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Vintage threads from the first ten years

Re: Problem with Millenium Bypass

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12/14/1999 9:24 AM
hys chip	Re: Problem with Millenium Bypass I built the Millenium 2 bypass and it worked great untill today I was messing with the diodes in the feedback loop of a ts clone and now the light will not go out in bypass mode...I used 2n7000, a 1n4148 diode(high leakage) and a 2n5210 collector-base for low leakage.. any ideas on how I killed my Millenium 2?? hys chip

12/14/1999 2:37 PM

If you didn't knock anything loose physically, you may have popped the 2n7000. MOSFETs are static sensitive and if the humidity is low (like, winter in a cold climate) you can build up a several-thousand-volt charge just by waving your arms.

Antistatic mats, wristbands and stuff really do help.

In case you're wondering, the failure mechanism goes like this: The gate is insulated from the conducting channel and the source and drain connections by a layer of Silicon Dioxide just a few tens of atoms thick. This layer can withstand 10 volts or so all day, and brief pulses of a few hundred volts (like static discharge) a few times. Those high-voltage pulses blow little holes in the oxide and the damage accumulates, or one big hole to kill the part all at once. It may litterally blow the gate off the transistor or short the gate to source, drain or substrate. Some failure modes you can't turn ON, soe you can't turn OFF.

JFETs are a lot less sensitive, but still, try to stay grounded if you can SAFELY do so (thru at least 1M ohm).

Good night, and have a pleasant tomorrow.

12/15/1999 9:04 AM
hys chip	thank you Don .what great insite into a mosfet.I tryed another mosfet and no dice. then tryed replacing all the parts..no dice.. so I just built another board ... and its working fine.. this leads me to another question. ..does flux residue become conductive ?? I am using kester "44" rosin core. probably a stupid qestion ..but just had to ask...hys-chip

12/15/1999 8:45 PM

It's not _supposed_ to, but if humid enough?

Kester, and others, have a no-clean flux that better not get conductive. Then there are the water-soluble ones. Flux is pretty nasty stuff (even the no-clean), so I'd suggest a water-soluble and a toothbrush. That would do two things for you - first, it gets all that gunk off the board so you can see if there are solder splashes or flakes ro something trying to make a short; second, it brushes most of those problems off all by itself.

To be honest, I rarely clean my boards either.

12/20/1999 10:57 PM
Llamma	Still Got Problems Well It gets weirder It started working fine after I replaced the switch, had a cheap crappy Proel switch which I replaced with a Carlin, and it started to work fine, Then I took it away for the Weekend and the Led wait time is about 1-2 minutes, It's really getting annoying Llamma

12/20/1999 11:19 PM
Fuzzman	read my reply a few posts back and see if adding the resistor helps any, or maybe changing the diode. FM

12/23/1999 8:17 PM

I used to have that problem. There are two main things to do: put a 100K resistor from the output of the effect board to ground, making sure it's after the output coupling cap, and making the pull-up diode a Germanium device. Germanium diodes are much leakier than Si diodes, and there's more leakage current available to turn on the JFET. Realize that what turns the FET on is the diode's leakage current and what turns it off is puling the gate down to within 100K of ground. So right there are your two areas to check if it's not turning on or off.

Farrow
http://www.skybolt6.com

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