Power Designs TP340A: Repair and facelift

[FlyingHacker]

As a flyer I gotta say, this is no Inverted Jenny!

[bitseeker]

Speaking of which, you can get the $2 commemorative reprint of Inverted Jenny.



https://store.usps.com/store/browse/productDetailSingleSku.jsp?productId=S_580004&categoryId=buy-stamps

[Sparky]

Pulled the busted 10-turn pot out and installed the new one. Works great and didn't even have to mess with the trim pots. The new pot takes a little more force to rotate, but I think it's better that way. The original ones turn much too easily.

This thread is 3 years old but still a goodie!  I need to replace the Bourns multi-turn pots on a unit I want to restore and I'm glad to read your comment that "the new pot takes a little more force to rotate".

I have a TP340A also...and it's perfectly fine...except one aspect that I find annoying --- the pots turn waaaaay too easily --- the control is extremely "light" (takes no effort) with zero static/dynamic friction of the pot shaft rotating.  I have to delicately let go of the knob when I reach the set voltage to avoid rotating it otherwise I could change the output by several volts!  I also tape down the voltage knobs with painters tape so I don't accidentally knock them when I'm using the power supply...

Do the Bourns pots wear out and they become friction-less?

On my HP 6227B the pots are very firm and you have to rotate them a lot to change even 1V.  I like the precise control without worry of accidental changes.  Anyway to have TP340A voltage control have a similar feel?

[bitseeker]

You can check datasheets for info on how much torque is required to rotate the wiper. It's among the mechanical specifications. I used a Bourns clone, which is why the feel is different (and I suspect the longevity will be, too).

I've not heard of these things getting easier to turn with age. I suppose it's possible if the wipers and/or shaft wear a lot. The little HP E361xA power supplies I have all use Bourns pots and, despite being newer than the TP340A, also turn with very little torque.

[Sparky]

You can check datasheets for info on how much torque is required to rotate the wiper. It's among the mechanical specifications. I used a Bourns clone, which is why the feel is different (and I suspect the longevity will be, too).

I've not heard of these things getting easier to turn with age. I suppose it's possible if the wipers and/or shaft wear a lot. The little HP E361xA power supplies I have all use Bourns pots and, despite being newer than the TP340A, also turn with very little torque.

Thanks for noting that about the torque in the mechanical specs -- I will check it out and probably choose the one with highest torque requirement!