Fixing a modded Boss DS-1

[FurnaceRocker]

Hey I am having some problems with my Boss DS-1 (has a Keeley Seeing eye/ultra mod).  I did the procedure based on what Aron posted for debugging pedals.  The pedal was not modded by me, so I can't be sure how closely the person doing it held to the circuit in the link, but I pointed out the differences I noticed.

1.What does it do, not do, and sound like?  Sounds good sometimes, but other times has a huge volume drop (even when it's off), seems to be after I've been playing for a little while (maybe a transistor overheating or something with the bypass?)
2.Name of the circuit = DS-1 with Keeley "Seeing Eye Mod"
3.Source of the circuit (URL of schematic or project) = I bought the pedal after the mod had already been made.  As far as I can tell this is the schematic http://www.diystompboxes.com/DIYFiles/up/Build_Your_Own_DS-1_Distortion.pdf Under "Seeing Eye"
4.Any modifications to the circuit? Y or N Listed above
5.Any parts substitutions? If yes, list them.  C1 is a film cap instead of mylar, and apparently they didn't install the diode coming out of the SPDT switch going into the LED on the front, D5 is a red LED.  There also appears to be a capacitor over where D6 is supposed to be, and the diode is coming out from that.
6.Positive ground to negative ground conversion?  I think positive
7. Voltage at the circuit board (no battery) end of the red battery lead = 0
Voltage at the circuit board (no battery) end of the black battery lead = 0
Voltage at the circuit board end of the red battery lead =9.1V
Voltage at the circuit board end of the black battery lead =0V

Q1
C =9.32
B =3.978
E =3.557

Q2
C=4.292
B=.608
E=.012

Q3
C=9.22
B=3.448
E=3.144

Q4
C=.048
B=.001
E=.646

Q5
C=.028
B=.001
E=.627

Q6
S=4.498
G=.081
D=4.493

Q7
S=4.501
G=.084
D=4.509

Q8
S=4.482
G=.007
D=4.505

IC
P1= 4.509
P2= 4.509
P3= 4.449
P4= .001
P5= 4.515
P6= 4.497
P7= 4.493
P8= 8.97

D1
A (anode, the non-band end) = .001
K (cathode, the banded end) = 8.95

D2
A = 6.358
K = 8.87

D4 (the one going to the switch side without the LED on it)
A = 4.42
K = 4.182

D5 (LED)
A = 4.42
K = 4.432

D6
A = .01
K = .043

D7
A = .087
K = 5.418

D8
A = .001
K = 4.365

LED
P1=4.402
P2=4.155

Thanks in advance to anyone who helps!  It seems to fail at the worst possible moments (i.e. when I am playing for church or something).  Thanks to this being the Christmas season, I may not be able to respond very quickly, but should be able to respond by New Years at the latest, so if there's no responses for a little while that is why.

Thank you!

[PRR]

Welcome.

> Q4
> C=.048
> B=.001
> E=.646
> Q5
> C=.028
> B=.001
> E=.627

These can't be right. E is hard-grounded and must be "zero", so that's just a pinout mixup. But you expect one C to be "high" (above 5V) and the opposite B to also be near 0.6V; the other C and B way-low. Tapping SW1 should give the same voltages but on the other transistors. Here we have ~0.6V twice on the same pin Q4 and Q5.

I would expect real problem getting any signal through?

As this may relate to the mod cap near D6, I am not sure what to think.

[Rob Strand]

Q4
C=.048
B=.001
E=.646

Q5
C=.028
B=.001
E=.627

Q6
S=4.498
G=.081
D=4.493

Q7
S=4.501
G=.084
D=4.509

Q8
S=4.482
G=.007
D=4.505

Besides the issue PRR pointed out the part of the circuit around Q4 and Q5 definitely has a problem.    When the collector voltage of one of these is 0V  the other should be over 7V.

Since Q4 drives Q8, and Q5 drives Q6 & Q7, the problem can also be seen in the gate voltages of Q8, Q6, Q7.  They are all at 0V.

[FurnaceRocker]

Ok, so I measured the voltage at R30 and 31, and they are showing 9V, with pretty much nothing on the other side (Q4 and 5 collector), so about a 9v drop across those resistors.  Looking at the schematic, that indicates that the problem would probably be either Q4 and 5, or C10 or 19 shorting to ground?  More likely the transistors? 

The low voltages on the other gates could probably be because of the shorting in that area.  Is that all correct?  I'm still new to electronics, but I think I'm starting to get it.

[Rob Strand]

We need to rewind a bit.  (I'm a bit confused on a couple of points.)

From PRR's post:   there's an issue with the B and E voltages.   B and E looked swapped.  Is this just a typo in your results?   or is it really like that?  If you have wired B&E in reverse it's not going to help.   
Can you re-check the measurements and pin-outs?

There's a few weird things about your first measurements:

- Both E's (or B's) are sitting at 0.6V.  Only one should be at 0.6V.

- C of Q5 is at 0V, this connects to D7, but the cathode of D7 is at  5.418 and this connects to Q5.C via the 1MEG.
(The anode of D7 is at A = .087V and that goes to the gate of A6 and Q7 which is at the same voltage - which does seem to be consistent.)

So these two points don't make sense.

One thing you can do is to look for shorts on the board in the area of Q5.

[PRR]

> Only one should be at 0.6V.

This assumes he does not touch SW1 between readings.

[FurnaceRocker]

Ok, so I'm going to remeasure those two, thanks.

Q4
C=.047
B=0
E=.646

Q5
C=.028
B=0
E=.017

Realized that PRR was right, I was turning Q5 on when measuring C  , so E was the same on both of them.  I checked these with the datasheets to make sure that I had the right pins for everything, and these should be correct.  From looking at the schematic, I guess the two transistors must be backwards (the emitters are connected on the schematic, and here the bases are connected). That could explain the problem, but does it explain how the pedal has worked before?

[Rob Strand]

Realized that PRR was right, I was turning Q5 on when measuring C  , so E was the same on both of them.

OK cool.

I guess the two transistors must be backwards (the emitters are connected on the schematic, and here the bases are connected). That could explain the problem,

Yeah looks like the problem.  It's certainly not helping the cause!

but does it explain how the pedal has worked before?

Pretty weird.  ATM,I'm too tired to do the mental gymnastics to work out why!
(Maybe the gates of the FET switches were floating.)

[FurnaceRocker]

So I flipped the transistors, and apparently they were on there properly, because now it won't turn on The data sheet I was using had a few extra letters that the bjt's on my pedal didn't have, so maybe it's an old one or something (couldn't find one with the exact lettering).  I checked the voltages on the transistors, and the collectors were sitting at 6V and the bases (where the bases are supposed to be) had about 2.5V, and the emitters were still at 0 (connected to ground).

Does this point back to the bjt's needing to be replaced or something else shorting to ground, based on the voltages from earlier (using the earlier posts to look at the voltages)?

Thank you guys!

[Rob Strand]

o I flipped the transistors, and apparently they were on there properly, because now it won't turn on The data sheet I was using had a few extra letters that the bjt's on my pedal didn't have, so maybe it's an old one or something (couldn't find one with the exact lettering).  I checked the voltages on the transistors, and the collectors were sitting at 6V and the bases (where the bases are supposed to be) had about 2.5V, and the emitters were still at 0 (connected to ground).

Something wrong here.  There seems to be some uncertainty about the transistor pinout.
Sometimes the datasheet is confusing for example it's not clear if you are looking up under the device or down through the device.

Maybe you need to workout which pin is which using the DMM:
- set the DMM to diode test mode
- By trying pairs of pins, find the pin such that when you have the +ve probe on it
  you get a reading of about 0.7V when you connect the -ve problem to each of the other pins.
  That pin is the base.
  (I'm assuming here that you meter gives a diode voltage reading on a diode with the +ve probe
   connected to the anode.   If it's not like that you meter is reverse for some reason or you have PNPs.)
- Now out of the two pins one of those pins will give a higher reading than the other.  That one is the emitter.
- So by default the last one is the collector.

You need to test the part out of circuit (especially the E C identification).

If after that, you think it was OK before, put it back that way.  Then maybe remove the on/off LED in case that part of the circuit is causing trouble.  Then re-check the voltages.  Also see if pushing the switch can make the collectors go off/on.

[FurnaceRocker]

So I tested the transistors, and the original way that they were was correct.  Poking around it looks like all the measurements from the original testing should be correct (with the exception of Q4 and 5 B and E being backwards, and the modification from the second).  Touching the collectors does turn the circuit on and off.  Do you have any advice about finding why the collectors are low?  I have a multi-meter and I'm not afraid to use it

[Rob Strand]

Touching the collectors does turn the circuit on and off.

In what way are you touching them?

It's a simple circuit.  It doesn't take much to stop it working.
It also doesn't take much to to put me on the wrong path - that's just how it is with this remote debugging stuff.  What takes 5 mins can take 5 posts back and forth!
I guess we need to recap.

The first question is do the collector voltages of Q4 and Q5 change when you press the foot switch?   When one is on we want the other to be off.

So try this:
1) Measure the collector voltage of Q4, measure the voltage at R32 (the C20 side).
2) Click the foot switch
3) Measure the collector voltage of Q4, measure the voltage at R32 (the C20 side).
4) Measure the collector voltage of Q5, measure the voltage at R33 (the C21 side).
5) Click the foot switch
6) Measure the collector voltage of Q5, measure the voltage at R33 (the C21 side).

Normally the collector voltages are 0V or about 6V.

The aims here are:
- work out if the collectors are changing
- are the collector voltages normal? (if not then they won't drive the JFET switches properly)
- is the collect voltage at least getting to the next part of the circuit (ie. to the cap/diodes)
- *** if you want, and if things look OK upto this point, check the voltages on the JFET side
  of D6 and D7 for all four cases.   This way we can see if the voltages are getting the next stage further.

If we can work out this much we are on our way for sure.

[FurnaceRocker]

Sorry it took so long to respond, got slammed with work, hopefully I'll have some chances to work on this now...

In what way are you touching them?

With my meter's probes.

The voltages change when I hit the pedal/touch the transistor's collectors.

So here's the voltages
1. Q4 is .047V, R32 is .043
3. measuring Q4 is going to switch it again (it will be .047), so I'm going to skip this measurement. R32 (with pedal off) is5.506V
4. Q5 is .028V, R33 is .026
6. R33 jumps around, but it's about 5V

So the collectors are changing, I'm not sure though if the 5ish volts is enough to drive the JFET switches, but I would think it would be (not a whole lot more you can put on them from a 9V battery).

With the pedal on
D6-.074
D7-.013
With pedal off
D6-.01
D7-.06

Is that high enough to be considered "getting to the next stage?"

[FurnaceRocker]

And super sorry for taking so long, I should have some more time after next week to give some more time to this project!

[FurnaceRocker]

bump

[alphahot1]

Hi, I know it's an old thread... but I have exactly the same symptoms! I also have very similar reading for Q4 and Q5, I didn't measure anything else because that thread went nowhere... does anybody have any clue? or is willing to help?
Thanks!!

[alphahot1]

ok guys maybe it could be useful to someone... my problem was that I was randomly loosing a bit of volume and I had a lot of crackling almost as the input wire wasn't properly connected and in fact... I disassembled everything and the brown input wire snapped off. The pedal is an old one so probably when it was opened after a lot of years the wire started to getting loose...