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….

 

[EGRENIER]

View attachment 25103

So the green point all checks out. However, for the red I get connectivity between the 100R and the 220n cap, but nothing to the trim pot lug.

Did a reflow, and still nothing ? Bad board ?

 

[music6000]

I Stuffed up, Opposite side of 100r & Trimpot Lug !!!

 

[EGRENIER]

That make sense now those contacts works.

Im really flabbergasted by that one. Nothing fails, but for some reason it’s not right !

 

[music6000]

Test your Tone Pot

That make sense now those contacts works.

Im really flabbergasted by that one. Nothing fails, but for some reason it’s not right !

Test your Tone Pot for Continuity!
Green & Blue Colours might need to be swapped on Legs 1 & 3 ????
Red is Correct!

 

[EGRENIER]

Test your Tone Pot

Test your Tone Pot for Continuity!
Green & Blue Colours might need to be swapped on Legs 1 & 3 ????
Red is Correct!
View attachment 25107

So you got green and blue right and I’ve got connectivity. However red I don’t. And I know I should, I guess it’s jumper time.

 

[EGRENIER]

@music6000, I think I may have found my problem. In C6 I installed a 0.033uf instead of a 33pf ! And that right in the clipping stage !

I looked into my capacitor stach and of course I don’t have a 33pf. But I have a 47pf or 2 15pf. What would be best here 30p using 2 15pf in parallels ? Or 47pf is close enough ?

 

[Chuck D. Bones]

Use 47pF - close enough.

So much of this would have been discovered in the beginning with a thorough visual inspection.

 

[EGRENIER]

Use 47pF - close enough.

So much of this would have been discovered in the beginning with a thorough visual inspection.

Thanks for the reply….

Well that’s the issue. I double check everything but miscalculated the 333 code of this cap twice. Grrrrr !

I found out because I was building a second board today and couldn’t find my 33pf caps… no wonder !

But there has been so many problem with this board… I really feel bad, I’ve never screwed up so many thing on one board !

 

[Chuck D. Bones]

We've all done it... it was just your turn.

 

[music6000]

Thanks for the reply….

Well that’s the issue. I double check everything but miscalculated the 333 code of this cap twice. Grrrrr !

I found out because I was building a second board today and couldn’t find my 33pf caps… no wonder !

But there has been so many problem with this board… I really feel bad, I’ve never screwed up so many thing on one board !

You gotta measure EVERYTHING before you put it on the PCB!!!!!!!!!!!!!!!!!!
How many times do I have to tell you people!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

It was a a Fun adventure, Glad we got it sorted!
The problem with this PCB is too many options available!!!
When you pull or remove a component, always check for Continuity to that area!

 

[EGRENIER]

You gotta measure EVERYTHING before you put it on the PCB!!!!!!!!!!!!!!!!!!
How many times do I have to tell you people!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

It was a a Fun adventure, Glad we got it sorted!
The problem with this PCB is too many options available!!!
When you pull or remove a component, always check for Continuity to that area!

Thanks for your support , it’s greatly appreciated. Now I have to post a build report.

For the record, I did have to jump the cap to the pot central lug. I must have damaged the board when swapping the tone pot.

I install the 47pf cap and she all lightened up. Now she’s a screamer.

if you didn’t remember, this is a frost bite with a Raincoat combo. Built it for a friend, I’m so glad I got it to work.

 

[Chuck D. Bones]

Good to hear, mark it SOLVED.

A warning: make sure that all of the pot bodies (especially the MID pot) and IN & OUT jacks make good electrical contact with the chassis. Otherwise stray coupling can cause high-freq (ultrasonic) oscillation. I know from experience with this one.