22 Nov
2012
22 Nov
'12
midnight
I'm looking to help protect against frying my DUTs, oscilloscopes, logic
analyzers during testing.
I've been thinking about purchasing an isolation transformers, and I've
watched a couple video blog entries on the subject. [1]
While I'm pretty careful what I'm probing, I don't want an inadvertent
short of the test equipment ground to the positive supply rail off my
DUT to blow stuff up.
The strategy I intend on using is this:
1. Connect the primary side ground of the isolation transformer to
ground with a normal(US) 3-prong plug.
2. Float the DUT by using a 3-prong to 2-prong adapter when plugging
into the secondary side of the transformer.
3. Keep the o'scope or LA grounded with a normal 3-prong plug.
My DUT for the most part is a commodore amiga that has an external 120v
to +12v,-12v, and +5v power supply. I'm not intending on opening
supplies, troubleshooting/repairing them or generally touching anything
that has live mains power following through it.
The signals I'm probing are generally ground-referenced single-ended
signals.
Does this approach sound reasonable? I'm looking for practical
actionable advice. I'm looking at the BK1604A. [2]
Thanks,
Keith
[1] http://www.toddfun.com/2011/04/30/isolation_transformers/ and
http://www.youtube.com/watch?v=xaELqAo4kkQ (which is eevblog #279)
[2] http://www.tequipment.net/BK1604A.html#
22 Nov
22 Nov
12:38 a.m.
Keith Monahan wrote:
My DUT for the most part is a commodore amiga that has
an external
120v to +12v,-12v, and +5v power supply. I'm not intending on opening
supplies, troubleshooting/repairing them or generally touching
anything that has live mains power following through it.
Generally speaking, the power supply (internal or external) for any
UL-listed computer (and most others) is isolated from the mains power,
so there's no problem with probing it with a scope or logic analyzer.
It's only when you're working on the power supply itself that you'd be
likely to run into trouble.
A common situation where people have damaged their test equipment is
working on a "hot chassis" (non-isolated) television. I haven't ever
seen a hot-chassis solid-state computer. I don't know whether many
tube-based computers were hot-chassis.
5:17 a.m.
----- Original Message -----
From: "Eric Smith" <eric at brouhaha.com>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Sent: Thursday, November 22, 2012 5:38 AM
Subject: Re: floating the DUT and isolation transformers
Keith Monahan wrote:
Almost certainly not , the only reason for the live
chassis on a TV was to
avoide the cost of a mains transformer.
Dave
My DUT for the most part is a commodore amiga
that has an external 120v
to +12v,-12v, and +5v power supply. I'm not intending on opening
supplies, troubleshooting/repairing them or generally touching anything
that has live mains power following through it.
Generally speaking, the power supply (internal or external) for any
UL-listed computer (and most others) is isolated from the mains power, so
there's no problem with probing it with a scope or logic analyzer. It's
only when you're working on the power supply itself that you'd be likely
to run into trouble.
A common situation where people have damaged their test equipment is
working on a "hot chassis" (non-isolated) television. I haven't ever seen
a hot-chassis solid-state computer. I don't know whether many tube-based
computers were hot-chassis.
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2221 / Virus Database: 2629/5409 - Release Date: 11/21/12
11:10 a.m.
Of course, it is possible for the power supply to short, making things that
were not intended to be hot, hot.
I once worked on a machine that I noticed the ground plug pin was cut.
I later found that it was because the input line filter was shorted and
they'd cut the ground wire to keep from popping the breaker.
The only outside equipment that it was connected to was a phone
modem that was run from a wall wort( no other ground path ).
Dwight
Date: Wed, 21 Nov 2012 22:38:33 -0700
From: eric at brouhaha.com
To:
Subject: Re: floating the DUT and isolation transformers
Keith Monahan wrote:
My DUT for the most part is a commodore amiga
that has an external
120v to +12v,-12v, and +5v power supply. I'm not intending on opening
supplies, troubleshooting/repairing them or generally touching
anything that has live mains power following through it.
Generally speaking, the power supply (internal or external) for any
UL-listed computer (and most others) is isolated from the mains power,
so there's no problem with probing it with a scope or logic analyzer.
It's only when you're working on the power supply itself that you'd be
likely to run into trouble.
A common situation where people have damaged their test equipment is
working on a "hot chassis" (non-isolated) television. I haven't ever
seen a hot-chassis solid-state computer. I don't know whether many
tube-based computers were hot-chassis.
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