Bad pot

[BOB URZ]

Well, not the kind you smoke anyway. (And that's Potentiometer to
LV to be politically grammatically correct). Just ran across a powered
sub woofer that was dead. Nothing seemed fried. Further tests showed no
continuity off the volume control. Pretty standard cheap dual gang 50K
control. Took it off expecting to see a cracked board. The board was not
cracked on either section. Thought this was quite strange. I fluked
across the carbon and it was OK. What seems to have happened in this
unit was where the carbon track gets riveted to the terminal developed a
open circuit condition. I have never seen one do that before. And it
happened on both sections. on more than one unit. Definitely a cheap pot
with a latent manufacturing defect. I have seen similar pots in pro
sound gear, so be on the look out. Its says "HV A50K" on this specimen.

Bob

 

[Rob Beech]

Well, not the kind you smoke anyway. (And that's Potentiometer to
LV to be politically grammatically correct). Just ran across a powered
sub woofer that was dead. Nothing seemed fried. Further tests showed no
continuity off the volume control. Pretty standard cheap dual gang 50K
control. Took it off expecting to see a cracked board. The board was not
cracked on either section. Thought this was quite strange. I fluked
across the carbon and it was OK. What seems to have happened in this
unit was where the carbon track gets riveted to the terminal developed a
open circuit condition. I have never seen one do that before. And it
happened on both sections. on more than one unit. Definitely a cheap pot
with a latent manufacturing defect. I have seen similar pots in pro
sound gear, so be on the look out. Its says "HV A50K" on this specimen.

Bob

Just run us through the model subs you were using, makes it alot easier.

Rob

 

[Bob Urz]

Just run us through the model subs you were using, makes it alot easier.

Rob

These subs were KLH, not pro units. But the pots are similar to what
found in many lower end pro devices. Its not the point of what they were
in, but the method of failure. With so many companies building cheaper
stuff in the pacific rim, this sort of thing is bound to crop up more
often.

Bob

 

[Mike T.]

Well, not the kind you smoke anyway. (And that's Potentiometer to
LV to be politically grammatically correct). Just ran across a powered
sub woofer that was dead. Nothing seemed fried. Further tests showed no
continuity off the volume control. Pretty standard cheap dual gang 50K
control. Took it off expecting to see a cracked board. The board was not
cracked on either section. Thought this was quite strange. I fluked
across the carbon and it was OK. What seems to have happened in this
unit was where the carbon track gets riveted to the terminal developed a
open circuit condition.

Yep, definitely seen that before. I used to do consumer electronic
(stereo) repair, back when the stuff was actually repairable.
I have only seen it on very inexpensive pots. I would not have
expected to see that crap in pro audio gear ten years ago.
But today ... it's everywhere.
Mike T.

 

[BillHart,KarenPierce]

where the carbon track gets riveted to the terminal developed a
open circuit condition. I have never seen one do that before.

I've got an NHT hifi amplifier sitting around that had this happen on
the ground end of the pot. So when you wiggle it it goes to near full
volume regardless of the rotation. Most annoying, and I haven't worked
hard enough to find a source for a dual volume control with small shaft.

BH