Ibanez FET switching help

[soffa]

I have an old Ibanez PT-9 phaser that has what seems to me like an odd problem. It was not passing the effect signal so I opened it up and started going through the circuit. Everything seemed fine up until the switching fet, which wasn't opening up even when seemingly hit with a "high" voltage from the rest of the circuit. OK, seems like a bad FET or so I thought... I replaced the FET and everything worked just fine - for a few days! I let the pedal sit and came back to it and guess what? same symptoms again. This time I pulled the FET out and on a whim put the same FET back in and whaddya know it works again. Now it's a few days later and the same thing happened again.

Does anyone have any ideas? Before anyone asks, I know that my solder joints are good!

soffa

[R.G.]

I'm not sure what Mother Nature is whispering in your ear right now, but if it's not the JFET that's the problem, it's the rest of the circuit. Just out of curiosity, what are the voltages on all the JFET pins when it's working correctly versus when it's not working? It seems to me that would be interesting.

[soffa]

Well, I kind of figured that it must be something else in the circuit besides the JFET but I didn't know if this was some sort of common problem... Maybe I used the lifeline too early on this one!

I checked the voltages at the FET and it seems like when it wasn't working the switching voltage (~6.5 V) dosen't make it past a diode that immediatley precedes the FET. I took that as a whisper that it was the diode that was bad, so I replaced that and it seems to work fine again. Then again, it worked fine when I replaced the FET the first two times!

We'll see how this works out after it sits for a few days in my closet, which seems to be the true test.

Thanks for your help...

[soffa]

OK... So sure enough, a few days later it isn't working again. I guess I've failed again.

Wehen I was looking at the schematic, I realized that I'm really not sure what "CR1" and "CR2" in the switching circuit are. I thought "CR" was typically a relay, but those sure don't look like relays!

I can't find a copy of the PT-9 schematic online, but this AD-9 schematic has the same switching section:

http://www.dirk-hendrik.com/Ibanez_ad9_analog_delay.pdf

Does anyone know what the "CR" parts are? They look like an odd ceramic cap to me but I'm hoping someone out there knows for sure.

In the meantime I'm going to pull out the transistors in the switching circuit and check those. I'm sure it will work as soon as i touch iron to stompbox!

[R.G.]

Wehen I was looking at the schematic, I realized that I'm really not sure what "CR1" and "CR2" in the switching circuit are. I thought "CR" was typically a relay, but those sure don't look like relays!...Does anyone know what the "CR" parts are? They look like an odd ceramic cap to me but I'm hoping someone out there knows for sure.

They are a resistor and a capacitor in parallel. Try 51K and 47pF.
You know, you can check the operation of that circuit without soldering. Connect a voltmeter to measure the voltage on the collector of one transistor. Activate the footswitch a few times. Each press of the  footswitch should make the collector flip between nearly ground and nearly 9V. Check the other collector for doing the same thing. If that works, the whole flipflop is working.

I'm sure it will work as soon as i touch iron to stompbox!

Isn't that the desired result? 

[Dirk_Hendrik]

Does anyone know what the "CR" parts are? They look like an odd ceramic cap to me but I'm hoping someone out there knows for sure.

A combination of a resistor and a capacitor in a package. In later Ibbie circuits like in teh soundtanks they changed over to a discrete version with a cap and a resistor.

Write me a mail or a PM with a mailadress and I'll mail you the PT9 service manual.