ROG EA Tremelo issues...

[Dragonfly]

hi guys,
 maybe you can help me out. i built the ROG EA tremelo today, using the layout posted on www.runoffgroove.com . well...no go ! as some of you know, i'm pretty "anal retentive" regarding my builds, and im pretty positive that it is exactly as the layout shows...i counted holes on every part...TWICE !

 anyway, no flashing led, no tremelo sound, though it does boost the signal quite a bit. below are the voltages of the battery, Q1, Q2, and Q3 . obviously no voltage is getting to Q2, so my assumption is that the problem has to lie between Q1 and Q2...i have voltage up until the positive side of the 22uf capacitor (1.24v), but no voltage shows on the negative lead or the drain of the mpf102 (Q2) . i changed the 22uf cap...no go. ive checked the orientation of the electros time and time again. ive verified the pinouts on all transistors. right now im stumped. i'll post the voltages in hopes that you guys might have some ideas as to what the problem(s) might be. if necessary, i also have top and bottom photos of the board that i can download.

thanks in advance,
   andy

VOLTAGE READINGS[/color][/b]

BATTERY: 9.56V

Q1:
DRAIN      4.66V
GATE        3.35V
SOURCE   1.42V


Q2:
DRAIN    0V
SOURCE  0V
GATE      0V


Q3:
COLLECTOR  .13V
BASE           .11V
EMITTER       0V

[RDV]

Pinout of Q2? & 3?

RDV

[Dragonfly]

Pinout of Q2?

RDV

checked....DSG....    :?

[Dragonfly]

& 3?

RDV

checked as well  :?

[R.G.]

Mother Nature is telling you, but you don't understand what she's saying.

You're getting signal boost - good! That means Q1 is working properly, a fact that is buttressed by the voltages being reasonable for a MOSFET as a linear amp (See "Designing and building your own MOSFET boosters" at GEO for the techie background.)

Mother's not saying much about Q2 other than that's what would be happening there if the LFO was not running - so we'll take that as a hint from Her and got to Q3.

Let's review:
For a bipolar transistor to work as a linear amplifier (even inside an oscillator) it has to have its base-emitter junction forward biased by the characteristic junction voltage of the material, and there has to be enough voltage left between collector and emitter to do some swinging around.

For an NPN - like Q3 - that means the base has to be 0.5 to 0.7V more positive than the emitter, and that there has to be some significant voltage left between collector and emitter.

The voltages say:

Q3:
COLLECTOR .13V
BASE .11V
EMITTER 0V

Which does not satisfy either condition. How can this be?

Well, there are some clues. If all three were 0V, there would be an open circuit to the +V. There is some voltage, however, it's too small for the collector-base bias resistor to bring the transistor into conduction. That implies that there's too big a resistance between collector and +9 to turn things on. If you have indeed wired it *exactly* per the layout, this could not be happening, so maybe Mother Nature is trying to give us a lesson in observation.

There are only two components, two wires, and seven solder joints between +9V and the collector of Q3. One of the solder joints could be high resistance. One of the wires could be almost-broken just inside the insulation. More likely, the LED could be wired backwards, or the 10K might be a much bigger value. I suppose the LED could be damaged in a high-resistance manner, but that would be very unusual.

Maybe what Mother is really telling us is that if we poke at each junction along that path from +9V -> 10K -> LED+ -> LED- -> colletor, we'll find the place where the voltage takes a sudden bigger than expected drop, and if we dig there, we'll find oil... er... the problem.

[pbrommer]

Can I say one thing?

For a diagnosis of a circuit, and involving quite a bit of 'techie' knowledge, that made perfect sense. It was clear, concise, and in freakin' English... Either - A) I've learned something or B) R.G. just put something into words that made sense (at least to me).

Again, thanks guys for all you do. And Dragonfly, good luck. It's always the simplest thing that gets you.

[Dragonfly]

Mother Nature is telling you, but you don't understand what she's saying.

You're getting signal boost - good! That means Q1 is working properly, a fact that is buttressed by the voltages being reasonable for a MOSFET as a linear amp (See "Designing and building your own MOSFET boosters" at GEO for the techie background.)

Mother's not saying much about Q2 other than that's what would be happening there if the LFO was not running - so we'll take that as a hint from Her and got to Q3.

Let's review:
For a bipolar transistor to work as a linear amplifier (even inside an oscillator) it has to have its base-emitter junction forward biased by the characteristic junction voltage of the material, and there has to be enough voltage left between collector and emitter to do some swinging around.

For an NPN - like Q3 - that means the base has to be 0.5 to 0.7V more positive than the emitter, and that there has to be some significant voltage left between collector and emitter.

The voltages say:

Q3:
COLLECTOR .13V
BASE .11V
EMITTER 0V

Which does not satisfy either condition. How can this be?

Well, there are some clues. If all three were 0V, there would be an open circuit to the +V. There is some voltage, however, it's too small for the collector-base bias resistor to bring the transistor into conduction. That implies that there's too big a resistance between collector and +9 to turn things on. If you have indeed wired it *exactly* per the layout, this could not be happening, so maybe Mother Nature is trying to give us a lesson in observation.

There are only two components, two wires, and seven solder joints between +9V and the collector of Q3. One of the solder joints could be high resistance. One of the wires could be almost-broken just inside the insulation. More likely, the LED could be wired backwards, or the 10K might be a much bigger value. I suppose the LED could be damaged in a high-resistance manner, but that would be very unusual.

Maybe what Mother is really telling us is that if we poke at each junction along that path from +9V -> 10K -> LED+ -> LED- -> colletor, we'll find the place where the voltage takes a sudden bigger than expected drop, and if we dig there, we'll find oil... er... the problem.

spot on, exactly 100% correct...the led was wired in reverse...works fine now !!!!

RG...you da man !



thanks again....makes me glad i posted those voltages !!!