the millenium bypass - half on or half off?

[duck_arse]

no, no, no - this is a real forum member and a real thread for real people to read and reply to. honest.

I have a mill built on a guzz fase, with a problem I'm not understanding. the fuzz works fine, and the mill is indicating fx_ON correctly, but when the time comes for fx_OFF, the led stays half lit. I measure 4V6 at the drain, and it doesn't vary with the volume pot setting (this time). shorting gate to ground doesn't turn the led dark either - does this indicate [boom tish] a ded fet?

what bizarre fail mechanism is it this time?

[bluebunny]

Let me write you an essay on your problem...   

[balkanizeyou]

I've had this problem a few times back when I was still using the millenium bypass on most of my builds. 100% of them were fixed by changing the MOSFET, though.

[Cozybuilder]

I had the same problem with 2N7000, maybe ½ of them, and it was driving me crazy. I switched to BS170 and haven't had that problem since. Bad batch? Go figure.

[duck_arse]

I won't mention [tadya] where my particular 2N7000 (tayda) mosfet came from, but I can tell you where it went. I cut it out, it measured resistance across the channel both directions. so I tested it on the BB, it didn't work, it did work, it didn't work, it did work. it measured good, it measured bad, it measusred .... you get the drift. it left the bench.

pulled another from the oddly not anti-static-in-any-way cardboard {tayda} strip, tested it on the BB, measures OK. fitting it to the perf, well, that's going to be an essay I might need help with.

[anotherjim]

High Z into the gate & enough capacitance in there so the mosfet remembers the last voltage that hit it & switches accordingly.
That voltage can come from everywhere/anywhere - humans, ducks, meter probe leakage, radio pickup, alien mind control signals...

Now your gate source voltage threshold for 2N7000 can be as low as 0.8v, so is your MB gate diode too leaky?

A 1M gate-source resistor ought to sort it out on the BB - give it Alzheimers. What was I saying?

My way to test (anti-static nazis please ignore)...
N-channel
One finger on 0V. Another on gate = channel high R
One finger on +V. Other still on gate = channel low R

[digi2t]

I had the same problem with 2N7000, maybe ½ of them, and it was driving me crazy. I switched to BS170 and haven't had that problem since. Bad batch? Go figure.

Same boat as Russ. I've had it happen a couple of times with 2N7000's, but never with BS170.

Thanks to Russ on turning me on to the BS170.

[duck_arse]

the problem part has gorn. the replacement part works as expected. the build is now a disgrace.

the old part - it did in fact do some remembering of state, and stayed where it was put, when it was functioning. I thought I'd found some magic wires or something; only when poked "like this" would the bluddy thing do.