# M800 - No Volume



## DrumBuster

Hello everyone, after neglecting my project for almost a year, I finally built my M800, when trying it out, I noticed I had no volume. Bypass works great, j201s all biased to the right voltage (4.5v ish) save for one of them not doing it. It stays stuck at 2.7, is it possible that is the culprit? I got a 2N5458 just in case is a faulty transistor. I check every solder and ground and everything seems fine, led lights up. What it can be the issue? Thanks


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## okstateblues

Pictures are worth 1000 words for this type of troubleshooting. Post a few front and backs for the group.


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## DrumBuster

Kinda late here but here's some pics I took a few hours ago, it's my first project and is quite messy, sorry.


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## DrumBuster

Better gut picture


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## temol

Use the audio probe and trace the signal, starting from the input. 
"One of them" - you have to be specific.

T


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## music6000

The one Trimmer is the *Tone *control, this effects the pedal greatly for overall Final sound per Amp being used! 
You really need to sort out that ''Rats Nest'' going to the Footswitch, Way to much to figure what's going to what!


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## okstateblues

Yes the wires could use some addressing. Also it seems as if your wiring connections are off based on the below diagram.


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## okstateblues




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## Chas Grant

Lets start with the basics,
1. All your wires are too long. These need to be shortened, they will act as antenna when the circuit is working.

2. Look up "Tinning Leads" or "Tinning Wire". Prior to soldering wire, the stripped leads need to be tinned. This helps the solder flow better when soldering wires to board or lugs. It also prevents bird caging of the wires when inserting them in the PCB holes.(power gnd to pcb and input jack to pcb wires exhibit this.)

3. When soldering wires to the PCB, get the insulation as close to board as you can with out touching the board, exposed wires are an easy path for a short. Once you do this a few times you will get it down.

4. Even with the rats nest of wire, something looks off about the 3PDT foot switch wiring. Double check this. 

5. The enclosure is not grounded. Take a Dremel tool and remove the powder coating on the inside top wall of the enclosure. Now the ring of the input and output jacks will ground the enclosure.

6. There are quite a few cold solder joints on the top side of the PCB. At least one or two on each potentiometer. You need to reflow most of the joints. Touch each joint with the solder iron until the solder re-melts and flows around the joint. If you see the solder pad before you touch the joint, then add the tiniest amount of solder. If there is already a lot of solder on joint, then just reflow it with out adding solder. Do the same on the bottom of the board.

7. CLEAN THE BOARD!! It looks as if you poured a bottle of rosin on the board before you soldered it. If you are using rosin core solder then this is unnecessary and detrimental to the board. Clean the board with a toothbrush and alcohol. Be careful not to use to much alcohol at once. You need to keep it out of the pots and trimmers. With as much rosin as you used, this may take quite a long time to accomplish. When you finished cleaning the board, and if using rosin core flux. Place that bottle of rosin out of your reach! Use it only when you have a stubborn joint or when using de-soldering wick. In the future, clean the board prior to attaching wire and pots. Its much easier then.

One question that needs to be asked, where did the J201's come from? They are TO-92's which are hard to come by. Most people are using the SOT-23 package on an adaptor board because of this.


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## DrumBuster

Thanks for the replies guys! The weird J201s are from Small Bear, the one that isn’t biasing is the one in the middle of the lower row. Sorry about the “rats nest” wiring in the switch lol, I did solder based in the wiring guide but I used different color wires I had around. Also thanks for the heads up about the rosin mess, this is the only solder I had at home, is so tacky when it melts, can I use alcohol to clean it up?


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## DrumBuster

This is how the switch looks


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## DrumBuster

Also, if if the bypass works, does it mean the switch works, right?


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## Chas Grant

Yes alcohol and a toothbrush, just not your wife's toothbrush! She might get mad. It may take some time. If it seems like your just spreading the rosin around, try gently wiping with an old t-shirt or thick sock inside out, that's damp with alcohol. The rosin can sometimes cause shorts between close leads. Another reason to clean it off.
And with the wires moved, the wireing seems to be correct, but still hard to see it all.


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## Chas Grant

DrumBuster said:


> Also, if if the bypass works, does it mean the switch works, right?


It means the bypass part of the switch works. Until you verify sound in and out of the PCB the switch could be at fault. You have to rule things out one at a time. You could do resistance checks with no power and switch in effect position. Try to check resistance from the PCB to the corresponding jack. If resistance is low then switch can be called good.


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## DrumBuster

Chas Grant said:


> It means the bypass part of the switch works. Until you verify sound in and out of the PCB the switch could be at fault. You have to rule things out one at a time. You could do resistance checks with no power and switch in effect position. Try to check resistance from the PCB to the corresponding jack. If resistance is low then switch can be called good.


Thanks! Will do that tonight after college, clean with alcohol and then try with the meter, is there a certain mode or I can just use resistance?


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## DrumBuster

Wire order is white, black, yellow and red, that’s from the pcb to the switch.


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## Chas Grant

Resistance for sure, if you have a continuity mode or diode mode that beeps when low that works too. Easier to use also.


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## DrumBuster

Cleaning up the flux mess, hopefully it solves my problem


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## DrumBuster




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## music6000

Can you confirm what is written on the JFet's, ie J201's. This pedal is Fussy about what is used!
We need to see the Solder side of the Board.


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## DrumBuster

Hello everyone, after neglecting my project for almost a year, I finally built my M800, when trying it out, I noticed I had no volume. Bypass works great, j201s all biased to the right voltage (4.5v ish) save for one of them not doing it. It stays stuck at 2.7, is it possible that is the culprit? I got a 2N5458 just in case is a faulty transistor. I check every solder and ground and everything seems fine, led lights up. What it can be the issue? Thanks


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## DrumBuster

music6000 said:


> Can you confirm what is written on the JFet's, ie J201's. This pedal is Fussy about what is used!
> We need to see the Solder side of the Board.


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## DrumBuster

Got them off Small Bear back in oct 2019, this side of the board has a rosin mess caused by the rosin core solder. I’m in process of cleaning it with 80% isopropyl alcohol


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## music6000

DrumBuster said:


> Got them off Small Bear back in oct 2019, this side of the board has a rosin mess caused by the rosin core solder. I’m in process of cleaning it with 80% isopropyl alcohol


You will have to bend those bottom 3 pots up & Clean under that!
Can you write what is on the JFET's?


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## DrumBuster

music6000 said:


> Can you write what is on the JFET's?


Sure, it says J201 07 2.


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## DrumBuster

music6000 said:


> You will have to bend those bottom 3 pots up & Clean under that!
> Can you write what is on the JFET's?


Can I brush under it?


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## Chas Grant

Does the LED light when you engage the effect?


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## music6000

Honestly, I don't use Isopryl or a Brush.
I use CRC Automotive Contact Cleaner, It's Brilliant!
Just spray & watch the Crud fall off. In your case, you may have to spray half a dozen times!
In the USA, you can purchase CRC Contact Cleaner.


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## Chas Grant

music6000 said:


> Honestly, I don't use Isopryl or a Brush.
> I use CRC Automotive Contact Cleaner, It's Brilliant!
> Just spray & watch the Crud fall off. In your case, you may have to spray half a dozen times!
> In the USA, you can purchase CRC Contact Cleaner.



Do you have an issue with it removing certain component markings? I used it on a PCB with white Kemmet caps and it removed the markings on the top on the caps.


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## DrumBuster

music6000 said:


> Honestly, I don't use Isopryl or a Brush.
> I use CRC Automotive Contact Cleaner, It's Brilliant!
> Just spray & watch the Crud fall off. In your case, you may have to spray half a dozen times!
> In the USA, you can purchase CRC Contact Cleaner.


I have CRC electronics cleaner, I should get CRC 5103, right?


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## DrumBuster

Chas Grant said:


> Does the LED light when you engage the effect?


Yes! The blue led is super bright!


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## Chas Grant

OK you have power to the circuit. I was wondering because the ground wire from the DC jack to PCB has a questionable solder joint. You may need to reflow all the solder joints. Also do you have an extra J201, if so try swapping each one out, one at a time.


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## DrumBuster

Chas Grant said:


> OK you have power to the circuit. I was wondering because the ground wire from the DC jack to PCB has a questionable solder joint. You may need to reflow all the solder joints. Also do you have an extra J201, if so try swapping each one out, one at a time.


I have a 2n5458, some guy recommended it to me to replace the faulty j201 if needed, if the other transistors are biased at 4.5v, they work, right?


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## DrumBuster

DrumBuster said:


> I have a 2n5458, some guy recommended it to me to replace the faulty j201 if needed, if the other transistors are biased at 4.5v, they work, right?


The tone trim doesn’t affect the transistor, does the transistor need to have 9v by default, right?


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## Chas Grant

DrumBuster said:


> The tone trim doesn’t affect the transistor, does the transistor need to have 9v by default, right?


Not Necessarily. A JFET is constructed differently than a BJT transistor.  The biasing trimmers are setting the voltage on the drain. With no input to the pedal you should have zero volts on the gate. Voltage on the drain should be same as voltage on the source. When you apply the input and it is going negative, the JFET will start to restrict the electron flow through the device and as you reach pinch off voltage, will stop the electron flow. Now drain voltage will go up and source voltage will go down. An easy way to think about it is like a garden hose. Turn it on and water flows freely, a JFET with out gate voltage. Now start to pinch the hose with your hand, water flow is reduced, pressure up stream of pinch goes up. When you pinch hard enough, flow stops. This is like a JFET as gate voltage is applied, when gate voltage reach Vgs off it doesn't conduct. 

So by bias voltage, I assume you are talking about drain voltage, which is pin 1 on a J201.

Also I'm not so sure a 2N5458 will substitute for a J201 in this circuit. A J201 has a Vgs off of -.5 to -1.5, a 5458 has a Vgs off of -1 to -7, what you would have to do is test a few out and find one that is in the -1 range. If it was a JFET buffer, than most likely it would work, but this is being used as an amplifier.


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## DrumBuster

Chas Grant said:


> Not Necessarily. A JFET is constructed differently than a BJT transistor.  The biasing trimmers are setting the voltage on the drain. With no input to the pedal you should have zero volts on the gate. Voltage on the drain should be same as voltage on the source. When you apply the input and it is going negative, the JFET will start to restrict the electron flow through the device and as you reach pinch off voltage, will stop the electron flow. Now drain voltage will go up and source voltage will go down. An easy way to think about it is like a garden hose. Turn it on and water flows freely, a JFET with out gate voltage. Now start to pinch the hose with your hand, water flow is reduced, pressure up stream of pinch goes up. When you pinch hard enough, flow stops. This is like a JFET as gate voltage is applied, when gate voltage reach Vgs off it doesn't conduct.
> 
> So by bias voltage, I assume you are talking about drain voltage, which is pin 1 on a J201.
> 
> Also I'm not so sure a 2N5458 will substitute for a J201 in this circuit. A J201 has a Vgs off of -.5 to -1.5, a 5458 has a Vgs off of -1 to -7, what you would have to do is test a few out and find one that is in the -1 range. If it was a JFET buffer, than most likely it would work, but this is being used as an amplifier.


Thanks for this info! I will check tomorrow with the meter, can’t find mine so will have to borrow one. Really hope is just a solder issue. Will have to order new JFETs if mine are fried, saw Mouser has them new for $3.49.


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## Chas Grant

DrumBuster said:


> Thanks for this info! I will check tomorrow with the meter, can’t find mine so will have to borrow one. Really hope is just a solder issue. Will have to order new JFETs if mine are fried, saw Mouser has them new for $3.49.


Read up on JFET's in the forum, Chuck's Boneyard. He knows his stuff STONE COLD. I have a working knowledge of them, but really didn't see them until I started down this rabbit hole of a hobby awhile ago. Most other components, I have worked with for quite a long time,  those JFET's though, they have bitten mine, and most peoples, behinds once or twice.


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## DrumBuster

Chas Grant said:


> Read up on JFET's in the forum, Chuck's Boneyard. He knows his stuff STONE COLD. I have a working knowledge of them, but really didn't see them until I started down this rabbit hole of a hobby awhile ago. Most other components, I have worked with for quite a long time,  those JFET's though, they have bitten mine, and most peoples, behinds once or twice.


Will do! Thanks, I saw the PF5102 are super close on VGS(off) but it has a different idss. Will ask Chuck just to be sure.


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## Chas Grant

One other thing to try is an audio probe. You can make on easily. I've got one on a jack and one on an alligator clip lead. I've also seen people suggest using an old multimeter probe ( which is a great idea. But its basically a 100nF cap with a short stiff wire on one lead and a wire thats long enough to allow you to work and have it connected to a jack so that you can run it into the amp. Connect the jack ground to pedal ground, now the probe is the input to the amp and you can check for audio at various places in circuit. I find it easiest to start a input and work my way to output. If you look at the schematic you can follow the audio patch through the circuit, its usually pretty straight. If you lose the signal you can find out where and concentrate there.


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## DrumBuster

Chas Grant said:


> One other thing to try is an audio probe. You can make on easily. I've got one on a jack and one on an alligator clip lead. I've also seen people suggest using an old multimeter probe ( which is a great idea. But its basically a 100nF cap with a short stiff wire on one lead and a wire thats long enough to allow you to work and have it connected to a jack so that you can run it into the amp. Connect the jack ground to pedal ground, now the probe is the input to the amp and you can check for audio at various places in circuit. I find it easiest to start a input and work my way to output. If you look at the schematic you can follow the audio patch through the circuit, its usually pretty straight. If you lose the signal you can find out where and concentrate there.


Interesting, will make one tomorrow, I’m sure I have a 100nf cap somewhere, is there a video / tutorial I can check out?


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## Chas Grant

If you Google "audio probe pedal" videos will come up, along with how to make them. Cap size isn't too important, any size cap above 10n to 220n will work. It's primary purpose is to keep DC from being passed to the amp if you touch the wrong lead.


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## DrumBuster

Hello everyone, after neglecting my project for almost a year, I finally built my M800, when trying it out, I noticed I had no volume. Bypass works great, j201s all biased to the right voltage (4.5v ish) save for one of them not doing it. It stays stuck at 2.7, is it possible that is the culprit? I got a 2N5458 just in case is a faulty transistor. I check every solder and ground and everything seems fine, led lights up. What it can be the issue? Thanks


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## DrumBuster

Chas Grant said:


> If you Google "audio probe pedal" videos will come up, along with how to make them. Cap size isn't too important, any size cap above 10n to 220n will work. It's primary purpose is to keep DC from being passed to the amp if you touch the wrong lead.


Hello, I used the meter. Q2 doesn’t seem to be on spec, when I have the trim pot at the minimum, it reads 0.005 on drain, when is on the right, it reads 2.5


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## DrumBuster

DrumBuster said:


> Hello, I used the meter. Q2 doesn’t seem to be on spec, when I have the trim pot at the minimum, it reads 0.005 on drain, when is on the right, it reads 2.5


Tried everything regarding continuity and everything seems alright


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## music6000

DrumBuster said:


> Hello, I used the meter. Q2 doesn’t seem to be on spec, when I have the trim pot at the minimum, it reads 0.005 on drain, when is on the right, it reads 2.5


Mark the suspicious J201 & SWAP it with a Good J201 & see if it is Good in Q2.


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## DrumBuster

music6000 said:


> Mark the suspicious J201 & SWAP it with a Good J201 & see if it is Good in Q2.


Will order another j201 or pf5102, might be luckier, Chuck said in another thread that it works just as right. Don’t wanna risk spending $7 in fake 201s, these ones were “generics” Small Bear sold, is there any other reputable site?


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## music6000

DrumBuster said:


> Will order another j201 or pf5102, might be luckier, Chuck said in another thread that it works just as right. Don’t wanna risk spending $7 in fake 201s, these ones were “generics” Small Bear sold, is there any other reputable site?


You need to swap it with One that has bias Good in the Pedal to make sure you don't have an issue in Q2!


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## music6000

music6000 said:


> You need to swap it with One that has bias Good in the Pedal to make sure you don't have an issue in Q2!





DrumBuster said:


> Will order another j201 or pf5102, might be luckier, Chuck said in another thread that it works just as right. Don’t wanna risk spending $7 in fake 201s, these ones were “generics” Small Bear sold, is there any other reputable site?


This is my Only request/ suggestion:








						MMBFJ201 JFET (Pre-Soldered) - PedalPCB.com
					

JFET




					www.pedalpcb.com


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## Chas Grant

DrumBuster said:


> Will order another j201 or pf5102, might be luckier, Chuck said in another thread that it works just as right. Don’t wanna risk spending $7 in fake 201s, these ones were “generics” Small Bear sold, is there any other reputable site?


Mouser has them, but they are expensive. music6000's suggestion is cheaper.


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## Chas Grant

These are the generic drain voltages that others are shooting for on this circuit. They may be helpful
Q1-3.78V     Q2-6.85V     Q3-4.02V     Q5-5.6V   Q6-2.7V


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## DrumBuster

Chas Grant said:


> These are the generic drain voltages that others are shooting for on this circuit. They may be helpful
> Q1-3.78V     Q2-6.85V     Q3-4.02V     Q5-5.6V   Q6-2.7V


Oooh, didn’t know they sold smd to to92 pre soldered.


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## music6000

Chas Grant said:


> These are the generic drain voltages that others are shooting for on this circuit. They may be helpful
> Q1-3.78V     Q2-6.85V     Q3-4.02V     Q5-5.6V   Q6-2.7V



I built the first M800 way back, It worked but I knew something was wrong with the lack of sustain:





						M800 Overdrive
					

Awesome JCM800 Emulation !!! All the Trimmers were adjusted to 4.5v & it was meh, 4.75, 5v, 5.25v & 5.5v, Louder with no Gain! Old School, Strummed a Chord & tuned each Trimmer by ear. Critical Trimmer is the Tone trimmer, This effects overall EQ & gives it the Power of The JCM800 sizzle! The...



					forum.pedalpcb.com


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## DrumBuster

Ordered 8 PF5102, based on Chuck’s recommendations in a thread, I bought 8 just to be sure.


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## music6000

DrumBuster said:


> Ordered 8 PF5102, based on Chuck’s recommendations in a thread, I bought 8 just to be sure.


Seeing yo have ordered replacement, Swap the J201 under the Tone Trimmer with Q2 to see if your voltage comes up!


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## Chas Grant

music6000 said:


> Seeing yo have ordered replacement, Swap the J201 under the Tone Trimmer with Q2 to see if your voltage comes up!


I agree!! Swapping parts is a very effective way of troubleshooting! Even more so when you have more on the way!


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## DrumBuster

I will! Thanks for the tips guys! Guess I’m falling down the rabbit hole in the diy pedal world lol


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## DrumBuster

I’m back guys! They arrived today, it has been a painful 2 week wait lol


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## DrumBuster

DrumBuster said:


> I’m back guys! They arrived today, it has been a painful 2 week wait lol


Swapped the faulty transistor, now I have a weird sound, is like noise. Plus when I adjust the trimmer of Q3, I hear crackles.


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## DrumBuster

All transistors have been biased to 5v as test, but I can’t hear my guitar at all


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## DrumBuster

I think I kinda damaged q3 and q2’s pads a bit, but they still read 9v


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## DrumBuster

The transistors have now been replaced with pf5102s, I now get that hum but no tone, just on bypass.


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## music6000

DrumBuster said:


> I think I kinda damaged q3 and q2’s pads a bit, but they still read 9v


Check Q2 & Q3 for Continuity with Matching Colours.
If you don't get continuity, It aint going to work!
You can get Voltage at the Drain, that doesn't mean the other 2 legs are working correctly:


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## DrumBuster

Hello everyone, after neglecting my project for almost a year, I finally built my M800, when trying it out, I noticed I had no volume. Bypass works great, j201s all biased to the right voltage (4.5v ish) save for one of them not doing it. It stays stuck at 2.7, is it possible that is the culprit? I got a 2N5458 just in case is a faulty transistor. I check every solder and ground and everything seems fine, led lights up. What it can be the issue? Thanks


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## DrumBuster

Okay, I tested all 6 transistors and their trim pots, all work but I noticed the tone trimpot (I know that transistor has a fixed bias so that trimpot doesn’t do anything besides eq), I don’t see anything on the meter


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## music6000

DrumBuster said:


> Okay, I tested all 6 transistors and their trim pots, all work but I noticed the tone trimpot (I know that transistor has a fixed bias so that trimpot doesn’t do anything besides eq), I don’t see anything on the meter


Are you getting around 9v+ from the Drain on Q4, If not we will have to do a Continuity test on that!


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## music6000

Continuity Test all these Colour matched Circles as requested & report:


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## DrumBuster

music6000 said:


> Continuity Test all these Colour matched Circles as requested & report:View attachment 8671


Thanks! Will try again


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## DrumBuster

Every color combination provided gave me good results when doing the continuity test


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## DrumBuster

I installed (horribly) the new transistors and they’re not biased at 5v ish each except the fixed one. But I noticed some capacitors at the bottom of the circuit arent responding to the test


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## music6000

DrumBuster said:


> Every color combination provided gave me good results when doing the continuity test


Continuity Test all these Colour matched Circles and report:


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## music6000

DrumBuster said:


> I installed (horribly) the new transistors and they’re not biased at 5v ish each except the fixed one. But I noticed some capacitors at the bottom of the circuit arent responding to the test


Are you getting around 9v+ from the Drain on Q4 (Fixed One).
Continuity only tests if the trace has been damaged between Solder pads, Not across components.


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## DrumBuster

music6000 said:


> Are you getting around 9v+ from the Drain on Q4 (Fixed One).
> Continuity only tests if the trace has been damaged between Solder pads, Not across components.


Typo, they’re biased! Sorry


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## DrumBuster

music6000 said:


> Continuity Test all these Colour matched Circles and report:
> View attachment 8678


No issues!


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## DrumBuster

I'm checking the transistors' drain voltage, just to be sure again. Noticed something, Q5's trimmer doesn't work at all, is still stuck at 8.9+v at drain.


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