2SK364 substitute for MP-2 Q200 & Q202

[Gregg]

One of Q200 or Q202 or both has/have gone bad in the compression section. They work when warmed up and fail when hit with freeze spray.

These transistors switch the compression in/out. What is the preferred substitute for the 3SK364 in this section of the MP-2?  I have seen recommendations for J112, J113, PN4393, and PN4394.

I am particular about my parts. Don't want to source from eBay or AliExpress as counterfeits abound.  Don't want to risk damage to the MP-2 due to a counterfeit or malfunctioning part.

Gregg

[rnolan]

Hey Gregg, hopefully MJMP will chime in here as I don't know the answer :-(.  I do remember a number of posts about the compressor issue where it would settle after warming up.  IIRC the unit wouldn't work until about 15 to 20 mins although I'm not sure if it's the same as what you are fixing.  A work around (for that issue) was to ensure you switched the unit off with the active patch (restored on boot) having the compressor switched on in it.  Moreover, this was one issue MJMP was never able to fix (back then anyway).  He changed all the associated parts and still couldn't sort it completely.

[Gregg]

The issue I have is almost the opposite.  First no sound, then when "luke warm" it only produces sound with the compressor in and nothing with the compressor out.  After some time, it works correctly compressor in and out.   After getting even warmer... it goes ape sh*t.  Spraying Q200 & Q202 with freeze spray repeats the cycle starting with no sound, then when warmer sound with compressor in, then working, then crazy...

Also noted Q203 & Q204 are temp sensitive as well.  Need to check the board carefully for bad solder joints and cracks under a microscope.

Gregg

[rnolan]

Hey Gregg, hmm, interesting. The manual schematic shoes comp first in signal chain with in/out bypass. Is this what these "thingys" turn on/off?

[Gregg]

Q200 & Q202 switch the compressor in/out
Q203 & Q204 are part of creating the WAH effect, don't fully understand their function, but they sit on the output of the input, compressor, and WAH section.

All of them are physically close so I will first touch up the solder joints and inspect the board before changing any parts. 

We let the thing warm up for an hour and according to my brother it worked perfectly.  You can hear for yourself here.

Sadly, we didn't get a sample of the sound after I hit it with freeze spray.

Gregg

[rnolan]

Hey Gregg, sounds good, as it should.  But then it goes to crap, not good.  Hopefully you can work it out.

BTW you might suggest to your brother that he holds the pick more with the very tip of thumb and index finger and bend the tip of his index finger (and try to relax the other 3 fingers)  Similar to making an OK signal underwater.  It will improve his picking.