What to do when it doesn't work

[RjM]

OK. We have a sample case.
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1.When I turn it on, the volume is cut in half. The gain knob is unresponsive, and the volume pot does work.
2.Dragonfly's Sparkleboost
3.http://www.diystompboxes.com/sboxforum/viewtopic.php?t=28818 ; http://img.villagephotos.com/p/2004-7/770357/SPARKLEBOOSTPERF.gif
4.No mods

OK so far. But

5. 3K9 subbed for 2K7, 10K pot for 5K,2.4M for 2.2M, MPF102 for NTE458, no indication LED

As I said, the first question I'll ask is if you checked the pinout of the subtituted part against the original.

I did. See http://pubpages.unh.edu/~aperkins/pdf/MPF-devices/MPF102.pdf for the datasheet, and notice that whether or not the MPF102 and the NTE458 are the same pinout, the MPF102 is pinned GSD and the layout is for SGD. If it is wired exactly like the layout, the gate and drain are reversed.  A quick look at the NTE458 has the SGD pinout.

Did you allow for that when you wired it up?

6.No
7.No battery

? You need a battery. Does this mean that you are powering it from a DC adapter in spite of the admonition to use a battery?
Also, you have not supplied the voltages of the red and black wires from (what should be) the battery. These are important, as they verify that the battery voltage has made it onto the board OK. We really need that info.

Q1;MPF102
D = 4.78 (its as close I could get it, it should be 4.5v)
G = 0.06
S = 2.02

Hmmm... I'm trying to think what would happen in that circuit if the gate and source were reversed. It ... might... give you those voltages.  

Meter set to 20k ohm; no power to circuit for these measurements
D = 4.24
G = 0.76
S = 4.09

I'm not sure why you did these. I only asked for voltages. Good commentary though - I'l clarify that.

So - can you check the things where I asked for more?

Here's the info I forgot to put in there.


DC jack voltages(yes, I am using a wall wart....  :roll: ) If you really think it'll make a difference, I'll wire up a battery clip and put in a fresh battery later.

positive wire to board- 9.53v
negative lug(s)-0.00v

I swapped the S and G so I wouldn't have to modify the circuit for the MPF102, so yeah, I checked and confirmed the pinouts.

I'm just not quite sure why I don't have a voltage reading for the Gate leg. I don't know if it is good or bad. The power supply seems to be fine. It should be, I bought it brand new about a week or two ago.

[petemoore]

Hope I'm not reapeating something .
 Continuity check between V+ and V- or ground. This one'll tell if you have a Prob right away, and's a real battery saver. If you have continuity here, do not connect the battery.

[RjM]

Hope I'm not reapeating something .
 Continuity check between V+ and V- or ground. This one'll tell if you have a Prob right away, and's a real battery saver. If you have continuity here, do not connect the battery.

I'm not sure what that means or how to go about doing it. Continuity check... is that just to make sure everything is grounded correctly or something? Where do I touch the probes of the multimeter, what readings am I looking for, and what do I do when there is no continuity?

[Tony Forestiere]

When I go to  www.JoesToplessBurgerAndEffects.com , I get "page cannot be found" Hmmmm? :roll:

Continuity is a resistance check between V+ and ground. Put your meter on the Ohms setting without a power source, go between V+ and ground, and see if you have a low (or zero) resistance. This will tell you if there is a voltage supply short.

[The Tone God]

I like to suggest a few more additions to R.G.'s outline.

If you are using any ICs specify the FULL part number. For example don't say 4013. Is it a CD4013, 74HC4013, HFE4013, GD4013, NTE4013 ?

If there are no modifcations made directly to the circuit but extra external circuitry beyond the standard wiring make mention of it. Is there a Mill. 2 bypass ? Did you put in a internal power supply ? Did you install an external foot control jack ?

Mention if this is the first time you are building this circuit or if this is another one you have made that has develped a problem.

Perhaps include your experience level as well so as to know how much detail information may be needed. Are you a first time builder, built a few things but are still a beginner, intermediate, etc. ?

Include what debugging you have done to this point to reduce replys covering what you already have done. Have you checked your pinouts ? Have you checked for shorts or bad soldering with your DMM ? Have you checked all your resistors are of the correct value (if needed use your aformentioned DMM too make sure) ?

Just a few thoughts and suggestions.

Andrew

[R.G.]

Since what we're after here is the principles I've set up the thread
"debugging the sparkle boost" for this one problem.

RJ - the ohmmeter setting on your meter will tell you how much resistance is between any two points. If it's 0 or almost 0, you may assume that they're shorted, either accidentally  or on purpose. That's what is meant by "continuity testing" - set to low ohms scale and use the meter to look for what is dead shorted.

[R.G.]

Sparkleboost:
By the way, start looking for why the gate is showing too low a resistance to ground. Is that "1M" resistor really a 1M? Is there a solder short under the board, stuff like that.
I forgot to tell, but I subbed a 820k for the 1M.... wait.... HAHAHAHAHA!!!! I accidentally subbed a 820 ohm for the 1M... definately way too low! Oh man, you called it.

Odd Green Ringer voltages:
Again, this fits with the analysis that Q2 is being turned off by Q1. I think your problem is a short or something making that 18K in Q1's collector look like 0 ohms.
well, im awe struck... amazing.
my lack of understanding lead me to stare at the q2 instead of what you suggested.
Rechecking the 18k resistor... for some reason it wouldn't hold its resistance... it would be full value for a second, then go to nothing...
i replaced it and fired it up.

[jimbob]

What to do when it doesnt work? Drink a few more beers, play your guitar, more beers, then go back and  giver another try. Repeat if needed. This all IS for fun. At least for me anyway.

Goodluck

[dpresley58]

I'm trying to do the RG mods on a TS10, but I don't think this is the place for the post.

Moving it to a seperate thread.