Recent content by wattsabundant

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    Friends of Phase Linear

    Somewhere around 1977 I was at a Peaches record store. They had a 700B driving a pile of JBL L26's through 70 volt transformers. It looked so cool. In 1982 I went too work for a pro sound company that outfitted rock & roll bands with racks of 400's. I learned how to fix them real fast...
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    Finally My WOPL 400 finished with wattsabundant Help

    A couple comments: Ron had already determined the negative 15 volt supply had failed. I started by connecting a variable power supply at the regulator input with the current limit set to minimum. The power supply immediately went in to current limit which suggested that Q2 failed. Further...
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    Hello. New to PL and PACF

    When the 4000 breaks run away fast. The few that Ive worked on had more than 100 cracked solder joints.
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    Audible Transformer Hum or Noise

    My first real job was at a transformer shop. I learned far more about transformers than I wanted to know and despised the job. It was a common practice to shim the coil with a wooden wedge. Then the transformer was dipped in a resin and baked in an oven to cure it. It would be possible to...
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    Variacs N Stuff

    All of my test equipment (load bank, power source, oscillators, scope etc) is rack mounted. The ac power source includes a voltmeter (taken on the output receptacle), and ammeter. I incorporated the series light bulb and switches into a 4 space chassis. I built the rack out of 3/4" plywood...
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    PL700II blues

    Here is the link to the scope forum. scopes It doesn't surprise me that the scope Perry listed is similar to Rigol I've got. the only difference being 2 channel vs 4. There are multiple vendors. I went with Saelig instruments as they've been around a while.
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    PL700II blues

    The Tek scope is plenty adequate for repairs. A popular 4 channel digital scope is a Rigol ds1054z at only $350. It's a 50mhz scope that can be cracked to 100mhz. The thing I don't like about it i the trace is not as fine as the analog scopes such as the Tektronix. Ed Blackwood commented on...
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    PL700II blues

    I'm guessing an oscilloscope is not an option. That would likely turn a difficult problem into a simple one. What is being described is an intermittent component that heats up and causes the bias transistor to turn full on. Whcih would rop the bias to nearly zero. An open bias pot would do...
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    PL700II blues

    Is the offending channel the same one that had the burnt base/emitter resistor on the driver transistor?
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    PL700II blues

    That burnt resistor suggests an open base/emitter connection on the corresponding transistor. Possible bad socket/broken wire. An open base emitter junction, although not impossible, is a rare condition on power transistors. The service manual is attached. Page 20 provides an excellent...
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    PL700II blues

    The picture of the xfmr & dc caps shows a display board resting on top of the chassis. Put a piece of cardboard under the display board so that it does not short to the chassis.
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    PL700II blues

    Looking at the pictures, the relay board is wired according to instructions which focused on minimizing rework. I have acknowledged that it is not the ideal grounding scheme and recommend following the White Oak grounding scheme when installing the driver board. I don't think the grounding...
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    Inrush current circuit

    What problem is the soft start solving? I've captured a number of current and voltage waveforms with a scope on 400's and 700's and the inrush current does not exceed the maximum surge current of the rectifier. Yes I've used a total of 40,000uf on 400's and 30,000uf on 700's. In addition...
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    With reference to the dual 500, did you install a soft start? I ask because I've done a fair...

    With reference to the dual 500, did you install a soft start? I ask because I've done a fair amount of research on inrush current on 700's and haven't seen a need for it there. I tend to think the impedance of the transformer limits the current to safe values. Note that the stock rectifier can...
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    MJ21195/93 and MJ21194/96

    My bad. Should be 96