Need Help Debugging Tycobrahe Octavia

[RightOnMusic]

Here is the checklist to fill out:

1.What does it do, not do, and sound like? doesn't pass any audio at all, not even in bypass.  LEDs don't light completely either.  just a dim hard to notice light from the on/off LED and nothing from the octave/fuzz LED.  i'm bummed...

2.Name of the circuit = Tycobrahe Octavia

3.Source of the circuit (URL of schematic or project) = http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=128&Itemid=26

4.Any modifications to the circuit? N

5.Any parts substitutions? None

6.Positive ground to negative ground conversion? N

7.Turn your meter on, set it to the 10V or 20V scale. Remove the battery from the battery clip. Probe the battery terminals with the meter leads before putting it in the clip. What is the out of circuit battery voltage? => 9.44

Now insert the battery into the clip. If your effect is wired so that a plug must be in the input or output jack to turn the battery power on, insert one end of a cord into that jack. Connect the negative/black meter lead to signal ground by clipping the negative/black lead to the outer sleeve of the input or output jack, whichever does not have a plug in it. With the negative lead on signal ground, measure the following:
Voltage at the circuit board end of the red battery lead = 9.19
Voltage at the circuit board end of the black battery lead = 0

Now, using the original schematic as a reference for which part is which (that is, which transistor is Q1, Q2, etc. and which IC is IC1, IC2, C1, and so on) measure and list the voltage on each pin of every transistor and IC. Just keep the black lead on ground, and touch the pointed end of the red probe to each one in turn. Report the voltages as follows:

Q1
C = 4.96
B = 4.32
E = 2.59

Q2
E= 9.13
B= 2.59
C= 2.03

Q3
E= 5.64
B= 2.44
C= 1.36


D1
A (anode, the non-band end) = 0
K (cathode, the banded end) = 0

D2
A = 0
K = 0

[PRR]

> 2.Name of the circuit = Tycobrahe Octavia

Tycobrahe Octavia Original Schematic
Tycobrahe Octavia Updated, Modernized Schematic
? ? ?

Ah, you say "LED" which is a clue.

> Q1
> C = 4.96
> B = 4.32
> E = 2.59

This looks wrong. It makes more sense if the three pins have been switched-around. However it is similar to the volt-chart posted on the product site.



OK, multiple issues. Your Q1 has the curved-side opposite to the PCB's marking. BUT the GGG page shows a PCB with its Q1 marking going the other way! Do two wrongs make a right?

That does not explain weak LED. Since the raw supply voltage is reasonable (9.19-9.13V), I'm thinking wrong-value or wrong connection someplace. (These are always good bets.) I can't squint those resistor values even boosted out of the shadows, you'll have to re-check the values and the what-goes-to-what.

[RightOnMusic]

regarding the Q1 orientation, i did check my pcb traces vs. the ones on the site and they match so i went with the orientation on the site...  should i try reversing it?

i triple checked each resistor before stuffing the board, but i'll whip out the old meter and check again.  - just checked all resistors and values are spot on.

it just weirds me out that it doesn't even carry signal flow in bypass.  makes me think it's a simple fix, although the weak LED is kind of a disconcerting symptom...

thanks for the feedback!

also - worth noting:  weak LED only occurs when using an adapter.  with only a battery theres no LED on whatsoever.


I GOT IT!!!  i've got my switches oriented 90 degrees off...  gonna correct that and see what happens.  biggest bonehead move ever....

[azrael]

Did you orient the switch the right way? It doesn't sound like it, if even bypass doesn't work.

[RightOnMusic]

Did you orient the switch the right way? It doesn't sound like it, if even bypass doesn't work.

that was problem #1.

i fixed this and now it bypasses audio flawlessly.  however, when i engage the effect, i get a farty distorted (not pleasant) sound that only passes audio above a certain volume and only when the knobs are all the way up.  also, the led is still off except when passing the farty audio.  it acts almost like a signal indicator...

so we've got from totally non functional to poorly functional.  PROGRESS!

any ideas?

edit:  voltages are more or less the same on transistors after switch fix.  and again, resistor values are quadruple checked and electro caps are all oriented properly.  might i need to change the orientation of Q1?

[petemoore]

  Led is like indicator...
  The LED circuit is simple [couple wires, an R, power supplied through switch 'when on'], if it is indicating input levels it is somehow not separate from the audio circuit.
  Verify or at least double check this once with DMM...test the switches before putting them in anyway.
  Looking through 3 eyelet lugs on the left row of a handy 3pdt switch = looking through a throw>pole>throw. There will then be 2 more identical rows of lugs to the right.
  You can tell which way the eyelets go through the lugs because the lugs, when viewed from bottom, are slightly rectangular, the eyelet holes go through between the short sides of the lug/rectangle.
   
 

[RightOnMusic]

you are correct.  check out the parts layout GGG supplies for this project:

http://www.generalguitargadgets.com/pdf/ggg_toct_lo_distsw.pdf

no resistor on LED and its long leg goes back to the pcb....  when i first started wiring up this made me   but i didn't wan't to disobey the instructions.  i mean if their instructions led to a dysfunctional unit, i'd imagine they'd have already gotten many frustrated emails from customers and corrected pretty quickly...

i'm not entirely sure what you're saying about the switch...  i did have the switches oriented improperly originally, but i have since corrected that...  is that what you were referring to?  perhaps i should update my original pic...

[PRR]

The LED is NOT a signal indicator. It lights when you have power and Sw1 is in a certain setting.

> no resistor on LED and its long leg goes back to the pcb.... 

There it runs to R15, 1K, and then over to V+.

The short leg goes to Sw1 and the to ground G.

I hate 3P3T switches. Too many terminals, and too easy to get turned 90 degrees.

The LED flaw makes me think something is misconnected.

Get clip-leads for your voltmeter. Black lead to point G. Now get voltages for BOTH legs of the LED, in bypass, in on-silent, and in on-farting.

OR (different diagnostic): slag the 3P3T switch for now. Wire Input jack Tip direct to point "I", and point "O" direct to Output jack Tip.

> might i need to change the orientation of Q1?

Leave it for now.

For this device pinout, "backward" swaps emitter and collector. Normally it "matters" which is Emitter and which is Collector. The emitter-base junction has higher gain and lower breakdown voltage. However in this application we do not need high voltage or high gain. I'm 99% sure that 99% of '5087s will, in this case, work just as well "inverted" as "correct". If your voltages were clearly wrong, I'd doubt myself. But they are too close to right to be called wrong.

AFAICT, some of the diagrams on the project site ARE "wrong", in that they have E and C reversed. And that may just show that, for this application, that it does not matter. If it was wrong and did not work, customer questions/complaints would have forced a revision or clarification.

[RightOnMusic]

get voltages for BOTH legs of the LED, in bypass, in on-silent, and in on-farting.

bypass led:

Long Leg in Bypass - 1.27
Short Leg in Bypass - 0

Long Leg On Silent - 1.26
Short Leg On Silent - 0.13


octave/fuzz led:

Long Leg in Bypass - 1.27
Short Leg in Bypass - 0.16

Long Leg On Silent - 1.26
Short Leg On Silent - 0.1




in the middle of doing this test, i've noticed several things.

1 - the "status light indicator" behavior ONLY seems to be occuring on the "octave/fuzz" LED when the octave switch is engaged.
2 - the farty noise only happens when the input is driven to hard and can be stopped by turning the pregain knob down
3 - when the farty noise is dialed out, all that passes through is just a weak signal that posses no qualities that even remotely resemble "octave" or "fuzz".
4 - after noticing the above items, i went back to finish testing the LED voltages only to find that my ~1.3 voltages had all now become ~0.7.  Tested the battery again and it was fine.  over 9.

should i even bother continuing this LED testing if the voltages seem to be fluctuating like this?

i'm going to perform your second suggested test, bypassing the switch entirely....  i'll report back.  thanks guys!!!

Reporting back:

ok so i wired the tip of the input jack right to the input on the pcb (this also bypasses the pregain pot) and the output of the pcb to the output jack tip.  i get an unaffected sound.  the volume pot does control the volume, but the intensity knob does nothing.

[PRR]

> unaffected sound.

That's extremely strange. I don't see how signal can pass through, including the volume pot, yet be "unaffected". It's a lot of gain, and then the diodes mangle it.

Re-check your ground wires and joints. The only thing I can figure is that the whole electronics "floats" with signal. But I admit this is a wild guess.

Go ahead and flip Q1. I'm pretty sure it is wrong. But if that changes anything, I'd be more surprised.

[RightOnMusic]

> unaffected sound.

That's extremely strange. I don't see how signal can pass through, including the volume pot, yet be "unaffected". It's a lot of gain, and then the diodes mangle it.

Re-check your ground wires and joints. The only thing I can figure is that the whole electronics "floats" with signal. But I admit this is a wild guess.

Go ahead and flip Q1. I'm pretty sure it is wrong. But if that changes anything, I'd be more surprised.

i'm gonna put the loop on and closely inspect all my solder joints...  i'll let you know what happens after i swap Q1.

also, unaffected is the wrong word.  the tone changes somewhat, but it sure ain't distorting in any kind of musical or even significant way.  and there's no octave either.  the tone also changes a bit when i hit the fuzz/octavefuzz switch, but it's hard to describe how.  it's subtle and, again, nothing in the ballpark of the intended purpose of the pedal.  would posting sound samples help?