Date
1 - 20 of 121
Can we talk safety for a moment?
|
Brendan
I would like to make my repair hobby as safe as possible. Can you pros please recommend an isolation transformer/isolation variac that would be suitable for scope/audio repair? Thanks. I know you guys will help me out :)
|
|
|
|
Kurt Rosenfeld
A worthwhile topic, perhaps for another thread, is safety best practices for electronics repair. Equipment is important, but there's a bunch of other aspects to risk reduction, e.g., keeping one hand behind one's back. I'm sure some people on this forum have wisdom in the area of best practices. Some of it might be hard-earned wisdom.
-Kurt
|
|
|
|
ed beers
I'm going to suggest a GFI breaker should be available on you bench.
toggle quoted messageShow quoted text
On 2/17/2018 2:47 PM, Kurt Rosenfeld wrote:
A worthwhile topic, perhaps for another thread, is safety best practices for electronics repair. Equipment is important, but there's a bunch of other aspects to risk reduction, e.g., keeping one hand behind one's back. I'm sure some people on this forum have wisdom in the area of best practices. Some of it might be hard-earned wisdom.
|
|
|
|
Richard Knoppow
Note that Variacs are autotransformers and do not provide isolation. You need an isolation transformer, preferably one with an electrostatic shield between windings (also called a Faraday shield). The latter prevents some common mode noise from going through the transformer. Such transformers were made by practically every maker of transformers.
toggle quoted messageShow quoted text
A Variac or other variable transformer, is useful but must be combined with an isolation transformer to provide safety. Also note that if the equipment has noise by-pass capacitors in it going to chassis ground, the chassis can be hot. A small value cap or caps will not pass much current but it can be enough to give you a bite.
On 2/17/2018 2:22 PM, lop pol via Groups.Io wrote:
I would like to make my repair hobby as safe as possible. Can you pros please recommend an isolation transformer/isolation variac that would be suitable for scope/audio repair? Thanks. I know you guys will help me out :) --
Richard Knoppow dickburk@ix.netcom.com WB6KBL
|
|
|
|
Richard R. Pope
Hello all,
toggle quoted messageShow quoted text
A GFI Breaker is not a bad idea. When I was in the AF we were thought to always use only one hand. I received a call out to the RAPCON to check out a noisy radio. I had another Airman with me and I was his supervisor. As always with newbies he was gung ho but not all that bright. He went right over to the radio and proceeded to disconnect the antenna. I yelled 'NO' at him just as the Antenna Lead came loose. He then shot all of the way across the room and came to rest against the far wall. He was OK but he was also stiff and sore for the next few days. He forgot the one hand rule but more important he forgot the turn it off, stupid rule! He had had one hand on the case and used his other hand to unscrew the Antenna Lead. Ouch. He was very fortunate that he wasn't injured in a far worst manner or even killed. Learn and Live. GOD Bless and Thanks, rich!
On 2/17/2018 4:57 PM, ed beers wrote:
I'm going to suggest a GFI breaker should be available on you bench.
|
|
|
|
Brendan
You guys are awesome. I knew you would have some great ideas. GFIC is next. I always TRY and keep one hand behind my back but its good to hear you guys reinforce how important that is because sometimes I forget.
|
|
|
|
Richard Knoppow
Amen, I was also taught to keep one hand in a back pocket and, around transmitters, always use a shorting stick.
toggle quoted messageShow quoted text
On 2/17/2018 3:22 PM, Richard R. Pope wrote:
Hello all, --
Richard Knoppow dickburk@ix.netcom.com WB6KBL
|
|
|
|
David DiGiacomo
On Sat, Feb 17, 2018 at 3:22 PM, lop pol via Groups.Io
<the_infinite_penguin=yahoo.com@groups.io> wrote: I would like to make my repair hobby as safe as possible. Can you pros please recommend an isolation transformer/isolation variac that would be suitable for scope/audio repair?Some common isolated variac units: B+K 1653 B+K 1655 Heathkit IP-5220 Sencore PR57 They are not as common on the surplus market as they used to be, but if you are patient you can find one at a reasonable price. If you need high current, you will have to assemble your own.
|
|
|
|
Harvey White
On Sat, 17 Feb 2018 14:57:26 -0800, you wrote:
I'm going to suggest a GFI breaker should be available on you bench.I'd do both. Just because. I have a sencore "AC powerite" which does 0-3 amps continuous, 0-4 amps intermittent. Has leakage meter, voltage and current for both input and output. Nice piece of equipment. Isolated variac with leakage metering. Harvey
|
|
|
|
Chuck Harris
Before we go anywhere, it is very important for you to understand
toggle quoted messageShow quoted text
that an isolation transformer's purpose is to protect the device under test (DUT), from your grounded test equipment. It is *not* there to protect you: At all. If you believe it will protect you, you are setting yourself up for a world of hurt. Second important thing to understand is never ever ever run your normally grounded test equipment (such as scopes, oscillators, etc.) from your isolation transformer. That may allow the scope's chassis, and all of the scope's grounds to be elevated to whatever voltage the scope probe's ground clip is connected to. And finally, it is never ok to disable any test equipment's, or device under test's safety ground wire. The safety ground wire makes sure that the parts you ordinarily might touch are at your local bench/power line ground. It is imperative that the power line's safety ground wire is continued from the isolation transformer's power cord through to the DUT's safety ground wire (if any). The best safety device is a well schooled brain. -Chuck Harris lop pol via Groups.Io wrote:
I would like to make my repair hobby as safe as possible. Can you pros please recommend an isolation transformer/isolation variac that would be suitable for scope/audio repair? Thanks. I know you guys will help me out :)
|
|
|
|
Dave Casey
You tube guys aren't worried about ESD, but anyone who has set up an
ESD-safe workstation in their lab should also be using GFCI on EVERYTHING at their bench (UUTs AND test gear). What happens if you are strapped in, working on some LV digital circuitry and your test gear develops a fault that leaks mains voltage to the front panel? Where I work, every single circuit in the lab has GFCI. Also, it's worth reminding everyone that GFCI does nothing for you if you get between line and neutral, only line and earth. Dave Casey On Sat, Feb 17, 2018 at 5:56 PM, Harvey White <madyn@dragonworks.info> wrote: On Sat, 17 Feb 2018 14:57:26 -0800, you wrote:I'm going to suggest a GFI breaker should be available on you bench.I'd do both. Just because. I have a sencore "AC powerite" which does
|
|
|
|
Richard R. Pope
Chuck,
toggle quoted messageShow quoted text
Another use of the safety ground is to insure that if a voltage supply wire should come in to contact with the case or some other part that the operator can come in contact with the circuit breaker or fuse will trip or blow. That radio in the RAPCON was a High Power Transceiver. The noise was being caused by a loss of the safety ground. When the safety ground was lost the case and the Antenna Lead had become charged with about 400 VAC. The Captain who was the duty officer of the day kept unplugging this unit from the wall and plugging it into a two wire extension cord so that he could plug his favorite AM/FM radio/clock and a fan into that outlet. This was the second time that I had gone out to the RAPCON on the same Radio. This time I cut extension cord into little bitty pieces and handed it to the stunned Captain. You should have seen the look on the Airman's face when a A1C did this. Of course they always did say that NCOMs were smarter than Officers. LOL! :) We didn't have any more troubles with that radio. The Captain never did make Major. GOD Bless and Thanks, rich!
On 2/17/2018 6:21 PM, Chuck Harris wrote:
Before we go anywhere, it is very important for you to understand
|
|
|
|
Dale H. Cook
At 05:22 PM 2/17/2018, lop pol wrote:
I would like to make my repair hobby as safe as possible. Can you pros please recommend an isolation transformer/isolation variac that would be suitable for scope/audio repair? Thanks. I know you guys will help me out :)I built my own: http://plymouthcolony.net/starcity/radios/pages/custom.html#variac Dale H. Cook, GR / HP Collector, Roanoke/Lynchburg, VA http://plymouthcolony.net/starcity/radios/index.html
|
|
|
|
Cliff Carrie
You may need two or three GFCIs for your bench: The first one is for most of your test gear and any DUT, probably after a master switch (key operated?) to safely shut down the bench. The second is for test equipment that must always have power. I have a recorder, a TCXO frequency counter, a GPS Disciplined Oscillator and a voltage standard that fall into this category. Finally, don't put your bench lighting on either of the first two GFCIs. Use a third GFCI for bench task lighting if you wish, but you really don't want to plunge the bench into darkness when a problem occurs, unless the lighting really is the source of the problem.
Many years ago I built a Power Distribution Unit for the first of the above, with a 10A breaker master switch, a front panel GFCI that also feeds rear panel outlets, neons for ground and line phase monitoring, a 5A DUT breaker after a Variac and isolation transformer (switch selectable), with switchable line / DUT voltmeter and DUT ammeter, and a front panel DUT outlet and binding posts. This thread reminded me I still need to add the GFCI for continuously powered gear. Regards, Cliff Carrie ________________________________ From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Dave Casey <polara413@gmail.com> Sent: Saturday, February 17, 2018 7:23:40 PM To: TekScopes@groups.io Subject: Re: [TekScopes] Can we talk safety for a moment? You tube guys aren't worried about ESD, but anyone who has set up an ESD-safe workstation in their lab should also be using GFCI on EVERYTHING at their bench (UUTs AND test gear). What happens if you are strapped in, working on some LV digital circuitry and your test gear develops a fault that leaks mains voltage to the front panel? Where I work, every single circuit in the lab has GFCI. Also, it's worth reminding everyone that GFCI does nothing for you if you get between line and neutral, only line and earth. Dave Casey On Sat, Feb 17, 2018 at 5:56 PM, Harvey White <madyn@dragonworks.info> wrote: On Sat, 17 Feb 2018 14:57:26 -0800, you wrote:I'm going to suggest a GFI breaker should be available on you bench.I'd do both. Just because. I have a sencore "AC powerite" which does
|
|
|
|
Dave Hills
I'll add another Air Force rule. No rings watches, or jewelry allowed at the workspace.
Dave
|
|
|
|
Don Lewis <dlewis11193@...>
NOT true.
toggle quoted messageShow quoted text
Modern GFIs detect differentials between line and neutral. If you just have the two wires, black and white, the GFCI will work. In fact, a GFCI is recommended in this situation because it will provide protection even though you have no equipment ground. DonN5CID ======================================================= ====================================================
On Saturday, February 17, 2018, 6:23:57 PM CST, Dave Casey <polara413@gmail.com> wrote:
You tube guys aren't worried about ESD, but anyone who has set up an ESD-safe workstation in their lab should also be using GFCI on EVERYTHING at their bench (UUTs AND test gear). What happens if you are strapped in, working on some LV digital circuitry and your test gear develops a fault that leaks mains voltage to the front panel? Where I work, every single circuit in the lab has GFCI. Also, it's worth reminding everyone that GFCI does nothing for you if you get between line and neutral, only line and earth. Dave Casey On Sat, Feb 17, 2018 at 5:56 PM, Harvey White <madyn@dragonworks.info> wrote: On Sat, 17 Feb 2018 14:57:26 -0800, you wrote:I'm going to suggest a GFI breaker should be available on you bench.I'd do both. Just because. I have a sencore "AC powerite" which does
|
|
|
|
On Sat, Feb 17, 2018 at 04:21 pm, Chuck Harris wrote:
Floating ground is a no do unless under DC battery operation if I understand correctly. I'm not sure the benefit actually at the moment. The video below reminded me of what Chuck is noting when working on the TDS5XX/6XX/7XXX or any other series. https://youtu.be/BAPWVEs5XDk?t=264 At about 7:48 tekhobbycap notes about performance enhancements with additional ground wiring, later noting to discharge the CRT screen to ground and also which I found the TDS520 didn't have a ground wire between the front panel board and metal case even though there were board and case holes present. I haven't looked into, though was wondering if there were any other later model ground wires added to improve performance and more safety of the device. I've also wondered about shielding components or sections of the boards to improve performance by reducing noise.
|
|
|
|
Frank DuVal
Well, you are both right.
toggle quoted messageShow quoted text
The GFCI looks at line and neutral, and when there is an ~5 mA difference, it opens the circuit. So, that is looking at a differential between line and neutral. However, if YOU get across line and neutral, it is still a balanced circuit, so you can conduct way past heart stopping current, and the GFCI will never open the circuit. It is when YOU provide a path from line to ground that the differential between line and neutral exceeds ~ 5mA and the circuit opens. I remember the picture in Popular Electronics (or was it Electronic Illustrated) back in the 60s when the inventor of the GFCI demonstrated his invention by holding a live wire in one hand and sticking his other hand under running water. That's believing in your product! Let's not get into the pros/cons of AFCI at this time, that is a discussion for the electricians on forums! :) Frank DuVal WA4CWM
On 2/17/2018 9:20 PM, Don Lewis via Groups.Io wrote:
NOT true.
|
|
|
|
ed beers
You do have 4M resistors in series with your strap don't you?
toggle quoted messageShow quoted text
On 2/17/2018 4:23 PM, Dave Casey wrote:
You tube guys aren't worried about ESD, but anyone who has set up an
|
|
|
|
ed beers
GFIs look for current flowing from the hot that doesn't return on the neutral.
toggle quoted messageShow quoted text
If the current is flowing from hot>you>neutral, it won't trigger.
On 2/17/2018 6:20 PM, Don Lewis via Groups.Io wrote:
NOT true.
|
|
|