Boss PH-1 phaser (original) switching problem

[beatnik]

Hi guys,

I need some help with a Boss PH-1 phaser.

The led doesn't latch on. The switching for bypass / fx on works ok, but the led just lights up when switch is pressed either way.

I am not familiar with boss switching circuit and I don't know how to debug it, maybe you can give some help?

here is the schematic

[beatnik]

i've replaced D2 with no results

[Mark Hammer]

So it stays on, or does it briefly go off when you press and then re-light when you take your foot off, whether in bypass or effect mode?

[zombiwoof]

Does it have this problem when using a battery?.  I think that should be a Boss pedal that requires an ACA adapter, which means you should be giving it at least 12 volts (neg center) if you are powering it with an adapter or power supply (my ACA adapter puts out over 14 unregulated volts).  Just wondered if you were aware of this.

Also, you can take those Boss switches apart and clean them, it could be that simple a problem.  User "Laurie" on the StompBox forum (the new version of the old Bossarea Forum) posted the procedure for cleaning the switch.  I don't know if this has anything to do with your problem, but it is possible.

Al

[cortezthekiller]

From what I remember early Boss pedals use the LED as a battery level "check", hence the name in the schematic.
It was intended to see visually how strong the battery was only when the footswitch was pressed in momentarily,
rather than latching on when the effect was engaged.

Hope this helps.

[R.G.]

IF the LED stays on all the time, check Q9 for damaged/shorted.

The voltage on Q8 collector should toggle between almost 9V and about 1V when you press the footswitch. If this works OK, check the voltage on Q9 base. If this goes up to about 0.6V and down to nearly ground when you press the footswitch, then check the collector on Q9. This should also go nearly to ground, and maybe 3-4V when repeatedly pressing the footswitch. I suspect that all works except that Q9 collector stays near ground all the time.

[beatnik]

hi guys thanks for the replies and sorry for me replying late but i had no connection for some days.

the led stays ON as soon as the footswitch is hold down. this happens both in bypass or active status.

it seems to work as cortezthekiller pointed out.

i've never seen such a behavior in boss pedals but this is a very old one so maybe they were made like this...

[R.G.]

If that's the correct schemo for your effect, no, it's not supposed to work this way.

For how it works, see the article at geofex.com on the technology of Boss and Ibanez switching.

What's supposed to happen is that Q7, Q8, and the surrounding parts make a digital flipflop where either Q7 or Q8 is ON (i.e. saturated to nearly ground), but not both, and that they stay where they are until the next press of the footswitch, which makes them flip. When Q8 is off (which means its collector is high, pulled up to nearly 9V by its collector resistor), it turns JFETs Q5 and Q6 on, and lets the effected signal through to the output. As a side effect, the high on Q8 collector raises the voltage to R41, letting current into the base of Q9, which pulls its collector down and turns on the LED. The resistor and zener in series with the LED limit its current and make it fade out as the battery gets too low, as a battery check indicator.

So you have the condition that pressing the footswitch makes Q9 turn on, but it goes off when you release the footswitch if I understand it correctly, and the effect still alternates between dry and effect (there isn't a real "bypass" in this pedal). That means that the flipflop is kind of working OK, and is doing *something* to Q9, but not enough to make it stay in the right condition.

There is no solution for measuring the operations. Take DC voltages of all the terminals of Q7, Q8, and Q9 in both effect on and effect off. That will either tell the tale or tell us where to look. Guessing from "it hurts when I do this" is going to be a long process.

[beatnik]

thank you very much R.G.

yes you have understand correctly what's the behavior. led is off when footswitch is released. and is on whenever the switch is pressed.

soon i'll make the measurements and post here. stay tuned

[cortezthekiller]

I had recently picked up 2 broken Boss PH-1 phase shifter pedals and have repaired both to fully functioning condition.
On one, the status LED only turns on when the footswitch is pressed, though doesn't stay lit in effect or bypass mode.
The other one has the LED staying on in effect mode and off in bypass mode.

The model that had the momentarily on LED has a beige coloured circuit board, while the one that stays on is a green coloured circuit board.
Again, both are model PH-1.

Hope this helps.