On Mon, 8 May 2006 10:46:31 -0400, you wrote:

>I have a MX-500 that I haven't been using much because it doesn't seem to
>put out the heat it once did, but works fine for small soldering  duties
>(smt).  If I try to use a STTC-017 tip on a larger solder joint the tip will
>cold-weld to whatever I'm soldering.  Over the weekend I opened it up and
>found a 1 watt or so carbon resistor that was nice and crispy but intact.
>The insulation on the outside burned off and I can see the metal wound
>around the resistor.  I can't read the resistor codes but it reads 182 ohms
>cold.  I don't have a schematic and am not sure what the resistor does but
>I'm thinking that it could be possible that the resistor may fail open once
>it gets hot.  Metcal's site doesn't have any support info on their site, but
>I am going to try calling them later.  So, on the off-chance that someone
>here might have one of these systems open, can you tell me what the value of
>R2 is?  Hopefully this resistor is the fault, but friend of mine who is an
>instrument tech at a large electronics company told me that he's never had
>to work on any of the MX-500's they have.  One thing he did tell me was that
>someone from Metcal told him that if the handpiece cord was crushed (for
>example by rolling a chair over the cord) that the coax can form a notch
>capacitor which can affect the performance of the tip.  Has anyone here who
>has one had this happen?
>
>Regards,
>Bob

R2 in mine is 180 ohms. It also shows no signs of having overheating, despite daily use for over 12
years, so I suspect your has been getting too hot. 

I have had a dodgy cable affect output so this may be the problem. Not convinced about the
capacitance thing - more likely broken strands in the cable.
 For reference mine measures 3.5 ohms across the plug with a tip fitted 


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