FPIII Input Switch question

[Frank Breech]

Hi, I'm a first timer (virgin?) and am working on an FPIII slowly but surely.  I was just connecting the RCA inputs to the input selector switch and kind of melted terminal 3 of the input selector switch.  Melted might be too strong a word -- I'm not sure how bad it is inside the switch, externally it LOOKS fine, but the terminal (metal piece) is now loose. I guess what happened is that it got hot enough to heat up the plastic it's seated in just enough to soften up and the terminal sunk into the switch a bit.  It's not that far down in there or anything but it's no longer snugly wedged in like the others. I'm concerned the contact inside is compromised.

Any thoughts on how I can test the selector switch (can I ring it out with a MM?) I don't know how it's wired up - or anythign else about it for that matter. I'm just following the directions! (Or trying to, anyway)  Also, I guess that terminal 3 corresponds to input three, which I'm unlikely to be using anyway (just plan on using 1 & 2 with my current setup CD player and yet to be built Seduction). In the worst case scenario I can just ignore input three, but then again I'd hate to do that ...

Thanks in advance for the help.

Mike

[Grainger49]

Mike,

Yes, ring it out and see if you have a good solid connection through terminal three.  If the resistance doesn't waver as you wiggle the selector switch shaft you are good.

Connect one lead of the MM to the RCA jack that is connected to terminal 3.  The output will go to one of the stepped attenuators.  It should be pretty easy to figure out which stepped attenuator it goes to. 

Like I say, if the resistance doesn't waver as you wiggle the selector switch shaft you are fine.

[Frank Breech]

Hi, Grainger,
Thanks for the quick reply.  Forgive my naivete; please indulge me a little further, if you don't mind.  I don't have the attenuators fully connected yet.  I'm attaching a shot of what this area of the amp looks like so far.  Maybe your message will be easier for me to understand when they are fully connected, if I don't have to wait for that point though, that would be great.  But if I do, I'll know exactly what to do -- I'll just need a little more guidance.
Please see my replies to your instructions:
"Connect one lead of the MM to the RCA jack that is connected to terminal 3."
Got it, no problem
The output will go to one of the stepped attenuators. 
I don't understand which output you mean. 
It should be pretty easy to figure out which stepped attenuator it goes to.
I'm looking forward to it

Also, is it sufficient to use the continuity tester setting for this test?  If not, which resistance setting is best?

Thanks a lot
Mike

[Grainger49]

Ok, according to the FP III manual, page 22, there is a black wire coming from the outer conductor, ground, of RI3.  Look to page 17 to identify RI3.  So put one probe on the outer conductor of RI3 and the other on .  .  .   well, I'm not sure.  

Try lug B in the center first, then A, I think it will be B because of the position of terminal 3.  When you rotate the selector switch to select input 3 (fully clockwise) the ground should show nearly zero ohms to lug B (or A).

The reason I am saying to go back to the RCA input jack is to test the full continuity from the input to the output of the switch.  Or you could just measure resistance from terminal 3 of the selector switch to B.

[Laudanum]

I think it's A.  Switch selector fully clockwise and check from 3 to A.  Should be 0 ohms and/or continuity beep.

[Frank Breech]

Thanks for the attention, guys. It's appreciated. I will try this tomorrow and post the results.
-Mike

[Frank Breech]

Good Morning,
I did the reading and I could hear the tone, the MM read 0, so this switch is OK, luckily.  Thanks again for jumping on this little issue and helping me out.

-Mike

[Laudanum]

Glad it worked out.   Im surprised the wire insulation isnt melted and pulled back a bunch, atleast it doesnt appear to be.   It's good wire but that polyprop. insulation is pretty easily melted.

[Frank Breech]

Laudanum,
I think it's probably because I actually didn't heat the individual wire too long, but just the terminal.  I actually made a mistake and terminated one of the other RCA input grounds to terminal 3.  I realized it when I got to terminal 3 in the directions and desoldered the wrong wire then resoldered on the correct wire.  I did it all in one fell swoop and I think that was what was too much for the plastic of the switch. 
Thanks again, and thanks in advance for next time.  I definitely want to pick some brains about safety before I get to the smoke test. Any input you have is appreciated.  Looking forward to getting this thing up and running.

Mike

[Laudanum]

Hi Mike.

Yeah, plastic and too much heat doesnt mix but stuff happens 
BTW, Im definitely not one of the gurus here but I give it a go when I do think I can help.  And there are plenty of savvy folks to help out with the more complicated problems.  You'll get good advice when you need it.