HELP DEBUGGING - BLUE MAGIC !! PLZ HELP

[solarplexus]

Hi there,

I got a blue magic assembled and it plain does not work. 

1.Name of the project: Blue Magic
2.Links to the source of the project: http://www.generalguitargadgets.com/index.php?option=content&task=view&id=25&Itemid=55
3.Some candid admissions about how closely you followed the suggested layout: Bought the PCB from GGG
4.Used Same Parts
6.What it does and does not do how it works:  The LED lights up with DC and Battery.  The trimpot has no voltage.  The volume knob does increase/decrease the hum, I read voltage at C3, C8a, C8b, C10, D1, R1, R6.  Voltage approx 9 volts.  Tested with a fresh battery.  NO VOLTAGE on Q2, 0.3 or less on Q3.  Tried to change Q2 to a MPF102, no changes.  Bypass works perfectly, no sound when engaged, sound goes through when in bypass.

PLEASE help me I am incapable of finding what is wrong... I used some old wires, could that be that one wire is torn up or something I don't know anymore!

The most frustrating is... I build a BSIAB II a year ago without flaws... and I can't build this! OMG! 

Thanks for ANY help you can provide!

Matt

[brad]

transistors are back-to-front?

[solarplexus]

Nope, the transistors are soldered correctly...

[petemoore]

NO VOLTAGE on Q2, 0.3 or less on Q3.
  What resistances do you read between say q3 drain and V+, same for Q2, and their gates, check that these values are about what the schematic says.
  If one is smaller value than they should be, see if there's another current path through the circuit on the schematic throw'ing the reading off...

[bent]

i got the same problem when building the mxr compressor, so i tcheck every resistor and realize that futurlec send me 5k6 instead of 56k (and was write on the bag 56k) so i replace it with a a 56k and the problem was solved...

so tcheck back every resistor , what i done i took a same resistor that the one on the board and read it with my meter, until i found the error....

good luck

bent

[solarplexus]

Do you think it's one of the input resistors or that maybe it is a resistor in the later part of the circuit?   Could it be a cold solder (although my soldering skills are quite good) ?

[petemoore]

What resistances do you read between say q3 drain and V+, same for Q2
  This can be tested by clipping the DMM in R mode to battery clip V+, then touching the drain, doing it this way also tests the continuity of the connections' between RDrain and drain as well as the drainR to V+.

[solarplexus]

ok I just checked the resistances... and I got R5, R8 and R9 that gives me no reading at all... could that be that they are not soldered properly or that they are just not working??

[petemoore]

  You have the DMM set to R Range, 20k for resistors less than 20k value, 200k...
  grab a resistor and see if you can get a reading, wiggle the dial?
checked the resistances... and I got R5, R8 and R9 that gives me no reading at all
  Unless they're shorted, ie a connection between the two ends of the resistor...or the DMM isn't reading resistances, with one probe at each each end of one resistor, on it's leads...the chances of three open or closed resistors is "impossible'
  I would taste the battery in the DMM.

[solarplexus]

I rechecked the resistances, they are fine.

Ok... let's say that I put my DMM on 10v DC.  And let say I try to get a reading from J1 tip to Switch lug... in all logical sense... should I get some kind of reading... cause I get nothing, but what I do get, is a reading from battery to DC jack input, and the LED lights up correctly, and the bypass works correctly... I don't know anymore...

any help?

[aron]

You need to put the black lead on ground and measure with the red lead on the board points. Set the meter to DC and then measure and write down the voltage on each leg of each transistor and tell us what you measure.

[solarplexus]

(BS170) Q1:

S: 0V
G: 0V
D: 5.7V

(J201) Q2:

G: 0V
S: 0,8V
D: 4V

Something is definitely wrong lol!

[Rafa]

Which value did you use on the first capacitor?? I built mine using mpf102 so Ihad to change it for a much larger one I tihnk 0,41 instead 0,01
Cheers
Rafa

[solarplexus]

I used the stock value 0.001 uF

[solarplexus]

... anyone?

[Rafa]

Its not a hughe peal so I would do this: 1) chek caps and resistors values with the schematic (sometimes I chek it man times and I keep on making the same mistake)                 
                                                         2) Check all solders
                                                         3) Check Transistors power supply and pots
                                                         
Cheers

Rafa

[solarplexus]

So you think that it might be just a bad solder or a value that is not right ?

[solarplexus]

Does the Q's reading help at all to see what is wrong with it?

[petemoore]

So you think that it might be just a bad solder or a value that is not right ?
  That...yupp...and those Dern Jfet pinouts are a good %age of troubles with Jfets..mosfets too, certainty of the exact transistor and related data sheet, this is NPN...so polarity of the Q's in question needs to be right.
  Does the Q's reading help at all to see what is wrong with it?
  Yes
  (BS170) Q1:

S: 0V
G: 0V on the gate means signal path = Gnd. = 0volts...all signal shunted
D: 5.7V
   I'd have to check my mosfet knowledge at the door though..but would check for continuity bewteen gate and ground...[if found then eliminate it], then apply the meter all-ways to the bias network.

(J201) Q2:
G: 0V
S: 0,8V 
D: 4V

  Q2, a Jfet, It's source above emitter, drain with room to move up/down in voltage without running out of supply...my guess is signal injected to it's input [gate] and monitoring it's output would say it's working.
 

[solarplexus]

Thanks pete!  I'll try to figure out what happened... I suck at this though