424 - Headphone output problem

[mikestlt]

Hi folks,

I have a 424 that's provided reliable service for 12 years, but I just pulled it out today and have a sudden problem with the headphone output.

There are violent cracks, pops, and assorted static in the headphones which I've never had before, and just the slightest increase on the track levels above zero causes the sounds on the tracks to be incredibly, ear-splittingly loud. The static and pops are there whether the tape is played or not. In other words, it's always there.

I tried a few different headphones with the same results.

I also mixed-down a song to see if the same thing happened through the stereo outputs. It didn't. The mix came out static-free, though much, much lower than what I was hearing through the phones.

At this point I believe it has something to do with the headphone monitor output hardware, but I'm not sure what.

Has anyone heard of this problem or have any idea what it might be?

Thanks!

[A Reel Person]

for about 5 minutes straight. This will clean up any oxidation that's on the headphone level control,... which is the likely cause of your problem, based on your description.

Someone on this board recommended looping a shoe string over the pot & pull it back & forth to rotate the pot,... kind of a labor saving method!

Either way, it sounds like a severely dirty headphone level pot.

[edge59]

Sometimes the solder connections need to be reflowed with the right wattage soldering iron. A lot of amps and electronic equipment I have seen over the years, this happens to especially when the pots are soldered directly to the printed circuit boards. Overtime, from turning these pots and depending how hard they were turned, causes the solder joint to break down, especially if there is no hold down nut on the pot to the chassis. Not that this is the problem, but its good to check this out from time to time.

Edge59

[andyhix]

I found some "TV tuner cleaner" - basically a cleaner/lube for pots - at radio shack and it was a saviour on another piece of equipment with scratchy pots. But I think that only works on pots that have an opening in them that you can squirt the stuff into. I'm pretty sure that the the pan knobs on a 424 aren't open (cause some of those on mine are scratchy and I looked), and therefore I'm assuming the headphone level knob is probably the same. If you pull the knob off, does there appear to be any hole that you could squirt a WD40-type straw into? If so, definately get some of this stuff.

If not (asking someone else out there), would it be worth squirting a small amount at the point where the shaft enters the housing, hoping that a bit works its way in there? Maybe that would not work, or maybe it would cause probs. Not sure...

[mikestlt]

Thanks for the suggestions, but the problem is still there after turning the pot back and forth for several minutes.

In fact, the super-loud crackling comes through the phones as soon as the machine is turned on, even with all pots and faders set to zero, which makes me think it's possibly a bad connection around the headphone port. I'm going to have to open it up and investigate.

[A Reel Person]

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