Debug suggestions/help

[fixr1984]

I'm  having some problems with a ts 808. I made one before using the same layout so I know that its
verified. Problem is low output. Controls seem to work but just very very low output. I have checked for correct
parts and orientaion. No visible solder bridges, all jumpers and track cuts are correct.
The voltage on the IC is most likely my problem as the voltages are off.
I dont want to post all the voltages and say here do it for me but was hoping for places to look so
I can figure it out as much as I can on my own.
Pins 1-4 are reading low by a few volts and pins 5-8 are all with in a volt or 2 of batt voltage. Pin 4 is 0 so i know its grounded

Going by that can you give me any ideas to look at. If my info is too scarce and you want to know everythig I can post it.

PS...I tried search and didnt find anyone with the same problem

[petemoore]

  Take a reading between Gnd. and V+, then one from Gnd. and the voltage divider resistors, it should be about 1/2v of supply V+.

[GibsonGM]

Last week someone had a micro solder bridge at their feedback diodes, and reported exactly the same problem...have you audio probed?

[fixr1984]

Broke my probe, i should probably make a new one
Petemore: using the tonepad schem Here what resistors are the voltage dividers?
Are they the two 10k's on the upper right with one going to ground?
Thanks

[R.G.]

Yes.

[fixr1984]

  Take a reading between Gnd. and V+, then one from Gnd. and the voltage divider resistors, it should be about 1/2v of supply V+.

From gnd to B+ i got 8.79v.
From gnd to source resistors i get 8.79v before the resistor, 2.47v after. and the second resistor I get
2.47v before and 0v after.

Like i said earlier if I'm being too vague I can give all the voltages.

[petemoore]

From gnd to B+ i got 8.79v.
From gnd to source resistors i get 8.79v before the resistor, 2.47v after. and the second resistor I get
2.47v before and 0v after.
  yupp..like this
Battery 9.x
Q1
C  1v
B  52v [lol]
E  0.V
OA1a
1
2
3
4
5
6
7
8
  Readings from all points taken with ground as reference point [0.0 volts]..clip the black DMM lead to ground.
  The power rails are Gnd and V+. These will have the largest voltage.
  10k > 10k resistors, series, strung across the power rails sounds about right...measure the node where the two equal value resistors meet and see 1/2v of supply v there.

[fixr1984]

battery=9.53
10k node=3.18
Q1
C=9.53
B=3.05
E=2.37
Q2
C=9.52
B=2.88
E=2.41

IC
1=3.15
2=3.18
3=3.17
4=0
5=.001
6=8.65
7=8.83
8=9.52

My IC volts are way off and I dont know where to look

[petemoore]

battery=9.53 good start !
10k node=3.18 whoops, somethings touching or..resistance needs measured, this should be about 1/2v.
Q1
C=9.53 [buffer has correct connection to V+]
B=3.05 
E=2.37
Q2
C=9.52
B=2.88
E=2.41 [These transistor buffers probably work, audio probe should hear a 1/1, unity, same sound when applied to base, then collector of a buffer].

IC
1=3.15
2=3.18
3=3.17
4=0   [ok]
5=.001  [hmmm...might need attention after the first order of business.
6=8.65
7=8.83  [these seem 'symmetrically' lopsided [on the other side of bias of /12v from the top three pins by similar voltage amounts]
  First order of business is the node at the voltage divider. Either the divider resistors arent' equal value or something else is pulling it toward ground voltage, do you measure 10k between the divider node and gnd?
 

[fixr1984]

From the node to ground I get 3.90k
both resistors are marked as 10k.

[R.G.]

It is very difficult to test resistances in circuit. All of the other stuff it's connected to appears in parallel with a resistor and messes up the result.

To get a good resistance read, you usually have to unsolder one lead of the resistor.

But you clearly have a problem there. I'd suspect a bad solder joint/short, bad cap or reversed cap at the reference resistors first.

Ask yourself - what would happen in the circuit if pin 5 was accidentally shorted to ground through a solder thread or some such? Would that load down the reference?

[fixr1984]

Ok I pulled the second 10k from ground, together they read 17.9k. when i take a voltage reading with the 10k soldered in
to ground I get 3.14v. if I lift the leg from ground and read the volts I get 4.71v

[petemoore]

what would happen in the circuit if pin 5 was accidentally shorted to ground through a solder thread or some such? Would that load down the reference?
  Pin 5 is dangerously close to ground, readings like that are often when a pin wants to rise above ground, but is pinned to ground.
  What is the continuity or resistance between pin 5 and ground?

[fixr1984]

pin 5 to ground is 715 ohms.

[R.G.]

pin 5 to ground is 715 ohms.

OK, now comes the figuring out part. WHY is it only 715 ohms to ground?

[fixr1984]

Found the problem, I looked up the data sheet to try to find out what each pin did in respect to the
other and from what I could gather the problem was definatly something that was connected thru pin
5 and nothing from another pin. While tracing the layout back from pin 5 to try to locate where the ground or short
was coming from I noticed that C5 (from the GGG layout) had a jumper in its place. C5 connects to pin 4. Ground.
Here is where the confusion as to why this mod is suggested. The GGG mod text Page 5 under the Aron Nelson mods shows to put a jumper in place of C5. Why would you do that? You are shorting it out like what I did. Is that just a typo maybe.

I pulled one leg of my jumper and all my voltages came back to normal so the was for sure the problem.