How to get rid of fluctuating voltage on soldering tip (T12 clone station)?

[Haggis McHaggis]

Hello,

i bought a T12 Quicko Mini soldering station and measured some voltage (0.5-3V) fluctuating (leakage current??) on the tip with my cheap DMM. Measured against the negative pole of stations DC input.

The station is a 24V DC version, which is powered via an old Lenovo laptop psu. The psu has PE on the primary, but only +/- on secondary side.

I want to solder some parts like a MCP1541. The respective datasheet says it's a CMOS. Thus i assume ESD safety is needed.

I read about earthing the tip could help, but i'm not sure how to do it correctly.

Any tips are welcome.

Thank you!

[sn4k3]

Hello,

i bought a T12 Quicko Mini soldering station and measured some voltage (0.5-3V) fluctuating (leakage current??) on the tip with my cheap DMM. Measured against the negative pole of stations DC input.

The station is a 24V DC version, which is powered via an old Lenovo laptop psu. The psu has PE on the primary, but only +/- on secondary side.

I want to solder some parts like a MCP1541. The respective datasheet says it's a CMOS. Thus i assume ESD safety is needed.

I read about earthing the tip could help, but i'm not sure how to do it correctly.

Any tips are welcome.

Thank you!

The best thing is open and check what inside the device, but since you connect it with a DC charger it means no earthing on tip

[Ian.M]

Odds are, because it has three pin power in with PE, the laptop PSU has the 0V (-) side of its DC out grounded. You can check that by checking for continuity, PE to 0V with  the PSU totally disconnected.

If the tip's floating you can ground it, so with the iron cold and power off, check resistance between the tip and the 0V side of its DC in jack.  If it reads open or very high resistance, its OK to ground the tip (via the barrel).   If it  shows as direct continuity, its already supposedly grounded so something else is going on e.g. your PSU doesn't have a grounded output so you'll need a seperate PE to 0V ground connection.   As with all Chinese clone stuff, you'll probably have to do some resistance measurements with a DMM or even a teardown to figure out if the handpiece already has a ground wire fitted separate from the heater connections, so you can simply mod the station.

Once you've I.D'ed the tip ground wire at the connector, try a 1K resistor between there and 0V.   Nearly all the stray voltage on the tip should go away.  If so you can link the tip ground wire directly to 0V.  If it doesn't, further investigation is required + possibly rewiring the handset.

N.B. After successfully grounding the tip, be *VERY* careful when working on circuits with charged capacitors or batteries.  If you touch the grounded tip to a circuit node that's got a significant voltage on it, shorting it out, if the discharge current is high enough, you'll damage the bit and possibly also damage the controller in the station.  If you've got no choice but to solder a battery terminal with the battery present, disconnect *ALL* other lead to the board or device to ensure there is no other ground connection to complete the circuit, and work on an ESD mat, *NOT* a grounded metal surface.

[Haggis McHaggis]

Thank you very much.

Odds are, because it has three pin power in with PE, the laptop PSU has the 0V (-) side of its DC out grounded. You can check that by checking for continuity, PE to 0V with  the PSU totally disconnected.

I just measured that. There is no connection between PE on the input to the DC output.

If the tip's floating you can ground it, so with the iron cold and power off, check resistance between the tip and the 0V side of its DC in jack.  If it reads open or very high resistance, its OK to ground the tip (via the barrel).   If it  shows as direct continuity, its already supposedly grounded so something else is going on..

The resistance between DC in (-) and the tip is around 13Mohm, no direct continuity.

The handle is a T12-9501 and has a 4 pin plug. One of the pins is connected to the tip and is connected to some pin on the controller pcb. I'm not sure how to check if this is the ground wire or there for other purposes.

[Haggis McHaggis]

I've attached a photo that shows a similar controller board, but with the same handle. On my unit there is no wire going to Earth (DC IN) on the board. It makes sense because there is no Earth input or terminal.

[Haggis McHaggis]

I measured the resistance with the psu plugged in but with no connection to mains. Between PE and tip i get around 13MOhm (this value is ascending the longer i measure) and between PE and DC output (-) around 1MOhm.

[Mechatrommer]

the odd is... its your laptop psu that is floating (not 0V relative to GND) i zapped few (new never been used) mosfets while connecting MK328 transistor checker with this type of smps psu, they are nasty arse when not earthed. my suggestion, ensure you laptop psu output is isolated from its mains input (using the smps transformer), if so, earth the DC- pin by shorting it to the gnd/earth pin or using some high value resistor if you want to be safe. this is my fix to my zapping smps psu. ymmv.

[Haggis McHaggis]

Thanks for your input.

my suggestion, ensure you laptop psu output is isolated from its mains input (using the smps transformer),..

How do you do this?

[Haggis McHaggis]

Here is a top view of the unit.

There is a 1KOhm resistor between on/off switch and DC in (-). I've no idea what the purpose of the resistor is.

The tip is connected via the green cable to the 4 pin connector (pin A1, pcb label 'E'). The 3 pin DC in connector has the mid green cable missing (pcb label 'E') unlike on the connection diagram posted earlier. I assume 'E' means Earth.

[Specmaster]

If you have the one that has a 2.1mm DC input jack like the photo above shows, then the chances are that your power pack / wall wart will not have the earth connecting through to the soldering station. This can be checked easily enough with DMM to see if there is continuity between the earth pin of the power unit and the DC jack. Do you need to have the tip earthed? sometimes it can an advantage to have it floating, especially if the power supply uses a isolated transformer winding for the power.

[Haggis McHaggis]

If you have the one that has a 2.1mm DC input jack like the photo above shows, then the chances are that your power pack / wall wart will not have the earth connecting through to the soldering station. This can be checked easily enough with DMM to see if there is continuity between the earth pin of the power unit and the DC jack. Do you need to have the tip earthed? sometimes it can an advantage to have it floating, especially if the power supply uses a isolated transformer winding for the power.

Yes, i have a 2.1mm DC input jack on my unit. I already measured some stuff (see above). The psu has no direct connection between the mains PE and the DC side.

Like mentioned in my first post, my primary goal is to avoid killing MCP1541's while soldering them in. Since i measured some voltage on the tip i concluded that i need to eliminate that first and then may look further at additional ESD safety measures.

I'm a noob, so i don't know whether i need to connect the station to mains PE or if its sufficient to connect the tip to DC (-).

[bd139]

It's not so much the 3V you can measure but the 90V or so floating around off those laptop supplies to ground. That'll pop a CMOS IC in a second.

The typical laptop packs are floating. Most of them don't even have an earth pin in the cable. You would have to provide a separate ground path. Note that you don't want the tip connected directly to ground but via a 1M resistor. You don't want to whip all the electrons out of the thing you are soldering instantly or it'll blow up anyway.

My T12 exploded violently anyway so it's dead now. I slung it on my neighbour's garage roof. Now use the Metcal and the T12 is dead to me much like my wife 

[Haggis McHaggis]

lol, thanks for chiming in bd139

How do i measure that 90V floating?

I've attached a photo of my psu. It has 3 pins in and 2 out (signal pin is not connected, the cable has only 2 cores)

[bd139]

Ahhh the old thinkpad 90W bricks. Good power supplies. Had a few of them! Try measuring AC volts between the barrel plug shield and something earthed. I actually used to get a tingle off my T420 when I had one of them.

[Specmaster]

Why is the 90 or so floating voltage an issue here, surely if your soldering anything on a laptop especially something that is sensitive, you'd remove the battery and unplug the power brick from it as well so the laptop is dead? 

[bd139]

The 90V is the leakage in the Y capacitors between the primary and the secondary on the SMPS. So the tip is likely 90V or so with respect to ground. If you go poking around CMOS stuff it can be an issue as you are closer to ground so the circuit goes:

mains -> Y2 capacitor -> secondary -> DUT -> you -> ground.

This is incidentally the reason you get that tingling on some floating SMPS stuff when you touch the metal parts.

[Specmaster]

The 90V is the leakage in the Y capacitors between the primary and the secondary on the SMPS. So the tip is likely 90V or so with respect to ground. If you go poking around CMOS stuff it can be an issue as you are closer to ground so the circuit goes:

mains -> Y2 capacitor -> secondary -> DUT -> you -> ground.

This is incidentally the reason you get that tingling on some floating SMPS stuff when you touch the metal parts.

Are saying then that the power cord is permanently attached to the laptop? The Y capacitors are located in the external SMPS and not in the laptop itself. If so then unplugging the DC  power jack leaves the laptop totally isolated from the Y capacitors and this leakage so the problem goes away? [emoji848]

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[bd139]

Where has the laptop come from?

[Specmaster]

Oh, I see, it's the iron that that is powered by the brick DOH, [emoji83]

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[Mechatrommer]

my suggestion, ensure you laptop psu output is isolated from its mains input (using the smps transformer),..

How do you do this?

There is a 1KOhm resistor between on/off switch and DC in (-). I've no idea what the purpose of the resistor is.

yes that 1KOhm resistor is probably meant to bring the DC- to same potential as as your soldering iron circuit GND, but looking at your picture i guess it will not do any good since there is no real earth wiring in there. the real earth wire only available in your laptop power brick. you need to modify your power brick that means opening it up. if there is no screw on the power brick you need to crack those glue open. if you dont want to do that, and dont want to zap your electronics component, then find another psu that is earthed, a classic 50/60Hz big transformer psu if you have one or have to. you wont appreciate the "floatness" until you zap your stock components for no apparent reason. that tinggling sensation bd139 is talking about? thats a early warning for you. you maybe lucky this time, or your lenovo power brick is not as bad as other smps psu so ymmv.

[Specmaster]

I have 2 if the T12 soldering stations but there are powered by 230 to 24v internal SMPS which have a proper grounding connection and that us the only really effective way to remove the risks associated with sensetive parts. I have replaced many mosfets with zero losses using this system. If you really must have a portable soldering solution then maybe a battery operated or gas powered system is the option that you should explore?

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[Haggis McHaggis]

Ahhh the old thinkpad 90W bricks. Good power supplies. Had a few of them! Try measuring AC volts between the barrel plug shield and something earthed. I actually used to get a tingle off my T420 when I had one of them.

measured AC voltages between:
mains PE and DC- = 0.1V
mains PE and DC+ = 36V

* used a switched off 230V soldering irons tip as mains PE
** a second (newer) lenovo psu shows the same voltages
*** used a cheap DMM

Edit: i measured the psu only, no soldering station connected

[Haggis McHaggis]

.. the real earth wire only available in your laptop power brick. you need to modify your power brick that means opening it up. if there is no screw on the power brick you need to crack those glue open.

Yeah, opening a glued psu will possibly look shitty afterwards. I thought about cracking it open and putting the guts into a larger soldering station case. But i'd have to order a larger case from seller which costs $$ and maybe don't fit in the end. What do you think about simply providing the PE by another device or a selfmade mains adapter? I could mount a 'earth' jack on the back panel and use this to connect to PE.

Edit: earth adapter img added

[Haggis McHaggis]

I have 2 if the T12 soldering stations but there are powered by 230 to 24v internal SMPS which have a proper grounding connection and that us the only really effective way to remove the risks associated with sensetive parts. I have replaced many mosfets with zero losses using this system. If you really must have a portable soldering solution then maybe a battery operated or gas powered system is the option that you should explore?

I think/hope my controller board is the same they use for the build in psu versions. It looks like they simply didn't connect earth (pcb label 'E') to anything other than the pcb and the tip. In other words the DC in connector on the board has 3 pins and the middle ('E') pin has the green cable missing.
A portable station is not what i'm after.

[Specmaster]

I have 2 if the T12 soldering stations but there are powered by 230 to 24v internal SMPS which have a proper grounding connection and that us the only really effective way to remove the risks associated with sensetive parts. I have replaced many mosfets with zero losses using this system. If you really must have a portable soldering solution then maybe a battery operated or gas powered system is the option that you should explore?

I think/hope my controller board is the same they use for the build in psu versions. It looks like they simply didn't connect earth (pcb label 'E') to anything other than the pcb and the tip. In other words the DC in connector on the board has 3 pins and the middle ('E') pin has the green cable missing.
A portable station is not what i'm after.

So if its not a portable version, you could perhaps sell the one you have on Ebay or something and buy a mains powered system with the built in psu? where the PE connection is taken right the way through to the iron tip?