[Billy]

It could be a number of possibilities poor connection or ground, faulty pot, something  shorting on the bare metal enclosure etc

if you get a consistent voltage from Q4 collector I’d concentrate there to see why you get nothing on Q3 gate

 

 

 

[Billy]

It won’t make a difference Steve 2N2 is easier to get hence the change

[Billy]

For some reason it wouldn’t let me post I’m at work right enough on trains so WiFi is a bit sketchy

Anyway I’d check everything after Q4 collector to Q3 gate C5, R10, P2 all you’re doing is checking voltage black probe on a ground connection red to whatever you’re checking if you’ve done that your good

First check continuity to make sure there’s an electrical connection here’s a PDF

https://drive.google.com/file/d/176vVBWeRaSQ0QvZlnozjKHE6AeHsvxFP/view?usp=drivesdk

Everything up to Q4 collector seems good

 

[Billy]

Q3 seems to be your problem

You need a small voltage on the gate less than the forward voltage of the transistor so less than 0.6v for a a silicon transistor

Check all your components from Q4 collector to Q3 gate including your A and B switch connections

Also check if you get a voltage on Q3 socket with the transistor removed

As far as I know it’s an AC voltage that makes it work as as a variable resistor which is controlled by the small gate voltage

Q4 collector looks good so at least we know that’s ok

 

[Billy]

Post voltages for all transistors Q3 with the kill switch in both positions, put simply Q3 is working as a variable resistor controlled by the gate voltage when you adjust P2 it should vary the voltage coming from Q4 which then changes the resistance between Q3 drain and source as it says in the control section

Q4 collector should vary up to what you’re getting off D1 cathode

It is a case of a process of elimination starting at D1 as you have making sure Q4 is getting what it should and moving into Q3 etc

All transistor voltages may tell us something and lead us to the problem

[Billy]

Not something I  would do but for ingenuity that’s an A+

I can’t see it doing any harm unless you short it or put too much voltage into it

Not all 9v adaptors put out exactly 9v hence why i wouldn’t do it, but yours seems fine check voltages on the anode + of D1 and the green side cathode ie when it’s switched to effects mode

[Billy]

Post what voltage is going in at the +9v and ground pad

Then all transistor voltages we need to track down where you loose voltage

[Billy]

Check with the rate about halfway

[Billy]

Yes I’m not at home at the moment check voltage on Q2 and from Q2 emitter through R8 / 9 and C4 you’re basically trying to find where you loose voltage

Do you get alternating voltages on Q4 collector

[Billy]

I don’t know about knowing my stuff I’m 100% DIY too and Fig knows what’s what I’d say

Anyway using your meter to check for voltages

Set your meter to 20 VDC (symbol below solid line and dotted line = DC) black probe in the COM socket red probe in V for voltage

First thing to do is place your black probe on the ground pad and red probe on the +9v pad just to get used to it you should see what your power supply is putting in less a little voltage drop

The accuracy of your reading will depend on the meter input impedance 10M ohm being what you want for fairly accurate voltage readings that will suffice for pedal circuits if your meter has a smaller input impedance you would just take that into account so no big deal if it’s lower impedance

Then you want to check the voltage you get in and around the LFO and control parts of the circuit blue and green areas shown below, these are what voltages to expect doesn’t have to be exact just round about these voltages

All you do is place your black probe on the ground pad or any ground point if it’s in an enclosure you can put it in a screw hole giving you 2 free hands shown below and touch the component you want to check with the red probe

Check what voltage you get on Q4 collector to start with then check Q3 voltages and report them like this

Q3

D

G

S

Q4

C

B

E

If you don’t know which transistor pin is which you can google 2N5088 pinout, 2N5457 pinout etc

Then all you would do is match it to the silkscreen flat side to flat side curved to curved

I don’t want to overload with information but just as an example take Q1 we can see from the schematic the drain pin labelled with the D comes straight from +9v with no components in between 9v and drain so we’d expect around 9v on that pin so what you are basically doing is checking you get the expected voltages and if you didn’t get 9v on Q1 drain you would trace it back to see where your problem is so anything preceeding that you’d check, the DC jack, C9, R2 for value, orientation, dry solder joints etc

In your case your looking for something affecting your LFO so you’d check those areas

You will get there Bafo and hopefully learn a few things for future reference, I know I continue to learn all the time, if you’re unsure of anything just ask none of us were born making pedals!

Here’s the transistor pinouts I always double check them

 

 

[Billy]

Try wedging in some cut off component legs to get a nice secure fit

Does the LED keep flashing when you hold Q4 in place?

If you got the kit from Bruce it’ll be top quality components

[Billy]

Fig mentioned the FETs where did you get your 2N5457s from

If you got them from Barry they’ll be genuine

It certainly sounds like an intermittent fault try holding Q4 into it’s socket to ensure a good connection or bend it over slightly in its socket, to see if you get the LED flashing then try Q3 set the rate pot to about halfway

Its usually something simple once you get your meter we can give you instructions

[Billy]

Make sure Q3 and 4 are located securely in their sockets

Try swapping Q1 and 3 or if you have an extra fet use that for Q3

As I’ve said without a meter it’s difficult to know where the problem lies you can buy decent meters fairly cheaply go for one with a 10M input impedance it’s definitely a requirement for pedal building

Did you reflow your 3PDT connections from S4, 5 and 6

 

[Billy]

Bafo without voltages it’s a case of reflowing solder joints

If you knew for example what voltage you were getting at Q4 collector you could trace it back to find the fault

In the build doc there’s a circuit block diagram and short explanation telling you what each section does

With D1 illuminating but not flashing with the rate pot is an indication the LFO isn’t functioning if that’s the case then Q3 may not be getting the necessary voltage to work either meaning no depth control

I’d advise reflowing all of the solder joints in the LFO section  including D1 and the 3PDT connections everything in the block diagram green section

Any joints that look dull grey ball like or crumbly for want of a better word if that doesn’t work I’d reflow every joint removing the transistors from their sockets as I said earlier

Before I used a temperature controlled iron I used a 30W iron I’m not sure if 40W may be too hot just touch your joints until you see the solder pooling nicely making sure you get a good connection between solder pad and component leg

[Billy]

I thought that Ray but there’s a red jumper there hard to see because of the red DPDT

[Billy]

Double check you haven’t accidentally mixed your transistors up Q4 should be a 2N5088 BJT

Q1 2N5457 fet

Q2 2N5088 BJT

Q3 2N5457 fet

From what I can see all your values and orientation looks correct

The LED D1 should flash in time with the rate knob indicating the LFO is working

You should get a pulsing voltage on the collector of Q4

Some of your solder joints look like they may be dry

I’d reflow all of your solder joints holding your iron on each for around 4 seconds until you get a nice flow removing your transistors from their sockets before you reflow

What temperature do you have your soldering iron set to

First check if you get a pulsing voltage on Q4 collector

 

 

[Billy]

Sounds like a fault with the LFO

Does your LED flash when you turn the rate knob

 

[Author]

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