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  1. Replies
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    Thanks for your response! Unplugging the jack...

    Thanks for your response!

    Unplugging the jack board and putting signal through tape in works perfectly.

    Removing all ICs from the jack board kills the noise, but when I add 3 or more in any...
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    877

    Peavey XR600C 2 minute hum

    There is something in the signal path of the preamp that is causing a buzz at cold start for a couple of minutes and then it fades away. The hum is only present when the 6-channel board is plugged...
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    633

    Q3 (A1941) 1. base 34.9 2. collector -0.1 3....

    Q3 (A1941)

    1. base 34.9
    2. collector -0.1
    3. emitter 34.9
    base to emitter 0.0

    Q4 (C5198)

    1. base -34.9
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    Sorry it took so long... ~+/-35VDC

    Sorry it took so long...

    ~+/-35VDC
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    Peavey MP-400

    Greetings,

    An MP-400 that I'm checking has distorted audio which increases as the volume is increased anything above a low setting. It appears to be happening in the power section, although there...
  6. Now that I've had the time to look it over I see...

    Now that I've had the time to look it over I see that it will need the power circuit board 4/4 as well as the button. Does anyone know where to get Yamaha pro audio parts?
    45715
  7. Thanks, g1. Although the EMX66M has the switch on...

    Thanks, g1. Although the EMX66M has the switch on the front, the part 30d does look familiar. I was not looking for it to be pcb mount. Probably some proprietary bs that I will have get from Yamaha. ...
  8. Forgive my poor choice of words: instead of...

    Forgive my poor choice of words: instead of saying “switch removed” I should have said “switch missing”. I will see if I can crop an image from the parts list.
  9. REQ: Yamaha p/n VU859100 cross reference

    I was given a Yamaha EMX66m with the power switch removed. The service manual has the part number as VU859100 for the switch and VU859000 for the button.
    I would like to add a suitable replacement...
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    Thanks for the replies! These do indeed use...

    Thanks for the replies! These do indeed use full-wave center-tapped rectification with positive and negative output terminals. What would be be best and easiest way to convert one to 18v? They have a...
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    Looking for ideas/uses

    I have been scraping out some medical equipment and have about 20 of each :

    1:1 torridal isolation transformer
    12v linear power supply
    24v linear power supply
    serial microprocessor
    fused,...
  12. Replies
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    2,260

    I found the source of the smoked area if the...

    I found the source of the smoked area if the board. It was C12 and C13. I didn't see that these spots were holes until I got it under a magnifier. Replacing them raised the +15v rail resistance to...
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    I'm pretty green and have not used resistance as...

    I'm pretty green and have not used resistance as a troubleshooting tool, so I guess I was just hoping to find an obvious change in resistance as a starting point. As far as strategy goes, given my...
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    The emitter of Q204 is just and easy place to...

    The emitter of Q204 is just and easy place to check the neg. voltage going to the preamp because it is tied to the header pin 1 via JP207. I pulled the pre just after getting the the supply right to...
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    35822 Here is the spot I mentioned. It's only on...

    35822
    Here is the spot I mentioned. It's only on the top; no damage to the trace. I just can't see where it came from unless it was from IC2.
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    J5 is basically a node connected to the neg. lead...

    J5 is basically a node connected to the neg. lead of C58. I agree it probably could use replacing. C13 and R13 are in channel 2 circuit. I had I time finding them on the schematic. I don't know what...
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    Here's what I know about the preamp: The...

    Here's what I know about the preamp:

    The feller what belongs to this amp has been using the the headphone jack as a direct out. He has it labeled as such.
    There is some soot at the feet of C13,...
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    You guys are my heros! I swapped D201 and D202...

    You guys are my heros! I swapped D201 and D202 with the Z15s, checked R203 and R204 (good), went ahead and replaced C203 and C204 and now I've got 14.9v and -14.1v on Q201 and Q202, respectively. A...
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    I didn't make myself clear on the RD16E...

    I didn't make myself clear on the RD16E "15.33-15.96v" - those were the original parts that I removed, and the rating is from the data sheet, not a measurement.

    I have two new candidates for...
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    Here are the results of the latest poll: Q210...

    Here are the results of the latest poll:

    Q210 good
    Q202 also good

    Voltage on Q201:
    Base 29.4
    Collector 50.4
    Emitter 28.6
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    I used a KSD1408Y for Q201 and KSB1017Y for Q202....

    I used a KSD1408Y for Q201 and KSB1017Y for Q202. I double-checked the pin-out and they should be drop right in. The zeners are some I had that regulate 15.5v rails in a Kustom PA head. The RD16EB2...
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    Roland KC-500 voltage problem

    Good morning/evening, whatever the case may be,

    Initially, I found these problems on this amp and fixed them:

    D201 and D202 were shorted
    Q202 and Q204 were blown, I replaced Q201 and Q202 with...
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    Thanks for the input... Dave was on the right...

    Thanks for the input...

    Dave was on the right track when he mentioned Q4, which happened to be crossed up with Q41. Fixing that got the polarities and voltage right on the mute fet and mute tr...
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    Roland KC-550 mute circuit

    Thanks for the forum! Googling my music electronic questions seems to always lead me back here.

    I need help with a KC-550 that seems to have a mute circuit problem. I have replaced 4 jfets on the...
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