SOLVED Frost Drive - Funky behaviour

[EGRENIER]

Ok, I was hoping never to have to do this, but here we are… my first troubleshooting thread… I think

I built a combo; Frost Drive in a Raincoat.

RainCoat seems OK. But the frost drive for a TS, doesn’t do what I would expect. And there‘s a few this that are just odd.

Here’s the list of odd behaviour:

- Tone knob goes from muddy to super bright in the last 1/20th clockwise.
- Level and Drive maxed out does induce much clipping, it more like just a boost
- Freq and Impedance trimmer doesn’t affect the sound at all
- Mid doesn’t seems to change the tone at all, I used a C100K Dual and applied the recommended changes to R4-5 and C3-4.
- Hi-Cut and Lo-Cut seems to work in different direction. Ex: Lo-Cut gets bright when going CW and Hi-Cut get dark going CCW. I used C10K from the same batch, so it’s not like one is a reverse pot.
- Dip switch seems to have no impact.

Troubleshooting performed so far:

Check the voltage at the MPSA18 +9V is coming in, and check the voltage at R14, -9V is there, so I concluded the charge pump is working fine.
Swap the MPSA18, no impact.
Swap both 4558 and the 1044, no impact.

So at this point’ I’m looking for pointers… In my list of options:

- Reflow the C100K Dual as the mid seems not to work. But inspection let me think it’s fine.
- Replace the C10K of the Tone, maybe it’s defective hence all the bright just at the end (I should measure it resistance to see if it’s just jumping at the end.

I’m attaching picture of the board before assembly, maybe you could spot a mistake.


Thanks in advance….

 

[music6000]

Well on schematic, we can’t tell what diodes is what. So if this is as below, that would explain why D4 get continuity on both legs.

View attachment 24210

As for replacing the 1M pot, which one are you thinking of, the C1M (Drive) or the Trim pot ?

And what would that do in terms of connectivity ?

 

[music6000]

The C1M Drive pot!
By putting the temporary 470K resistor on Legs 1& 2 will simulate it at the 1/2 way mark.
It will prove if the Pot is Bad?

 

[EGRENIER]

The C1M Drive pot!
By putting the temporary 470K resistor on Legs 1& 2 will simulate it at the 1/2 way mark.
It will prove if the Pot is Bad?

I can test it with my DMM, I actually think I did, but will confirm.

 

[EGRENIER]

Bumping this up hoping for help !

I'm still chasing a ghost problem here. While the pedal works, I'm certain I'm not getting the gain out of the Frost Drive that I should get.

Compared to my LGSM where if I crank the Volume and Drive I get loads of gain and boost of the volume, I have to run the Frost Drive at max volume/Max drive to get what seems very little volume boost and almost no clipping/gain.

I've probe the Opamp outpout and I don't seem to see volume/gain lost after the second OpAmp. There a difference between the gain between IC1 and IC2 but it seems very low considering I'm cranking volume and drive knobs to 12!!!

Calling for helps @PedalPCB @jjjimi84 @fig @Chuck D. Bones !!!

Seriously, I'm desperate

Thanks

 

[music6000]

Bumping this up hoping for help !

I'm still chasing a ghost problem here. While the pedal works, I'm certain I'm not getting the gain out of the Frost Drive that I should get.

Compared to my LGSM where if I crank the Volume and Drive I get loads of gain and boost of the volume, I have to run the Frost Drive at max volume/Max drive to get what seems very little volume boost and almost no clipping/gain.

I've probe the Opamp outpout and I don't seem to see volume/gain lost after the second OpAmp. There a difference between the gain between IC1 and IC2 but it seems very low considering I'm cranking volume and drive knobs to 12!!!

Calling for helps @PedalPCB @jjjimi84 @fig @Chuck D. Bones !!!

Seriously, I'm desperate

Thanks

Did you remove the Drive Pot?

 

[jjjimi84]

@music6000 you made some really great images for troubleshooting, hats off to you.

@EGRENIER I would recommend cleaning the board completely first. Scrub all of that flux off and then touch up solder joints.

 

[EGRENIER]

Did you remove the Drive Pot?

I tested a new one and replace it. I know the one in it now is good. So I know this one is good.

 

[music6000]

I tested a new one and replace it. I know the one in it now is good. So I know this one is good.

Have you checked your MPSA18 Transistor is OK, is it solid in the socket?
Do you have another to swap it out, I'm not a fan of Sockets on transistors!!!

 

[EGRENIER]

Did you remove the Drive Pot?

OK so after I replied to you I went back and tested the new Pot that I have now on the board. Here's what I find very strange. If I connect my DDM to leg 1 and 2 (facing underside of the pot testing on the right lug and the central lug). I can only read from 0 to 187K. If I test between 1 and 3 (facing underside from right lug to left lug) I get the same reading range 0 to 187K. Now I don't understand that as I would have expected to get no reading from1 to 3. If I test 2 to 3, I get 0ohm regardless of the pot position.

I went back and tested the pot I removed and off the circuit it now read from 0 to 1M from lug 1 and 2 and from 2 and 3. Nothing form 1 to 3 as expected.

How can this be ? I don't get it.

 

[EGRENIER]

Have you checked your MPSA18 Transistor is OK, is it solid in the socket?
Do you have another to swap it out, I'm not a fan of Sockets on transistors!!!

I've tested 3 different MPSA18, didn't see difference on any. Also tried a full new set of all the other IC (4558 and 1044)

 

[music6000]

OK so after I replied to you I went back and tested the new Pot that I have now on the board. Here's what I find very strange. If I connect my DDM to leg 1 and 2 (facing underside of the pot testing on the right lug and the central lug). I can only read from 0 to 187K. If I test between 1 and 3 (facing underside from right lug to left lug) I get the same reading range 0 to 187K. Now I don't understand that as I would have expected to get no reading from1 to 3. If I test 2 to 3, I get 0ohm regardless of the pot position.

I went back and tested the pot I removed and off the circuit it now read from 0 to 1M from lug 1 and 2 and from 2 and 3. Nothing form 1 to 3 as expected.

How can this be ? I don't get it.

When you test a pot, you measure across Legs 1 & 3 to get the resistance, ie 1M Pot will be 1M !!!
If you can't get a reading across Legs 1 & 3 out of the Circuit, the Pot is Bad!!!!!!!!!!!!!!
If it's a B linear pot and you set the pot at halfway, you will get equal resistance between, ie 1 & 2 = 2 & 3.

 

[EGRENIER]

When you test a pot, you measure across Legs 1 & 3 to get the resistance, ie 1M Pot will be 1M !!!
If you can't get a reading across Legs 1 & 3 out of the Circuit, the Pot is Bad!!!!!!!!!!!!!!
If it's a B linear pot and you set the pot at halfway, you will get equal resistance between, ie 1 & 2 = 2 & 3.

Wait, are you saying I should get a variable resistance reading when testing between 1 and 3 ?

Now you confused me I always understood that the resistance was applied between 1-2 and 2-3, hence like you said a 50-50 distribution of the resistance when set to noon (half way).

 

[music6000]

I've tested 3 different MPSA18, didn't see difference on any. Also tried a full new set of all the other IC (4558 and 1044)

All Pots maximum resistance is measured ON Legs 1 & 3 !!!
A C1M should read approx. 1M ON Legs 1 & 3.
At halfway it should be 800K + between 1 & 2.
Around 200k or less between 2 & 3.

 

[EGRENIER]

All Pots maximum resistance is measured ON Legs 1 & 3 !!!
A C1M should read approx. 1M ON Legs 1 & 3.
At halfway it should be 800K + between 1 & 2.
Around 200k or less between 2 & 3.

OK so I went back to it. And yes, out of the circuit a new pot (and the one I removed for that matter) is behaving exactly as you said.

Consistent 997K between 1 and 3 regardless of pot position
Variable between 1-2 and 2-3 based on pot position.

So in the circuit, should I get the same reading, cuz I'm not and now I'm wondering if that's a clue of my issue...

 

[EGRENIER]

@music6000 you made some really great images for troubleshooting, hats off to you.

@EGRENIER I would recommend cleaning the board completely first. Scrub all of that flux off and then touch up solder joints.

I guess I could do that, however it means removing the dual pot, impossible to fold that one up to redo the solder joints under it.

Unless you have a trick I don't know ?

Also, I've always heard to be careful washing off flux with the Pot. I could be careful of not getting the large pot wet, but there's also 2 trim pots on the board, I'm more concern about those...

 

[music6000]

I guess I could do that, however it means removing the dual pot, impossible to fold that one up to redo the solder joints under it.

Unless you have a trick I don't know ?

Also, I've always heard to be careful washing off flux with the Pot. I could be careful of not getting the large pot wet, but there's also 2 trim pots on the board, I'm more concern about those...

In circuit, it will not behave the same so I don't believe the Pot is your issue.
Isopryl is too messy, I only use Electrical Contact Cleaner in a Pressure pack can to clean all my PCB's.

 

[EGRENIER]

@music6000 you made some really great images for troubleshooting, hats off to you.

@EGRENIER I would recommend cleaning the board completely first. Scrub all of that flux off and then touch up solder joints.

Thanks again for your support @music6000 and @jjjimi84…. It’s greatly appreciated.

So I retouched everything I could. Getting under the dual pot is nearly impossible so I worked those from above.

As I was testing now I notice my tone does nothing. So I started investigating. The pot give me variable 0-20K resistance between 1-2 and 2-3 with consistent with out of circuit behaviour. If I test lug 1 to ground, I get the extra 100k from the resistance at R10, however between lug 2 to ground I would have expected to get the trim pot (freq) as a reading.

Where can I test the trim pot ?

 

[music6000]

Thanks again for your support @music6000 and @jjjimi84…. It’s greatly appreciated.

So I retouched everything I could. Getting under the dual pot is nearly impossible so I worked those from above.

As I was testing now I notice my tone does nothing. So I started investigating. The pot give me variable 0-20K resistance between 1-2 and 2-3 with consistent with out of circuit behaviour. If I test lug 1 to ground, I get the extra 100k from the resistance at R10, however between lug 2 to ground I would have expected to get the trim pot (freq) as a reading.

Where can I test the trim pot ?

 

[EGRENIER]

View attachment 25102

Thanks but that’s impedance and a connectivity test. I’m wondering how I can test that the Frequency trim pot is working ….

At this point, I’m thinking of starting a new one from scratch. I realized today that I have a second frost board. I just hate admitting defeat.

 

[EGRENIER]

View attachment 25103

Thanks… I’ll report back in a minute