Author Topic: Low voltage soldering iron necessary in oscilloscopes?  (Read 3911 times)

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Offline moonpieTopic starter

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Low voltage soldering iron necessary in oscilloscopes?
« on: December 28, 2013, 09:42:03 pm »
Hi all

I have an old analog Philips PM3214 2-channel oscilloscope that needs soldering.
It is the first resistor just after the input BNC connector on one of the channels that is loose and needs to be soldered.

The scope has a double insulated transformer and is NOT grounded to mains earth.
The service manual (for similar model PM3217) says: "When you are soldering inside the instrument it is essential to use a low-voltage soldering iron, the tip of which must be earthed to the mass of the oscilloscope."

Will I be OK if I ground the case of the scope, and then use my 220V iron on it? The tip of my 220V 15/30W iron is grounded.
What are the dangers of not using a low voltage iron? Static electricity?

moonpie
(An electronics newbie)
 

Offline oldway

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Re: Low voltage soldering iron necessary in oscilloscopes?
« Reply #1 on: December 28, 2013, 09:52:01 pm »
First select the ampl/div switch of the channel on 10V/div before soldering, and there is no risk of damage any more.
 

Offline c4757p

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Re: Low voltage soldering iron necessary in oscilloscopes?
« Reply #2 on: December 28, 2013, 09:52:15 pm »
The tip of my 220V 15/30W iron is grounded.

You're fine.
No longer active here - try the IRC channel if you just can't be without me :)
 

Offline nanofrog

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Re: Low voltage soldering iron necessary in oscilloscopes?
« Reply #3 on: December 28, 2013, 10:04:40 pm »
 

Offline Nerull

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Re: Low voltage soldering iron necessary in oscilloscopes?
« Reply #4 on: December 28, 2013, 10:33:17 pm »
Some - mostly older - irons have voltage from the heating element exposed on the tip from leakage, which can damage sensitive components. If your tip is grounded, you should be fine.

My old ratshack firestarter didn't even have a grounding plug.  :scared:
« Last Edit: December 28, 2013, 10:37:41 pm by Nerull »
 

Offline oldway

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Re: Low voltage soldering iron necessary in oscilloscopes?
« Reply #5 on: December 28, 2013, 10:37:34 pm »
Do'nt trust this too much.
My computer is grounded but when I touched the case, I felt an electric shock.
I asked an electrician to check this and he found that the ground of the main plug was not conected. :--
 

Offline Nerull

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Re: Low voltage soldering iron necessary in oscilloscopes?
« Reply #6 on: December 28, 2013, 10:38:46 pm »
In that case your computer was not grounded.

Nothing will be properly grounded if your mains ground connection is faulty.
 

Offline oldway

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Re: Low voltage soldering iron necessary in oscilloscopes?
« Reply #7 on: December 28, 2013, 10:44:20 pm »
It was "apparently" grounded...nobody check if this is really the case.
With the ampl/div switch of the channel on 10V/div before soldering, there is no risk at all, correctly grounded or not.
 

Offline moonpieTopic starter

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Re: Low voltage soldering iron necessary in oscilloscopes?
« Reply #8 on: December 29, 2013, 03:48:03 pm »
Thanks for all the input. I will not worry too much then.
 

Offline KJDS

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Re: Low voltage soldering iron necessary in oscilloscopes?
« Reply #9 on: December 29, 2013, 04:20:40 pm »
If in doubt, touch the tip of the iron to the case of the scope before anything else. If it sparks, use a different iron.


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