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Dynakit ST-35 - quiet static (popping noise) in one channel. Help!

Coming in late : i would purchase an complete board from kevin, the problem might be in the
board itself, and you are already burning money by replacing stuff.
 
Heh. Not quite 'burning' money yet. Replacing the coupling caps however might be considered a bit steep. Good point though on the board. After replacing the resistors and if no luck, swapping transformers, the board will be on the list. At least I can move my nice new parts to a new board. :P
 
TravAndAlex said:
Heh. Not quite 'burning' money yet. Replacing the coupling caps however might be considered a bit steep. Good point though on the board. After replacing the resistors and if no luck, swapping transformers, the board will be on the list. At least I can move my nice new parts to a new board. :p
Click to expand...
I was thinking of a populated board ( or a board with brand new components )
 
I was thinking about switching in some basic film coupling caps, which are not expensive, but I see that this doesn't look to be where the issue lies.
 
Waiting for the new resistors to arrive, and I'm trying a 120mm fan on in front of and behind the offending board. This has greatly improved the popping noises. It seems to happen much less, mostly during warmup. Clearly heat is involved in the issue.
 
So have you try the reverse? Use a heat gun and gently heat the components to find the offending one.
 
Brice said:
So have you try the reverse? Use a heat gun and gently heat the components to find the offending one.
Click to expand...

I have not... although that is a good idea! Just have to figure out how to isolate the heat enough so it isn't spilling over all the components.
 
TravAndAlex said:
I have not... although that is a good idea! Just have to figure out how to isolate the heat enough so it isn't spilling over all the components.
Click to expand...
Easy; first heat the whole board, then spray coolingspray on one component.
An old fault-finding technique
 
I'm sure you have tried this, but if not, first thing to do is pull out all the tubes and use caig deoxit on all the tube sockets.
 
peterh said:
Easy; first heat the whole board, then spray coolingspray on one component.
An old fault-finding technique
Click to expand...

Hey. Makes sense! I'm learning!

Cliff O said:
I'm sure you have tried this, but if not, first thing to do is pull out all the tubes and use caig deoxit on all the tube sockets.
Click to expand...

Yup... tried that one early on. Used a tiny dental brush as well on on the sockets.

Here's something new... just got home and turned it on, and a high pitched squeal came from the bad side speaker. Fairly loud (and independent of volume setting). That indicate anything in particular to anyone?
 
Does that point to an issue with a particular component?

I'd love to hear that failing resistors are most often the cause of oscillation. :)
 
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UPDATE - Resistors arrived. Replaced them all on the bad board. Took some extra time to clean up wires and clean off flux. Plugged it in and *success* (at least for the last 30 minutes). Hoo rah! Thanks all who contributed. Damn those carbon resistors.
 
FFS! The crackle is back in the left channel. The only things that are left on that side is the board, the sockets, and the 3 large capacitors. Does it make sense that something is taking out one or more of the resistors over time and this is causing the crackle to come back after a few months?

I think I'm almost at the point of building new boards from scratch, moving components from the right channel to a new board, and using all new components on the left board. I just don't know what else to try.

Is there any way the remaining 3 capacitors could be causing this to happen after a few months? GAH (this is making me crazy).

Going back through and re-reading everything, one of the first suggestions was bad sockets... could it be that easy?


Edit to give a quick refresh on what has been done:
  • Tried it without the front 7247 tube on the left side and NO popping noise. Swapped the tubes and put them both back in and the popping is back.
  • Ensured the Russian coupling capacitors are not contacting the chassis.
  • Replaced the solder trace with a jumper from Solder Pad 10.
  • Cleaned each pin socket with De-Oxit and a small dental brush.
  • Tightened each socket with a dental pick.
  • Traded around tubes and tried rocking them gently in place while on.
  • Replaced the black silver mica caps on the boards.
  • Tested all components on the board with a multimeter and compared to the other side. I found one resistor (R5) that measured differently (basically no resistance) from the same on the good board. Replaced and this seemed to make the issue go away for a couple months.
  • Swapped the 3 large capacitors on both boards (to try to see if the issue moved to the other channel). No improvement nor change.
  • Replaced (again) the resistor that was previously an issue (although measured fine this time). No improvement nor change.
  • Replaced all the resistors on the board with film. Problem resolved for a couple months.
 
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Everything is possible.

I had one a faulty wire which was cut inside the sleeve so invisible to the eyes, and on top of that was making contact sometimes, sometimes not. I just find this out when I replaced all wires as it came off in my hand...

Another time with a stubborn amplifier noise. I then decided to change ALL components as I could not find the source of the problem.

Brute force yes but it worked ! Problem vanished with the faulty something... I was happy.

Why don't you buy a new board, publish it with only new high quality components and swap the board to see if the problem persists. It's not a big expense for a ST35 and most likely will solve your issue.
If it does, you'll have the piece of mind that the problem is gone with the faulty board/socket/whatever.

IMO, there is nothing wrong to be a brute sometimes :rockon:
 
I'd buy a new board from dynakitpart, a populated board. Then move the tubes and listen to the music.
 
peterh said:
I'd buy a new board from dynakitpart, a populated board. Then move the tubes and listen to the music.
Click to expand...

That's likely a perfect solution. Just seems like such a waste after working on and upgrading. Ugh.

Of note... the misbehaving channel has much more hiss when my ear is up near the speaker. Audible from a foot away.
 
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