Thermionic Deluxe Clicking/Tapping Sound on One Channel

[Hexjibber]

Hi all,

It's late here in the UK but literally just plugged in my Thermionic Deluxe build, one channel works great and sounds awesome but the other channel (the top row of components on the PCB) is making a strange clicking/tapping oscillation of sorts and the signal is much quieter as well as being quite fuzzy. Before I start the painful procedure of checking it over and getting voltages etc just wondered if anyone could hazard a guess what it is likely to be so I can focus my search a little? I was dreading there being a problem with this due to the high parts count but hey I'm sure I'll get to the bottom of it!

Any help great appreciated!

Cheers,
Graham

 

[Nostradoomus]

Definitely post some pictures man! With that many parts it’s good to get more eyes on your values.

 

[Hexjibber]

 

[Hexjibber]

Here’s a quick pic in case there’s something obvious! I’ll give it a proper look over tomorrow and start taking some voltages. The good thing is I can more or less just compare it with the working channel so hopefully the answer will leap out!

 

[Nostradoomus]

Is that big ceramic disk cap for sure 100p? Looks like it might say 104 on it and it’s much bigger than the one on the other channel below.

 

[Nostradoomus]

 

[Hexjibber]

Pretty sure it’s a 101, thanks for having a look though!

 

[Hexjibber]

Had a look through the other caps all they all look correct. Going to measure some voltages next and compare

 

[Hexjibber]

Upon removing the board from the enclosure to measure voltages (no anomalies found so looks fine) and prepare myself for some desoldering the problem is gone! So must be one of the pots in circuit A grounding on something presumably as obviously both circuits share the jacks, DC jack etc. It narrows it down which is good! Not quite sure what is actually happening though, the pots all have sleeves on so shouldn't be anything awry there, will just have to start wiggling stuff about!

 

[Hexjibber]

Well I put it back together and there is something odd going on with a couple of pots making contact with something if the nuts are tied too tight, I seem to have resolved it though by not over tightening so all sorted.

 

[Nostradoomus]

Awesome!

 

[Chuck D. Bones]

Well I put it back together and there is something odd going on with a couple of pots making contact with something if the nuts are tied too tight, I seem to have resolved it though by not over tightening so all sorted.

So it fixed itself, hmmm? Don't be surprised if the problem recurs. Tightening the nuts on the pots stresses the solder joints if the alignment isn't perfect, which it never is, right? You might want to inspect the solder joints on the pots very closely. They all look ok in the pic, but there is not nearly enough resolution for us to be sure. Reflow anything that is the least bit suspect. The most likely candidates are the pads that connect to the ground plane because they are the most difficult to heat.

 

[Hexjibber]

So it fixed itself, hmmm? Don't be surprised if the problem recurs. Tightening the nuts on the pots stresses the solder joints if the alignment isn't perfect, which it never is, right? You might want to inspect the solder joints on the pots very closely. They all look ok in the pic, but there is not nearly enough resolution for us to be sure. Reflow anything that is the least bit suspect. The most likely candidates are the pads that connect to the ground plane because they are the most difficult to heat.

Yeah you're absolutely right, I wasn't really satisfied that it was truly 'fixed' but it's been fine so far ?. I will have a look at reflowing those joints as would certainly fit the problem, thanks for the tip!

 

[Chas Grant]

Have you checked the pots themselves. With so many pots so close together, any misalignment can cause one of the pot leads to get bent / misaligned. Where the pot leg does the 90 degree bend to go to the PCB could be pushed up a bit, so when you tighten the pot the leg shorts out on the enclosure. A double layer of electrical tape run under the pot holes may fix this, if so you know what's causing it and you can then figure out which pot and correct it.

 

[Hexjibber]

I reflowed all the pot joints last night, there were some dodgy looking ones tbh and it does seem to have helped, I tightened the nut on the offending pot and the problem has gone! Thanks Chuck! Also random side question; I've just bought a Hakko FX 888 soldering station and it's great but it obviously has a lot more power than my junky old Antech one, I have it set at 400C as use lead free solder but occasionally it seems to boil the solder?! Or at least that what it looks/sounds like, have I got it set too hot and could that be a cause of some my troublesome joints?

 

[Chas Grant]

Try lowering temperature to 380C and test it out. This temperature is from the Hakko website. https://www.hakko.com/english/lead_free/pages/

 

[Hexjibber]

Try lowering temperature to 380C and test it out. This temperature is from the Hakko website. https://www.hakko.com/english/lead_free/pages/

Thanks Chas, ah yes it's all there and black and white isn't it! I've never been the best at just reading the instructions! ?

 

[Chas Grant]

Thanks Chas, ah yes it's all there and black and white isn't it! I've never been the best at just reading the instructions! ?

Yeah, Me neither! I usually read them after the fact or when a question arises or something goes wrong! It has bitten my behind quite a few times.

 

[Nostradoomus]

I run mine at about 640f/340c, works like a charm. But I use leaded solder!