Date   

TM50X DC ripple?

Michael W. Lynch
 

I have TM506 that I have had for some time.

I have a PG506 that works but it shows terrible distortion on the top and bottom of the square wave when installed in any compartment the TM506. Just as a test, I inserted the PG506 into both the TM504 and TM501 and it works perfectly, the distortion is gone.

I am attributing this to excess ripple in the DC Supplies of the since the 506 shows a 500-900mV @ 120Hz (unloaded). The distortion on the PG506 square wave looks like a miniature version of the ripple waveform that you read in the TM506. The TM504 and 501 both check with much less ripple that the 506.

Am I diagnosing this correctly or is my observation and reasoning faulty?

The service manuals do not show a specification for ripple that I can find. Have I just missed it or is the spec just not there? What would be an acceptable level of ripple?

Thanks!
--
Michael Lynch
Dardanelle, AR


An informative web site for test equipment repairs

Brad Thompson
 

Hello--

I just finished spending a couple of enjoyable hours reading through this web site...

https://emperoroftestequipment.weebly.com/

...In which the author describes experience acquired while repairing assorted test equipment,
most of which had multiple problems. Like many (most?) of us test equipment
collectors, the author looks for equipment described as "not working, doesn't power up"
that's priced accordingly.

Have fun!
73--

Brad  AA1IP


Re: broken coupler

 

DaveH52 wrote:

(eBay link)
None available - all gone
That's too bad (though the price was nothing to get excited about) but searching on "flexible coupler" turns up all kinds of apparently suitable modern alternatives, all also available through Amazon (and other retailers), many at extremely reasonable prices. While I'm a bit obsessive about getting authentic parts for external dress on Tek products, I'm much less concerned when the replacements are out of public view.


Re: 465 - Successfully Replaced HV multiplier

Michael W. Lynch
 

On Fri, Jan 29, 2021 at 05:34 PM, Jeff Dutky wrote:


gradual power up can harm more recent equipment that uses switch mode, rather
than linear power supplies (I don't think that this applies to either the 465
or 465M, but I'm not intimately familiar with either scope, so again, maybe
off-base)
Jeff,

Correct, the power supplies in the 455 / 465 / 475 and many others are linear, so they are OK to start on variac. You are 100% right about SMPS, like the 485 and other more modern scopes, should never be started on a variac as far as I have learned.

If you use a Variac, make sure that you know if your equipment uses SMPS or Linear supply.

--
Michael Lynch
Dardanelle, AR


Re: broken coupler

DaveH52
 

QService has them listed but no stock.


Re: broken coupler

DaveH52
 


Re: 465 - Successfully Replaced HV multiplier

Michael W. Lynch
 

On Fri, Jan 29, 2021 at 06:12 PM, n4buq wrote:


I may be wrong as well, but since the HV multiplier is fed from an oscillator,
once the voltage is sufficient and the oscillator kicks in, then there
wouldn't much difference between that point and when full line voltage is
applied. Is that incorrect?
Barry,

I would tend to agree with you. The HV Multiplier in the 465/475 and 455/465M are just failure prone parts. I have had them die right in front of me after just a few minutes of operation.

--
Michael Lynch
Dardanelle, AR


Re: Sloppy front panel BNC connector - 475

Torch
 

I can't see any sign of a set screw. Unless it is hidden under the mounting nut.

Not going to be fun to get that connector out.


Re: What are the differences between the P6302 and A6302 current probes?

Steve Lindberg
 

Try Tek Probes group. I was in Tek probes engineering for 7 years so started the group.


485

Steve Lindberg
 

Still looking for vertical knob assembly. Mine dried out an fell apart.


Re: 465 - Successfully Replaced HV multiplier

n4buq
 

I may be wrong as well, but since the HV multiplier is fed from an oscillator, once the voltage is sufficient and the oscillator kicks in, then there wouldn't much difference between that point and when full line voltage is applied. Is that incorrect?

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Jeff Dutky" <jeff.dutky@gmail.com>
To: TekScopes@groups.io
Sent: Friday, January 29, 2021 5:34:29 PM
Subject: Re: [TekScopes] 465 - Successfully Replaced HV multiplier

randolphbeebe wrote:
I had both a 465 and a 465M have the same failure after a day or two of
purchasing them.
Both had been unused for a long time. I am wondering if, just as a
precaution it might help
powering up and old scope gradually with a variac might help.
Maybe I'm completely off-base here, but if the problem was that power was
applied too quickly (and which would have been either remedied or revealed
by gradual power up on a variac) wouldn't we expect the failure to be
immediate, rather than happen after a couple of days?

I understand that gradual power up is a common tactic when working with
certain kinds of old electronics, and I even used it myself (based purely on
internet hearsay, not on personal experience or wisdom), but I also
understand (also on hearsay) that gradual power up can harm more recent
equipment that uses switch mode, rather than linear power supplies (I don't
think that this applies to either the 465 or 465M, but I'm not intimately
familiar with either scope, so again, maybe off-base).

Also, wouldn't the HV multiplier suffer MORE stress, not less, being powered
from a lower input voltage?

If a variac would have helped I would have expected the failure to be
essentially immediate. Am I wrong about this?

-- Jeff Dutky






Re: Tek 7T11A issues

Dan G
 

On Fri, Jan 29, 2021 at 06:29 PM, n49ex wrote:

No, I don't think it's the locate button. It behaves just like when on a
regular analog scope you use the delayed time base in the intensify mode,
where a piece of the primary trace is brighter for a segment corresponding to
the delayed time based time setting, and can be scrolled across the primary
trace. That's what appears on the TDR trace. E.G. with the fastest time
settings, say 100pS, only a short piece of trace is intensified, and with the
distance/delay knob, it can be walked across the trace, and the trace stays
exactly the same for all the settings, instead of focusing in with decreasing
time scales.
I believe Albert is right. N49ex, what you are describing sounds exactly like
how the 7S12 is supposed to behave when the LOCATE mode is enabled.
On a properly functioning 7S12, the LOCATE button is a mechanical toggle
(every time you press it, it should alternate between being pushed in and
popped out -- there should be a visible yellow ring around the base of the
button when it pops out to let you know that it's in locate mode).

When LOCATE is pushed in (i.e. not in locate mode), the bright portion of
the trace should expand horizontally to fill the whole screen, and the
entire sweep should have uniform brightness.

Perhaps your 7S12 is permanently stuck in locate mode.


dan


Re: 465 - Successfully Replaced HV multiplier

 

randolphbeebe wrote:
I had both a 465 and a 465M have the same failure after a day or two of purchasing them.
Both had been unused for a long time. I am wondering if, just as a precaution it might help
powering up and old scope gradually with a variac might help.
Maybe I'm completely off-base here, but if the problem was that power was applied too quickly (and which would have been either remedied or revealed by gradual power up on a variac) wouldn't we expect the failure to be immediate, rather than happen after a couple of days?

I understand that gradual power up is a common tactic when working with certain kinds of old electronics, and I even used it myself (based purely on internet hearsay, not on personal experience or wisdom), but I also understand (also on hearsay) that gradual power up can harm more recent equipment that uses switch mode, rather than linear power supplies (I don't think that this applies to either the 465 or 465M, but I'm not intimately familiar with either scope, so again, maybe off-base).

Also, wouldn't the HV multiplier suffer MORE stress, not less, being powered from a lower input voltage?

If a variac would have helped I would have expected the failure to be essentially immediate. Am I wrong about this?

-- Jeff Dutky


Re: Tek 7T11A issues

n49ex
 

No, I don't think it's the locate button. It behaves just like when on a regular analog scope you use the delayed time base in the intensify mode, where a piece of the primary trace is brighter for a segment corresponding to the delayed time based time setting, and can be scrolled across the primary trace. That's what appears on the TDR trace. E.G. with the fastest time settings, say 100pS, only a short piece of trace is intensified, and with the distance/delay knob, it can be walked across the trace, and the trace stays exactly the same for all the settings, instead of focusing in with decreasing time scales.


Re: 465 - Successfully Replaced HV multiplier

toby@...
 

On 2021-01-29 5:38 p.m., randolphbeebe@gmail.com wrote:
I had both a 465 and a 465M have the same failure after a day or two of purchasing them. Both had
been unused for a long time. I am wondering if, just as a precaution it might help powering up and old scope gradually with a variac might help.
I had a 466, purchased off ebay, lose trace within a few minutes of use.
I haven't tried debugging it yet but I wonder...

--Toby

Randy





Re: What are the differences between the P6302 and A6302 current probes?

Stephen
 

Thank you.

I may get one and get creative to probe in smaller areas.


Re: 465 - Successfully Replaced HV multiplier

randolphbeebe@...
 

I had both a 465 and a 465M have the same failure after a day or two of purchasing them. Both had
been unused for a long time. I am wondering if, just as a precaution it might help powering up and old scope gradually with a variac might help.

Randy


Re: 549 transformer question

Tom Lee
 

Chuck has done more extensive research into this than anyone I know. It appears that it is a chemical change, not simple moisture absorption/adsorption. Short version: There’s no simple fix. None. Zip. Nada. Must replace or rewind.

Sent from my iThing, so please forgive typos and brevity.

On Jan 29, 2021, at 12:19 PM, greenboxmaven via groups.io <ka2ivy=verizon.net@groups.io> wrote:

Having never seen a bad 549 transformer, I was imagining it with an epoxy block molded over the winding and loading it down because it had become conductive. Like the ignition system on an engine on a very damp cool morning, dripping with dew. The idea of X-raying it was to know exactly how deep you could carve or grind the epoxy without hitting the winding. I can now see that is not likely to do any good because the epoxy is in the windings and loading them down from within. Is the problem moisture embedded in or absorbed by the epoxy, or is there a chemical change involved? If it were embedded moisture, heating the transformer in a vacuum might be able to draw it out. I have seen plastics and varnishes become quite conductive at high frequencies but very good insulators to DC. Brown fibre insulators in RF and IF coils and flyback transformers in old TVs, especially RCA, seemed very prone to this. I have repaired many RCA flybacks by making a new terminal board from Lexan and installing it. I think it may at least partially explain the legends about the BC-348 "Q" model receivers, not made by RCA, being the best to have today, even though they all had to originally meet the same specs.

Bruce Gentry, KA2IVY








On 1/25/21 18:06, Timothy W. Koeth wrote:
Bruce & all,

Bruce, that is a great question. X-rays will probably be insufficient for
seeing defects in plastics and resins and low-Z (low atomic number)
materials, such as resins and epoxies, etc. The contrast in an x-ray comes
from the metals and high-Z materials stopping x-rays.

However, you've triggered the idea of neutron imaging! This is sort of the
complement to x-rays, neutrons can see through metals, but are stopped by a
plant leaf. Neutrons are absorbed by hydrogen and low-z bearing materials,
such as resins, wax, epoxy. Unlike every dentist's office having an x-ray
machine, neutron imaging machines require a neutron source, such as a
nuclear reactor, so they are generally not as accessible.

I have access to our Nuclear Reactor's neutron imaging system at the
University of Maryland. If someone is willing to send me a known dead HV
transformer, we can take neutron images of it to see if we can locate a
specific defect...

To get a sample idea of the images you can get with neutron imaging, please
have a look at: http://radiation.umd.edu/neutron-imaging/

Please let me know if this is something folks would try to do. Disclaimer,
this would be something new to try, and you might not get your transformer
back if there is some long-lived activation of the transformer, most often
this does not happen, but has happened once to me.

I am pursuing this type of imaging for looking for defects in additive
manufacturing. This could be a super cool application of it.

- Tim



Dr. Timothy Koeth
Assistant Professor
Material Science & Engineering
Institute for Research in Electronics and Applied Physics
University of Maryland
301-405-4952 (office)
609-577-8790 (cell)

https://mse.umd.edu/clark/faculty/676/Timothy-W-Koeth

radiation.umd.edu

Amateur radio call sign K0ETH "K-zero-ETH" (formerly N2LPN)


On Mon, Jan 25, 2021 at 3:57 PM greenboxmaven via groups.io <ka2ivy=
verizon.net@groups.io> wrote:

Has anyone ever tried grinding and carving the epoxy encapsulation down
to a very thin layer on the winding to see if the leakage would be
reduced? The work would require skill and patience to avoid damaging the
winding, getting it X-rayed before staring would help. Is the epoxy
transparent enough that the winding could be seen once you were close to
it without going too far? I have wondered if the conductivety goes all
the way through the epoxy, or if it is just below the surface.

Bruce Gentry, KA2IVY

On 1/25/21 15:12, Joel B Walker wrote:
I have a very nice 549 that I have owned for nearly 35 years. It worked
flawlessly at first, but then began showing the infamous epoxy HV
transformer potting issue. Back when it started doing this ('87-'88) I had
never heard of the epoxy problem before. I replaced the 6GE5, tested and
subbed caps and diodes in the circuit to no avail. Of course the screen
voltage on the 6GE5 was rising way over spec. so I knew it was being
overworked. Spraying the Transformer with freeze mist would bring
everything back to normal temporarily so finally decided the transformer
must be bad.
In the last few years I have been reading about everyone's troubles with
this same problem on many Tek scopes. I know Chuck Harris had been winding
these in the past but has stopped. So the dreaded question is; Is he going
to start back or is someone else going to start, is there a new solution,
or are we all SOL?















Re: What are the differences between the P6302 and A6302 current probes?

cmjones01
 

I have a small collection of these probes in various states of disrepair.
My one "known good" one is an A6303. I find it really handy when working on
power supplies and motor drivers - the fast response and high current
handling are perfect for the job. The smaller A6302 probes very quickly
reach their limits with the peak currents in even quite modest switch-mode
power supplies.

The only downside of the A6303 is its enormous size. I think it dates from
an era when things handling high currents were expected to be big and
chunky themselves. That's no longer the case, so some ingenuity can be
required to get it in to the right place to probe.

Chris

On Fri, 29 Jan 2021, 18:39 Stephen, <stephen.nabet@gmail.com> wrote:

A bit off topic, sorry, but is the P6303 even worth getting at all?






Re: Sloppy front panel BNC connector - 475

Tom Lee
 

Hi SC,

You were very clear in your first comment, and of course absolutely correct. The bias-dependent excess noise of a carbon comp. is a non-issue in this case, ‘cause there’s no bias.

—Cheers,
Tom

Sent from my iThing, so please forgive typos and brevity.

On Jan 29, 2021, at 1:37 PM, SCMenasian <scm@menasians.com> wrote:

I wasn't being specific about the type of noise; my point was that noise generated by this resistor in this circuit is probably completely insignificant. The resistor appears to be between the input and a high impedance attenuator. The current through the resistor is so low that no type of excess (above thermal) noise generated by the resistor would be significant. Shot noise (which is current dependent) would amount to much less than a nanovolt in the worst case - much less than the input noise spec of the typical oscilloscope. Other, material dependent, types of noise might be present in a carbon resistor; but they are probably also not significant in this circuit.




6321 - 6340 of 183516