Looking for assistance with Metcal STSS-002 problem - Page 1
Forum section: electronics / general

author: wkb
author_rank: Super Contributor
timestamp: November 20, 2011, 06:07:39 pm
content: Yesterday my Metcal STSS-002 decide to quitSuddenly it would not warmup anymore.I've repaired the coax lead between the station and the actual iron before (like 2 years ago?) as it hadsort-of broken at the station side.But this is new: nothing works. I've tried another tip (a used one, I don't have any new ones). No luck either.I checked the RF out on the station. The scope tells me it outputs a sine wave, around 60Vtt, at around 13.5MHz.The frequency sounds OK to me, but what about the voltage? Does anyone have the same Metcal model and is willing tomeasure the voltage?Any suggestions are more than welcome!Wilko

author: longpole001
author_rank: Contributor
timestamp: April 17, 2012, 09:50:44 am
content: how did you go repairing the unit as i haveing the same problems with voltage on the inverter chip at pin 14 is 2.5v and thats sounds wrong to me

author: free_electron
author_rank: Super Contributor
timestamp: April 17, 2012, 12:11:03 pm
content: Check you 'coax repair' ... If you have a bad contact in there so there is a capacitive path instead of a resistive path you cannot get energy in that tip.Take the handpiece off and measure the impedance. An ohmmeter is ok. You should have a few ohms between center and shield. Then unplug the tip. Now you should have infinite between center and tip.Hopefully you did not shorten the cable too much ... You could create a standing wave in the cable. You are dispersing the energy there in stead of in the tip. That is the problem with these RF heaters... The cables are length tuned ...How does the metcal stay at tempereature : the tip is actually a matching network. When below the ideal temperature the is perfectly matched to the transmitter. So power transfer is maximum to the heating . When at temperature the tip mismatches. The base station sees a lot of reflected energy and decreases its power output. If you shorten the cable the reflection starts too early .. And the system goes whack...

author: robrenz
author_rank: Super Contributor
timestamp: April 17, 2012, 12:32:02 pm
content: Quote from: free_electron on April 17, 2012, 12:11:03 pmThis is not what metcal describes as thier temp control method. It is purely induction heating of a metal tip. But the metal that the induction coil is surrounding has a metalurgicaly tuned curie point. Once that metal reaches the curie point it is more or less transparent to the inductive field. as it cools it crosses back over the curie point and induction heating begins again.There may be aspects of what you described going on also but I dont think it is the primary mode of control.I am a JBC fan anyhow

author: free_electron
author_rank: Super Contributor
timestamp: April 17, 2012, 03:15:04 pm
content: That's just a different way of describing it ...the tip is an inductor with a metal core. heat that core until the curie temperature at the core loses its magnetic properties....what happens to an inductor you pull the core out of ? its inductance changes ... so at that point it becomes mismatched to the transmitter.that transmitter in the base is tuned to deliver energy to the coil. ( actually that coil is a transformer .. one with a shorted secondary when the tip is below curie point , and a transformer with an open secondary at curie point. )so at curie temperature there is a mismatch. The Rf energy will reflect and care must be taken not to destroy the transmitter. so they have a bridge that detects too much reflection and scales back the output.so , if you mess with the cable you can introduce mismatch .... the base can detect this and scale back the output power . result : a non working station.

author: robrenz
author_rank: Super Contributor
timestamp: April 17, 2012, 03:41:02 pm
content: Thanks, I can understand that with your description. My last sentence was in case there was an aspect I didnt understand. (of course that is a common occurence)

author: wkb
author_rank: Super Contributor
timestamp: April 18, 2012, 07:21:57 pm
content: Quote from: free_electron on April 17, 2012, 12:11:03 pmThe generator is specifically designed to survive high SWR. The SWR changes a *lot* during heating/cooling, or if the operator unplugs the heating element without switching off the generator.Note that there is a small capacitor in the handle to tune the heating element, this is an LC circuit. Without the cap it won't work squat (I speak from experience :-)

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 18, 2012, 07:54:15 pm
content: QuoteIn the unplugging case, the RF supply is cut off - there is a DC path through the element used to sense this.I have a MX-500 schematic if it's of interest - probably not too different to the STSS

author: free_electron
author_rank: Super Contributor
timestamp: April 18, 2012, 07:59:20 pm
content: yes it is designed to survice, but if the standing waves 'belly' lands in the tip.. you have no energy transfer there .... that is the problem with standing waves. you have 'dead points'the cable is tuned so that the soldering irons tip sits on the crest of the wave 1/4 wavelength and not in the dead point. shorten or lengthen the cable and energy transfer will not be as efficient. land in the dead point and you get nothing ...

author: SuperFungus
author_rank: Contributor
timestamp: April 20, 2012, 04:58:07 am
content: I'm not seeing your point? If it's matched SWR = 1 and there is no "crest" or "trough" anywhere on the line (constant amplitude). The only reason I could see cable length mattering is if the base expected a certain phase from the tip when it started to mismatch for the control loop to work, which seems unlikely. Even if it was critical, you'd have to try pretty hard to induce significant phase error at 13.5 MHz.I agree with your suspicion of the coax fix as the likely culprit, I am just unconvinced the cable length is actually critical.

author: charliex
author_rank: Frequent Contributor
timestamp: April 20, 2012, 09:06:47 pm
content: this may or may not be of any usehttp://www.ebay.com/itm/METCAL-REPAIR-KIT-VN0109N5-AKA-VN67AD-ANDZTX749-/270958201129?pt=LH_DefaultDomain_0&hash=item3f165e0929#ht_500wt_1156common parts that fail on the metcals.

author: wkb
author_rank: Super Contributor
timestamp: April 21, 2012, 06:06:59 pm
content: Quote from: SuperFungus on April 20, 2012, 04:58:07 amI had to cut like 5cm or so off the coax of my hand piece. No probleem.It is easy enough to check, put some 75Ohm coax with F-connectors between the generator and the hand piece.My bet it is will work like a charm.

author: SuperFungus
author_rank: Contributor
timestamp: April 21, 2012, 06:36:16 pm
content: Quote from: wkb on April 21, 2012, 06:06:59 pmYa, throwing an extension in there would be a good check. Is it marked 75 Ohm anywhere or are F-connectors 75 Ohm only or something? 5cm is so small next to the 20m wavelength at 13.5MHz I'm not really sure if it even proves anything, but it is a good datapoint.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: March 15, 2013, 02:43:17 pm
content: I have a Metcal STSS-002 , got used from eBay .Lately I have noticed that randomly when the 2nd lite , or right-hand lite comes on the tip will not heat , this is happening more often now .I have downloaded info on other models , but having issues finding info on the older units like mine .No manual or service found so far .I did find a deal on the desoldering gun and dual position stand with switch .Any help in finding manuals , thanks

author: grenert
author_rank: Frequent Contributor
timestamp: March 15, 2013, 05:11:51 pm
content: The amber light is the ground fault light. If you have a problem with the ground to your power supply it will come on. I think it will also come on if the coax cable connection on the back of the power supply is not solid.

author: mamalala
author_rank: Unknown
timestamp: March 15, 2013, 07:10:07 pm
content: The amber/orange light has nothing to do with a ground fault, from what i can see. It simply signals a fault on the RF output, which can either be an unplugged handpiece, unnplugged cartridge, cable short or malfunction of the RF generator having too much voltage. It is coupled to the RF generator enable, and it latches.Also, i highly doubt the theory that the cable length of the handpiece is somehow tuned. Lambda/4 would be 5 meters in this case, and that cable is nowhere near that length. Plus, from building my own RF supplies i can say with confidence that it does not matter if i plug in the handpiece directly, or if i put a few more meters of RG58 or RG59 in between. If there is any difference i simply don't notice it, performance wise.As others have mentioned, if you already repaired the cable once, re-check that it is still OK. Another possible point of failure is the FET in the output stage. It sits in a socket and is not directly soldered. So if the cable is OK, that is what i would check next. It's always possible that over time the contact becomes bad, causing all sorts of problems.Greetings,Chris