# Son of Ben Troubleshooting



## CanadianDave (Oct 1, 2019)

Hey,

This Benson build is driving me nuts.

I’m getting no output, and also, very low voltage at my transistors.

Without transistors in the socket, I’m getting 9v at the socket.
Once I have transistors in, I’m measuring 1.6v to .4v

I found a faulty electrolytic, and reflowed my solder, but nothing has worked. 

Any ideas?


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## Nostradoomus (Oct 1, 2019)

Where did you get your j201s?


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## CanadianDave (Oct 1, 2019)

Nostradoomus said:


> Where did you get your j201s?



I’ve tested it with EBay probably-knock offs, and Fairchild j112’s. Same results with both. I have legit j201’s, but I’m waiting until I know the circuit is 100% before dropping those in.


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## Nostradoomus (Oct 1, 2019)

If you are able, post a few good pictures of the top and bottom and off board wiring


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## CanadianDave (Oct 1, 2019)

All of the soldering was touched up. There's electrical tape under the pots to avoid shorts.

The 10K resister that is positioned "wonkey" was replaced as a test, because that's where the voltage was dropping so significantly. I also swapped out the 22nf capacitors under the tone controls with no luck either.

There's also a visible bad solder under that treble pot. That's where there optional 10uf capacitor was, and I removed it while troubleshooting.


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## moonlightpedalbuilds (Oct 1, 2019)

Show wiring on 3pdt switch


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## Joshdrain (Nov 1, 2019)

Mine is doing the exact same thing. Still haven’t figured out why.


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## CanadianDave (Nov 1, 2019)

I had a few issues.

One is that a few capacitors were blown. Not 100% certain why.

I pulled out the jfets and traced the voltage leading from the power supply through to the jfet to find the faulty ones.

I also had bad jfets too. The ones from small bear took care of the job.


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## zgrav (Nov 1, 2019)

even though the tape under the pots is probably OK for insulation, I would bend them up a bit away from the board while you are trying to get it working to eliminate one possible cause.


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## Chuck D. Bones (Nov 1, 2019)

Are you not able to dial in the drain voltages in accordance with the Build Docs?  Do the J201 leads fit firmly in the sockets?


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## Barry (Nov 2, 2019)

I'm not a fan of that type socket


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## Joshdrain (Nov 4, 2019)

I had this identical issue which is documented on another thread. I ordered J201's from three different places and the first two batches were fakes.  With no other change other than new J201's I went from max just above 1v on the drain to 6v and easily dialed them down to 4v. Now it sounds great.  I would find another place to source your transistors.


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## Chuck D. Bones (Nov 4, 2019)

Would it be possible for you to measure Idss & Vp on some of the "fake" J201s?  To satisfy my curiosity as to whether they are just enough out of spec to not work or if they are way out of spec.

I regret not buying more legit J201s from SB when I had the chance.  The 3 I did get are in my Corduroy and working well.  I picked up 50 of the PF5102s.  They are hotter then J201s, but should work in the M800, Pineapple, Stinger & Tantric.  The Deofol & Benson would require resistor tweaks to use them.


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## moonlightpedalbuilds (Nov 29, 2019)

I got my J201s from china via ebay. Marked as Fairchild components. Trim1 set to 2k ohms and Q2 and Q3 Drain to 4.0v. Sounds good. I also mounted the smd version using PedalPCB Sot23 Adapter. MMBFJ201 came from Tayda. I tested both on....




Both of them are read as NPN transistors. I have other JFets that are read as NJFET.

Question is, did I get fake ones on both MMBFJ201 and J201?


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## Chuck D. Bones (Nov 29, 2019)

If they were NPN transistors, you would not be able to achieve 4V on the drains and it would either sound like crap, or you'd get no sound at all.  Based on the evidence presented, you got real J201s, or something close enough.  If you want to be sure, measure Vp & Idss.


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## moonlightpedalbuilds (Nov 30, 2019)

Chuck D. Bones said:


> If they were NPN transistors, you would not be able to achieve 4V on the drains and it would either sound like crap, or you'd get no sound at all.  Based on the evidence presented, you got real J201s, or something close enough.  If you want to be sure, measure Vp & Idss.



As always Chuck, you are the best. Thank you!


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## Robert (Nov 30, 2019)

pedjok said:


> Both of them are read as NPN transistors. I have other JFets that are read as NJFET.
> Question is, did I get fake ones on both MMBFJ201 and J201?



You're the third person to say that a genuine MMBFJ201 tested as an NPN on that semiconductor tester.


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## temol (Nov 30, 2019)

Do not use those LCR meters for JFETs. Use DMM and a battery instead. My LCR meter sometimes identifies JFETs as BJT transistors or gives me false readings of Vp.

T.


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## Nostradoomus (Nov 30, 2019)

Robert said:


> You're the third person to say that a genuine MMBFJ201 tested as an NPN on that semiconductor tester.



Fourthing this! I had a 5 pack of 201 from smallbear I forgot about and 2 of them read that way but are fine. Can’t expect too much out of the cheap little fella haha


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## Chuck D. Bones (Dec 1, 2019)

I have the 2019 model of the $17 Chinese everything tester.  It identifies JFETs correctly, but does not measure Vp or Idss.  It finds an operating point and reports Vgs and Id for that operating point.  It has never misidentified a JFET and I've tested a few dozen.


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