Isolation transformer source
in [Repair]
|
Prev: Simple hack to get $500 to your home
Next: This inmate needs to be paroled, not given a second life sentence
From: tm on 12 Jun 2010 14:19 <PlainBill47(a)yahoo.com> wrote in message news:j7g716l13t96u9322qmqjiv8r5ppua3tdj(a)4ax.com... > On Sat, 12 Jun 2010 10:32:04 -0400, "tm" <noone(a)msc.com> wrote: > >> >>"JW" <none(a)dev.null> wrote in message >>news:0qo616dhg4nsgshqjsia9l39venjef4bt6(a)4ax.com... >>> >>> 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/redirector.jspx?action=ref&cname=AGILENT_EDITORIAL&ckey=1000000384-1%3Aepsg%3Aman&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 >> >> > 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.
From: Wild_Bill on 12 Jun 2010 18:10 Apparently you assume that I didn't understand that. -- Cheers, WB .............. "Phil Allison" <phil_a(a)tpg.com.au> wrote in message news:huukoc$q2e$1(a)news-01.bur.connect.com.au... > > > The question is not about the number but the nature of the item. > > > .... Phil > > >
From: Michael A. Terrell on 12 Jun 2010 19:38 PlainBill47(a)yahoo.com wrote: > > On Sat, 12 Jun 2010 10:32:04 -0400, "tm" <noone(a)msc.com> wrote: > > > > >"JW" <none(a)dev.null> wrote in message > >news:0qo616dhg4nsgshqjsia9l39venjef4bt6(a)4ax.com... > >> > >> 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/redirector.jspx?action=ref&cname=AGILENT_EDITORIAL&ckey=1000000384-1%3Aepsg%3Aman&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 > > > > > 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'. That advice was quite valid when two channel scopes weren't seen outside of a factory or research center. -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
From: Michael A. Terrell on 12 Jun 2010 19:39 "Dave Plowman (News)" wrote: > > In article <j7g716l13t96u9322qmqjiv8r5ppua3tdj(a)4ax.com>, > <PlainBill47(a)yahoo.com> wrote: > > 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'. > > 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. Not true. You connect the chassis of the UUT to the test equipment, so ANY voltage you contact inside the UUT is referenced to ground. -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
From: Phil Allison on 12 Jun 2010 21:44
"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 |