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Tek 585A - for your entertainment!
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I'm new to the group and sadly a long, long ago degreed EE. I pickup up free scope that hadn't been used in MANY years and I personally haven't touched a scope literally in 45 years!
In my excitement, I plugged it in, waited for it to warm up, saw a faint trace, grabbed a 10x probe and foolishly tried to read line voltage. My GFCI powering the outlet immediately tripped. No now trace. Any thoughts on what I've damaged? Please try to hold the laughter. I can already hear it! haha .... |
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On 03/11/18 19:51, jamesvyu via Groups.Io wrote:
I'm new to the group and sadly a long, long ago degreed EE. I pickup up free scope that hadn't been used in MANY years and I personally haven't touched a scope literally in 45 years!Starting points, before doing anything else: Tektronix¡¯ ABCs of Probes Primer Fundamentals of Floating Measurements and Isolated Input Oscilloscope Floating Oscilloscope Measurements ¡ And Operator Protection |
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Hello,
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Do you have a copy of the 585A service manual? If not, you can get it here. I think your first step id to grab a copy of the manual and do some study in the reading room. Next, grab a DVM and do some resistance readings, maybe starting with the power cord and the fuse. Confirm the line and neutral wiring and the safety ground is all correct and good. Have fun, winter is just starting and this is the scope to have in the winter. Regards ----- Original Message -----
From: "jamesvyu via Groups.Io" <jamesvyu@...> To: <[email protected]> Sent: Saturday, November 03, 2018 2:51 PM Subject: [TekScopes] Tek 585A - for your entertainment! I'm new to the group and sadly a long, long ago degreed EE. I pickup up free scope that hadn't been used in MANY years and I personally haven't touched a scope literally in 45 years! In my excitement, I plugged it in, waited for it to warm up, saw a faint trace, grabbed a 10x probe and foolishly tried to read line voltage. My GFCI powering the outlet immediately tripped. No now trace. Any thoughts on what I've damaged? Please try to hold the laughter. I can already hear it! haha .... |
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John Griessen
On 11/3/18 2:51 PM, jamesvyu via Groups.Io wrote:
grabbed a 10x probe and foolishly tried to read line voltage. My GFCI powering the outlet immediately tripped. No now trace. Any thoughts on what I've damaged?Did you connect the probe ground clip to anything on the outlet? If so, that could be the trouble that caused the current that tripped the breaker. You might have connected scope ground to 120VAC. That would not automatically cause the scope to die though. High short current in the ground lead and power cord could have made the power cord go open. Measure with a DVM that power cord ground pin still connects to scope case and ground of BNC inputs. After that, get a manual for it and check that volts get inside to the power supply from the power cord. About no trace now...does the scope have cal outputs? They're good to start with. You can try varying intensity knobs with no probe and set on auto trigger and see if anything is happening. Then you'll need a battery operated DVM to troubleshoot and references like Tom said. |
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Bob Albert
Connecting the ground of the oscilloscope to the power line is not a good idea.? There are other ways to measure line voltage.? You can use an isolation transformer on the line, although that might change the waveform viewed.? A way around that is to isolate the oscilloscope, at great shock hazard.? Having said that, I know of no one who ever got electrocuted with 120 Volts, although it certainly gets your attention.? You can mitigate the shock hazard by attention to the power cord setup.
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I recently refurbished an old EICO capacitance bridge and, while connecting various components to it, got a bit of a tingle.? So I measured the voltage applied to the unknown and it turned out to be around 50 Volts.? Certainly noticeable, and even enough to destroy some components.? In those days of tube circuits, most components could handle that, but even then some cathose bypass capacitors were only rated for 25 Volts.? Test equipment has its limitations and it isn't intrinsically safe for humans or some components or even for itself. There is no substitute for understanding how stuff works.? Manuals are of limited help, and these days devote more space to operator safety than anything else.? A mark of a good engineer/technician is the ability to think about those things that can go wrong, and to guard against causing problems.? I have seen more than one instance of someone making a measurement and, when through, first disconnecting the ground connection.? That is a common error, and they don't teach you that in school. Bob On Sunday, November 4, 2018, 9:29:27 AM PST, John Griessen <john@...> wrote:
On 11/3/18 2:51 PM, jamesvyu via Groups.Io wrote: grabbed a 10x probe and foolishly tried to read line voltage.? My GFCI powering the outlet immediately tripped.? No now trace.? Any thoughts on what I've damaged?Did you connect the probe ground clip to anything on the outlet?? If so, that could be the trouble that caused the current that tripped the breaker.? You might have connected scope ground to 120VAC.? That would not automatically cause the scope to die though.? High short current in the ground lead and power cord could have made the power cord go open.? Measure with a DVM that power cord ground pin still connects to scope case and ground of BNC inputs.? After that, get a manual for it and check that volts get inside to the power supply from the power cord. About no trace now...does the scope have cal outputs?? They're good to start with. You can try varying intensity knobs with no probe and set on auto trigger and see if anything is happening. Then you'll need a battery operated DVM to troubleshoot and references like Tom said. |
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Thanks to everyone for their inputs. I will read everything suggested.
In answer to the questions, the scope illuminator works, pilot light comes on and the cooling fan is running. Scope definitely sounds like it is going through its "warm up" routine. Scope does have cal output. I do believe the probe ground was connected either to 115vac line neutral or hot. |
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On 04/11/18 18:08, jamesvyu via Groups.Io wrote:
Thanks to everyone for their inputs. I will read everything suggested.Hopefully the scope's case was well connected to the earth wire in the lead, and the earth wire was well connected to the protective mains earth. In that case hopefully the large current from the 115Vac live or neutral went to the PME via the probe's shield and the scope's case - not via you nor the scope's internals. When you look inside, slowly and carefully examine everything for scorch marks, particularly around the inputs and the PSU. |
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What are the beam position lights telling you? Is there any response of these lights when you change Vert Pos to the extremes? Do the Hor Pos lights follow the sweep when you choose a slow sweep rate (and AUTO trigger)?
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If you have the Type 82 plugin, did you try both channels? (I first thought that you might have turned off the scope too soon after you saw no trace. But since you noticed that the calibrator signal is present you at least waited long enough for the time delay relay to switch in.) Albert On Sun, Nov 4, 2018 at 07:08 PM, <jamesvyu@...> wrote:
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It sounds like you just tripped the breaker on protective ground overcurrent. The scope probe ground lead connects to the case and back to the protective ground of the power cord.
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The next step after you read the manual is to do power supply checks in the scope. See the service manual. The -150 volt supply serves as the main reference for all the other voltages so it must be correct. To the group: does the 585A suffer from HV transformer insulation failure? ----- Original Message -----
From: "jamesvyu via Groups.Io" <jamesvyu@...> To: <[email protected]> Sent: Sunday, November 04, 2018 1:08 PM Subject: Re: [TekScopes] Tek 585A - for your entertainment! Thanks to everyone for their inputs. I will read everything suggested. In answer to the questions, the scope illuminator works, pilot light comes on and the cooling fan is running. Scope definitely sounds like it is going through its "warm up" routine. Scope does have cal output. I do believe the probe ground was connected either to 115vac line neutral or hot. |
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This usually smokes the clip on ground lead on the probe
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Sounds like the giving did its job though, I would be surprised if there was any damage. On Nov 4, 2018, at 12:59 PM, Bob Albert via Groups.Io <bob91343@...> wrote: |
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Chuck Harris
The 585A EHT uses beeswax/paraffin as its insulation
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and does not suffer from transformer problems. If you wash the scope, don't let the power transformer get wet. There can be leakage issues caused by conductive salts that get into the windings, but not rinsed out. There is a modification that must be made to the power supply, if it hasn't already. A relay needs to be rewired slightly. I don't remember the details anymore, but I recall that if it isn't done, there is a chance of burning up the expensive 7787 vertical output tubes.... Someone out there knows. -Chuck Harris Tom Miller wrote: It sounds like you just tripped the breaker on protective ground overcurrent. The |
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Chuck Harris
GFCI's sometimes trip due to RF filtering capacitors that
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go from the line or neutral pins to ground. You need to know that the chassis of the scope, including the BNC connector grounds, is connected to the power line bond wire. That includes the grounding clip leads on the probes. If you connected the grounding wire to either the hot, or the neutral, the GFCI will trip... It is designed to sense current imbalance between the hot and neutral wires... in other words, all current that comes out of the hot wire, must return to the neutral wire. If it doesn't, the GFCI will trip. Resist the temptation to disconnect that bond wire in the power cord. Doing so will allow the scope to have unsafe voltages on the front panel, AND MAY KILL YOU. -Chuck Harris jamesvyu via Groups.Io wrote: I'm new to the group and sadly a long, long ago degreed EE. I pickup up free scope that hadn't been used in MANY years and I personally haven't touched a scope literally in 45 years! |
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HI...the GFCI is what we call and RCD, a residual current device. At a pre=set (factory) leakage of commonly 30mA, though that may be as low as 23 in my experience, they interrrupt the supply. That's what leak-down from Active to ear tripped the cth is intended. They have no protection for humans in an active to earth situation, unless the breaker curcuit protection is exceeded,
Theoretically your CRO should be able to read a/c up to its specification and would have but leakage through the probe into the CRO tripped the circuit...result was likely a spike through house wiring inductance into the CRO transformer and another inside the CRO itself which may have caught some diodes at moment in the cycle when their piv was exceeded. Diode might also =transistor.. As the p/s would otherwise be unharmed light etc should come back when breaker reset. A thought, does your CRO have a fuse behind the probe socket? I'm way behind you blokes on CRO's and a little knowledge....?....however I do know some ssockets are fused. -- Be happy that your life-protecting device works...while cursing the problem. I suppose I'd be looking first at p/s diodes...if they are solid state diodes If my suggestion is like hearing the wind blowing in the trees then I apologise for butting-into a conversation above my level. Regards..... Jack |
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What?????
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Way to promote electrical unsafety! OK, maybe you do not personally know a person who was electrocuted by 120 volts, but that does not mean it does not happen. NIOSH report: I'll copy/paste page 15 information (deaths by electrocution US 1982 to 1994): Two hundred twenty-one (99%) of the incidents involved alternating current (AC). One incident involved direct current (DC). Two incidents involved AC arcs. Of the 221 AC electrocutions, 74 (33%) involved less than 600 volts and 147 (66%) involved 600 volts or more. The number of electrocutions by voltage level is listed in Figures 9 and 10. Forty (54%) of the lower-voltage electrocutions involved household current of 120 to 240 volts. Figure 10 shows 33% of the under 600 volt electrocutions were 110/120 volts. Tell those dead people they were not killed by 120 volts. It is just their imagination getting attention. Remember, most shocks on 240 in residential (US system) is just a 120 volt shock, as one would need to contact both hot wires to get 240 volt shock. Much easier to just touch one hot wire while another part of the body is grounded. 120 volts are also involved in most water electrocutions. Usually from faulty dock wiring, or an extension cord not plugged into a GFCI circuit. Here is just one news report: Glad to know you don't now anyone electrocuted at 120 volts. I also do not know one. I would like to keep it that way. Frank DuVal On 11/4/2018 12:59 PM, Bob Albert via Groups.Io wrote:
Having said that, I know of no one who ever got electrocuted with 120 Volts, although it certainly gets your attention. |
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On Sun, Nov 4, 2018 at 12:34 PM, Jack wrote:
Something I' d like to correct....my keyboard is getting above its station yet again!!...time to discipline it. I'll correct my opening remark by upper-case letters: That's what leak-down from Active to earTH trippING the C/B is intended TO DO. TRCD's/GFCI have no protection for humans in an active to earth situation, unless the breaker cIrcuit protection is exceeded, I should add....in this correction....leakage is cumulative on each individual "GFCI" Other devices may already have been causing say 17mA leakage (or of course more...or less..) leaving only say 10mA leakage for your Oscilloscope to trip the breaker....Look at the resistor value in your probe to get a 'start' idea of the leakage current it produced, though of course any other resistance in the shortest trail to earth would also be involved. Everything did as intended but as is sometimes the case, diodes 'blow' not on turn-on but on turn-off. Theoretically your CRO should be able to read a/c up to its specification and would have but leakage through the probe into the CRO tripped the circuit...result was likely a spike through house wiring inductance into the CRO transformer and another inside the CRO itself which may have caught some diodes at moment in the cycle when their piv was exceeded. Diode might also = transistor.. As the p/s would otherwise be unharmed, light etc should come back when breaker reset. A thought, does your CRO have a fuse behind the probe socket? I'm way behind you blokes on CRO's and a little knowledge....?....however I do know some ssockets are fused. -- Be happy that your life-protecting device works...while cursing the problem. I suppose I'd be looking first at p/s diodes...if they are solid state diodes If my suggestion is like hearing the wind blowing in the trees then I apologise for butting-into a conversation above my level. Regards..... Jack -- Jack |
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Hi Frank and others....Bear in mind that voltage is the electrical pressure applied to a situation to enable current to pass. Rule of thumb is that the higher the voltage the greater the current accompanying it through the resistance of the situation. 10mA for a duration is lethal to humans and you do not need to be actually holding the supply point to be 'hooked-up'. I have experienced it at 240v from extended arm to extended arm....across my chest...I can remember it precisely as my brain was still working though I was otherwise paralysed. I thought calmly and logically and one thought was that there was no way I was going to get off. I was going to die in full awareness from fibrolation. My contact area with the active was about 1/64th of an inch.
Likely to have been 10 seconds my guardian angel intervened and I was hurled backwards into a partition wall. My hands were damaged and in considerable pain for some time. I do know people close to me who have been electrocuted, If the body could pass enough current from a 12v battery, it could be electrocuted, It doesn't happen because our bodies limit the current. Even though body resistance varies considerably within people and within situations, 110 volts can provide that 10mA but 30mA is taken to be the point at which fatality is likely and is thus the rating, in my country, for the RCD or the RCD portion of a ''combo-breaker'. Higher rated RCD's...say 100mA... are used to protect whole industrial premises installations against say fire or calamity or accumulated leakage ...rather than have a whole establishment lose power owing to a lower rated RCD failing. -- Jack. |
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Chuck Harris
It can be done, but usually you have to work at it.
Some examples: Take a bath with a toaster, or other appliance. Grab a defective device, whose exposed case is at 120V to ground, while standing barefoot on a damp cement floor. Dry adult human skin generally has a high enough resistance at 120VAC, that sufficient current will not enter the inner core of your body, to stop your heart. The US NEC forbids 240V circuits to be used in residential settings, where the 240V is not center tapped to local ground. The same cannot be said of 240V AC in Europe.. I am not sure a discussion like this is any cause for you to get so shrill. -Chuck Harris Frank DuVal via Groups.Io wrote: What?????... |
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On 2018-11-04 5:42 p.m., Frank DuVal via Groups.Io wrote:
What?????Twelve years, so about six per year. Cars kill 40,000 a year in the USA alone. --T NIOSH report: |
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On Sun, 4 Nov 2018 at 15:42 Frank DuVal via Groups.Io <corvairduval=
[email protected]> wrote: What?????Of course it happens, and of course unsafe practices shouldn't be promoted. You do however have to be exceedingly unlucky or persistent to die from a 120V AC shock. Your numbers support this, as household mains is by far the most common AC source come into contact with, yet the deaths from household mains are not a majority of cases. I didn't read the report, but I'd wager most of the deaths are due to secondary injuries, e.g. received a shock and fell from ladder, died from fall caused by shock - kind of thing. |
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