Isolation transformer source

[PeterD]

Nice price. I'm working on a 1KW HP 6032A power supply (with outputs
unloaded in this case, so I don't need *too* much current capability) and
need to connect my scope to the hot side of a switching transformer -
specifically the source and drains on the output FETs.

Service manual: (3MB)
http://www.home.agilent.com/agilent...384-1:epsg:man&lc=eng&cc=US&nfr=-35687.384731
Page 113 shows the schematic of the FET board.

With an isolation transformer, I *think* I would connect the scopes GND
lead the source of Q1 and probe the it's gate to check the it, then move
the scopes GND lead to Q3's drain lead to check it's gate drive.

Given that, would that Ebay transformer be the right choice, and do I need
to isolate (disconnect) the ground on the 6032A power supply under repair?

Thanks.

You need to make 100% sure your life insurance is fully paid up. <g>

 

[tm]

Nice price. I'm working on a 1KW HP 6032A power supply (with outputs
unloaded in this case, so I don't need *too* much current capability) and
need to connect my scope to the hot side of a switching transformer -
specifically the source and drains on the output FETs.

Service manual: (3MB)
http://www.home.agilent.com/agilent...384-1:epsg:man&lc=eng&cc=US&nfr=-35687.384731
Page 113 shows the schematic of the FET board.

With an isolation transformer, I *think* I would connect the scopes GND
lead the source of Q1 and probe the it's gate to check the it, then move
the scopes GND lead to Q3's drain lead to check it's gate drive.

Given that, would that Ebay transformer be the right choice, and do I need
to isolate (disconnect) the ground on the 6032A power supply under repair?

Thanks.

This is a "bad idea". Better to use a differential input and two probes. Do
you have a two channel scope with invert on channel 2?

Tom

 

[Phil Allison]

"Dave Plowman " Rabid Pommy Nutcase"

Surely an isolation transformer is just that...

** Shame it is not so in the USA

- you Steaming Great Fuckwit ...............




.... Phil

 

[[email protected]]

Nice price. I'm working on a 1KW HP 6032A power supply (with outputs
unloaded in this case, so I don't need *too* much current capability) and
need to connect my scope to the hot side of a switching transformer -
specifically the source and drains on the output FETs.

Service manual: (3MB)
http://www.home.agilent.com/agilent...384-1:epsg:man&lc=eng&cc=US&nfr=-35687.384731
Page 113 shows the schematic of the FET board.

With an isolation transformer, I *think* I would connect the scopes GND
lead the source of Q1 and probe the it's gate to check the it, then move
the scopes GND lead to Q3's drain lead to check it's gate drive.

Given that, would that Ebay transformer be the right choice, and do I need
to isolate (disconnect) the ground on the 6032A power supply under repair?

Thanks.

That SHOULD be the correct isolation transformer. And yes, the ground
must be isolated. Note that this may well leave the metal chassis of
the power supply at some potentially lethal voltage, so use extreme
caution.

Somewhere in my kit (probably with the isolation transformer I can't
find) is an adapter to use a grounded (three prong) plug in an
ungrounded (two prong) outlet. I used that when working with any
devide that required the isolation transformer. I also carefully
verified that the isolation was indeed effective; I had no desire to
watch my scope probe's ground lead vaporize.

PlainBill

 

[[email protected]]

This is a "bad idea". Better to use a differential input and two probes. Do
you have a two channel scope with invert on channel 2?

Tom

That would be news to large numbers of electronics technicians who had
to use an isolation transformer when servicing TVs and other 'live
chassis' consumer electronics. There IS a reason the advice was 'to
always keep one hand in your pocket'.

PlainBill

 

[Meat Plow]

action=ref&cname=AGILENT_EDITORIAL&ckey=1000000384-1%3Aepsg%
3Aman&lc=eng&cc=US&nfr=-35687.384731
That would be news to large numbers of electronics technicians who had
to use an isolation transformer when servicing TVs and other 'live
chassis' consumer electronics. There IS a reason the advice was 'to
always keep one hand in your pocket'.

PlainBill

Serviced many GE VIR portables with a Sencore PR57 Powerite.

 

[tm]

That would be news to large numbers of electronics technicians who had
to use an isolation transformer when servicing TVs and other 'live
chassis' consumer electronics. There IS a reason the advice was 'to
always keep one hand in your pocket'.

PlainBill

You can do it anyway you want. Just that many good scopes have a way to add
the inverted second channel and can be used to look at a signal that is
raised above
ground. No isolation transformer is needed and it is IMO, safer.


YMMV.

 

[Phil Allison]

"tm"

You can do it anyway you want. Just that many good scopes have a way to
add
the inverted second channel and can be used to look at a signal that is
raised above ground.

** The problem with that idea is the very limited common mode range
available with that scope function.

The buffers on most ( analogue) scopes become overloaded with input signals
that exceed full screen hight by a factor of 2 or 3 times.

Say you want to examine a 1 volt p-p signal and you set the scope input
atten to 0.5 volts per division - then the largest undistorted input
allowable is gonna be about 0.5 x 8 x 3 = 12 volts p-p.

Not much use with the ACTUAL common mode signal is several hundred volts p-p
from rectified AC supply.

No isolation transformer is needed and it is IMO, safer.

** Fraid that is just not true when dealing with off-line SMPS.



..... Phil

 

[Phil Allison]

"Dave Plowman " Rabid Pommy Nutcase"

Phil Allison



But I'm not in the USA and neither are you.

** But the OP is in the *** USA *** !!!!!!!!!!!

- and he asked for a 120 volt AC tranny too !!!!!!!!!


You colossal, fucking POMMY MORON !!!


..... Phil

 

[Phil Allison]

"Wild_Bill Top Poster from Hell"

Apparently you assume that I didn't understand that.

** Could not be plainer that you did NOT understand the issue.

 

[Phil Allison]

"Wild_Bill Top Poster from Hell"

My point,

** The only point you have, pal, is on the top of you fat head.

was that you're not going to teach anyone proper grammer or composition
on usenet..

** Could not be plainer that you did NOT understand the issue

AT ALL !!!!!!!!!!!!!!!!!!



..... Phil

 

[Phil Allison]

"Dave Plowman (Rabid Pommy Nut Case) "

Why is the test equipment grounded?

** Not merely stupid, but dangerously fucking STUPID !!





..... Phil

 

[PeterD]

"Dave Plowman (Rabid Pommy Nut Case) "




** Not merely stupid, but dangerously fucking STUPID !!





.... Phil

Phil: consider it to be "self correcting" instead...

 

[Phil Allison]

"PeterD"

Phil: consider it to be "self correcting" instead...

** If only that were true ...



... Phil

 

[PeterD]

Yawn. You really do need to sort out how to work in a safe environment.
All it needs is some common sense. Do you ground one side of a battery DVM
too?

Dang, you confirm stupidity... Amazing! Any test equipment DESIGNED to
not be grounded isn't grounded. And test equipement that is designed
to be grounded damned well better be grounded.

 

[GregS]

It certainly seems to me stupid to have the same name for different
devices like this. What is the point of an isolating transformer which
doesn't isolate?

Noise reduction.


greg

 

[GregS]

Thanks Chuck. Looking at these for the moment:
http://www.mcmelectronics.com/product/TRIPP-LITE--POWER-PROTECTION--IS500-/28-1
0160
http://www.mcmelectronics.com/product/TENMA-72-1097-/72-1097

The Tripp-Lite device has secondary attached to GROUND. This is NOT
want you want. All Tripp-Lite supplies are attached to ground forming a new neutral to
make a noise reduction device, period.

I hope the second device has ground isolation.

Greg

 

[GregS]

If using a proper isolating transformer, there will be no reference to
ground even with a 'live' chassis. The only way to get an electrical shock
is to touch both outputs from the transformer.

Proper is the key. I would say over 98% of so called isolation transformers
are for noise control, not serving chassis.

Greg

 

[GregS]

The Tripp-Lite device has secondary attached to GROUND. This is NOT
want you want. All Tripp-Lite supplies are attached to ground forming a new
neutral to
make a noise reduction device, period.

This is the description in the specs...............

Neutral to ground bonding at the secondary eliminates common mode noise and provides an isolated ground reference for sensitive
equipment

What they really mean is a new ground to neutral reference. They make it confusing.
For testing chassis, you need a ground isolating isolation transformer.

greg

 

[Chuck]

Thanks Chuck. Looking at these for the moment:
http://www.mcmelectronics.com/product/TRIPP-LITE--POWER-PROTECTION--IS500-/28-10160
http://www.mcmelectronics.com/product/TENMA-72-1097-/72-1097

A bit more than I wanted to spend and a little less current capability,
but those may be the breaks.

Check out stock number 72-6670 isolation transformer $65.00. We've
had one for years and it works very well. Chuck