Date   

Re: Air filters for big 500 series scopes

stevenhorii
 

For cleaning aluminum filters, has anyone tried steam cleaning? I have
tried steam cleaning on greasy oven pans (stainless and enamel) and it
works like a charm, though you want to be careful where you let the
condensed steam drip - it carries the oil and grease with it.

On Tue, Oct 20, 2020 at 12:43 PM Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:

On Mon, Oct 19, 2020 at 08:32 PM, stevenhorii wrote:


chlorinated detergents
Yes... I think chlorinated mainly for those compound's sanitization
properties... but unless one is trying to sanitize those old filters
(wouldn't hurt: right?)... I'm skeptical that chlorinated compounds add
much to the cleaning ability of such detergents, relative to detergents
containing phosphates. (I don't know that there are any modern, for sale,
formulated detergents that perform as well as the discontinued/banned
phosphated ones.)
To clean some really dirty, and old, 500 aluminum filters, I tried a lot
of different solvents, and cleaners... and finally I settled on TSP. The
difference, as Dr. Beaker would say, was most satisfactory.






Re: Tek 4654M; No Trace, No +5V, No +95V; Help

Michael W. Lynch
 

Made a similar repair to my 455 scope. I have a small 3D printed enclosure for the HV Multiplier that I will share the STL File for. I built the same multiplier for my 455.

Photos of results are here: https://groups.io/g/TekScopes/album?id=253227

--
Michael Lynch
Dardanelle, AR


Re: Tek 4654M; No Trace, No +5V, No +95V; Help

adesilva_1999@...
 

On Tue, Oct 20, 2020 at 09:47 AM, <adesilva_1999@yahoo.com> wrote:


Page 3 will be has the most of the important info.
That should read as: Page 3 will have the most of the important info."

Sorry for the error.


Re: Tek 4654M; No Trace, No +5V, No +95V; Help

adesilva_1999@...
 

I have a 465M where the tripler died in the U550 block. If you want to see what I did, follow this thread: https://www.eevblog.com/forum/repair/tektronix-465m-repair-210933/msg2695668/#msg2695668

I have posted many pictures and notes there. If necessary, I can provide answers as to anything that might need explanations. It is a long thread as I did it over a period of time. Page 3 will be has the most of the important info.

The tripler section is really a 3x multiplier. The final EHT on the CRT anode is 10 kV as printed on the aluminum screen over the U 550.


Re: Air filters for big 500 series scopes

Roy Thistle
 

On Mon, Oct 19, 2020 at 08:32 PM, stevenhorii wrote:


chlorinated detergents
Yes... I think chlorinated mainly for those compound's sanitization properties... but unless one is trying to sanitize those old filters (wouldn't hurt: right?)... I'm skeptical that chlorinated compounds add much to the cleaning ability of such detergents, relative to detergents containing phosphates. (I don't know that there are any modern, for sale, formulated detergents that perform as well as the discontinued/banned phosphated ones.)
To clean some really dirty, and old, 500 aluminum filters, I tried a lot of different solvents, and cleaners... and finally I settled on TSP. The difference, as Dr. Beaker would say, was most satisfactory.


Re: Scope, cooling ICs - refresh or not?

Tom Phillips
 

Hello Staffan,

You said "This unit has quite a few coolers and they got reasonably warm just during the time it took to adjust the display."

Those "coolers" are the heat sinks and the fact that they quickly get warm indicates that they are in good thermal contact with the component they are cooling and are therefore doing their job.

Personally, I do not recommend removing heat sinks just to replace the thermal compound between the heat sink and the device they are cooling.

Cheers,
Tom


Re: 485 Power Supply Problems

Kevin Oconnor
 

Surprised no response yet. This is likely one of the common ps faults in the interlock system. Many years since I worked on one, but shorted tantalum caps are often the cause. Search the archives, as this has been discussed before.


Re: smd precision resistor "paint layer" peeled off while soldering *** advice needed ***

Chuck Harris <cfharris@...>
 

In short no, 99% IPA won't even touch the electrolyte,
except for that which gets removed by physical scrubbing.

The electrolyte is a water soluble mix of some sort of
glycol compound and a salt that doesn't corrode aluminum,
or aluminum oxide.... but does a job on copper. Water
and detergent is what you need to remove it.

If you don't want to dry the board over night in an oven,
blow it off with compressed air, and put it in a convection
oven at 50C for 2 hours. I use my environmental chamber.

As a drier, IPA has to be able to reach the nooks and crannies
that the water gets to, and it has to be able to move the
water through evaporation... mostly what happens is the
alcohol evaporates, and leaves the deep water behind.

You need to get the water out from under the IC's, and other
packages that almost touch the board, but not quite.

Watch the temperature! Cooking isn't exactly good for some
parts... especially the NVRAM.

And, yes, the electrolyte is a glycol based mix, and the
glycol gives the dead fish smell when it is burned with
your soldering iron.

-Chuck Harris

Richard in Edenton NC via groups.io wrote:

Chuck, would 99% isopropyl alcohol do the same thing, but without having to put it in a oven overnight? Also I assume that the electrolyte (that leaked from the caps) being heated is the cause of the smell like rotten fish? Good to know. Thanks for sharing

73 Richard W4MCD






Re: smd precision resistor "paint layer" peeled off while soldering *** advice needed ***

Richard in Edenton NC
 

Chuck, would 99% isopropyl alcohol do the same thing, but without having to put it in a oven overnight? Also I assume that the electrolyte (that leaked from the caps) being heated is the cause of the smell like rotten fish? Good to know. Thanks for sharing

73 Richard W4MCD


Re: smd precision resistor "paint layer" peeled off while soldering *** advice needed ***

Chuck Harris <cfharris@...>
 

Lost shine... aka milky white solder joints...

-Chuck Harris

Chuck Harris wrote:

Hi Roger,

The electrolyte is water soluble. Use hot water, dish detergent
and a soft toothbrush or paintbrush.

Put some electrical tape on the tops of trimmers and dip switches,
and scrub away.

The shine is an indication of corrosion. It tells you that the
electrolyte has been there... so you should scrub there.

When the board is rinsed, get the loose water off, and put it in
a warm oven... usually the oven light is more than hot enough...
for overnight.

-Chuck Harris

Rogerio O wrote:
Chuck,
Thank you for your reply.
Yes I could smell this while working on the components around the place where the are located.
Is it necessary to repair each and every solder joint that is not shinny?
I have washed these parts of the board with tap water and than with IPA.
I am letting the board dry while I wait for the replacement parts.
Roger










Re: Signal occasionally disappears on 492, needs to be power-cycled by unplugging

Chuck Harris <cfharris@...>
 

The 492, 494, and 496 SA's are compact devices simply stuffed to
capacity with good RF stuff. To make sure they had absolutely the
optimal space for that good RF stuff, they developed a state of the art
switching power supply with a rather high watts/cubic inch rating.

That high watts/cubic inch power supply gets hot, very hot... especially
if the air filter is clogged, or blocked by walls or junque on your
bench.

Every time I have taken one of these SA's apart, I have found many
of the electrolytic capacitors in that supply that have gotten so hot
that they have shrunk the plastic heat shrink sleeves to a point where
they look like kids that have out grown their clothes.

Start there.

Second point worth noting. These are long instruments, and there are
only a couple of places where it is safe to let them overhang the
edge of your bench with the covers off. If you set them in one of
the places where the bench edge puts the weight of the SA on internal
modules, you will create needless repairs, as you break solder joints
and connector pins in blind spots in the modules.

Third point worth noting, many of the SMA connectors are not well
mounted. Tek did things like bolt the connector to the thin aluminum
can of a module, and solder the center pin to a circuit board that is
inside of the thin aluminum can of the module. If you over torque the
SMA, and make it turn in the can, you will break the center pin off of
the SMA making an intermittent. Use a torque wrench. An intermittent
SMA connector can never be fixed by simply tightening it above the spec.
You can sometimes fix it by loosen it and then re-torque it, but never
above the spec.

-Chuck Harris

dododude700 wrote:

Hi there! New to the group, I posted this on Reddit at /r/rfelectronics first and was referred to here.

I recently got a Tektronix 492 spectrum analyzer on eBay. I paid around $320 for it in a Best Offer, and apart from the issue in the title and the trace rotation needing some adjustment, everything I've been able to test on it does work, so I'm still pretty happy with the purchase.

That said, it does have one quirk I haven't been able to diagnose. It can operate as normal, but if left plugged in, eventually (after anywhere between ten minutes to a day or two), everything but the noise floor will disappear, as if the DUT was simply unplugged. This happens even with e.g. an antenna looking at broadcast signals, so the signal is certainly still there, it just stops seeing it. This doesn't require any kind of physical jolt (I don't think it's a connector being bumped out, for example), can happen when the instrument is on or off (you'll find out when you go to use it again), and can happen as the user is interacting with it or when it's just sitting there. When this happens, the device still "works" - you can look around the noise floor, change settings, all as expected, but no amount of disconnecting and reconnecting the DUT, making sure everything's plugged in right, or fiddling with the knobs will bring the signal back. The only fix is to either power cycle it with the front switch, off for 30 seconds, after which it will work for a few seconds, or to unplug the power cable for about 30 seconds and then plug it back in, after which it's back to normal for minutes to hours until it happens again and necessitates another brief unplug. This seems especially weird given that, as I understand it anyway, the power switch on the 492 is not a soft on/off - I'm surprised there's a difference between power cycling with the switch and power cycling at the plug. The failure is sudden - I've seen it happen, the input doesn't slowly fade into the noise floor, it disappears abruptly and sometimes in the middle of a trace. I haven't discounted that I may be doing something wrong - this is my first "real" RF instrument and I may be missing something obvious - but I'm not doing anything when it fails that doesn't work as normal any other time. I also don't think it's some out-of-spec input signal (too much power or DC on it or something) messing up the frontend, as the failure is temporary and I've seen it happen with just a normal, passive antenna connected. I don't hear relays click when it stops working, so I don't think it's accidentally enabling the attenuator or something.

Given the relatively easy workaround, this is more of an annoyance than a dealbreaker issue, but I'd still like to fix it. What could cause what's seemingly an input problem (given that everything but the actual measurement keeps going) but need a full power cycle and seemingly, time to discharge power supply caps, to resolve? Is there some always-on power rail powering whatever's failing that power cycling from the switch wouldn't affect? Is this a known problem?

Thanks!






Re: 519 -- broken rate generator; stuck at a very high frequency?

Sean Turner
 

I hadn't tried this adjustment while looking at the signal with another scope...I may have stumbled upon this without knowing since the slowest sweep on the 519 is rather fast compared to general purpose scopes.

Now to move onto two other problems...namely the reed relay appears to be dead and the sweep is kinda messed up at 2ns/cm, mainly on the right side of the crt. The trace sort of coils into a spiral at the end of the sweep...it's weird. Maybe an artifact of the rf power tube that drives the time base?

Sean

On Mon, Oct 19, 2020 at 08:23 PM, Tom Lee wrote:


I'm a bit confused, because I thought you had already tried this, but if it's
all ok now, it's all ok now!

Congratulations!

-- Cheers,
Tom


Re: Air filters for big 500 series scopes

stevenhorii
 

In my experience for removing grease and oil from stuff (foam filters,
aluminum filters, clothes, etc) I use Dawn detergent. It does not contain
phosphates. It is biodegradable and is fairly gentle on the skin. Some
other discussion groups - specifically one on aircraft and cleaning of
them, warn against any cleaners containing chlorinated detergents for
cleaning aluminum. The makers of Dawn list all their ingredients:

https://dawn-dish.com/en-us/dawn-faqs/what-dawn-is-made-of-ingredients

It does contain sodium hydroxide. By itself, sodium (or other alkali metal)
hydroxides will attack aluminum. Dawn uses it as an adjuster for pH not as
a primary cleaning agent. It does contain sodium chloride and is used as a
thickener. I have not had a problem using it on aluminum, but if the
aircraft folks recommend not using it, I would not for structural parts. I
do rinse the parts off very thoroughly.

On Mon, Oct 19, 2020 at 22:39 Roy Thistle <roy.thistle@mail.utoronto.ca>
wrote:

On Sun, Oct 18, 2020 at 11:56 PM, snapdiode wrote:


Scrubbing Bubbles
It doesn't use phosphates (which are not good for the environment)... but
might not clean these old scope filters as well as a phosphate cleaner.
Instead of phosphates, Scrub Bub uses a surfactant, combined with a water
softener. Scrub Bub seems safer, for the aluminum filter, and for the user
too.






Re: 519 -- broken rate generator; stuck at a very high frequency?

Tom Lee
 

I'm a bit confused, because I thought you had already tried this, but if it's all ok now, it's all ok now!

Congratulations!

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/19/2020 20:20, sdturne@q.com wrote:
Tom,

I think I found it. Page 5-15 in the manual describes it:

"76. Set the MULTIPLIER switch to OFF and check to see that the waveform disappears from the screen of the Type 519.

If Abnormal...

The Avalanche stage is free running. Adjust the AVALANCHE SET control to the point where the generator just stops free running. If the adjustment cannot be made, check R933, R932, R931 and 0934."

I was able to make this adjustment with the help of another oscilloscope that offers slower time base settings, and it now appears to be under control of the rate generator controls!

Sean

On Mon, Oct 19, 2020 at 08:06 PM, Tom Lee wrote:

I agree that looking for an open circuit somewhere, whether within or between
components, makes sense.

One clue is that the free-running frequency of the output is too high.
Injection-locking needs the free-running frequency to be below the locked
frequency. If the avalanche stage is running too fast, then the RC that
controls the free-run rate isn't doing its job.

You are very close to finding it, I'm sure.

Good luck!

-- Tom


Re: 519 -- broken rate generator; stuck at a very high frequency?

Sean Turner
 

Tom,

I think I found it. Page 5-15 in the manual describes it:

"76. Set the MULTIPLIER switch to OFF and check to see that the waveform disappears from the screen of the Type 519.

If Abnormal...

The Avalanche stage is free running. Adjust the AVALANCHE SET control to the point where the generator just stops free running. If the adjustment cannot be made, check R933, R932, R931 and 0934."

I was able to make this adjustment with the help of another oscilloscope that offers slower time base settings, and it now appears to be under control of the rate generator controls!

Sean

On Mon, Oct 19, 2020 at 08:06 PM, Tom Lee wrote:


I agree that looking for an open circuit somewhere, whether within or between
components, makes sense.

One clue is that the free-running frequency of the output is too high.
Injection-locking needs the free-running frequency to be below the locked
frequency. If the avalanche stage is running too fast, then the RC that
controls the free-run rate isn't doing its job.

You are very close to finding it, I'm sure.

Good luck!

-- Tom


Re: 519 -- broken rate generator; stuck at a very high frequency?

Tom Lee
 

I agree that looking for an open circuit somewhere, whether within or between components, makes sense.

One clue is that the free-running frequency of the output is too high. Injection-locking needs the free-running frequency to be below the locked frequency. If the avalanche stage is running too fast, then the RC that controls the free-run rate isn't doing its job.

You are very close to finding it, I'm sure.

Good luck!

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/19/2020 19:49, sdturne@q.com wrote:
I tried another thing, just to be sure...I substituted a 2N2369 (I have a lot of them on hand for building avalanche pulsers) that seemed to have largely similar curves as the existing transistor...this changed nothing as to the lack of control over the frequency of the output...but it did avalanche nicely when I adjusted the avalanche control. :o)

At this point, I'm honestly thinking it could be a cold solder joint. I'm going to need to get the scope on it's side up on a suitable work surface....this working on the ground is for the birds!

Sean




Signal occasionally disappears on 492, needs to be power-cycled by unplugging

dododude700
 

Hi there! New to the group, I posted this on Reddit at /r/rfelectronics first and was referred to here.

I recently got a Tektronix 492 spectrum analyzer on eBay. I paid around $320 for it in a Best Offer, and apart from the issue in the title and the trace rotation needing some adjustment, everything I've been able to test on it does work, so I'm still pretty happy with the purchase.

That said, it does have one quirk I haven't been able to diagnose. It can operate as normal, but if left plugged in, eventually (after anywhere between ten minutes to a day or two), everything but the noise floor will disappear, as if the DUT was simply unplugged. This happens even with e.g. an antenna looking at broadcast signals, so the signal is certainly still there, it just stops seeing it. This doesn't require any kind of physical jolt (I don't think it's a connector being bumped out, for example), can happen when the instrument is on or off (you'll find out when you go to use it again), and can happen as the user is interacting with it or when it's just sitting there. When this happens, the device still "works" - you can look around the noise floor, change settings, all as expected, but no amount of disconnecting and reconnecting the DUT, making sure everything's plugged in right, or fiddling with the knobs will bring the signal back. The only fix is to either power cycle it with the front switch, off for 30 seconds, after which it will work for a few seconds, or to unplug the power cable for about 30 seconds and then plug it back in, after which it's back to normal for minutes to hours until it happens again and necessitates another brief unplug. This seems especially weird given that, as I understand it anyway, the power switch on the 492 is not a soft on/off - I'm surprised there's a difference between power cycling with the switch and power cycling at the plug. The failure is sudden - I've seen it happen, the input doesn't slowly fade into the noise floor, it disappears abruptly and sometimes in the middle of a trace. I haven't discounted that I may be doing something wrong - this is my first "real" RF instrument and I may be missing something obvious - but I'm not doing anything when it fails that doesn't work as normal any other time. I also don't think it's some out-of-spec input signal (too much power or DC on it or something) messing up the frontend, as the failure is temporary and I've seen it happen with just a normal, passive antenna connected. I don't hear relays click when it stops working, so I don't think it's accidentally enabling the attenuator or something.

Given the relatively easy workaround, this is more of an annoyance than a dealbreaker issue, but I'd still like to fix it. What could cause what's seemingly an input problem (given that everything but the actual measurement keeps going) but need a full power cycle and seemingly, time to discharge power supply caps, to resolve? Is there some always-on power rail powering whatever's failing that power cycling from the switch wouldn't affect? Is this a known problem?

Thanks!


Re: 519 -- broken rate generator; stuck at a very high frequency?

Sean Turner
 

I tried another thing, just to be sure...I substituted a 2N2369 (I have a lot of them on hand for building avalanche pulsers) that seemed to have largely similar curves as the existing transistor...this changed nothing as to the lack of control over the frequency of the output...but it did avalanche nicely when I adjusted the avalanche control. :o)

At this point, I'm honestly thinking it could be a cold solder joint. I'm going to need to get the scope on it's side up on a suitable work surface....this working on the ground is for the birds!

Sean


Re: Air filters for big 500 series scopes

Roy Thistle
 

On Sun, Oct 18, 2020 at 11:56 PM, snapdiode wrote:


Scrubbing Bubbles
It doesn't use phosphates (which are not good for the environment)... but might not clean these old scope filters as well as a phosphate cleaner. Instead of phosphates, Scrub Bub uses a surfactant, combined with a water softener. Scrub Bub seems safer, for the aluminum filter, and for the user too.


Re: Scope, cooling ICs - refresh or not?

DaveH52
 

If you're talking about the hybrids with the 4 screws holding them, leave them alone. Other heatsinks may be thermal-epoxied to the chip and would be a lot of trouble to clean up and re-epoxy. Not to mention you've got to find and buy special thermal epoxy to use.

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