Boss CE-2 weird loud electrical noise when off

[zamproject]

Did you check the flip-flop with a scope ?
It's a bistable, but maybe could run as astable multivibrator (oscillator) if something wrong ?!?
The attached sound seem like digital clock, square waves...
Maybe try to disconnect D3 and/or R43/44 to neutralize the flip flop ?

 

[RoadrunnerOZ]

- Currently D4 is disconnected to let the flip flop out of the equation, is having Q9’s gate leg floating an issue?

Yes - Q9 acts as a switch and passes the effect signal (or not) - the flip-flop turns it on or off. Did you replace the Zener diode D7 - and are you getting 9V at + rail and 4.5V at centre rail - wiper of VR3 trimpot?

 

[RoadrunnerOZ]

Q1 and IC1 - these are actively in circuit for bypass mode - the rest is not summed in at pin 2 of IC1 if Q9 is off - Q1 is the input buffer and IC1 acts as the pre-emphasis/de-emphasis filter. If you get low level in bypass mode then something is wrong with either of those or the filter elements. I presume you have IC sockets in place for easy chip replacement. When you replaced transistors did you use equivalent or actual to type replacements? It pays to check pin out of replacements that are not originals - base collector reversals are common.

 

[Golgoth]

Did you check the flip-flop with a scope ?
It's a bistable, but maybe could run as astable multivibrator (oscillator) if something wrong ?!?
The attached sound seem like digital clock, square waves...
Maybe try to disconnect D3 and/or R43/44 to neutralize the flip flop ?

Hi, I did not check the flip flop with a scope, where should I be probing for oscillation?
D3 does not exist on my board and is just a jumper wire, disconnecting R43/R44 did not fix it.

 

[Golgoth]

Yes - Q9 acts as a switch and passes the effect signal (or not) - the flip-flop turns it on or off. Did you replace the Zener diode D7 - and are you getting 9V at + rail and 4.5V at centre rail - wiper of VR3 trimpot?

Hi, D7 was replaced and both rails look healthy with a MM everywhere in the circuit!

 

[Golgoth]

Q1 and IC1 - these are actively in circuit for bypass mode - the rest is not summed in at pin 2 of IC1 if Q9 is off - Q1 is the input buffer and IC1 acts as the pre-emphasis/de-emphasis filter. If you get low level in bypass mode then something is wrong with either of those or the filter elements. I presume you have IC sockets in place for easy chip replacement. When you replaced transistors did you use equivalent or actual to type replacements? It pays to check pin out of replacements that are not originals - base collector reversals are common.

I have sockets installed indeed, and tried different chips for each IC, without luck. The noise is still present with no IC installed.
Regarding transistor replacements I used: K30A, C945 and BC239, installed in the same orientation as the originals. I will double check that.

 

[RoadrunnerOZ]

I have sockets installed indeed, and tried different chips for each IC, without luck. The noise is still present with no IC installed.
Regarding transistor replacements I used: K30A, C945 and BC239, installed in the same orientation as the originals. I will double check that.

What did you use for Q9 - K30A?

Hi, I did not check the flip flop with a scope, where should I be probing for oscillation?

Junction of R44, 46, 49, 50 and collector of Q7 are all one common point, if it’s oscillating you’ll see it there - is the bypass LED still working?

 

[Golgoth]

What did you use for Q9 - K30A?

Junction of R44, 46, 49, 50 and collector of Q7 are all one common point, if it’s oscillating you’ll see it there - is the bypass LED still working?

K30A for Q9 yes

I don't see any oscillation at that junction at all, like I see at the output.. New (?) issue I did not pick up earlier but the LED is on all the time. The switch is not turning it off..

 

[RoadrunnerOZ]

The flip flop at the junction mentioned before feeding Q9 should alternate between high and low DC voltage when you press the bypass switch - you can check with a multimeter or the scope in DC mode.

 

[Golgoth]

The flip flop at the junction mentioned before feeding Q9 should alternate between high and low DC voltage when you press the bypass switch - you can check with a multimeter or the scope in DC mode.

Q7 collector pin? Stuck on 0.65VDC when the switch is pressed or not..

 

[RoadrunnerOZ]

Q7 collector pin? Stuck on 0.65VDC when I press or not..

Flip flop’s not working - check the switch and its wiring, or the transistors in the flip flop - one may be faulty.

 

[RoadrunnerOZ]

Junction of R41&42 should be high until you push the switch - go low while switch is pushed and revert to high when switch disengages. Momentary action provides trigger pulse to swap state of the flip flop.

 

[Golgoth]

Flip flop’s not working - check the switch and its wiring, or the transistors in the flip flop - one may be faulty.

Just replaced Q6 & Q7 with no changes, wiring is okay.

 

[Golgoth]

Junction of R41&42 should be high until you push the switch - go low while switch is pushed and revert to high when switch disengages. Momentary action provides trigger pulse to swap state of the flip flop.

That's working as expected, 7.7V disengaged, 1mV when pushed!

 

[RoadrunnerOZ]

But you’re getting a low output on the collector of Q7 - for Q8 to turn on the LED it needs to have the base taken high by the flip flop at the collector of Q7 - Q8 must be shorted?

 

[Golgoth]

But you’re getting a low output on the collector of Q7 - for Q8 to turn on the LED it needs to have the base taken high by the flip flop at the collector of Q7 - Q8 must be shorted?

I appreciate the help and your time, Q8 was dead, I should have checked it before installing it. The flip flop is fixed!

Now on to the noise.. I narrowed it down to a couple of components, I will report back if I find anything!

 

[RoadrunnerOZ]

I appreciate the help and your time, Q8 was dead, I should have checked it before installing it. The flip flop is fixed!

Now on to the noise.. I narrowed it down to a couple of components, I will report back if I find anything!

Cool - happy hunting. Is it passing signal in bypass now?

 

[Golgoth]

Cool - happy hunting. Is it passing signal in bypass now?

It does! 30db quieter than the input. I only have IC1 installed at the moment.

The noise seems to be located around the output after Q9 (C15, R23, C16, R24, R25, C17, pin 5) and around IC2 (pins 1, 6 before the resistor to ground, 8, 10, 11). Pin 7 to ground is not noisy.

 

[RoadrunnerOZ]

When Q9 is off only Q1, IC1/1 and IC1/2 are involved in the audio circuit - Q9 off disconnects the feed of effect. If you’re getting low level in bypass then either Q1 is faulty, Q2 could possibly be faulty shorting the output of stage 1, IC1 pin 7. The redrawn schematic you are referring to has errors - shows output on IC1 pin 3 at both ends - input on a 4558 (after Q1) at stage 1 should be pin 6, output 7 and input after Q9 should be pin 2, output pin 1. Look at the original schematic I posted earlier in this thread.

 

[RoadrunnerOZ]

Did you check the polarity of C2, - to emitter Q1, + to R4 C3 junction.