Tourbus Troubles (the bus burned down)

[freshmex18]

Had a working Tourbus pedal.  Been a few months since I used it.  Built a new pedalboard.  Plugged it into the same 18V plug on the OneSpot power supply on the new board.  Noticed the pedal ticking in bypass.  Opened it up to take a look and adjust the trimmers to see if I could get the ticking to stop.  After a while, a tiny puff of smoke from the region of the 4047 IC.  Panic ensues.  Cut the power.  Removed daughterboard.  Could not confirm the origin of the smoke.  Replaced all of the components in the immediate area of the 4047 including the IC.  Reflowed all connections on main board.  Pedal is not powering up.

How should I proceed?  Is there troubleshooting to be done or does smoke = trash the bus and start again on a new board?

[jimilee]

How does D1 look and can you post your voltages?


Sent from my iPhone using Tapatalk

[freshmex18]

Diodes seem fine

IC1
9.10
5.38
4.94
3.24
4.94
5.35
9.14
17.44

IC2
2.06
0.6
0.6
3.23
6.54
0.27
11.71
2.87
2.88
11.78
0.82
6.21
17.44
0.59
0.59
2.15

IC3
9.44
6.26
5.71
3.57
5.71
6.22
9.14
17.43

IC4
9.68
1.25
1.16
1.97
1.24
1.17
9.69
17.42

IC5
8.44
8.55
0.61
17.42
17.41
17.40
1.97
1.97
1.97
5.80
5.79
1.96
6.12
17.42

IC6
9.23
7.93
7.87
5.67
7.87
9.96
9.21
17.41

IC7
17.42
5.65
0.04
0.05
1.99
5.65
0.02
0.13

IC8
9.19
7.00
6.50
5.68
8.15
8.35
9.19
17.41

IC9
17.42
5.65
0.04
0.04
1.99
5.65
9.20
0.18

[madbean]

Something is obviously very off. Your voltages don't resemble the voltages listed in the build doc in any way. So, something is wrong with the power supply area or perhaps with how you measured the voltages on your build.

[freshmex18]

Is there a different procedure for reading voltages on a positive ground circuit like the Tourbus that I am not aware of?

[madbean]

Is there a different procedure for reading voltages on a positive ground circuit like the Tourbus that I am not aware of?

No, your black lead should still be connected to ground and your red lead is what you will use to measure voltages. In the case of the Tourbus, you should read negative voltages all around because it is a positive ground circuit (so 0vDC is the highest voltage reading you should see as opposed to the lowest on a single supply negative ground circuit).

For example, on IC1 pin 4 should be about -15v (which is the supply voltage) and pin8 should be 0v (which is still ground).

[madbean]

To make this process easier, try this:

Remove the daughter board. Now remove all the ICs on the main board except IC1. Power up the board again and record the voltages on the 8 pins of IC1. List those here and then we'll move onto step 2.

[freshmex18]

I have the very first version of the circuitboard.  Is there anything different about that board with the documentation on the site vs the current version?  The current documentation shows DC In connected to the long terminal of the DC jack and Ground connected to the short terminal and that is what i have currently.  I did disconnect those wires when troubleshooting and reconnected them as per the current documentation

[freshmex18]

With daughterboard and all ICs but IC1 removed

IC1
9.15
2.21
0.62
1.09
0.61
2.22
8.87
17.42

[freshmex18]

Hello?  Anyone still here?

I reflowed all of the connections again and got a new, better multimeter.  Whichever it was that helped, here are the new readings with the daughterboard and all ICs but IC1 removed

IC1

-0.582
-1.67
-1.741
-1.151
-0.888
-0.521
-0.473
0.0

[madbean]

Something is still not right there. Let's try this:

Take DC voltage readings here:
Both sides of D1. Cathode side should be about -18v and anode side should be a little less.
Output leg of the LM7815 regulator. Should be about -15v.

[freshmex18]

D1
Cathode -17.64
Anode -17.36

Output leg of regulator
-15.67

[madbean]

That's perfect! So, we've narrowed it down. The issue seems to be on the VC power rail. Since one end of R38 is connected to the output leg of the regulator, and we have -15.67 there we know power is getting out. So, let's take the voltage reading on the other end of R38. That's the VC rail which powers IC1, where we are getting a wrong reading on your build. Looking at R38 on the PCB, it's oriented vertically. You want the reading on the top pad. The bottom pad is the one that should already read -15.67v.

Also, verify you've got 10 Ohm in R38 and that C37 is oriented the right way on the PCB.

[freshmex18]

So both of those parts are ones that I replaced as possible causes of the smoking.

And you called it.  Somehow, I replaced the 10R with a 330k.  I have no idea how I even did that.

R38 was reading -1.153 on the top pad with the 330k.

R38 now reads -15.56 on the top pad

C37 is correctly oriented

IC 1 now reads
-7.83
-7.83
-7.79
-15.56
-7.75
-7.83
-7.84
0.0

[madbean]

You nailed it!