Boss phaser PH-1 switching problem

[Helmholtz]

To get a clear picture, I need answers to the following questions (even if you already mentioned it somewhere/somehow):

Does the unit work properly including the LED with a battery?

Does the effect work fine with the power supply except for the LED flashing?

What does LED flashing mean? Is it an unusually bright flash followed by normal LED brightness or is the LED off after the flash?

[pontiacpete]

The effect works perfectly with battery and the power supply(now without D5 andR45) but the LED comes on when stepping on the switch but goes completely off after releasing the switch.

It seems like this switch should not be a momentary switch. It’s a strange size, not the usual boss square shaped ones but white and rectangular.

[Helmholtz]

The effect works perfectly with battery and the power supply(now without D5 andR45) but the LED comes on when stepping on the switch but goes completely off after releasing the switch.

Both with battery and power supply?

If yes, measure voltages across the LED as well as across the D2 zener with effect engaged.

[pontiacpete]

Is D2 a zener? I know you said that before and i didn’t ask then but it looks to me like a regular diode. There’s D1 and D3 that look to me like zeners on the schematic.
Anyway across the LED is .25v and across the LED and D2 there’s 3.5-4v.

[Helmholtz]

Is D2 a zener? I know you said that before and i didn’t ask then but it looks to me like a regular diode. There’s D1 and D3 that look to me like zeners on the schematic.
Anyway across the LED is .25v and across the LED and D2 there’s 3.5-4v.

The schematic notes identify D2 as a 5.1V zener. The circuit wouldn't work with a reverse biased regular diode. So the schematic symbol is wrong.

The voltage across the LED should be between 1.6V and 2V when powered.
The voltage across D2 should be 5.1V.

What is the voltage between collector and emitter of Q9?

[g1]

I have read elsewhere that this (flash only) is the normal operation and design, to save battery life. If you can find the instruction manual, it should say so.
If true, you will need to modify the led circuit to keep the led lit.

edit: see pg.2 of attached (check light)

[pontiacpete]

It looks like you are right G1 if i’m reading this from the owners manual correctly.

CHECK LAMP
While pedal is trod down, this lamp
tights if battery is normal. Thus this
lamp lets you confirm the changeover
between Effect and Normal modes, and
also battery state.

[Helmholtz]

Instructions are not clear in this respect.

That would be the only pedal I've heard of that doesn't keep the LED lit with the effect engaged.
Doesn't need much current to light an LED.

I mean how would the player know if the effect is on or off before he/she hits a note?

[pontiacpete]

Is there a way this could be changed so it lights when on?i

I wonder if i use the same value of some of the resistors that differ. The one I’m thinking of is R44, 1K. This pedal has a 22R resistor here

[Helmholtz]

Is there a way this could be changed so it lights when on?i

Start with answering my questions.

As long as the collector of Q8 is high, the LED should be on.
This is if the LED is good and Q9 has enough Hfe

[g1]

Instructions are not clear in this respect.

That would be the only pedal I've heard of that doesn't keep the LED lit with the effect engaged.
Doesn't need much current to light an LED.

I mean how would the player know if the effect is on or off before he/she hits a note?

Agree instructions about light are vague. And Q8 must be latching on and off for effect to work. So something in Q9 circuitry must not be working right.

[Mick Bailey]

Check the voltage at Q8/R41 to see how it behaves in relation to the LED operation. It should be a constant voltage and if not there may be an issue with the flip-flop circuit if it goes high then drops (corresponding with the LED illumination). If the voltage holds up OK trace it through R41 and check the drop across the diode (D8?) to the base of Q9. The B-E voltage should be 0.6v or so. When Q9 switches on the LED the C-E voltage should be close to 0v. You've already established that the LED/D2/R42 are good.

[Helmholtz]

With the LED cathode grounded there is no flash of theLED

Does that mean the LED stays lit?

[pontiacpete]

Does that mean the LED stays lit?

No, the LED does not come on at all..


This schematic is not easy to navigate through. Something seems very different here. This pedal has 2 ICs 3403, and 6 FETs 2sk30s and two 2sc536s. If the 536s are some equivalent to the c945s, there are only two, one is missing.
When I trace from the switch on lug connects to the 22R top left of board. The other lug on switch is connected to the diode just above the trim pot. Looks like it could be D4. The other end of D4 connects to one of the FETs in the middle of the board with the little white paint on the top it. How could this be a FET if this is the switching circuit?
And where is Q9?
Obviously I’m confused.

[Helmholtz]

To which transistor does the LED connect?