Boss NF-1 repair success story

[Marek]

Friends,

I got this Boss NF-1 Noise Gate on E-bay for EUR 6.9o.- in a non-working condition. It simply wouldn't switch on (and the LED was broken, but that is a minor problem)

So I took the guts out, checked the wiring & found the faulty spot. It took me only 1 hour for the whole procedure :-)

It was the DC jack. There is this red wire which goes from the V+ of the battery 'through' the DC jack and the little switch inside. On the first pin of the DC jack it had 8,5 V, and on the other pin it was showing no voltage... but it normally should, as long as you don't plug anything in the jack, thus opening the switch inside.

So I first tried with some contact spray. E-e. No go. I compared it to my other boss pedal, and than I saw the problem: the little 'tongue' which should be touching the first pin of the DC jack from inside was bent, so that the effect  was getting no battery power. I bent it back with a small screwdriver, and then it worked. Easy, no? :-)

BTW, that thermistor SDT-1000 in the NF-1, is it just a 'dummy' to scare away potential circuit cloners, or does it have a significant role in the circuit? Cannot I just put a normal resistor instead ?

Greetings,
Marek


p.s.
NF-1 Service Manual can be found here:
http://krustykorp.tripod.com/bossng.htm

There is also a SG-1 Service manual there:
http://krustykorp.tripod.com/bosssg1.htm

[Paul Perry (Frostwave)]

Marek, just looking at the circuit, I think the function of the thermistor is to provide an 'automatic gain control' function with a long time constant, so the unit adjusts to long-term input level shifts.
If I am right, then you can put a resistor here and it will function pretty much the same, but you would have to pay more attention to adjusting the input level.
That's my guess, anyway!

[Marek]

Thanks for the answer.

I have another question regarding this effect:

Will the circuit benefit from upgrading that old  u741 to some modern opamp? ( e.g. I have here OP27 and OPA134PA )

Here's what somebody suggested:

http://www.ne.jp/asahi/bdx/info/bdxtech/nf-1-bdx.txt

They have other mods for other Boss pedals, as well.

Greetings,
MArek

[cd]

Will the circuit benefit from upgrading that old  u741 to some modern opamp? ( e.g. I have here OP27 and OPA134PA )

I don't think so.  The opamp is not even in the signal path, it's part of the envelope detector.  The guy doesn't even explain the result of his mods.