Modem potentiometer problem

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My modem, which I am using now, has a weird problem. It connects just
fine, but there is no audio. So I dont hear the dialtone or connecting
tones. It's a US Robotics 56K model 5686  V.92. However, on occasion it
will suddenly make sound (volume is on high). but that lasts a few
seconds and it goes silent again.  

I can live without the sound, but I am used to it working on my other
identical modem, and if I dont hear it, I am not sure if it's
connecting. (My ISP tends to be "sleeping" every so often, so I have to
dial several times to wake it up). So, that sound helps me know what's
going on.

I removed the board from the case and connected it to thge computer. I
found that if I apply a fairly strong downward pressure with my fingers
on the potentiometer shaft, I do get sound.  

I have another identical DEAD modem. I am thinking of taking the pot out
of that one and swapping them.  
yea, I already used deoxit and put the soldering iron on the pot
terminals, so it's obvious the pot itself is bad.

I'm posting this because I am a little leary to do this. This is the
sort of stuff I dont normally work on. It's all surface mounted parts on
both sides of the board, and so frikkin small I can barely see the
solder joints even with a magnifying glass.

Since this board has traces on both sides, do I need to get the solder
all the way thru the board?  I've even heard of some boards having
traces inside the board itself, so I guess they are laminated.  

How anyone can work on this sort of thing is beyond me. I guess thats
why people throw them in the trash and buy a new one.
To even solder some of the tiny parts on it, would need a soldering iron
tip about as thick as a sewing needle.

Fortunately this pot is on the edge of the board and has bigger
terminals than most ot the other components, but it's still very small.
I'd rather not risk killing the modem entirely, but I will replace the
pot if I'm not dealing with a multi layered trace board.

Side note, I could probably remove the pot and just solder a resistor in
place. I normally have them set at half volume and never change it once
it's set.  





Re: Modem potentiometer problem
With all due respect, leave it alone. I can almost guarantee that if you stard digging, you will wind up with two dead modems.  

But, if you are insistent on doing 'something' - try tapping it or wiggling a connector and see if something is loose inside. These are mostly SMT devices - not for the faint-of-heart if not experienced *and* properly equipped.  

Peter Wieck
Melrose Park  

Re: Modem potentiometer problem
snipped-for-privacy@aol.com says...
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Tubes vs SMT has got to be a good contrast. Still, there are lamps on  
the market that look although they have filaments but are actually LEDs.  
So maybe there will be convergence...

Mike.

Re: Modem potentiometer problem
On Tue, 14 Nov 2017 03:16:08 -0600, snipped-for-privacy@tubes.com wrote:

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Assuming the pot is open, it would be even easier and less risky to
solder a resistor across its terminals without removing the pot.  

Re: Modem potentiometer problem

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Yep, it's open. I measured the resistance on the pot in the dead modem,
which appears to have a good pot. 10K ohms across the outer terminals
(in circuit), and the center (wiper) varies when turned (like it
should).

When I measure across the outer terminals on the modem with no sound,
it's infinate resistance.

The pot has a metal housing around it, so I cant see what is goingv on
inside, but there must be a crack of sorts.  

If 10K is what it is. I'll clip a 5K resistor in there That shoujld give
half volume.If that sounds right, I'll jusat tack that resistor in it.



Re: Modem potentiometer problem
This should be fun.....

Re: Modem potentiometer problem
On Tuesday, November 14, 2017 at 10:43:27 AM UTC-5, snipped-for-privacy@gmail.com wrote:
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Schadenfreude.

Peter Wieck
Melrose Park, PA  

Re: Modem potentiometer problem
On Tuesday, November 14, 2017 at 10:25:11 AM UTC-6, snipped-for-privacy@aol.com wrote:
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Well we have tried to educate.... that having failed, we may as well enjoy.

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