Boss DS1 no output when in “on” mode

[DPLAudio]

Hi guys, first time poster here.

I have a Boss DS1 someone gave me a few years back, which I am trying to fix.

Problem: Pedal passes Audio in bypass mode, but no signal when in "on" mode.
LED comes on when switched on.

I am reading voltages that seem too high on the IC.

Here are my readings:

Q1
E 3.22V (on)
C 8.79V (on)
B 3.66V (on)

Q2
E 0.008V (on)
C 5.33V (on)
B 0.533V (on)

Q3
E 3.82V (on)
C 8.79V (on)
B 3.91V (on)

Q4
E 0.0003V (on)
C 0.057V (on) 5.81V (off)
B 0.649V (on)

Q5
E 0.0003V (on)
C 5.85V (on) 0.026V (off)
B 0.0206V (on)

Q6
S 4.48V (on) 4.43V (off)
G 0.84V (on) 0.29V (off)
D 4.88V (on) 4.02V (off)

Q7
S 4.52V (on) 4.47V (off)
G 0.3V (on) fluctuates (off)
D 4.52V (on) 4.44V (off)

Q8
S 4.49V (on) 4.44V (off)
G Fluctuates (on) 0.247V (off)
D 4.52V (on) 4.44V (off)

IC1
Pin1 8.02V (on) 8.05V (off)
Pin2 8.02V (on) 8.05V (off)
Pin3 8.9V (on) 7.55V (off)
Pin4 0.0003V (on and off)
Pin5 0.006V (on) 8.05V (off)
Pin6 8.59V (on and off)
Pin7 8.79V (on and off)
Pin8 8.79V (on and off)

I took a reading either side of C10 and it measured 4.51V on one side (connected to C11 and R16) and 4.53V on the other side (Connected to R20).

D1
A 0.0008V
C 8.79V

D2
A 4.24V
C 8.79V

LED
A 0.057V
C 1.88V

D4
A 4.54V
C 4.52V

D5
A 4.52V
C 4.54V

D6
A -0.285V (on) 0.208V (off)
C 0.056V (on) 5.23V (off)

D7
A 0.203V (on) -0.317V (off)
C 5.23V (on) 0.026V (off)

D8
A 0.0009V
C 8.89V (on) 7.54V (off)

Here are my readings from the power stage:

C23
+ 8.8V
- 0.0002V

R24
+ 8.78V
- 4.49V

R25
+ 4.49V
- 0.0002V

C15
+ 4.49V
- 0.0003V

All resistors are reading within tolerance.
Electrolytic capacitors reading within tolerance for capacitance, and with no terrible ESR readings.

C2458 transistors looking as expected in diode check mode with digital multimeter.
C2240 transistors test ok with diode check.

M5223AL chip gives readings in diode check mode of:
Between Pin 2 and 1 = 0.744V
Between Pin 6 and 7 = 0.744V

[Govmnt_Lacky]

With that much supply voltage on that many pins, I think you can be sure that the IC chip is done for. Pull it, clean up the pads, and replace.

[Marcos - Munky]

First of all, welcome.

While I'm not sure your IC1 is damaged, isn't the voltages on some Qs too low? Maybe a non working switch caused by some faulty parts. It is switching something, since led turns on and off, but maybe part of it doesn't work (like the part which should send guitar signal to the circuit, or the part which should receive the distorted signal).

2 questions:
- do you know why it stopped working? I mean, it just gone dead or did the previous owner plugged a wrong power supply?
- do you know how to inject and trace signal, or how to use an audio probe? This way we can check if the switching is good, and where the signal stops.

[DPLAudio]

I'm not sure what voltages I should ideally be seeing on Qs.
I am using an AC/DC wall wort power supply to power it. This is supplying 8.8V.

To answer your questions;

- I'm not sure why it stopped working, I was just given it as not working, problem being as I originally posted - no sound output when powered on.

- I am injecting a 1kHz 0.4V sine wave from a signal generator. I have my oscilloscope set up and have channel 1 monitoring the input signal. Channel 2 I can start to trace through the board.

[Govmnt_Lacky]

You should be reading ~4.5V on Pins 1, 2, 3, 5, 6, and 7 of the IC. You are reading input power. Replace the IC

[DPLAudio]

So I traced a 1kHz 0.4V signal through from input to IC. Here are the results:

Q2 base


Q2 Emitter


Q2 Collector


IC non inverted input pin 3


IC Inverted input pin 2
Same for output 1 on pin 1
Same for Non Inverted input 2 on pin 5


IC Inverted input pin 6
Same for output 2 on pin 7
Same on pin 8



Is this all pointing to a dead IC?

[Marcos - Munky]

The voltages on the ic are indeed pretty odd, but that could not be the only issue. Not disagreeing with Govmnt_Lacky because I don't know those odd voltages can indicate a dead ic or they're resulting on something else, I'm just looking at other places (those Q voltages).

What's the ic on your unit? The DS-1 had two different ics, and since your have 8 pins it's probably not a TA7136. Asking that to confirm which schematic we should follow to help you. And since you can inject signal, it'll make the job easier.

Also, take a good look at the board and try to find any damaged part.

[DPLAudio]

It is the Mitsubishi M5223AL IC.

I'm not seeing anything obviously damaged. Also check for shorts and cold solder joints and reflowed anything that looked suspect.

Resistors are all testing just fine - I took a good few out of circuit to check this. Took all electrolytic caps out and tested them, looking fine. The only caps I haven't taken out and tested are the ceramic caps. Pots are testing ok.

Everything up to input on pin 3 of the IC looks about right on the signal trace. I'm just not so sure the output of pin 1/input pin 2 should be looking like that in the picture I posted.

[DPLAudio]

One thing I did want to try was bringing up the Gate of Q7 and Q8 on the scope. The voltage was fluctuating on opposing transistors depending on the pedal being switched on or off. Wondering if this might show something up on the scope.

[11-90-an]

One thing I did want to try was bringing up the Gate of Q7 and Q8 on the scope. The voltage was fluctuating on opposing transistors depending on the pedal being switched on or off. Wondering if this might show something up on the scope.

switching JFETs. probably shouldn't be a problem. a good test to see if they're working would be to put yer signal on the drain and your probe on the source (or reverse them, there shouldn't really be a problem) then click the pedal on and off. probably no need to test the gates.