Boss PH-1 switching issue

[electrosonic]

This has come up before but I can't find a definitive answer.

It works fine, except the led only lights while the footswitch is depressed. I have the service manual schematics and layout for the PH-1 so I pull it apart.

My unit is close to this layout but not exactly the same, it is missing Q9 (bottom right of schematic) and rearranged a bit in that area. This makes me think that very early models of the PH-1 didn't toggle the LED on or off, but just lit it up to indicate the foot switch was pushed.

Andrew.

[GibsonGM]

Weird symptom...compare with this, see what you get:  http://www.geofex.com/Article_Folders/bosstech.pdf

[dwmorrin]

My unit is close to this layout but not exactly the same, it is missing Q9 (bottom right of schematic) and rearranged a bit in that area. This makes me think that very early models of the PH-1 didn't toggle the LED on or off, but just lit it up to indicate the foot switch was pushed.

The early Boss LED do just flash.  One of the service manuals should include the conversion process.  Try all the XX-1 manuals.

[electrosonic]

I will check the layout diagram I have and see what other components are missing. I suspect it is just the R41, D8 and Q9 and the LED is connected directly to the switch or maybe  R44.

Looking form the DM-2 schematic from a little later (1981) they drive the LED straight from one of the toggling LEDs, no driver. So I wonder why they didn't do that here.