7904 & scope cart on Facebook Markteplace
Tektronix Oscilloscope model 7904 + Tek Lab Cart model 3
$700 in Lake Oswego, OR
|
Re: 7854 to 7804N Conversion PCB (K7-1286-XA). TOPIC WAS: 067-0912-00 needed
Dennis,
I¡¯d be interested.
George
toggle quoted message
Show quoted text
On Oct 23, 2020, at 4:15 PM, Clark Foley <clarkfoley@...> wrote:
Keyboard error...allow me to continue
The only thing that is peculiar is that the mode control buttons (LEFT, ADD, CHOP....) require initialization after each power cycle. There is no memory for momentary button. It's a way to put a donor mainframe to use after stripping some of the digital cards or for troubleshooting the analog section.
Clark
|
Re: Scope grounding and generators
I fried my refrigerator and the digital display board in my freezer when
I connected them to a generator during a hurricane. They worked for a while
but soon developed problems. Since then I've picked up a largish 440 or 220
to 220 or 110 volt transformer with dual primaries and dual secondaries
that I can strap for the necessary voltage and I will connect my devices to
the generator through it. Hopefully it will filter out some of the voltage
spikes and higher frequencies (> 60Hz). Large transformers like this are
frequently found in large commercial machinery and there's little demand
for used ones so they aren't hard to find. The one that I have weighs about
40 pounds and is rated at 10kW IIRC so it should be able to handle my 5kW
generator. A constant voltage transformer should work even better and they
show up on places like E-bay frequently and usually sell for next to
nothing because of their size and weight and the difficulty and cost of
shipping them. I have several 300 W sized ones and they're slightly larger
than a shoebox and weigh probably 20 pounds. I've been using them on my TV
and some other equipment and none of it has ever been damaged despite
nearby lightning strikes that took out a lot of unprotected equipment. The
trick to buying things like this is to watch E-bay and look for ones within
driving distance and to pick them up in person instead of shipping. Because
of the shipping costs, these items get few bids and typically sell for the
opening bid price. Also look for a dealer in surplus industrial and/or
electronics equipment in your area.
toggle quoted message
Show quoted text
On Sun, Oct 25, 2020 at 12:39 AM <tenareze32@...> wrote: Be careful connecting appliances with a standby mode to a generator. On a
couple of power cuts I connected my coffee maker to the generator and both
times fried the standby circuit.
Simon
|
Re: Please help with TDS340A
Hi all,
Another call for help to improve my scope. Does anyone know what might be causing this problem? I have unsoldered all the alu caps and checked, a couple were marginal and I replaced since it seemed sensible to do so, but none were way off spec. Issue remains.
Do I just junk the scope and if so what models are good replacements for tube audio work at the hobbyist end of the market? Thanks as ever!
|
Re: Scope grounding and generators
Isolating the scope may protect the scope from catastrophic
currents, but it does nothing to protect the scope's operator.
The front panel on most lab grade scopes is grounded to
the same ground as the BNC's, and as such the scope probes.
If you connect the scope probe's ground to a voltage that
is other than earth ground, the scope's front panel and
chassis will be elevated to the same voltage as the scope's
probe's ground clip lead.
Don't do it!
If your intention is to connect anything to *ANY* pin on
a running generator, the generator must have its grounding
point connected to a good earth ground.
If you do not ground the generator any single point fault
in the generator or load that shorts the hot lead to earth
ground will elevate the generator's case 120 or 240V above
ground.
If your intention is to use a 465M, it too must have its
chassis grounding point connected to a good earth ground.
The only valid exceptions involve a whole lot of thinking,
and isolating of the operator, scope, and generator from
dangerous contact.
Isolating grounds on test equipment and generators is a
very dangerous "rookie" mistake.
Read the "OPERATORS SAFETY SUMMARY" that is in some form
in every Tektronix scope's manual since Tektronix stopped
being rookies themselves.
Why do I harp on such stuff?
Because I made that rookie mistake when I was a teenager
working alone. I was tuning up a transmitter, and for
stability, I had the hand holding the diddle stick on the
chassis of the transmitter, when I smelled smoke. Wanting
to avert a catastrophe, I quickly reached over with my
other hand and flipped the metal bat handled power switch
on my intentionally ungrounded (for "safety" reasons) power
supply.
I woke up in a very battered state crumpled on the floor,
up against a cement block wall.
You don't have to repeat this experiment. It has already
been done too many times.
-Chuck Harris
Jean-Paul wrote:
toggle quoted message
Show quoted text
Robert: Most generators have a distorted sine output, depends on rating, and design.
Some have quite high THD. Other have terrible transients and EMI. Normally the mfg will have complete specs.
Rule of thumb: Larger size and high cost - (10..50 kVA) are closer to sinewave, low THD and transients
Cheaper consumer generators eg from Costco, under a few KVA, worse in every respect!
What is your intended use, and what power levels, make and model of generator?
I have used battery operated portables like TEK 212, rather than line powered scopes like 465M.
But you can float the 465 with an isolation trsf.
Good luck,
Jon
|
Wanted: Tek 2236 CTM readout display board
Hi all,
It¡¯s been a couple of years since my last appeal. I¡¯m looking for the vfd display used in the counter timer of the 2236.
Part number is 670-7423-01 for the small board and 150-1110-00 for just the display tube. The display tube also known as a
Noritake Itron p/n FG94C1.
If you¡¯ve seen one in the wild please let me know.
Thanks, Dave
|
Re: Scope grounding and generators
For safety, the generator should be grounded to the single point utility ground for the building it will be providing power to.
The NEC probably requires this, I do not currently have access to a copy.
MIL-HDBK-419 (available on the web) addresses grounding.
Safety first.
Ensure all grounds are bonded together.
Glenn
toggle quoted message
Show quoted text
On 10/24/2020 11:49 PM, Chuck Harris wrote: At issue is how the generator is internally connected, and
the possibilities of accidents.... and on whether or not you
are willing to bet your life that the generator is connected
the way you think it should be, and that it hasn't any faults.
For instance, you scope's ground wire is connected to earth
ground through the power cord.
Your generator should also be grounded, but if it isn't, an
accidental connection between the generator's hot lead and
the scope's ground, could cause the generator to be elevated
120V, or more, above the scope's front panel.
As I stated earlier, I use a filament transformer for such
measurements. Its fidelity is very good, and most are isolated
for several hundred volts... actually many of the older
filament transformers are good for 3000V.
-Chuck Harris
Robert Simpson via groups.io wrote:
Since I will not be connecting the generator to house power, I should be safe connecting house ground for my scope test. I want to see the shape of the power, the frequency and peak voltage. I think a scope will be my best tool for that. Besides, why have a scope if I don't use it whenever possible?
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
|
Re: Scope grounding and generators
Robert: Most generators have a distorted sine output, depends on rating, and design.
Some have quite high THD. Other have terrible transients and EMI. Normally the mfg will have complete specs.
Rule of thumb: Larger size and high cost - (10..50 kVA) are closer to sinewave, low THD and transients
Cheaper consumer generators eg from Costco, under a few KVA, worse in every respect!
What is your intended use, and what power levels, make and model of generator?
I have used battery operated portables like TEK 212, rather than line powered scopes like 465M.
But you can float the 465 with an isolation trsf.
Good luck,
Jon
|
Re: Scope grounding and generators
Be careful connecting appliances with a standby mode to a generator. On a couple of power cuts I connected my coffee maker to the generator and both times fried the standby circuit.
Simon
|
Re: Scope grounding and generators
At issue is how the generator is internally connected, and
the possibilities of accidents.... and on whether or not you
are willing to bet your life that the generator is connected
the way you think it should be, and that it hasn't any faults.
For instance, you scope's ground wire is connected to earth
ground through the power cord.
Your generator should also be grounded, but if it isn't, an
accidental connection between the generator's hot lead and
the scope's ground, could cause the generator to be elevated
120V, or more, above the scope's front panel.
As I stated earlier, I use a filament transformer for such
measurements. Its fidelity is very good, and most are isolated
for several hundred volts... actually many of the older
filament transformers are good for 3000V.
-Chuck Harris
Robert Simpson via groups.io wrote:
toggle quoted message
Show quoted text
Since I will not be connecting the generator to house power, I should be safe connecting house ground for my scope test. I want to see the shape of the power, the frequency and peak voltage. I think a scope will be my best tool for that. Besides, why have a scope if I don't use it whenever possible?
|
Re: Scope grounding and generators
Even if you have a dedicated ground rod for your generator, please bond (connect) that ground and your house ground (generally a bare wire coming from the ground rod to the electrical panel). Since a (three wire) extension cord from the generator to an appliance (eg refrigerator) will connect the generator's ground potential to the appliance, any difference between generator ground and house ground will present a shock hazard.
In general, all earth ground rods should be bonded together.
Using a small filament transformer or repurposed wall wart (older iron core transformer type with AC output) is an excellent idea for safely observing the power line. As noted, the distortion is minimal and having no direct ohmic connection to the power line gives protection against unpleasant surprises in the case of the wiring not being as it should be.
|
Re: Scope grounding and generators
Bob, I am reproducing your email with a few response comments...? and it might also be helpful if you indicate what type of generator you have (KW rating, voltage/phases output, etc).? Also, whether you plan to monitor the generator's output with the scope receiving AC power from the house, or the generator itself: On 10/24/20 9:59 PM, Robert Simpson via groups.io wrote: Also, I just checked the main breaker panel and the ground and neutral are on the same bus bar. US National Electrical Code requirements call for the neutral (grounded conductor) to be bonded to the ground (grounding conductor) at the "service entrance" of any building service (but nowhere else); this is in accordance with "code". My extension cord for the scope will have a triple tap on the end. So I can use one of the ground hole sockets to connect to the generator frame lug for this test . That way the scope ground and generator ground will be connected electrically close. Yes, this will serve as an interconnection between the house ground system and any other loads (such as a scope plugged into the extension cord), or the generator's ground system.? However: make sure that the wiring from the house to the scope (or generator) has not been compromised (insofar as maintaining the correct continuity of identification/wiring of neutral, ground, and "hot" wire) all the way from the service entrance, through intermediate outlets and the extension cord, to destination load(s) or generator. And you probably already know this, but I'll state it anyway- don't under any circumstances interconnect the neutral and/or "hot" wires between the house and the generator. Mike D. N4MWP Bob
|
Re: Scope grounding and generators
Also, I just checked the main breaker panel and the ground and neutral are on the same bus bar.
My extension cord for the scope will have a triple tap on the end. So I can use one of the ground hole sockets to connect to the generator frame lug for this test . That way the scope ground and generator ground will be connected electrically close.
Bob
|
Re: Scope grounding and generators
Since I will not be connecting the generator to house power, I should be safe connecting house ground for my scope test. I want to see the shape of the power, the frequency and peak voltage. I think a scope will be my best tool for that. Besides, why have a scope if I don't use it whenever possible?
|
Looking for 519 accessories
Hi all,
As you might know, I recently joined the 519 club with a excellent specimen. It came with a few accessories, namely 2 x 50T/125T throughs, 1 x 50T/125N through, and 1 x 1000MC timing standard. One thing that would be nice to have is the piece of 125 ohm coax mentioned in the manual. Essentially, since the 519 is basically a museum piece I'd like to gather as complete a collection of accessories as possible to keep with it.
Please feel free to contact me off list if you have 519 accessories you'd like to part with.
Thanks!
Sean
|
Re: Scope grounding and generators
Yes, I would check the outlet to be certain that the neutral and "hot"
connections are not swapped. But I would probably do this with a
commercial grade plug-in tester (available at most hardware stores;
typically under 15 USD, I believe); such devices typically have three
neon lamps; two of which are supposed to glow, and one of which is
supposed to stay dark with a properly wired outlet.? Although an
oscilloscope could also be used for this; I just think the
special-purpose tester unit is the way to go.? Or a multimeter can be
used for the same purpose by measuring the voltage from the "hot" outlet
terminal to ground, and from the outlet "neutral" terminal to ground.?
This applies to both the house wiring and the generator wiring.
In the several decades during which I've been a homeowner, every one of
the several homes that I've owned has had at least one outlet that was
miswired when I bought it.? So it's a worthwhile thing to check.? I've
never owned a generator; I suspect that the manufacturers generally know
what they are doing, but it's a simple thing to check.
Mike Dinolfo N4MWP
toggle quoted message
Show quoted text
On 10/24/20 6:37 PM, stevenhorii wrote: Would you check the outlet the scope is plugged into to be sure hot and
neutral have not been switched?
On Sat, Oct 24, 2020, 17:54 Mike Dinolfo <mdinolfo@...> wrote:
Robert:
I don't see any reason why you can't check the generator output by
connecting it to a scope (to monitor the waveform and/or voltage),
subject to the following (in the US, at least). I assume that your
generator is producing single phase power, either 120 VAC single phase
or 120/240 VAC single phase:
1. To begin with, there's no reason why you can't connect the
generator's ground to your house ground. But do not make any other
connections from generator wiring to house wiring. The ground (the
National Electrical Code "grounding conductor") will generally be
identified as a bare, or green insulated, or green with yellow stripe
insulated, conductor. Generator (and house) current carrying conductors
will be either neutral conductors (National Electrical Code "grounded
conductor"), which are generally colored white or grey, or phase
conductors (colored differently from the assigned colors for grounded
and grounding conductors.)
2. Power up the scope from "house" power, using a probe with a
sufficient voltage rating (many 10x probes are rated to 600 V). You
will need to make a grounding connection from the scope ground (scope
chassis) to the generator ground; this can be either an individual
"stand alone" conductor, or the shield/braid of the scope probe. I
recommend a separate conductor rather than the scope probe shield; an
alligator clip jumper cable should be sufficient. (Note: beware of
cheap alligator clip jumper cables with crimped connections at the
alligator clips; the connections should be soldered.)
The US standard NEMA 5-15R (15 amp) and 5-20R (20 amp) 3-terminal
outlets have the grounding terminal sized to accept a 3/16" diameter
metal rod; I've successfully used pieces of round copper or brass rod to
provide a good grounding stud, and then used alligator clip leads to
extend the ground connection.
3. Provided that you've got the ground jumper in place, you should be
able to probe the generator's output connector individual pins with the
scope probe's tip. And you won't need to connect the scope probe's
grounding clip to the generator's frame (as this connection will be
accomplished by the alligator clip jumper cable described above. If
probing a 120 VAC outlet (3 terminal), you should wind up reading 0.0
volts when probing the ground pin, and 0.0 volts when probing the
neutral pin, and ~170 VAC peak (340 volts peak-to-peak) when probing the
"hot" terminal of the 120 VAC outlet. Of course, make sure that you've
got the scope set up with a "less sensitive" vertical deflection; 5
V/div should be adequate if you are using a 10X probe.
I know that there have been quite a few threads on TekScopes dealing
with possible safety issues when using isolation transformers, or
autotransformers (e.g. Variacs) that "carry thru" a ground connection
when testing switch mode power supplies, but I don't see any of these
issues applying for what you are describing. But I've been wrong
before, so I hope others will correct me if I'm wrong on this issue.
Mike Dinolfo N4MWP
On 10/24/20 3:59 PM, Robert Simpson via groups.io wrote:
Is there a safe way to use my 465M to look at my generator output? The generator I recently acquired will have its own ground separate from my
house. In use that won't be a problem as I will only be hooking appliances
to the generator with extension cords separate from house power . However,
since I don't want to initially power the scope from the generator until I
check the generator output, I am worried about working with two different
ground connections.
Bob
|
Re: Scope grounding and generators
Would you check the outlet the scope is plugged into to be sure hot and
neutral have not been switched?
toggle quoted message
Show quoted text
On Sat, Oct 24, 2020, 17:54 Mike Dinolfo <mdinolfo@...> wrote: Robert:
I don't see any reason why you can't check the generator output by
connecting it to a scope (to monitor the waveform and/or voltage),
subject to the following (in the US, at least). I assume that your
generator is producing single phase power, either 120 VAC single phase
or 120/240 VAC single phase:
1. To begin with, there's no reason why you can't connect the
generator's ground to your house ground. But do not make any other
connections from generator wiring to house wiring. The ground (the
National Electrical Code "grounding conductor") will generally be
identified as a bare, or green insulated, or green with yellow stripe
insulated, conductor. Generator (and house) current carrying conductors
will be either neutral conductors (National Electrical Code "grounded
conductor"), which are generally colored white or grey, or phase
conductors (colored differently from the assigned colors for grounded
and grounding conductors.)
2. Power up the scope from "house" power, using a probe with a
sufficient voltage rating (many 10x probes are rated to 600 V). You
will need to make a grounding connection from the scope ground (scope
chassis) to the generator ground; this can be either an individual
"stand alone" conductor, or the shield/braid of the scope probe. I
recommend a separate conductor rather than the scope probe shield; an
alligator clip jumper cable should be sufficient. (Note: beware of
cheap alligator clip jumper cables with crimped connections at the
alligator clips; the connections should be soldered.)
The US standard NEMA 5-15R (15 amp) and 5-20R (20 amp) 3-terminal
outlets have the grounding terminal sized to accept a 3/16" diameter
metal rod; I've successfully used pieces of round copper or brass rod to
provide a good grounding stud, and then used alligator clip leads to
extend the ground connection.
3. Provided that you've got the ground jumper in place, you should be
able to probe the generator's output connector individual pins with the
scope probe's tip. And you won't need to connect the scope probe's
grounding clip to the generator's frame (as this connection will be
accomplished by the alligator clip jumper cable described above. If
probing a 120 VAC outlet (3 terminal), you should wind up reading 0.0
volts when probing the ground pin, and 0.0 volts when probing the
neutral pin, and ~170 VAC peak (340 volts peak-to-peak) when probing the
"hot" terminal of the 120 VAC outlet. Of course, make sure that you've
got the scope set up with a "less sensitive" vertical deflection; 5
V/div should be adequate if you are using a 10X probe.
I know that there have been quite a few threads on TekScopes dealing
with possible safety issues when using isolation transformers, or
autotransformers (e.g. Variacs) that "carry thru" a ground connection
when testing switch mode power supplies, but I don't see any of these
issues applying for what you are describing. But I've been wrong
before, so I hope others will correct me if I'm wrong on this issue.
Mike Dinolfo N4MWP
On 10/24/20 3:59 PM, Robert Simpson via groups.io wrote:
Is there a safe way to use my 465M to look at my generator output? The generator I recently acquired will have its own ground separate from my
house. In use that won't be a problem as I will only be hooking appliances
to the generator with extension cords separate from house power . However,
since I don't want to initially power the scope from the generator until I
check the generator output, I am worried about working with two different
ground connections.
Bob
|
Re: Scope grounding and generators
Robert:
I don't see any reason why you can't check the generator output by
connecting it to a scope (to monitor the waveform and/or voltage),
subject to the following (in the US, at least).? I assume that your
generator is producing single phase power, either 120 VAC single phase
or 120/240 VAC single phase:
1.? To begin with, there's no reason why you can't connect the
generator's ground to your house ground.? But do not make any other
connections from generator wiring to house wiring.? The ground (the
National Electrical Code "grounding conductor") will generally be
identified as a bare, or green insulated, or green with yellow stripe
insulated, conductor.? Generator (and house) current carrying conductors
will be either neutral conductors (National Electrical Code "grounded
conductor"), which are generally colored white or grey, or phase
conductors (colored differently from the assigned colors for grounded
and grounding conductors.)
2.? Power up the scope from "house" power, using a probe with a
sufficient voltage rating (many 10x probes are rated to 600 V).? You
will need to make a grounding connection from the scope ground (scope
chassis) to the generator ground; this can be either an individual
"stand alone" conductor, or the shield/braid of the scope probe.? I
recommend a separate conductor rather than the scope probe shield; an
alligator clip jumper cable should be sufficient.? (Note: beware of
cheap alligator clip jumper cables with crimped connections at the
alligator clips; the connections should be soldered.)
The US standard NEMA 5-15R (15 amp) and 5-20R (20 amp) 3-terminal
outlets have the grounding terminal sized to accept a 3/16" diameter
metal rod; I've successfully used pieces of round copper or brass rod to
provide a good grounding stud, and then used alligator clip leads to
extend the ground connection.
3. Provided that you've got the ground jumper in place, you should be
able to probe the generator's output connector individual pins with the
scope probe's tip.? And you won't need to connect the scope probe's
grounding clip to the generator's frame (as this connection will be
accomplished by the alligator clip jumper cable described above.? If
probing a 120 VAC outlet (3 terminal), you should wind up reading 0.0
volts when probing the ground pin, and 0.0 volts when probing the
neutral pin, and ~170 VAC peak (340 volts peak-to-peak) when probing the
"hot" terminal of the 120 VAC outlet.? Of course, make sure that you've
got the scope set up with a "less sensitive" vertical deflection; 5
V/div should be adequate if you are using a 10X probe.
I know that there have been quite a few threads on TekScopes dealing
with possible safety issues when using isolation transformers, or
autotransformers (e.g. Variacs) that "carry thru" a ground connection
when testing switch mode power supplies, but I don't see any of these
issues applying for what you are describing.? But I've been wrong
before, so I hope others will correct me if I'm wrong on this issue.
Mike Dinolfo N4MWP
toggle quoted message
Show quoted text
On 10/24/20 3:59 PM, Robert Simpson via groups.io wrote: Is there a safe way to use my 465M to look at my generator output? The generator I recently acquired will have its own ground separate from my house. In use that won't be a problem as I will only be hooking appliances to the generator with extension cords separate from house power . However, since I don't want to initially power the scope from the generator until I check the generator output, I am worried about working with two different ground connections.
Bob
|
Re: Scope grounding and generators
Probably the safest way would be to use a filament transformer. It will
affect the fidelity of the signal somewhat, but is way better than you
might think.
-Chuck Harris
Robert Simpson via groups.io wrote:
toggle quoted message
Show quoted text
Is there a safe way to use my 465M to look at my generator output? The generator I recently acquired will have its own ground separate from my house. In use that won't be a problem as I will only be hooking appliances to the generator with extension cords separate from house power . However, since I don't want to initially power the scope from the generator until I check the generator output, I am worried about working with two different ground connections.
Bob
|
Scope grounding and generators
Is there a safe way to use my 465M to look at my generator output? The generator I recently acquired will have its own ground separate from my house. In use that won't be a problem as I will only be hooking appliances to the generator with extension cords separate from house power . However, since I don't want to initially power the scope from the generator until I check the generator output, I am worried about working with two different ground connections.
Bob
|
Glydeck
Jean-Paul
Mike Dinolfo