Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old November 8th 18, 04:07 PM posted to sci.electronics.repair
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Default Variac question

On Thursday, 8 November 2018 06:37:49 UTC, Phil Allison wrote:
tabby wrote:
Phil Allison wrote:


Isolation transformer are used a lot in servicing certain type of
electronic equipment (e.g. tube TVs, amplifier, radio transmitters,


** But only those examples where the items have no AC supply isolation
transformers - IOW they are *HOT CHASSIS* designs. All of them very old

and very obsolete.

Well, they were standard & widespread in the 1990s.


** Live chassis tube TVs and radios " standard & widespread " in the 1990s ????


Live chassis TVs were very common in the 90s. Live chassis radios disappeared in the 60s.

FYI:

The OP did NIT even mention "live chassis" so his post was wrong and so is yours.


I was responding to your mention of 'hot chassis' not the OP's. What the OP mentioned is irrelevant.


Contemporary use of 1:1 isolation transformers would be for
servicing devices like SMPSs.


It removes the direct path to ground of the electrical power,
significantly reducing the chance of death.

** That is wrong.

Using an isolation transformer allows one to connect the common
rail ( or any other point) of an off-line SMPS to safety ground.
After which you can use a scope in the normal way to investigate
various waveforms, maybe small ones like MOSFET drive signals.



One can, but they are also used to reduce shock risk.


** Biggest safety myth out.

Using an isolation transformer unnecessarily INCREASES electric shock risk.


The UK government certainly disagrees with you. We have used isolation transformers for decades in bathrooms to reduce shock risk. Of course you're free to explain your pov.


NT

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Old November 8th 18, 05:31 PM posted to sci.electronics.repair
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One of the things you will learn about Phil is that he suffers from a congenital fixation with the fallacy of illicit transference - meaning that what is true of the parts is true of the whole. My cat is grey, therefore all cats are grey (apologies to Ben Franklin).

There are unique conditions in which an isolation transformer does not prevent the risk of electric shock. Therefore they increase the risk of electric shock.

Idiots will find a way to solve for the most idiot-proof safety measures as conceived, because they were not conceived by idiots. And if one inserts one's self into an electrical circuit, one will be shocked.

If you want to twist the dragon's tail, just get Phil started on newly-made multi-section can-caps.

Peter Wieck
Melrose Park, PA
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Old November 8th 18, 06:50 PM posted to sci.electronics.repair
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On Thursday, 8 November 2018 16:31:37 UTC, wrote:

One of the things you will learn about Phil is that he suffers from a congenital fixation with the fallacy of illicit transference - meaning that what is true of the parts is true of the whole. My cat is grey, therefore all cats are grey (apologies to Ben Franklin).

There are unique conditions in which an isolation transformer does not prevent the risk of electric shock. Therefore they increase the risk of electric shock.

Idiots will find a way to solve for the most idiot-proof safety measures as conceived, because they were not conceived by idiots. And if one inserts one's self into an electrical circuit, one will be shocked.

If you want to twist the dragon's tail, just get Phil started on newly-made multi-section can-caps.

Peter Wieck
Melrose Park, PA


I know he's a character. Some things he understands well, but no-one gets everything right.

I've put myself into an electrical circuit numerous times without getting shocked.


NT
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Old November 8th 18, 08:14 PM posted to sci.electronics.repair
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I've put myself into an electrical circuit numerous times without getting shocked.... that I remember.
  #36   Report Post  
Old November 8th 18, 11:04 PM posted to sci.electronics.repair
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On Thursday, November 8, 2018 at 3:38:08 PM UTC-5, Jeff Liebermann wrote:


.....I've gotten my share of RF burns, but those
don't count as getting shocked.


Sure they do. It's different in that you get a shock that can burn right to the bone and cauterize itself so it doesn't bleed. Got lots of those. Yep, good times.

Still get whacked mostly by power supplies that hold 400V across the PFC cap for a couple of days. Those will get your attention.

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Old November 8th 18, 11:16 PM posted to sci.electronics.repair
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On Thursday, 8 November 2018 20:38:08 UTC, Jeff Liebermann wrote:
On Thu, 8 Nov 2018 09:50:30 -0800 (PST), tabbypurr wrote:


I've put myself into an electrical circuit numerous times without getting shocked.


Were you wearing a Faraday cage or chain mail armor suit?
https://esfstream.com/faraday-cage-suit/
https://www.flickr.com/photos/stevencaton/sets/72157631825725155/


No. I might go & connect myself to 10,000v tonight

I haven't been zapped since tubes and hi-v were displaced by lower
voltage transistors. I've gotten my share of RF burns, but those
don't count as getting shocked.

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Old November 9th 18, 12:51 AM posted to sci.electronics.repair
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wrote:

Phil Allison wrote:



Well, they were standard & widespread in the 1990s.


** Live chassis tube TVs and radios " standard & widespread " in the 1990s ????


Live chassis TVs were very common in the 90s.



** But not TUBE sets as the above requires.

I have a 1990s 12 inch GE color portable where the whole chassis is live and only isolated by the antenna balun.


FYI:

The OP did NIT even mention "live chassis" so his post was wrong and so is yours.


I was responding to your mention of 'hot chassis' not the OP's.
What the OP mentioned is irrelevant.


** Bull****. I was responding to the OP post - so what he wrote is totally relevant.



Contemporary use of 1:1 isolation transformers would be for
servicing devices like SMPSs.


It removes the direct path to ground of the electrical power,
significantly reducing the chance of death.

** That is wrong.

Using an isolation transformer allows one to connect the common
rail ( or any other point) of an off-line SMPS to safety ground.
After which you can use a scope in the normal way to investigate
various waveforms, maybe small ones like MOSFET drive signals.


One can, but they are also used to reduce shock risk.


** Biggest safety myth out.

Using an isolation transformer unnecessarily INCREASES electric shock risk.


The UK government certainly disagrees with you.



** More arrogant bull****.



We have used isolation transformers for decades in bathrooms ....


** FFS you congenital context shifimg **bull****ter **

- the TOPIC here is electronics servicing with an Iso in the AC supply!!!!!!


Go away, stay there.


..... Phil


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Old November 9th 18, 01:07 AM posted to sci.electronics.repair
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Default Variac question

On Thursday, November 8, 2018 at 6:51:21 PM UTC-5, Phil Allison wrote:
wrote:

Phil Allison wrote:



Well, they were standard & widespread in the 1990s.

** Live chassis tube TVs and radios " standard & widespread " in the 1990s ????


Live chassis TVs were very common in the 90s.



** But not TUBE sets as the above requires.

I have a 1990s 12 inch GE color portable where the whole chassis is live and only isolated by the antenna balun.


FYI:

The OP did NIT even mention "live chassis" so his post was wrong and so is yours.


I was responding to your mention of 'hot chassis' not the OP's.
What the OP mentioned is irrelevant.


** Bull****. I was responding to the OP post - so what he wrote is totally relevant.



Contemporary use of 1:1 isolation transformers would be for
servicing devices like SMPSs.


It removes the direct path to ground of the electrical power,
significantly reducing the chance of death.

** That is wrong.

Using an isolation transformer allows one to connect the common
rail ( or any other point) of an off-line SMPS to safety ground.
After which you can use a scope in the normal way to investigate
various waveforms, maybe small ones like MOSFET drive signals.


One can, but they are also used to reduce shock risk.


** Biggest safety myth out.

Using an isolation transformer unnecessarily INCREASES electric shock risk.


The UK government certainly disagrees with you.



** More arrogant bull****.



We have used isolation transformers for decades in bathrooms ....


** FFS you congenital context shifimg **bull****ter **



.... Phil




Jeebus Phil you were doing so well recently.
  #40   Report Post  
Old November 9th 18, 01:08 AM posted to sci.electronics.repair
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Default Variac question

wrote:



There are unique conditions in which an isolation transformer
does not prevent the risk of electric shock.
Therefore they increase the risk of electric shock.



** What I wrote was that if the use of an iso tranny is not essential, you are better off not using one and taking all the usual precautions instead.

This detailed article by Rod Elliot explains why using an iso is hazardous - not that reading it will have the slightest impact on wooden heads like you or NT.

http://sound.whsites.net/articles/iso-xfmr.htm

FYI:

The use of an RCD, ELCB or other earth leakage detector ( aka safety switch) on a workbench is a safety essential.


..... Phil







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