Metcal MX-500P (nonscreen) Won't Heat.

[Egress.]

Hi all, First post here. I bought a metcal mx500P off of ebay a few months back, and just now got around to using it. I'm running into an issue however, when I flip the switch on the amber light immediately comes on & the tip doesn't heat up. the tip I am using works with my STSS-02 but not the MX500. I opened it up earlier today but didn't visibly see anything wrong with it. Is there something I'm missing?

[kawal]

The MX has a switch to switch between the  2 outputs make sure its on the right setting.  Might be  defective the switch itself. The other issue it could be a bad RF jack.

These are very robust  stations so most likely one of the issues mentioned.   

[Runco990]

I have fixed a few of these and own 4!

The switch and jack don't really fail.  I have changed a few capacitors on high hour units, but often the FET goes as well as a smaller drive transistor.  There IS a schematic and repair guide floating around the net which I also used...  Google metcal repair...  Or..  http://colinoflynn.com/wp-content/uploads/2012/05/MX-500P-11.pdf

These aren't that hard to fix.  The hand pieces tend to fray and break the cables right at the strain relief at the handle.  This will eventually happen.  The hand piece can be taken apart (CAREFULLY) it IS glued... and the cable can be shortened slightly and re-attached.  It is a coax.  For future FYI, as the hand pieces are expensive.

If the coax goes bad, you will also just get the yellow light.

[Egress.]

the cable and hand piece both work fine on my STSS-02 power supply, so I don't think the cable is broken, unless the mx500 doesn't work with my cable.

[Runco990]

If it's a coax, it should work.  It's an RF heated system.  If the handpiece and tip heat up, they should also work on the MX-500.  I just want to be sure you have a KNOWN working handpiece before you tear open a power base!  The sense circuit is tripped if the cable or tip is bad or even just flaky.

I actually HAVE a cable/hand piece tester that came from a Metcal facility.  It does a good/bad test on the hand piece, it even detects just damaged but not yet broken outer braid.  I'm really happy to have this... fixed a few hand pieces thanks to knowing they were "damaged" but still working.

Check the PDF and take some readings.  The base isn't hard to fix, but the FET does go bad.  Problem is getting the CORRECT part to replace it.

[Egress.]

what should the resistance of the cable be with a tip plugged in? is there a value that is out of spec & would cause the self check to fail?

[Runco990]

Well, that's a tough one and I can't give you an answer.  The tip is heated with RF energy, the base is basically a transmitter.  The tip is not heated with DC like other irons.

My cable tester checks for continuity AND RF leakage.  I bad cable can still have continuity but the damaged braid is leaking enough RF that the damaged spot gets warm or even hot, although frequently the iron still works... just not well.

However, I will measure my known good one and post back on at least that.  I suspect resistance varies by type of tip.  The cable however, is just a thin but 100% braid shield coax.  So It should read near 0 ohm ground to ground and inner conductor to inner conductor.  Easier said than done on the hand piece if you don't have a special test wand to stick in it.

It's likely the base.... you could try to open it and just flip the hidden switch from broken to fixed!    If that doesn't work... check the FET.

I'll post back with resistance on my hand piece and tip in a few when I go to the shop.  That info may benefit someone in the future.

[Egress.]

alright, opened it up & took the board out, no noticeable skid marks so thats good. I noticed that the cable i'm using has a small gash in it about 1/2 the way down from the socket. wondering if that might be the source of my issue.

[Runco990]

Possibly.

Edit:  I'm getting about 4 ohms across my hand piece with a tip.

[testpoint1]

Possibly.

Edit:  I'm getting about 4 ohms across my hand piece with a tip.

in my hand, about 30 tips, use the mOHM tester, the resister value is 200 mOHM (0.2 OHM), test tip only; if include hand piece, 3.0 OHM.

[Egress.]

after doing a bit of research, looks like it might be the handpiece lacking the resistor that the rm3e has. its an rm3 handle.