Need help with my first Tubescreamer

[mojotron]

One thing I just noticed, I only get readings on the transmitters if I use the ground on the input jack. I get nothing if I use the board ground.

Ok I have to take that part back.  I do get the same transistor readings using the board ground.  Must have been getting sleepy.   :oops:

Here's what I think is happening: based on the initial indications...

And you should check for 0 ohms between all of the components connected to Q1 an Q2 emitter and base(s) - looks like you might have a bad solder joint or open copper trace somewhere in the R9/R10 to Q1/Q2 base.

What this looks like, to me, 2 things that might be going on... a simple cause and a complex cause...

Simple one... Q1/Q2 emitters are not connected to ground... and you are reading voltages that are affected by the meter possibly completing the circuit... make sure the board ground is connected to the ground on the plug, and the - side of the battery - from the picture, it looks like you are missing one ground wire connection on the left hand side of the top picture... check this out and remeasure the voltages on Q1 and Q2... Also pin 3 and pin 2 should be at about the same voltage on the IC/4558.

The more complex situation is that you may be sourcing the voltage for the VR bus from pin 1 on the IC, and perhaps pin 3 as well - but pin 3 is really the base of an internal transistor (inside the 4558) so you're likely not pulling too much current from there.... (this is due to no connection/open some where on the VR bus) But, looking at the voltage at the R9/R10 junction and the higher voltage on pin 2 of the IC, with the lower voltage at pin 3 looks like you are drawing current from either pin 1,2, or 3 on the opamp, causing pin 2 on the opamp steady state/DC voltage to raise due to a current draw from pin 1....

So, you need to check all of the component conections to VR (should be 0 ohms...), including, but not as important, a check on the components that connect to them (such as the Q1/Q2 bases...).

Just a few thoughts... not being there I can't really tell for sure what's going on... but give these ideas a shot...

[murdoow]

ok . . . so i removed Q2 to isolate the problem on Q1, as its connections looked a little dicey anyway.  but am still getting the same readings on Q1:
C=8.0
B=2.5
E=3.2

I have measured resistance between components on the Vr and all traces and they check out ok.  that is, if i am measuring right.  All I am doing is setting the meter on the lowest Ohm setting, 200, and putting tips on either ends of the traces.  it comes up in the range of 0.1-0.6.  i have tried these tests for all things that should be connected; jumpers, the whole ground strip all the way to the jack, etc. . basically i have tested all the runs of traces wherever there is a long strip of copper and they all say 0.  (except one point on the "Collector" rail always says -0.2?)  am i measuring this correctly and (mojotron) is this what you mean by "check all of the component conections to VR (should be 0 ohms...), including, but not as important, a check on the components that connect to them (such as the Q1/Q2 bases...)."  

as far as the ground goes, I have the negative terminal of the battery connected to the ring or middle post of the jack.  the sleeve or inside post is connected to the board ground.  the tip or post closest to the box is connected to the switch.  the parts layout diagram shows another ground going to the dc jack, which i don't have.  instead i have the + terminal of the battery as well as the led-resistor assembly connected to the same point on the board, as shown in the battery only diagram mentioned before.

I have also:
- checked all the parts again and measured all the resistors.  all good.
- reworked any slightly dull joint.
- removed a leg of a diode and checked it out, ok.
- replaced transistor with 2n5088.  

questions:
- the layout says "r6 resistor is standing on end".  i took this to mean it is still connected to both pads but they are spaced so that it has to stand up.
- i am testing the transistors in this way.  meter at 20 volts.  mono plug inserted in input jack.  effect turned on, led lights up.  black tester on jack ground, red on legs of transistor.  
- i am measuring resistance on the traces in the same way, with the meter set to 200 ohms.

ok ok.  so i am about to put this thing in the box regardless of what my meter is saying, as it still is "working", somehow, even with the transistors showing the bias reversed.  if anyone has any last minute ideas, please let me know.  it has turned into a brain teaser now and its driving me nuts!

if all else fails, i bought enough parts to make two of these, and i am going to just put the other one together and see what happens.  whether it  works or doesn't work should answer some questions, (and i am a much better solder-er already).

thanks mojotron and everyone for all the help thus far.

[mojotron]

Well my friend, I'm afraid I'ld have to be there to help anymore - you've done all the right things though - hate to see you get frustrated on this.

If you want you can send it to me and I'll take a look at it - PM me if you are interested - just include enough for return postage. I've been fixing/designing gear since 1980 and I have built/modded a lot of these kinds of circuits - I still have a few around here that I can use as working examples of the GGG circuit too.