C122/222 are all new. [/quote] Yes, but since you have a real LCR meter, you really should check C111 and C211 carefully. E-caps usually have a +/-10% or +/-20% tolerance, and that includes brandnew ones. At least part of your channel imbalance could originate from these 2 caps. [quote user="krais"] I used a XJW01 LCR meter at 1KHz (not professional by any means but accuracy should be decent
    Posted to The Workbench (Forum) by manfy on Sun, Jun 20 2021
  • Re: Beomaster 1500 - DC offset problem

    (this thumbsup is in reference to Martin's post!) Particularly C111/C211 seem critical! I just simulated different values and ESR from 0 to 3500ohms for all those caps. C117 and C121 showed little change in the signal level (I suppose because of the amplifier feedback to the filter network, which "balances itself" and adjusts the gain level accordingly). But minor changes in capacitance or ESR of C111 showed a direct impact on the output signal level! PS: Just a disclaimer: My spice
    Posted to The Workbench (Forum) by manfy on Sat, Jun 19 2021
  • Re: Beomaster 1500 - DC offset problem

    Thanks! So, I connected a 1kHz sine signal to the input, at 0dBV = 1.0Vrms, 300ohms and measured rms values at following points: 1) Signal-In = output signal generator 2) Filter-Out = cathode of C117 3) Signal-Out = cathode of C121 all voltages in mVrms in order 1/2/3 - ideal cap values as per schematics: 994m/4.89m/952m - actal values L channel: 994m/4.87m/947m - actual values R channel: 994m/4.88m/948m For the fun of it, I changed C112 to 5nF and C114 to 20nF: - 5n/20n highpass: 994m/3.67m/664mV
    Posted to The Workbench (Forum) by manfy on Sat, Jun 19 2021
  • Re: Beomaster 1500 - DC offset problem

    Yeah, 0.5 on the balance slider sounds a bit too high. Check that the caps in the tone control filters are balanced. They have a surprisingly high impact on the voltage level. Preferrably check and match them out of circuit. C112 and C114 should be matched to each other and to C212, C214. Same procedure with C115, C116 and C215, C216. Post the actual values of those caps and I'll run them through a Spice simulator.
    Posted to The Workbench (Forum) by manfy on Thu, Jun 17 2021
  • Re: Beomaster 1500 - DC offset problem

    Is that channel imbalance audible in the speakers? How far do you have to push the balance slider to get a balanced signal on both channels (according to the multimeter)? [quote user="krais"] I've checked the treble and bass potentiometers for corrosion but they seem fine. [/quote] How did you check that? Oxidation is not really easy to see with the naked eye. Did you try any sort of cleaning?
    Posted to The Workbench (Forum) by manfy on Thu, Jun 17 2021
  • Re: Beolab 4000 red led no Green led

    [quote user="chti59"] Hi Just checked and the other speaker tweeter is also dead, so certainly to much volume. [/quote] Hmmmm, I think you're jumping to conclusions -- in this case a potentially wrong one! It can't be an excursion fault because tweeter coils don't travel that far. It can't be overheating because you would see a fried voice coil or at least signs of overheating. The connecting wire definitely wouldn't fail of overheating -- mechanical stress and aging
    Posted to The Workbench (Forum) by manfy on Wed, Jun 16 2021
  • Re: Beolab 4000 red led no Green led

    Interesting! I'd say it's unlikely that the voice coil wire broke because of overload. If so, that would have happened somewhere within the coil. Probably the previous owner was "playing around" and accidentally broke those wires. Yes, you cannot easily solder them. Similar to transformer wire it is lacquer coated and it can withstand temperatures up to 200+ Celsius. On thick wire the lacqer needs to be scratched off for soldering, but don't do that here! It could damage the
    Posted to The Workbench (Forum) by manfy on Tue, Jun 15 2021
  • Re: Beolab 4000 red led no Green led

    Congratz on your successful fix of the original problem! [quote user="chti59"]. Their is plenty of number on the back, which number ? [/quote] I just googled the net and it seems that some replacement tweeters do show the db-level on their label while others do not. Here's one example with -0.2dB: If you don't have that, you're out of luck. All you can do is to assume that it has a flat frequency response and adjust 2R51 as if the chassis were 0.0dB. Alternatively you could
    Posted to The Workbench (Forum) by manfy on Tue, Jun 15 2021
  • Re: Beosound 9000 MK1 power problem

    [quote user="Peter"] The original fault described in my first post ist still there, thus the powersupply might have died due to this error (after some time 3-5 minutes, the device shuts down with a "plopp"). [/quote] The first step is taken. Congratz! No, this diode did not die from an overload coming from a connected board. First, the switching controller limits the output current to 1.8A and the back EMF coming from such low current is easily handled by that Schottky. Besides
    Posted to The Workbench (Forum) by manfy on Sun, Jun 13 2021
  • Re: Beolab 4000 red led no Green led

    Thanks! - 'speaker on' signal from power link: 4.5V is good! The power link specs say: ON-signal should be >=2.5V, OFF-signal <=0.5V - 'DC Fail' signal at 0V: good! The signal gives the difference between the two speaker outputs. Normally this should be 0V. If the DC-offset goes beyond approx +/-2V, the DC-Protection circuit (TR91/92/93) will switch the relay off and you cannot on the speaker unless you cycle the power. - emitter of TR93 at 0V: NOT GOOD! At standby you should
    Posted to The Workbench (Forum) by manfy on Sun, Jun 13 2021
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