开云体育

Harvey,

That is another critical factor, one that I took into serious consideration. I used carbon comp resistors only as a temporary measure, simply to test the rest of the system, a "proof of concept" if you will. The ones I used were 5% accuracy, so way too little precision for the job. This was evidenced by the pair having a "calculated value" of 60K and an actual resistance measured at 58.8K, so still a ways off from the desired 60.4K (+/-1%). It was simply not worth the time to try to come up with 2,3 or 4 carbon comps that theoretically could have been grouped to give the 60.4k that was specified. Much easier to just buy the right parts and fix it permanently and correctly. The repair also looks more professional as a major benefit. I have been buying Metal film resistors, whenever possible, since they do not cost that much more, they are more stable and more reliable. Thanks for your comment.

--
Michael Lynch
Dardanelle, AR

On Tue, 30 Apr 2019 12:47:26 -0700, you wrote:

Hi All,

I need one, good working scope to get started on repairing the other 30 or so scopes around here. I have a multitude of Tek 7000 frames to choose from but I think the 7904 (or 7904A) is a good place to start. Once that's working + cal'ed I can at least troubleshoot and maybe repair the others.

Where can I get one professionally calibrated in the greater Detroit area? I can drive a fair distance, but I'm scared to ship. I've had two 7934's, a 7834, and a 7704A crushed in separate shipping mishaps.

Can't help you there, I'm in the southeast. However...

Also...which plug ins are recommended to cal for building my golden scope? I have a collection...

The typical plugins for a 7904 (and that's a good choice, IMHO) are at
least one if not two 7A26, and a 7B92A (which I happen to like). If
you want the flexibility of two sweep plugins, the 7B80 and 7B85 will
do. If you have a 7103/4 and a 7B10 and 7B15, you could use them but
the sweep is not calibrated at the highest frequencies, but those
could be moved over to the 7103/4 when needed.

For things you'd want:

067-0587-01 signal standardizer. The 01 is intended for 500 mhz
scopes, the 00 is for lower bandwidth, and the 02 is for the 1GHz
bandwidth scopes. Needed to keep the mainframes all agreeing with
each other as well as provides some nice linearity and gain signals.
You could use the 00, but it wouldn't allow you to check out the
frequency response to the limit of the scope's bandwidth for higher
bandwidth scopes.

PG506/TG501 SG503/SG504 TM500 plugins that provide calibration
signals for vertical and timebase checking, as well as frequency
response. Those will do any scope. The signal standardizer is
specifically for 7000 series mainframes.

You could also go with a CG501 (TM500) or a CG5001 (TM5000) module
with the appropriate frame. Note that the CG series may need a
specific head to supply the right signals. Those heads may be
difficult to find.

My favorite (depending) setup in a 7904 is a 7A26 (or 7A24 if I need
more bandwidth and can tolerate a 50 ohm input plugin), a 7D12 with an
M2 (sampling) module, a 7D15 counter, and a 7B92A sweep.

Harvey

Hi All,
? ?There is no such thing as "canned air" really.? ?All of the "canned air" products on the market have some sort of gas (not air), which when compressed, becomes liquefied.? ?It is the vapor pressure of the liquid which provides the pressure to blow off the dust.? As you let some gas out of the can, more evaporates to maintain a relatively constant pressure until the liquid runs out, and then the pressure quickly drops.? ?
? ? If instead you take a old can of "canned air" and put a Schraeder valve on it so you can re-fill it with an air compressor and put actual air in it, you will be sorely disappointed (as I was).? ?The physics is pretty simple and the pressure will just decrease exponentially as you let the air out of the can, and it rapidly becomes useless.? ?I get about 5 seconds of useful dusting pressure out of a can before I have to re-fill it.? It's good for a blast or two.?
? ?I HIGHLY recommend using an air compressor and plumbing your shop as opposed to using portable canned air products.? Even the Non-CFC versions are really nasty stuff to the environment.? They don't kill the ozone layer, but they contribute substantially to global warming.? See:


? I don't mean for this to roam off-topic, but since it was brought up, figured I'd mention it.? ?Also hope no one wastes their time trying to re-fill a duster can as it just doesn't work.
Dan

On Tue, 30 Apr 2019 17:46:08 -0700, you wrote:

Hi Micheal,
Thank you for the nice repair summary!
It was good that Dave Hills brought some of his logic, reason and
knowledge to your problem.
The online 'parallel resistor calculators' show that your 150k and 100k
pair give you exactly 60k of resistance.
I wonder if it would be okay to leave your pair of resistors in there as
a permanent fix?

They're carbon composition, and possibly will drift. The film
resistor that's the specified replacement should drift less with age
and perhaps temperature.

Harvey

Maybe some kind soul will comment on that question for us amateurs?
Those Tektronix Service Manuals are like a series of college courses on
analog electronics!
tom jobe...



On 4/30/2019 4:21 PM, Mlynch001 wrote:

On Mon, Apr 29, 2019 at 08:07 AM, Dave Hills wrote:

With 134v on Q1496 collector, you should see +61v at Q1490's base. This will
completely shut down the regulator by reverse biasing Q1494 b-e. That said it
only leaves R1483, Q1496, CR1498, and R1488 as likely suspects. R1483 would
have to have drifted VERY low, (unlikely), or R1488 VERY high, (possible, but
not likely to cause these symptoms), leaving a leaky or shorted Q1496 or
CR1489. Note that an OPEN CR1489 would likely cause Q1496 to subsequently
fail. Also, check that CR1489 has not been installed backward.

Please forgive the caps, not shouting, just no other way to highlight for
emphasis.

Dave

Dave:

Your advice helped me find the issue! Tom Jobe suggested that I study the 110V regulator circuit description and the schematic, which I did as well. Lots of good advice from everyone got me pointed in the right direction.

Here is what I found and how I fixed the issue:

After the aforementioned study and re-reading all the comments, I decided to pull CR1489 off the board and test it. It tested good on my curve tracer, meter and component tester. Reinstalled on the board and there was no change. (of course) I also pulled all transistors, including Q1496 (again) and tested it on my little home built curve tracer and re- ran it through two additional transistor testers, all showed it to be good. (again, no Change) You mentioned that Q1490 should have a base voltage of about 61V with the 110V rail at 135V, I found it to actually be low, at 41.5V, the schematic calls for 50V, and since you said I should have about 61V; I knew that the voltage divider formed by R1486 and R1487 was not right. R1487 tested 49.9K so I moved on to R1486 and it tested "weird", meaning high resistance sometimes and then open at others. This prompted me to remove it completely from the board. After getting it off the board, I found it to be "open", so un-soldering the

component probably finished it off.. I took a 68K resistor from the bench and temporarily soldered it into place of R1486, checked the 110V rail and BANG! the 110V rail was now at 119.4V (down from 135V) with no other changes. This told me I had found the issue, now I had to find a proper replacement for R1486, which was originally 60.4K (321-0364-00 - RES.,FXD,FILM: 60.4K OHM, 1%,o.125W). Doing a little math, I found that installing 100K and 150K resistors in parallel would deliver 59K, so VERY close to what I needed. Installed these two resistors parallel in place of R1486, re-tested, this brought the base of Q1490 to 50.06V and gave me exactly 110.65V on the 110V rail. Now all I have to do is find the proper replacement part and my scope in good to go! THANK YOU ALL for your advice!

Sincerely,

On Tue, 30 Apr 2019 20:44:20 -0400, you wrote:

After accidentally leaving my 1502 on overnight I came back to find
it dead. I eventually traced it down to a HV problem.

This circuit is so simple it's ludicrous but I'm hampered by having
lost my HV probe. In any event, the output across the HV transformer
is a square wave of about 50V; it's supposed to be 500V. If I
disconnect C4328 (connected directly to the transformer), I see the
expected 500V across the transformer. The HV diodes appear to be OK,
but something is loading it down. I've disconnected the CRT and
controls with no change, so it has to be on the board.

I repaired my 1502's high voltage section. I saw capacitors that had
cracked, and the diodes weren't all that happy either. IIRC,
microwave oven diodes work. I just tested and replaced all the bad
capacitors.

I don't see any unusually low ohm readings either.

Any ideas for tracking down the failed component or should I just
shotgun the multiplier and replace everything? One cap is 0.033
at 600V and the other 3 are 0.027 at 1200V.

It's been noted that sometimes HV capacitors are OK at lower voltages
and leaky at higher ones.

I do have a 1KV supply so I could check leakage on them, although
I hate to remove good parts from a board.

I had to bite the bullet on this one. The HV transformer had gotten
rather warm with the increased load on it. I think I had to replace
it, too. (luckily, I had a deceased 1502, bad TD).

I used the parts to repair both the 1502 and the 1503 I have.

Harvey

BTW, instead of those little pin connectors, the CRT cable and
intensity control cable are soldered directly to the board. This looks
like a repair attempt to me.

thanks

I plumb the shop with a compressed air (and a compressor in the garage). I
use a small dryer in-line with the spray naucial (sp).

Photographer as well as a repair tech here, and I say do not shake cans of commercially available compressed air used for blowing dust away. They can splatter whatever is in the can onto lens coatings, or in the old days negatives, ruining them.

Not knowing what is in the can, but knowing that it can blow droplets of whatever it is into what you are cleaning means that while you are blowing dust away, you are also blowing moisture of some kind on what you are cleaning. If that moisture is oily then it will become a dust collector.

I’ve heard some say that you can invert the cans of compressed air, like Dust Off or other dust blowers, to use them for cold testing components. If so just be sure to clean up afterwards.

FWIW,
Don Kemper

"Canned Air" is simply liquefied R134a refrigerant in a
can with a trigger nozzle. The cans are the same cans
you can buy at the auto parts store to charge your car's
air conditioner... but with a trigger nozzle screwed to
the top of the can.

If you hold the can upside down while you press the trigger,
you will get liquid refrigerant spraying out the nozzle...
this is also known as "freeze" spray.

I prefer not to use the "Canned Air" because it sprays quite
cold, which tends to cause condensation... and because I think
it very irresponsible to release refrigerant into the air.

-Chuck Harris

cheater cheater wrote:

Ah, I somehow lost the first sentence of the email which was: "should one
shake compressed air or not?"

I guess i need to learn how to post!

I hear conflicting reports on what one should do. What's your take?
Are there different types where you should or shouldn't?

Druckluft 67 (aka Dust Off 67) from Kontakt / CRC says not to shake
the can "or otherwise the fluid might come out", but is it always the
case with all types? What is that fluid for, anyways?

I read reviews of some cheaper compressed air products on amazon and
they complained about the quality. What can go wrong with compressed
air? Two things people brought up were one brand produced very weak
pressure, and another produced flammable rather than inert gas.
Druckluft 67 touts as being oil free. Are there other things that
might go wrong?

Why would someone use canned compressed air rather than an air compressor?

Thanks.

H Reginald,

Do you mean something like this?
/g/TekScopes/message/125605
with pictures
/g/TekScopes/album?id=13203 .

Albert

On Tue, Apr 30, 2019 at 07:46 PM, tom jobe wrote:

Hi Micheal,
Thank you for the nice repair summary!
It was good that Dave Hills brought some of his logic, reason and
knowledge to your problem.
The online 'parallel resistor calculators' show that your 150k and 100k
pair give you exactly 60k of resistance.
I wonder if it would be okay to leave your pair of resistors in there as
a permanent fix?
Maybe some kind soul will comment on that question for us amateurs?
Those Tektronix Service Manuals are like a series of college courses on
analog electronics!
tom jobe...



On 4/30/2019 4:21 PM, Mlynch001 wrote:

On Mon, Apr 29, 2019 at 08:07 AM, Dave Hills wrote:

With 134v on Q1496 collector, you should see +61v at Q1490's base. This

will

completely shut down the regulator by reverse biasing Q1494 b-e. That said

it

only leaves R1483, Q1496, CR1498, and R1488 as likely suspects. R1483

would

have to have drifted VERY low, (unlikely), or R1488 VERY high, (possible,

but

not likely to cause these symptoms), leaving a leaky or shorted Q1496 or
CR1489. Note that an OPEN CR1489 would likely cause Q1496 to subsequently
fail. Also, check that CR1489 has not been installed backward.

Please forgive the caps, not shouting, just no other way to highlight for
emphasis.

Dave

Dave:

Your advice helped me find the issue! Tom Jobe suggested that I study the

110V regulator circuit description and the schematic, which I did as well.
Lots of good advice from everyone got me pointed in the right direction.

Here is what I found and how I fixed the issue:

After the aforementioned study and re-reading all the comments, I decided to

pull CR1489 off the board and test it. It tested good on my curve tracer,
meter and component tester. Reinstalled on the board and there was no change.
(of course) I also pulled all transistors, including Q1496 (again) and tested
it on my little home built curve tracer and re- ran it through two additional
transistor testers, all showed it to be good. (again, no Change) You
mentioned that Q1490 should have a base voltage of about 61V with the 110V
rail at 135V, I found it to actually be low, at 41.5V, the schematic calls
for 50V, and since you said I should have about 61V; I knew that the voltage
divider formed by R1486 and R1487 was not right. R1487 tested 49.9K so I
moved on to R1486 and it tested "weird", meaning high resistance sometimes and
then open at others. This prompted me to remove it completely from the board.
After getting it off the board, I found it to be "open", so un-soldering the
component probably finished it off.. I took a 68K resistor from the bench and
temporarily soldered it into place of R1486, checked the 110V rail and BANG!
the 110V rail was now at 119.4V (down from 135V) with no other changes. This
told me I had found the issue, now I had to find a proper replacement for
R1486, which was originally 60.4K (321-0364-00 - RES.,FXD,FILM: 60.4K OHM,
1%,o.125W). Doing a little math, I found that installing 100K and 150K
resistors in parallel would deliver 59K, so VERY close to what I needed.
Installed these two resistors parallel in place of R1486, re-tested, this
brought the base of Q1490 to 50.06V and gave me exactly 110.65V on the 110V
rail. Now all I have to do is find the proper replacement part and my scope
in good to go! THANK YOU ALL for your advice!

Sincerely,

Hey Tom,

I have ordered the correct parts to replace the temporary repair. I have 25 resistors coming, so I can pick through them and find the best of the lot to make the final and permanent repair. Again, I appreciate your comments and guidance in making this repair possible.

Sincerely,

--
Michael Lynch
Dardanelle, AR

On Tue, Apr 30, 2019 at 08:24 PM, Raymond Domp Frank wrote:

On Wed, May 1, 2019 at 02:46 AM, tom jobe wrote:

The online 'parallel resistor calculators' show that your 150k and 100k pair
give you exactly 60k of resistance.
I wonder if it would be okay to leave your pair of resistors in there as a
permanent fix?

Obviously, using 5% tolerance resistors of 100 kOhm and 150 kOhm in parallel
will not guarantee to get 60 kOhm. The values of R1486 and R1487 as such
aren't critical but their combination basically determines the 110 V: V110 =
V50 * (R1486 + R1487) / R1487. I haven't checked the circuits in detail but
accuracy worse than 1% for the combination may spoil scope calibration state.
You may consider using 3 resistors in a parallel/serial config for R1486 - or
even slightly changing R1487 to get the correct ratio but checking with your
DVM will be necessary unless you use 1% resistors. Building R1486 from a
series connection of a fixed, reasonably stable (metal film) 56 kOhm resistor
with a 10 kOhm trimpot in series is another possibility, giving enough
resolution in trimming with a range between about 110 V plus and minus 5%,
since it allows varying R1486 from about 56 kOhm to about 66 kOhm. The
Ohmmeter function on almost any DVM will be accurate enough for trimming.

Raymond

Raymond,

Not to worry! This is not going to be a "permanent fix". I have ordered the correct value 1% resistors for R1486 and R1487. They are cheap and easy to find exactly what is needed Tom Jode is exactly correct, the calculator indeed shows the value of the 100k/150k pair as 60k. When I installed the pair, I measured the actual value as a pair for the 5% parts I used and found that they were about 58.9K. I did not take a lot of time to "trim out" the pair, Since I was committed to obtain the correct value resistors as a permanent fix. As far as affecting the calibration, this rail does not seem to have any visible affect at all on the display on the CRT. When the 110V rail was at 135V, the scope worked perfectly, without any evidence of distortion of the signals, when I went back to 110V, the signal displayed on the CRT did not observably change, either in amplitude or frequency. I compared the 110V results to the 135V and the 119V results with identical test signals that were fed into the scope. Amazingly, all the other rails' voltages never changed, regardless of the 110V rail voltage. I was afraid that these voltages would swing one way or another and therefore checked each one as i made adjustments to the 110V rail. I am pleased to report that those other voltage rail regulators seem to have a wide input range and very tight control over their areas of responsibility. It is a testament to the careful engineering and great quality of these TEKTRONIX instruments that they can continue to work when everything is not perfect. It is evident that someone designed these circuits with just this scenario in mind.

--
Michael Lynch
Dardanelle, AR

"Is the method of attachment so good that it has no reflections and mismatch."

It is unrealistic to expect that the SG503 will be feeding an exactly 50 ohm load. So the design must address that.

All the frequency domain information is present in the TDR result. But it requires a bit of mathematics to do the conversion.

I am waiting on receipt of a pair of 1 MHz square wave <40 ps rise time generators from Leo Bodnar.

Once those arrive, I am going to write a long series on doing vector network analysis in the time domain using a DSO on the EEVblog forum. Aside from the tutorial aspect, I'll be writing software to take data from a DSO and generate magnitude and phase vs frequency. I'll probably leave creating Smith charts to some one else, but I will do the basic time to frequency part as I am very familiar with that. And that's the hard part for most EEs. I'm a geophysicist. So TDR is my natural habitat, though elastic waves at less than 250 Hz rather than EM waves at 10 GHz.

I requested the 1 MHz clock instead of the standard 10 MHz because most DSOs have such horrible front ends. The lower clock rate lets me window off the ringing from the step. It still needs to be accounted for, but it's a lot easier if things don't overlap in time. A 10 ft RG58 delay line should suffice for most low end DSOs.

I have an 8753B/85046A VNA & S parameter set, so I'll be comparing TDR using Leo's unit and a DSO to the HP VNA, and if I can get my Tek 11801 to transfer data to a PC using the 20 ps calibrator and an SD-26 head.

My motivation is pretty simple. 35 years ago while in grad school I tried to build a 40 m DC receiver. It did not work. I later confirmed that the reason was a lack of any test gear other than a 5 MHz recurrent sweep Heathkit IO-18 and a Radio Shack DMM and VOM. My input BP filter was fine except it was about 500 KHz to low.

On Wed, May 1, 2019 at 02:46 AM, tom jobe wrote:

The online 'parallel resistor calculators' show that your 150k and 100k pair
give you exactly 60k of resistance.
I wonder if it would be okay to leave your pair of resistors in there as a
permanent fix?

Obviously, using 5% tolerance resistors of 100 kOhm and 150 kOhm in parallel will not guarantee to get 60 kOhm. The values of R1486 and R1487 as such aren't critical but their combination basically determines the 110 V: V110 = V50 * (R1486 + R1487) / R1487. I haven't checked the circuits in detail but accuracy worse than 1% for the combination may spoil scope calibration state.
You may consider using 3 resistors in a parallel/serial config for R1486 - or even slightly changing R1487 to get the correct ratio but checking with your DVM will be necessary unless you use 1% resistors. Building R1486 from a series connection of a fixed, reasonably stable (metal film) 56 kOhm resistor with a 10 kOhm trimpot in series is another possibility, giving enough resolution in trimming with a range between about 110 V plus and minus 5%, since it allows varying R1486 from about 56 kOhm to about 66 kOhm. The Ohmmeter function on almost any DVM will be accurate enough for trimming.

Raymond

Hi Reginald,
Testing cables with a TDR reveals important characteristics of how a cable will respond when a pulse is applied to it. It is a quick way to check a cable at a glance. But it misses many other characteristics, which depending on the ultimate use of the cable, might be equally important, and in some cases, even more important.

If I had a Vector Network Analyzer I would have tested all three cables that way because it will reveal some of those other characteristics but I ran out of time.

I do have a Scalar Network Analyzer which I thought about using for the test but I had to get back to other things.

Your comment touches on this aspect of the cables characteristics I have often wondered about. No matter how well it is made it is going to have issues such as you have pointed out. This is an unavoidable fact of physics. And it will have an effect on how this cable performs in the frequency domain.

Dennis Tillman W7PF

Hi Micheal,
Thank you for the nice repair summary!
It was good that Dave Hills brought some of his logic, reason and knowledge to your problem.
The online 'parallel resistor calculators' show that your 150k and 100k pair give you exactly 60k of resistance.
I wonder if it would be okay to leave your pair of resistors in there as a permanent fix?
Maybe some kind soul will comment on that question for us amateurs?
Those Tektronix Service Manuals are like a series of college courses on analog electronics!
tom jobe...

After accidentally leaving my 1502 on overnight I came back to find
it dead. I eventually traced it down to a HV problem.

This circuit is so simple it's ludicrous but I'm hampered by having
lost my HV probe. In any event, the output across the HV transformer
is a square wave of about 50V; it's supposed to be 500V. If I
disconnect C4328 (connected directly to the transformer), I see the
expected 500V across the transformer. The HV diodes appear to be OK,
but something is loading it down. I've disconnected the CRT and
controls with no change, so it has to be on the board.

I don't see any unusually low ohm readings either.

Any ideas for tracking down the failed component or should I just
shotgun the multiplier and replace everything? One cap is 0.033
at 600V and the other 3 are 0.027 at 1200V.

I do have a 1KV supply so I could check leakage on them, although
I hate to remove good parts from a board.

BTW, instead of those little pin connectors, the CRT cable and
intensity control cable are soldered directly to the board. This looks
like a repair attempt to me.

thanks

--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Unix & Windows

Are you planing to make the book in electronic format? I would like to be
able to search for specific words ... etc.
Printed book is better than nothing, but I don't have space for all the
books I would like to have, so I buy them in electronic format.
Thanks
Tony Fleming

On Tue, Apr 30, 2019 at 7:35 PM Dave Brown <davebr@...>
wrote:

As mentioned previously, Stan gave the museum authorization to reprint his
book and we do sell it on CD on our eBay store. We are in the process of
reprinting it in softbound. We have our review copy back and are making
final tweaks. I'll update the group when we have them available on our eBay
store. Our first run will be small as we don't know how much demand there
is for this book. When we run out, we will reprint more.

vintageTEK