Metcal PS-900 Soldering station heats up to over 400 °C

[nemail2]

Hi

i have a Metcal PS-900 iron since 05/2016 and earlier this year it failed on me, heating up constantly with all power it has, to over 400 °C until the whole shaft of the tip starts glowing red(!).
I have changed the induction heater in the handle once (they are designed to be replaceable) + the tip multiple times, nothing helped.

This year I replaced it with a JBC BT-2BWA soldering station which I like very much too but I thought it was a pitty to get the rust on the Metcal so I'd love to repair it.

What I have done so far, is replacing the IRF644 MOSFET which is heatsinked within the main box /w power supply, just because I had it laying around and to give it a shot. Unfortunately didn't work out, still the same issue.

Does anyone know this particular model or is this maybe a common issue with Metcals or at least this model?
I don't really want to poke around within the unit when it is connected to mains because I'm a hobbyist and that station is not worth risking my life so I can't really measure any voltages when it is powered on.
Playing around with 230V AC is just not worth it for me, that's where the fun ends...

Suggestions, anyone?

Thanks!

[Rasz]

I don't really want to poke around within the unit when it is connected to mains because I'm a hobbyist and that station is not worth risking my life

sell it with detailed failure description, you will easily recover half its value

[nemail2]

sell it with detailed failure description, you will easily recover half its value

will do that if I can't repair it at all.

I'd be happy to invest like up to 50-100 EUR in new parts so if there are any obvious ones which could be the culprit I'd replace them one by one until the Metcal works normally again.

I was hoping that you much smarter than me people out there maybe could have a clue which parts might be causing this.
Somewhere I read, I think, that there is a feedback loop going to the DC-DC converter IC on the motherboard which then controls the voltage.
I know that Metcals don't have any temperature sensors and that they regulate their tips by themselves with some RF voodoo (curie effect).

The caps look fine, at least they are not bulged. If I don't get any other advice, the next thing to swap out would be the DC-DC converter IC, i guess? I also read somewhere that this thing gets rather hot and I once forgot to turn off the iron over night so maybe it is fried...

Thanks for any idea!

[MosherIV]

Do you have more than 1 tip?

If so, does it do the same thing with all your tips?

[nemail2]

Do you have more than 1 tip?

If so, does it do the same thing with all your tips?

yeap, replaced the tip several times and also repleaced the induction heater in the handpiece (it is designed to be changed by the end user).

[bd139]

These work by measuring SWR on the output I think. Might be the power sensing feedback loop that is shot. Can you post any photos of the board at all?

I have a PS900 as well. Hasn’t blown up (yet)

Also did you replace or test the handpiece cable? The connector isn’t great.

[Rasz]

sell it with detailed failure description, you will easily recover half its value

will do that if I can't repair it at all.

going to be less than quarter value after you fail to fix it ;-)


Heater is builds into the tip and should not be able to get that hot due to already mentioned Curie point, afaik those fail cold. What exactly is going red hot? induction coil? that would suggest pure DC from the unit

[nemail2]

These work by measuring SWR on the output I think. Might be the power sensing feedback loop that is shot. Can you post any photos of the board at all?

I have a PS900 as well. Hasn’t blown up (yet)

Also did you replace or test the handpiece cable? The connector isn’t great.

I can post photos when I get home (in about 7 hours).

No, I didn't replace the handpiece with the cable yet. I already suspected the connector as well but I didn't put mechanical stress on it EVER so didn't check that thoroughly yet.
@ 400+ °C it is also a bit difficult to steadily measure the temperature and e.g. wiggle around with the cable and connector to see whether the temp changes.

[nemail2]

going to be less than quarter value after you fail to fix it ;-)

only if i make it worse ;-)

Heater is builds into the tip and should not be able to get that hot due to already mentioned Curie point, afaik those fail cold. What exactly is going red hot? induction coil? that would suggest pure DC from the unit

The area which gets red is marked in the attached image.

No, the heater is not in the tip, there is an induction heater in the handpiece which can be disconnected and replaced (which I did already).

[Rasz]

No, the heater is not in the tip, there is an induction heater in the handpiece which can be disconnected and replaced (which I did already).

Afaik that wasnt the heater, its an induction coil. Heater aka element actually producing heat is just a cylinder shaped piece of metal inside the tip itself.

[nemail2]

Afaik that wasnt the heater, its an induction coil. Heater aka element actually producing heat is just a cylinder shaped piece of metal inside the tip itself.

ok now we're talking. that now depends on how you define heater. for me it was the peace which consumes energy to make something hot. as it is induction, for me it was the induction coil in the handpiece. the metal in the tip is picking up the induction and heats up, just like a pot on an induction stove. At least that's how I understood it.

Anyway, these are pics of the PS-900 board:
https://owncloud.ne-mail.net/s/WpLaspzrHWpPifY/download?path=%2F&files=20181121_224302.jpg
https://owncloud.ne-mail.net/s/WpLaspzrHWpPifY/download?path=%2F&files=20181121_224359.jpg
https://owncloud.ne-mail.net/s/WpLaspzrHWpPifY/download?path=%2F&files=20181121_224414.jpg

[Rasz]

the coil is just an antenna, it shouldnt be getting hot. Tip cant get as hot as you report, suggests your unit is sending DC to the coil and burning it

[nemail2]

the coil is just an antenna, it shouldnt be getting hot. Tip cant get as hot as you report, suggests your unit is sending DC to the coil and burning it

ok and now i understand what you were saying, sorry for the confusion :-)
yes, the coil should not get hot. not entirely sure how the tip is constructed, in theory where it gets hot (near the coil) could be a piece of metal which is picking up the induction as well so it MAY be that it isn't the coil itself which is heating up but as well it may be possible that it is like you are saying.

The tip itself (not only the shaft where the coil sits) is getting (reasonably fast) ridiculously hot  as well, I measured 470 °C yesterday, so obviously the HEATING works  don't know if that would work if the coil is being fed with DC.

suggestions what part to replace next to give it another shot?

[bd139]

Good point with the DC to the coil. If it’s passing DC I wonder if a cap has gone short on the board. I’d have a poke around with DMM.

[nemail2]

Good point with the DC to the coil. If it’s passing DC I wonder if a cap has gone short on the board. I’d have a poke around with DMM.

how'd you measure that without desoldering, if there are more caps on a rail it'd be any cap - without desoldering you'd never know or am i missing something?
would be glad if I hadn't to desolder every cap :-)

[bd139]

I would establish whether or not anything is short first. You can worry about those details later

[nemail2]

I would establish whether or not anything is short first. You can worry about those details later

LOL well that's true. Guess I need another coffe. Hope it is shorted. Stupid bastard thing of a bloody doomed soldering brick piece of sewer-stinking sh*t.

[bd139]

I’m hoping mine doesn’t do this. I really like it

[nemail2]

I’m hoping mine doesn’t do this. I really like it

i like(d) mine too very much, that's why I am calling it names now.

but I must admit after using my new JBC for a while, the handpiece of the metcal seemed really monsterious and bulky.

[bd139]

The business end of it is a bit large, I'll give you that.

[nemail2]

The business end of it is a bit large, I'll give you that.

nah, the whole thing. it feels like it is twice as thick and twice as long (obviously it isn't) and the cable weighs like a ton in comparison.
didn't believe it first, cause I didn't have any issue at all with the metcal when I was using it (before having the JBC).

[bd139]

I was using a Weller TCP before so it's a world better than that. I have a couple of T12 irons as well. Those are much smaller.

[nemail2]

I was using a Weller TCP before so it's a world better than that. I have a couple of T12 irons as well. Those are much smaller.

The Metcal PS-900 is definitely a superior iron, didn't ever want to deny that. It is just that the handling of the JBC is just so much better (at least for me, that's often very subjective) and I really got used to it and therefore it really surprised me how chunky the Metcal handpiece really is in comparison (while still having great handling). But one thing on the JBC is really superior to the PS-900, the cable is MUCH thinner and lighter, it's really a bummer that the Metcal's is so fat in comparison.

[I2R]

Hi,

I've a Metcal PS-900 with the same symptom. I think it may be due to a missing turn on L3.

We've a few of the PS-900's at work, an older OKI branded one from about nine years ago and a more recent batch of about 15 including the problem one. The older one has been rock solid and never caused any problems. The newer ones seem prone to burning out elements with a noticeable number of failures - that may be related but I've not had a poke at any of them yet.

The PS-900 schematic (attached) is very similar to the older SP-200, the higher power output appears to be enabled by a reduction in the number of turns on L3. On the older (reliable) PS-900 L3 has 41T while the problem unit only had 40T. (The SP-200 has 46T for the equivalent part).

I'm not sure if this is a production error or a factory modification that doesn't quite work as expected (unless they're trying to sell more spare parts!), I'd need to open up some more of them to check.

Running the iron from a bench power supply, rather than the internal 48V switch mode power supply to make it easier to measure power/current (and to save me electrocuting myself), shows an input power in excess of 72W at power up when the tip is cold. That's the current limit for my supply, it's obvious the circuit is trying to draw more. Adding an additional turn to L3 (41 turns) reduces the peak power demand to slightly over 60W; the circuit is regulating power rather than the bench supply. It's nominally a 60W iron, although Metcal's not very clear about this.

The change does seem to work although I should mention that I've only got a tip cartridge from my SP-200 to test with - it's effectively the same thing in a different package. I've used a big heatsink and a blob of solder to check the maximum power output when the tip is up to temperature.

L3 is the one that's mounted flat on the PCB with a blob of silicone underneath.

Hope that's of interest  :-)

[Marcel G]

http://www.pa4tim.nl/?p=6082

Regards,

Marcel