Neovibe audio section question

[snoof]

Regarding the Neovibe using GGG board, I can't seem to get audio signal past C18 or C6??  Any idea what could be happening with that??  Checked/replaced both caps.  Could the LDR be loading it down so much that it's killing it??

[oskar]

http://www.diystompboxes.com/smfforum/index.php?topic=29816.0
http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=121&Itemid=26

Regarding the Neovibe using GGG board, I can't seem to get audio signal past C18 or C6??  Any idea what could be happening with that?? 

Need voltages... badly!

Checked/replaced both caps.

First use audioprobe. Two caps failing at the same time doesn't sound very likely.

Could the LDR be loading it down so much that it's killing it??

LDR's don't really go to zero ohm. they are more likely to be around 1k when full on. And even if it would be shorted
you still have c6!!!

skar

[snoof]

I'll have to double check the voltages on the trannies in the audio portion.  I have done all the regular debugging in that area of the crkt, correct values etc.  I have audio probed it, thats how I know that the audio is not passing through C6 and C18.  I can jumper C18 and get very low level audio at the cap side of R35, but nothing on the vol pot side.  I'm continuing to debug, but I just wanted to post just to see if anyone had experienced this(oh yes, def check this specific component cause that will cause what you are describing,etc) sorta thing.

[oskar]

Aha! In that case my guess is shorting c18 provided a path to ground instead of what r8,9 should be up to. check them!

[snoof]

Will double check R8,9.  Would not that kill the sig prior to C18, 6 though if they were bad/wrong value??  I've got sig pre-cap at those two locations.

[oskar]

Will double check R8,9.  Would not that kill the sig prior to C18, 6 though if they were bad/wrong value??  I've got sig pre-cap at those two locations.

And there was me thinking I was clever... 
If you have signal before c18 and not after I can think of only two explanations.
1. The cap is bad,bad,bad... ( polarity? c18 + toward Q3)
2. The dead side of the cap is shorted to ground.

    VOLTS AND OHMS PLEASE!   

[snoof]

OK, upon re-checking voltages on Q3, they were way off.  Turns out it was shot, all better after replacement.  The audio section is fine now!  But, now I can't get Q10 in the LFO to bias up correctly.  B=14v, C=.7v, E=.3v.  Should be 14, 6, and 5.5.    Replaced it, still no dice.  I'm gonna check all the surrounding component values tomorrow.  All other Q's in the LFO read correct voltages.  Man this thing is bear.

[R.G.]

But, now I can't get Q10 in the LFO to bias up correctly.  B=14v, C=.7v, E=.3v.  Should be 14, 6, and 5.5.

I think you have your terminology messed up. There's no condition other than broken that would have an NPN transistor with a base at 14V and collector/emitter both at under a volt.

You know, posting all of the voltages would help a whole lot more, even if it's only the LFO section. Very often the problem lies where you don't expect it, and that's part of the shotgun approach to measurement - it forces you to measure and think about things you'd otherwise miss if you just focus on where you ...think... the problem is.

[oskar]

OK, upon re-checking voltages on Q3, they were way off.  Turns out it was shot, all better after replacement.  The audio section is fine now!  But, now I can't get Q10 in the LFO to bias up correctly.  B=14v, C=.7v, E=.3v.  Should be 14, 6, and 5.5.    Replaced it, still no dice.  I'm gonna check all the surrounding component values tomorrow.  All other Q's in the LFO read correct voltages.  Man this thing is bear.

Q10 is in the filter section, aight?
Do you mean the ( unmarked ) transistor that drives the lamp?
I'm currently eating what we in sweden call knäckebröd.

What are you reading on the supply filter caps?
What transistors are you using?

You know, posting all of the voltages would help a whole lot more, even if it's only the LFO section. Very often the problem lies where you don't expect it...

true

[petemoore]

  Probe is good for finding the general location of signal loss = problem.
 Ohms law finds solutions. Voltage measurements find more exact locations of problems, often the solution pops up in the first sweep.
 

[snoof]

I'll post all the transistor voltages tonight after work.  Thanks for the help so far guys