# No output on M800



## JetFixxxer

Adjusted all drains J112/PF5102 to 5v.

Looked for cold solders, bridges, and cleaned the bottom.

Verified resistor value again.


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## JetFixxxer

It's my attempt of two in one..  The Twill Deluxe sounds Amazing! Now I just need to get the M800 working.

I did a little more tracing from input lug to "3" of Q1 (1) to Gain Pot to Q2 (3).. etc.. everything seems fine.
The spare wiring are ground which I had to the jacks.  Disconnected for t/s.


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## JetFixxxer

Used Signal Gen and put 440 into the input and used an old amp speaker as audio probe.  I had tone up into 3 of Q1.  Check Gain Pot at the 3 lug and not getting a tone.


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## JetFixxxer

Suggestions?


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## music6000

JetFixxxer said:


> Suggestions?


Your M800 has some Pot lugs that look suspect in Solder joints.
The M800 Top Left Footswitch Lug looks like a Dry Joint.
You may need to reflow a few others.
If you look at your Build in Supersize with the + option you will see.
Make sure your transistors are Firmly in position, I'm not a fan of  transistor sockets.


I use 3.5 % Glasses when doing this Pedal work.
My prescription glasses are 2.25%

Cheers music6000


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## Robert

JetFixxxer said:


> Used Signal Gen and put 440 into the input and used an old amp speaker as audio probe.  I had tone up into 3 of Q1.  Check Gain Pot at the 3 lug and not getting a tone.



Looks like you're losing signal at the first gain stage.       

Check for signal on pin 1 of Q1.   If there is no signal measure the voltage on pin 1.   You should have somewhere near 4.5V.


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## JetFixxxer

Thanks will try and report back.

Isnt PIN 1 the drain?  At pin 1 I measured 9v and trimmed it down to 5v.


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## Jiuk

Check your J201. I bought 100's of J201 from Chinese seller on Ebay and received 100's of bipolar TR but marked J201. It's all fake.


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## JetFixxxer

Thanks will try and report back.

Isnt PIN 1 the drain?  At pin 1 I measured 9v and trimmed it down to 5v. Unless I'm reading the pinout wrong.


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## JetFixxxer

Jiuk said:


> Check your J201. I bought 100's of J201 from Chinese seller on Ebay and received 100's of bipolar TR but marked J201. It's all fake.


I'm using J112 and PF5102.  Got them from Small Bear. I might just get the J102 with adapters if everything else checks good.


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## JetFixxxer

music6000 said:


> Your M800 has some Pot lugs that look suspect in Solder joints.
> The M800 Top Left Footswitch Lug looks like a Dry Joint.
> You may need to reflow a few others.
> If you look at your Build in Supersize with the + option you will see.
> Make sure your transistors are Firmly in position, I'm not a fan of  transistor sockets.
> 
> 
> I use 3.5 % Glasses when doing this Pedal work.
> My prescription glasses are 2.25%
> 
> Cheers music6000


Thanks.  The foot switch lug was taken care of already. I will reflow the pots


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## Robert

JetFixxxer said:


> Isnt PIN 1 the drain?  At pin 1 I measured 9v and trimmed it down to 5v. Unless I'm reading the pinout wrong.



Yep, Pin 1 is Drain, but also the "output" of that gain stage.   So you should see signal there, preferably with higher amplitude than Pin 3.


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## JetFixxxer

Robert said:


> Looks like you're losing signal at the first gain stage.
> 
> Check for signal on pin 1 of Q1.   If there is no signal measure the voltage on pin 1.   You should have somewhere near 4.5V.


Q1 Pin Drain = 5.98v
Q1 Pin Source = 2.4v
Q1 Pin Gate = -1.7v

I'm assuming Pin1 = Drain, Pin2 Source, Pin3 Gate


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## JetFixxxer

Did reflow the pots and still nothing.

Here's what I did with the Signal Gen with it set to 440ish going into the input.  The Dark Green Circle is loud, the lighter green are lower volume, pink is barely audible, and the red lines no tone. Verified the no tone with scope.  

Check with my scope
R2 = Sine
R3 = Triangle
Q1 = Triangle
R4 = Square

Gain Pot
Lug 1 & 2 getting square wave
Lug 3 I get nothing





Checked the rest


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## Chuck D. Bones

How did you manage to get a negative voltage on Q1's gate?  Or is that a typo?  Are you measuring everything w.r.t. GND?

Your sig gen amplitude should be set to something like 100mVp-p.  Looks like you are overdriving Q1.  I'll assume that you meant to type 1.7V for Q1's gate voltage.  That makes Vgs = 1.7V - 2.4V = -0.7V which is correct for a J201.  Drain voltage looks good too.  You're getting signal on one side of R4 but not the other.  A short to ground at R4, C3 or the GAIN pot would do that.  Can you explain how it is possible to have no signal at the GAIN pot but have signal at Q2?  Q2 gets its signal from the GAIN pot.  You'd need more shorts to get signal to sneak around the GAIN pot.  Possible, but not likely.  You might want to re-check your measurements.  We'll get lost real quick if we're troubleshooting with bad information.


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## JetFixxxer

Chuck D. Bones said:


> Can you explain how it is possible to have no signal at the GAIN pot but have signal at Q2?.



I can't..
If I go from Q1 pin 3 to ground the reading is - (negative).. I've tried other PF5102 and J112 with the same result.  I get no tone on the Gain pot.

Vp-p is set to 100mV.

If I measure from R4 to Lug 3 of the GAIN POT I get 470k


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## music6000

1. Is Gain pot Lug 1 going to Ground & on the PCB pad.
2 Has the Gain pot been tested.


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## JetFixxxer

music6000 said:


> 1. Is Gain pot Lug 1 going to Ground & on the PCB pad.
> 2 Has the Gain pot been tested.



Lug 1 to Ground and PCB pad.  yes
Testing it in the PCB getting. yes


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## JetFixxxer

Any other suggestions?


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## Chuck D. Bones

Let's recap what we saw/heard in the video.  When you probe the bottom end of R3, which is supposed to be ground, you get the same signal as when you touch the input on the footswitch.  How is your board grounded?  I'm thinking it's not.  I see a black wire dangling and another one going to a lug on the output connector, but I can't tell if it's the correct lug.  Where is your audio probe grounded?


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## JetFixxxer

Adjusted all drains J112/PF5102 to 5v.

Looked for cold solders, bridges, and cleaned the bottom.

Verified resistor value again.


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## Nostradoomus

Did you trim the wire on the dc splitter so the protruding ends on the solder side aren’t making contact with the nut?


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## JetFixxxer

Chuck D. Bones said:


> Let's recap what we saw/heard in the video.  When you probe the bottom end of R3, which is supposed to be ground, you get the same signal as when you touch the input on the footswitch.  How is your board grounded?  I'm thinking it's not.  I see a black wire dangling and another one going to a lug on the output connector, but I can't tell if it's the correct lug.  Where is your audio probe grounded?



The wires dangling one comes from the TWILL PCB and the other is the PCB of the M800.  Which when I first completed the build the Twill was grounded to the output jack and the M800 was grounded to the input jack.  

The probe I ground to the enclosure or the ground on the output jack.   I've also just grounded the dangling wires to the enclosure as well. 

The Twill works without issues.

I get 9.1v to the PCB.


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## JetFixxxer

Nostradoomus said:


> Did you trim the wire on the dc splitter so the protruding ends on the solder side aren’t making contact with the nut?



Yes.


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## Chuck D. Bones

And the problem with the M800 still exists?  I'm trying to figure out how you got a tone in your audio probe when you touched the ground end of R3.


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## JetFixxxer

Chuck D. Bones said:


> And the problem with the M800 still exists?  I'm trying to figure out how you got a tone in your audio probe when you touched the ground end of R3.


Twill works M800 Doesn't. 

I don't know why I'm getting tone on R3.  I took a 20x Jeweler loupe and check all the solder joints on the bottom of the PCB.  Everything looks good no bridges of solder to terminal.  Cleaned it again with alcohol with a toothbrush.


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## Chuck D. Bones

Can you measure the resistance from the bottom end of R3 to the ring of each jack?  Not the terminal, the actual ring on the outside of the box.   Also provide an updated photo if you did anything to change the wiring.


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## JetFixxxer

.5 Ω to both the input and output jack from the bottom end of R3.  This is assuming bottom end is toward Q2. .  Top end I get around 25MΩ.


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## Chuck D. Bones

You were touching R2, not R3 like I had thought.  This troubleshooting by remote control is tricky stuff!  Hard enough to do when you're there.  
The signal on R4 was very weak.  Does Q1-D (pin 1) sound the same as the bottom-end of R4?  Q1's drain voltage was good the last time you reported it.  Maybe C2 is bad or has a bad connection.  Check the resistance from pin 1 to pin 3 on the GAIN pot.  Should be 1Meg with the GAIN set to 0, 5 or 10.


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## JetFixxxer

GAIN pot 0, 5, and 10 = .976mΩ.
Very low tone on the drain of Q1.  Have to put my ear to the speaker to hear it.  It's lower than R4.  Drain 5.6v.
Will check C2 and see if that's it.


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## Chuck D. Bones

Little "m" is usually reserved for "milli," capital "M" signifies Meg.  I'm gonna go out on a limb and assume you meant 0.976M as in 976K.  No signal on Q1 drain, but drain has the correct DC voltage.  Hmmmmm...
Maybe Q1's gate is shorted to ground or source?  Measure resistance from Q1-G (pin 3), or the top end of R2, to ground.


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## music6000

Chuck D. Bones said:


> Little "m" is usually reserved for "milli," capital "M" signifies Meg.  I'm gonna go out on a limb and assume you meant 0.976M as in 976K.  No signal on Q1 drain, but drain has the correct DC voltage.  Hmmmmm...
> Maybe Q1's gate is shorted to ground or source?  Measure resistance from Q1-G (pin 3), or the top end of R2, to ground.


That's why It would be Good to see a Pic of the back of the Board!!!
I been thinking Solder bridge on Q1 socket.


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## JetFixxxer

Sorry didn't proof read. You're correct about the M..


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## JetFixxxer

Q1 G to Ground 1.05MΩ, same from top of R2 to GND.


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## Chuck D. Bones

Fire it up again and see if it's still broken.  Maybe there was a short and now it's gone?  I've run out of (good) ideas.


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## JetFixxxer

Chuck D. Bones said:


> Fire it up again and see if it's still broken.  Maybe there was a short and now it's gone?  I've run out of (good) ideas.



Thanks for you help.  This weekend I will mess with C2.


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## music6000

JetFixxxer said:


> Thanks for you help.  This weekend I will mess with C2.


Remove Q1 & TEST for Continuity between D & S, S & G pins to rule out Bridging.
 Can you do a Continuity Test matching the Coloured Dots.


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## JetFixxxer

music6000 said:


> Remove Q1 & TEST for Continuity between D & S, S & G pins to rule out Bridging.
> Can you do a Continuity Test matching the Coloured Dots.
> 
> View attachment 1763


OL = D&S, S&G.
Continuity between matching color dots.


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## PKRPedals

I hope you get this working. I have built 2 of them and neither one worked out for me. I get sound but it is terrible. Good luck.


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## JetFixxxer

PKRPedals said:


> I hope you get this working. I have built 2 of them and neither one worked out for me. I get sound but it is terrible. Good luck.


That doesn't give me hope


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## PKRPedals

Don't give up, you'll get it.


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## JetFixxxer

Adjusted all drains J112/PF5102 to 5v.

Looked for cold solders, bridges, and cleaned the bottom.

Verified resistor value again.


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## JetFixxxer

PKRPedals said:


> Don't give up, you'll get it.



Not many more components to go through.  C2 is my last suspected component.


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## music6000

What Voltage are you getting on Q4 Drain & Gate?.
Where is Tone Trimmer set?


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## JetFixxxer

music6000 said:


> What Voltage are you getting on Q4 Drain & Gate?.
> Where is Tone Trimmer set?



Drain 8.8v, Gate 5.5v, and Source 6.2v
Tone trim is midway


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## music6000

JetFixxxer said:


> Drain 8.8v, Gate 5.5v, and Source 6.2v
> Tone trim is midway


Next!
Are you getting 22nF from each Green Dot to Pink Dot?
470K from each green dot to Lug 3 of Gain Pot?


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## JetFixxxer

music6000 said:


> Next!
> Are you getting 22nF from each Green Dot to Pink Dot?
> 470K from each green dot to Lug 3 of Gain Pot?
> 
> View attachment 1801



22.6nF throughout.


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## music6000

JetFixxxer said:


> 22.6nF throughout.


I'm just about out of Ideas!
Test the Footswitch Pads for Continuity in On & Bypass modes.
Also check they are not bridged paralell.


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## JetFixxxer

music6000 said:


> I'm just about out of Ideas!
> Test the Footswitch Pads for Continuity in On & Bypass modes.
> Also check they are not bridged paralell.
> 
> View attachment 1802



That checks good as well.


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## music6000

JetFixxxer said:


> 22.6nF throughout.


What about 470k from each Green dot to Lug 3 ( Left Pad ) of Gain pot


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## JetFixxxer

I'm getting 470k from each green dot to Lug 3.

I need to setup a camera so I can record what I'm doing..


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## music6000

JetFixxxer said:


> I'm getting 470k from each green dot to Lug 3.
> 
> I need to setup a camera so I can record what I'm doing..



Try This!
Plug it In, Turn your Volume & Gain pots to Max.
Bass 10.00 & Mids, Treble to 2.00 O'clock.
Flip it over & Turn each Trimmer in order Q1, Q2, Q3, Q5, Q6 & Wiggle each Transistor to make sure it is making Connection by* Ear *til it gives the loudest audible signal if possible while hitting a Chord on the guitar.
Repeat Trimmer Adjustment 2 more times!
( Tone Trimmer to 9.00 O'clock)
Hopefully, It might fire up!


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## music6000

When I built mine (Fairchild J201), it was set to 4.5v on each Trimmer & it was not Good, I adjusted up to 5.5v in .25v increments.
It got Louder but was loosing Drive & Sustain.
So, I did what I have suggested above, It's very selective about  jfets being * =* !
To dial it in where it works at its Best, This was it:
Q1 = 2.75v
Q2 = 2v
Q3 = 3.1v
Q5 = 4.71v
Q6 = 3.35v

Q4 = 8.65v which is  Fixed , the Tone Trimmer is a Internal Tone pot!

4.5v is a reference voltage, Then you can fine tune.
I believe Members here got close to 4.5v on all trimmers, they used Siliconix  J201's which I think are the most Stable ones.
They are Hard To Find & you pay a Premium price!!!
Ultimately, they should be all matched if you have a Stockplie of them!
Maybe  J112/PF5102 are not an alternative in this circuit?


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## JetFixxxer

music6000 said:


> Maybe  J112/PF5102 are not an alternative in this circuit?



This is what I'm thinking.


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## JetFixxxer

For clarification you want me to move all the trimmers to full. You want me tap again or just turn to full to see if they are audible?


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## music6000

JetFixxxer said:


> For clarification you want me to move all the trimmers to full. You want me tap again or just turn to full to see if they are audible?


Adjust the Trimmers that are Dead over their Full rotation & confirm if Audible which the Screwdriver should do?
Which Jfet is Audible,  J112 or PF5102 ?
*Update: * I just did what you did in the video above & its more audible when you tap the actual Screw.
You only have to be a whisker off adjustment & there is a massive Volume drop on the Trimmers.
Try adjusting each Trimmer as I described by Ear to the most loudest sound point.
Even pressing too hard on the Screwdriver can have an effect.
You have to repeat this 2 times as each trimmer effects Voltage to the others.


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## Chuck D. Bones

Banging on the trimmers vibrates everything. The may well be an intermittent short or open somewhere. Try banging on just the board, not on a component.

I think you should audio probe each lead on Q1 & R4 again.  We must have missed something.  First set Q1's drain to approx 4.5V.

According to the schematic, turning the trimmers clockwise makes the resistance decrease.  All the way to zero Ohms (more or less) at full CW.  Here's the thing: depending on which trimmer you buy, the rotation could be backwards.  Bourns trimmers come both ways.  I have experienced this.  Either end of the trimmer rotation will kill the gain of that stage because at zero Ohms, the JFET is driving a short circuit and at the maximum resistance, the JFET saturates (or gets pretty close to it).  The trimmers interact in the sense that each one affects the level & distortion of the signal driving the next stage.  You should be able to dial the drain voltages to 4.5V and get some sound to pass through the board.  TRIM2 might be the only exception, 4.5V on Q2's drain might be too low because R8 is relatively large.  On Q2's drain, I'd shoot for 6V for starters.  PF5102 should work fine in this circuit, their specs are very similar to J201.  Last I heard, we're not getting any signal at the GAIN pot.  If that's still the case, then messing with anything downstream is futile at this stage in the game.


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## JetFixxxer

Set the Drains to 4.5v except for Q4 which is at 8.9v and gate 4.5v.   If I tap the PCB and the also the enclosure I'm getting the audible pop.   It's getting grounded somewhere.


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## Chuck D. Bones

You measured ~1Meg from GAIN pin 3 to ground, so no short there or on the other side of R4.  You measured 470K from the junction of C2, C3 & R4 to GAIN pin 3, so we know R4 is good.  You measured 22nF across C2, so it's good.  Check the source (pin 2) voltage on Q1.  Is Q1 tight in its socket?


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## JetFixxxer

2.9v on Source.  It's tight in the socket...

I  guess it a pedal that should have been.. I put too much time into this trying to get it work.


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## Chuck D. Bones

You must have a J112 installed for Q1 because that source voltage would be out of spec for J201 or PF5102.  You should be getting signal on Q1-D that is louder than Q1-G.  The resistance of TRIM1 must be set to around 4K ohms, which is pretty close to the end of the travel for a 100K pot.  PF5102 would be a better choice for Q1, but it should still work with J112.


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## JetFixxxer

You are correct about the J112.  I've been swapping J112 and PF5102.. I will put a PF back in Q1.

Set Drain to 4.4v and source is now .95v and getting nothing on gate.

Replaced two PF5102 with newer ones and now I'm getting some signal...

I think it might have been the J112.. I replaced all but one J112 and seems to be getting better.


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## JetFixxxer

Adjusted all drains J112/PF5102 to 5v.

Looked for cold solders, bridges, and cleaned the bottom.

Verified resistor value again.


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## music6000

We Shall Not Surrender !!!!


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## JetFixxxer

I'm going to order some J201 and see if that changes anything.  

Mouser has some in stock or I might just try SMD w/TO-PCB92.  Not sure if 90° header would be better or just the standard header.


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## Nostradoomus

You definitely want right angle headers if you’re using adapter boards...most of the time anyway


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## Chuck D. Bones

Gate voltage should be zero on Q1.  If you measure anything other than zero on Q1's gate, then Q1 is bad.  Those source and drain voltages look ok.  It's important to check source & drain voltages on each FET.  They should always be a few volts apart.


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## JetFixxxer

Received my J201 and everything it works.  Now in the process of tweaking. I'm pretty close, but will give it a few days of messing around with it.  

Also any suggestion on securing the J201 into the sockets better.  They feel a little sloppy to me.  I was thinking using a glue gun and adding a dab of glue.


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## zgrav

JetFixxxer said:


> Received my J201 and everything it works.  Now in the process of tweaking. I'm pretty close, but will give it a few days of messing around with it.
> 
> Also any suggestion on securing the J201 into the sockets better.  They feel a little sloppy to me.  I was thinking using a glue gun and adding a dab of glue.



I have followed a suggestion from another forum member to flow a little bit of solder onto the transistor leads to slightly increase their size for a better fit.


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## Chuck D. Bones

Or if you're done swapping JFETs, remove the sockets and solder the JFETs in.


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## DrumBuster

Hey! Finally got to check my pedal, is it normal that Q2 to be 2.5v all the way to the trim pot?


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## Chuck D. Bones

At one end of the trimpot's travel, Q2-D will be at +9V.  +2.5V at the other end is ok.  What's most important is finding a place on the trimpot that sounds good.


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