Help with Scrambler

[foozertone]

Okay I'm stuck with a scrambler from the GGG layout. I have bypass but no sound with the effect on. Hopefully someone can see something?

Batt: 10.06
brd:9.79

Q1 E:9.27     Q2 E:0.28     Q3 E:9.40     Q4 E:7.14
     B:9.33          B:0.94          B:9.81          B:7.72
     C:9.88         C:3.72          C:9.81          C:8.42

All Q's are 2n5306 except Q2 is 2n3904
Hopefully This means something to someone.


Thanks
Jeff

[foozertone]

Can anyone help?

Thanks

Jeff

[PerroGrande]

Q1 has got issues, most certainly. 

Q1's collector voltage looks good, as the schematic indicates that this is connected directly to V+.  However, the base should be around 4.5 volts (it is biased via two 1M resistors in a voltage divider), and I would expect around 3.2 volts on the emitter of Q1. (Q1,3,4 are darlingtons, thus the larger drop Vbe).

Oh -- and make sure you have the pinouts correct on those 2N5306 transistors!  With the flat side up, the pins are (from left to right) E-C-B.  (Double check this with the data sheet).

So -- start by checking the orientation of all three 5306 trannies.  Then lets work on getting the right voltages to Q1 and go from there.  The other ones look wrong, too, but let's get one thing at a time done...  Improper orientation *could* explain a LOT of these issues.

[foozertone]

Thanks so much for your help. I can't believe it but I've spent like two months looking at those transistors and thinking the pinout was E-B-C when you have clarified that it is E-C-B!! I feel a little dumb right now. I'm getting a new iron tommorrow so I'll be able to redo those q's (assuming I haven't trimmed the leads too much when I initially soldered them in.) I'll get back to you if I still have trouble. Thanks alot for your insight.

Thanks

Jeff

[foozertone]

Okay I found an old iron to use (I've been waiting 10 days and at least 2 more days for a new one from Electronix express,) and I turned around the transistors to their proper orientation. Now, not only do I have bypass but I get seemengly unaffected signal. The txture knob does nothing and the blend doesn't do anything until it gets close to max, at which point it goes out and I get silence. I'm hoping one of you can help me sort this out.Here are my new readings.

Q1:E=3.91    Q2:E=0.28     Q3:E=1.06    Q4:E=1.09
     B=9.85          B=1.07          B=1.94         B=1.78
     C=9.88          C=3.71         C=9.87         C=1.27

I really apreciate any help.

Jeff

[PerroGrande]

The base of Q1 is out of whack.  It should be around 4.5v with no input signal.  Check the wiring -- there are 2 1M resistors that should form a voltage divider.

The base of Q2 looks low -- would expect more like 0.65v.

Emitter of Q3 and Q4 should both be around 4v.  Q4's collector looks off, too -- should be around 8.2. 

But let's get the base voltage of Q1 fixed first and go from there.

[foozertone]

I'm sorry to be so ignorant but what am I exactly looking for? All the parts seem to match the layout. I've checked all the points for continuity and they seem good. Also what area am I looking at for Q1? Sorry again and thanks also.

Jeff

[PerroGrande]

Jeff,

No problem -- we'll keep working on it until it rocks!   One of the biggest problems is continuity where there shouldn't be continuity -- a solder bridge, a lead soldered to the wrong trace, etc, etc.

Q1 voltages should be something like:

E: 3.5v
B: 4.5v
C: 9v (or whatever your battery actually reads -- 9.88 perhaps, based on your previous post).

Your base reading is unexpectedly high, and leads me to believe that there is a wiring error, or a glob of solder somewhere that is causing it to read an abnormally high voltage on the base.  The base is reading essentially the same as the collector, which is not good.

One thing to do -- remove the Q1 transistor from the circuit (if you used sockets, of course), and check the base voltage at the socket.  If it reads around 4.5, you *probably* have a bad tranny.  On the other hand, if it reads high (9v), you've got a wiring error.

[foozertone]

Well Q1 wasn't socketed but I yanked it out anyway. My new readings are E & B = 0.00  and C= 8.88. I can see there's a problem but I can't seem to find it. Any thoughts? I'm  still plugging away, checking everything over but I don't know (beyond cold joints or blobs etc) what I'm looking for.

On a side note, am I right by saying a resistor read from end to end, you get no continuity. Is this right?

Thanks

Jeff

[PerroGrande]

A resistor has resistance, so with a simple continuity checker, depending on how the meter is set up, might read open or closed depending on the resistance.  To check a resistor (they almost never go bad unless they get overheated or smashed), you need to set your meter to the correct range and measure -- then you should see the actual value.  This usually requires the resistors to be out of circuit for it to be accurate.

What did you use for your layout?  Vero board, perf board, circuit board? 

[foozertone]

I used a PCB and GGG's layout

[PerroGrande]

Is this board one from GGG, or did you etch it yourself? 

http://www.generalguitargadgets.com/diagrams/scrambler_lo.gif

Is this the correct layout to work from for additional testing?

[foozertone]

I'm using that layout and a board purchased from GGG. Thanks for going the extra mile to look up the link. I couldn't figure out how to tack it onto a post. Thanks.

[PerroGrande]

Okay -- time to go to  work with the voltmeter.

While you still have Q1 out of the circuit, let's take a few measurements.  With the board oriented the way it is in the link (R2 in upper left) and the circuit on with the input quiet (shorted):

Put the black lead on the lower side of R1 or any other good ground location.  Measure the voltages at:

Top of R2
Bottom of R2
Top of R3
Top of R8
Bottom of R8
Top of R12
Bottom of R13
Top of R13

Re-install Q1 and repeat the same list.

Also -- check the orientation of the larger caps that are polarized. (C2-C3-C4-C5-C6-C7) -- make sure they're in the correct way.

[foozertone]

Okay here are my readings

          Q1out        Q1 (in)
R2 (top) 9.19  /   9.15
R2 (bot)8.30   /   8.26
R3(top) 0.00   /   9.14
R8(top) 1.05   /   1.04
R8(bot) 9.21   /  8.63
R12(top)9.20   /  9.16
R13(top) 1.18   /  1.16
R13(bot) 1.17   /  0.00

also mytranny read E:8.57   B:9.14   C:9.15

Thanks for the help

Jeff

[PerroGrande]

Carefully check the connections and traces around R2 and R3.  Make sure there aren't bridges, breaks, damaged traces, etc, in this area.  Also make sure that you have installed the correct resistors in these positions.  They should both be 1 Meg (Brown, Black, Green).

Do the same checks with R12 and R13.  In this case, the two resistors should both be 220K (Red, Red, Yellow). 

You're not getting the correct voltages out of what should be basic voltage dividers.  This can be caused by bad connections or incorrect values installed.

[foozertone]

Okay here's what I've done

First I replaced the transistor in Q1 because it read a short and now it reads  E:0.00   B:0.93    C:9.31

Then I checked r2 and found one end unsoldered so I fixed that

Then on of the leads was undersoldered on R13 so I fixed that.

So now my readings are

R2T:9.31
R2B:0.93
R3T:0.93
R8T:1.30
R8B:9.30
R12T:9.31
R13T:1.30
R13B:0.00

Am I making any progress?
Thanks for all the help.

Jeff

[PerroGrande]

Did you check the resistance values?

[foozertone]

I don't know how to read resistance. No idea.

Thanks

Jeff

[PerroGrande]

Via the color codes -- did you verify that you have the proper value resistor installed in the correct location?

For example, R2 and R3 should be 1 Meg -- colored stripes should be Brown - Black - Green.