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Colorsound Power Boost - Another issue!!!

Andy Betts

Hi guys,

 

Been a long time since I posted here and i have another issue for you that hopefully you might be able to help with.

 

I've just recently built another Power boost pedal for a client. I etched the board myself using the photo resist method, it came out not too bad save for a couple of areas where the tracks were broke. i patched them up with copper tape that has conductive adhesive. I've checked for continuity and all is fine where the patches are. Here are the pictures of the board and also for reference the schematic.

 

 

image

 

image

 

I've built a few of these now and have had no issues with the circuit or builds until now. I built this one, wired it to my test rig and there is no sound at all.... it's totally dead as if it's not in the circuit at all. I've checked for voltage on input and it's ok. I've checked for continuity in the circuit and it seems ok. i don't know what the voltages should be in the various sections of the circuit so haven't checked them. I've gone basic and checked the input and output wires for breaks and they're ok. I've also checked the test rig with a known good circuit and it's OK.

 

i think there might be a duff component but not sure on first steps to troubleshoot.... Any help will be greatly received.

Parents

  • In a next version, I'd drill mounting holes in the board.

    If it hangs in the pedal, held up by the potentioleter pins, I predict that you'll get broken solder joints.

    A pedal gets some abuse when used on stage. And your PCB, with the electrolytes, has a decent mass.

  • in reply to Jan Cumps

    @Jan Crumps Only the pots are board mounted, the on/off switch is separate.

    @Gerald Schwarz The board is an exact replica of an original. All the parts are as an original 0.5w resistors, and Vishay axial capacitors. Here are some photos of some original powerboosts. All the other boards I've made have been perfect, with no issues. This has clearly got to be a component issue.

     

    imageimageimage

     

    The transistors are BC183L the same as an original and are orientated correctly, although I will check to be sure. Pinout is ECB when looking at the transistors from the pin end with the flat on top. The only difference with mine is I've had to mount the pots on the reverse side of  the board as the pot shaft isn't long enough to locate on the board and go through the enclosure. The originals used the pot shaft to mount to the board, where mine use the 3 pins. Also, the originals had the pins bent in the opposite direction to standard angled pot. The originals used custom made pots by Omeg and are not readily available.

  • in reply to geralds

    The polecap is orientated correctly, the polecap is on the V in not the output..... Here is a photo of a board from 1969 which my pedal is based on... It's pretty much Identical. The output polecap is the little on e on the far left of the board.

     

    image

     

    Below are 2 photos from 2 previous builds I did which worked perfectly.... No change in any component placement.

     

    imageimage

     

    here is my board design on the left, and the original on the right for comparison. You can see I've marked the "+" signs on my board to prevent incorrect orientation

     

      imageimage

  • in reply to Andy Betts

    Yes, thank you.

    It was my mistake, I didn't mirror my view (top // bot mirroring) in this area.

  • in reply to Andy Betts

    Hello Andy,

    Now you have fixed the possible break in the track could you measure the voltages around Q3 again ?

     

    I'm very puzzled that you got 0.58 V on the base - which implies a base current, which ought to make volts across the 1k resistor. - but you saw 0.

     

    Might be time to take Q3 out and measure the voltages without it in circuit.

     

    MK

  • in reply to Andy Betts

    As I asked yesterday, did you checked the transistor Q3? On top of that transistor seems that has a burning hole.

  • in reply to Andy Betts

    Even if the transistor was a dead short in all directions it couldn't make these results because the emitter resistor would have current and therefor volts across it.

     

    I'm baffled.

     

    The only conclusion is that the rest of the circuit is not what the diagram says, due to a fault no one has spotted yet.

     

    The best I can offer you is that if you want to pop it in the post I can bring bigger guns to bear on it and see if I can fix it for you.

     

    Alternatively, with the power off, measure the resistance from base to earth, base to emitter, emitter to earth and collector to 18V.

    And let me know what meter you are using, because this may affect the results.

     

    MK

  • in reply to geralds

    it's just a mold line.. nothing to worry about

  • in reply to michaelkellett

    I have an audio probe being made today... i'll have a go with that before doing anything drastic like posting it off to you

  • in reply to Andy Betts

    Good luck, you could try the power off resistance measurements while you're waiting image

     

    MK

  • in reply to Andy Betts

    Your meter, is this switched for DC_V measure, or AC_V?

     

    Normal on the Base of Q3 you can measure about 3V_DC..,. or a bit more, so 3,4V_DC in respect to GND.

    180(k) / 33(k) = 5.45 -> 18V_DC / 5,45 = 3,302 V_DC bias_V.

    If you don't measure somewhat here, GND -> R_Base, then one of the tracks is broken, or you have a "cold solder", solder is broken.

     

    What do you measure on all transistors?

    B-E, B-C, E-C, and all of them in respect to GND?

     

    Any of the polcaps, are they ok?

    The blue 180k resistor, is this really a resistor, not an inductance?

Reply
  • in reply to Andy Betts

    Your meter, is this switched for DC_V measure, or AC_V?

     

    Normal on the Base of Q3 you can measure about 3V_DC..,. or a bit more, so 3,4V_DC in respect to GND.

    180(k) / 33(k) = 5.45 -> 18V_DC / 5,45 = 3,302 V_DC bias_V.

    If you don't measure somewhat here, GND -> R_Base, then one of the tracks is broken, or you have a "cold solder", solder is broken.

     

    What do you measure on all transistors?

    B-E, B-C, E-C, and all of them in respect to GND?

     

    Any of the polcaps, are they ok?

    The blue 180k resistor, is this really a resistor, not an inductance?

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