NAD 3140 and Triac on power switch

[pwdiya12]

I am refurbishing a NAD 3140 and found an NTE 5645 Triac inserted in the AC to the power switch- not an original part!


(photo attached)


I assume it was an attempt to reduce turn on thump (which the owner says the amp still does)- any insights as to what it is intended to do is appreciated.


I am recapping the unit top to bottom.

 

[pwdiya12]

with photo

 

[jaycee]

I REALLY hope the tab of that triac is not bolted directly to the case - given that it will be live!!!!

 

[latala]

A lot of triacs are glass passivated this means the mounting tab is insulated and will not be live
I suggest this was a remote turn on device
Trev

 

[pwdiya12]

it is insulated with a mica washer


I am planning to remove it

 

[llwhtt]

It's there to take the load off of the cheap power switch. Now the power switch only has to turn on the Triac.

Craig

 

[Mooly]

The implementation is shocking... literally... although the basic idea is sound enough.

If the switch is not an original then it may be a type unsuited to switching an inductive load like a power transformer and hence the reason for mod.

 

[pwdiya12]

The power switch is original, the triac is the retrofit.


My inclination is still to remove it


and thanks for all your insights


Peter

 

[Goldie99]

I would hazard a guess that you bought it from someone who's been reading this one....

Is your unobtainium power switch worth $5 and an hour or so of your time? | Audiokarma Home Audio Stereo Discussion Forums

 

[Ozark HiFi Doctor]

It is shocking that people (as with who did this work, originally)
take little or no pride in doing what they do...
some TV repairmen of the day...

I would expect to see some electrical tape in the chassis...

 

[pwdiya12]

@goldie99- good guess, though I am doing this work for the owner- they took it to a local repair shop complaining about turn on thump (and given some of the other "fixes") and possibly some other repairs- maybe chasing the same problem



@ozark- yes the choice of antique carbon resistors that they installed (inc the one for the triac) supports that view

 

[rsavas]

People usually put in these triac mods because the original power switch contacts are shot. I myself like using a chassis mounted relay with a line voltage AC coil instead.