Milan,
Thanks for this explanation, it makes sense to me. I've noticed that component values that were common 50 years ago (or more) are not common today, so the reverse is also understandable. It was also suggested that this was an attempt to make a higher wattage part than was either available, or than would fit in the space provided. The resistors are bigger than 1/4 W ones, but the manual only specs them as 1/2 W.
Regardless, they've drifted pretty far out of spec (more than 20%) and will need to be replaced. I've ordered a selection of 1/2 W resistors that should include 7.5 K Ohm parts.
-- Jeff Dutky
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Re: Fix or Part Out a Tek 475A
So I went in an desoldered CR1352 to verify that it was shorted, and it is, so now I need to replace it. It's a 1N4152, which appears to be hard to come by, but I'm seeing things on line that suggest that a a 1N4148 is a suitable replacement. Now, I'm no electrical engineer, so I don't really understand how you would select a diode for a given application (aside from knowing that a diode permits current to flow in one direction, with an approximately constant voltage drop, and that different diodes have different maximum power dissipation).
The 1N4152 is a 500 mW part, with a capacitance of 2 pF, a recovery time between 2 and 4 ns, and a forward voltage drop of 500-750 mV.
The 1N4148 is also 500 mW, with a capacitance of 4 pF, a recovery time of 4 ns, and a forward voltage drop of 1 V.
None of those specs (except for the power dissipation) sound similar to me, but again, I don't know how you would select a diode for a given application, or what the actual requirements of the diode in this application are, so maybe it's fine.
Now, I happen to have a bunch of 1N4148 diodes ready to hand, and I suppose that they're better than nothing (and better than a shorted diode), so I could just use it and hope for the best. The wattage and reverse breakdown voltage specs seem pretty good (the 1N4148 has a reverse breakdown voltage of 75-100 V, which should be fine for this circuit, and far exceeds the reverse breakdown voltage of the part that it's replacing).
(actually, just writing this I have mostly convinced myself that the 1N4148 will be fine, but only because I can't really break the scope any more than it's already broken).
If anyone is willing to try to make me less ignorant on this topic it would be appreciated.
-- Jeff Dutky
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Jeff, the resistors connected end to end are an attempt to make a required resistance that was not available as a standard resistor value. Shortage of parts? Engineering change? Select in test? Who knows. I have a few of those in my 453 scope.
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Re: Choosing the right replacement cap
Thanks Craig and Mark,
Yes, this is C1419 on a 465. Actually C1418/C1419, the two 22uF parallel caps on higher SN scopes. Mine is 29X,XXX (don't have it right in front of me at the moment). One of the two is shorted.
I started with a search on 47uF, 50v as someone in an earlier thread regarding this cap noted the marginality in this supply filter. The supply is "15v unregulated", but many note the actual value can be in the 20s. Making the 25v 22uF's right at their limit. And then adding temperature effects further stresses them/it. I felt 50v was a good "over spec" to handle the application.
So I did follow the link that came up for Mouser, and one of the selection criteria in their results is operating temperature. Considering this caps environment I selected 135+ C, just to see what it turned up. The result is a Nicicon UBW1H470MPD. It is an Aluminum Electrolytic and all of the specs look good for the application. But when I look at, for example Digikey I see other parameters. After some study I see what's meant by ESR, and understand leakage current as it applies to cap usage. I am an EE by trade, so I'm not completely ignorant. But there's a vast difference between some academic understanding and the real world application of discrete components. All my cap experience/understanding is IC parasitic cap.
One spec I don't know what to do with is "Series". I see various references to this alpha-numeric code, as Mark mentioned above. But I haven't found an explanation of it yet. A little tutorial would be helpful and appreciated. A link is fine. I have more studying to do.
I do now know better why the Nicicon is a far better choice than the cheap results on Amazon. So I feel comfortable making an order of, like, 10 of them from Mouser.
Is that way overkill? Or is it good to get a high temp cap like that? I'll try and re-read Marks answer and understand some more of what he's saying. But I hope I've clarified where I'm at better. Any further help narrowing choices and helping me understand WHY those are better choices is greatly appreciated.
Thanks,
Dave
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Re: Choosing the right replacement cap
Dave,
C1419 is a sealed tantalum that usually does not go bad. If it goes bad, a 47 or 56mfd 25 or 35V Nichicon ULD is what I would recommend. That series is low ESR, high temperature and long life. The UCY and UHE is also very good for life. The low ESR is best. If you change a tantalum with an electrolytic, higher capacitance is recommended to compensate for the lower ESR tantalums have. The ULD is close in ESR to a tantalum so a small raise in capacitance is fine. You may need to increase the rated voltage at times because the manufacturer was too cheap to use the proper voltage, e.g. 16V cap off a rectifier for 12V when the cap should be a 25V type. I use film types for low values such as 4,7mfd 50/63V and smaller values. Higher voltage films with over a mfd I will use on screen decoupling, e.g. signal or video output. Film has very low ESR. I use CDE 318LX/383LX, Nichicon LGR, LGZ (450V snap in), Kemet ALS and others that have the above specs when a snap in or screw type is needed. For restuffing FP style cans, the diameter and length are needed to know if they fit. Doing the power supplies in the 465/475/A will require sizes that will not fit in the cans. Solid wire on the leads for ones that are larger than original and jumpers on the negative lugs on the pc board. The diameter of a few are larger than the original cans. I will use larger capacitance than original for better filtering/decoupling. I usually use the ULD or UCY in the cans unless a snap in is needed in the can. I am picky about the type of electroytics I get. I will usually increase the capacitance from original, if physically possible, for stiffer voltage regulation. I have found that spending more time and money to do a job right the first time has worked for me. I do not like going back to redo work that should have been done right to begin with. A good friend of mine is a broadcast engineer. That is a big reason I make or repair things to run around the clock (for new design) or to run with as few repairs as possible over the years. Buy from places like Mouser, DigiKey or other distributors. They will have new stock and give the specs of their products. Avoid off-brand or old stock. Avoid 85 deg.C types. Those are low hour life and ESR is not low except for a few series in a few brands. Sometimes finding the best quality capacitor can take some time when specs are compared for a number of ones that are suitable in that application. Make sure to see the ones that are in stock from a supplier. The lead times for some parts can be a few weeks to a year and some are subject to a minimum amount if it is a special order. Avoid the exotic types the audiofools like to overpay for. I am telling you about the types I have found that work for myself and customers. What I use is not the only types that will work. I can only give information I know and have had experience with.
Mark
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Re: Choosing the right replacement cap
This is the typical C1419 for a 465 scope
You might run the part number and look on eBay
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Choosing the right replacement cap
What parameters besides capacitance, voltage, and temperature are appropriate for replacement capacitor selection?
I guess configuration and size, of course. What fits.
This is the typical C1419 for a 465 scope. Just did an online search and am overwhelmed by the number of varieties.
Are there most reliable, quality, trusted brands? Are there some to be sure to stay away from? How to choose!?
Thanks,
Dave
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Re: Fix or Part Out a Tek 475A
Hi David,
The trigger slope knobs (and the entire trigger level/slope knob assembly) seems to be very prone to breakage. I have looked at a lot of 475s and 475As on eBay, and most of them have some kind of damage to the trigger level/slope knob. If you can find a scope without damage to the knobs, the sellers are usually asking a significantly higher price for it. The good news is that, for things like the trigger level/slope knobs, you can use many of the 400 models as donor scopes, so you might look for a dead 465 that might be had cheap.
The other problem with the smashed trigger level/slope knobs is that the slope switch shaft is often bent as well, would mean that you would have to replace both the pot/switch assembly behind the panel as well as the knobs.
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Re: 2710 Spectrum Analyser 'Cannot count VCO, IF' error
Hi all,
I acquired a 2710 as non-functional, and the 100 MHz Osc had failed. I
put in something cobbled together, and enjoy it working fine.
Cheers, Jochen DH6FAZ
Am 25.11.2020 um 01:13 schrieb WB6GHK:
toggle quoted message
Show quoted text
Hi guys, 2710's, oh what fun!
For the "Cannot count VCO, IF" I have found that the majority of the time the 100 MHz timebase module has failed or degraded. The absolute quickest way to determine if it has failed is to sub in a know good working one. It will save you hours of troubleshooting. Find a friend with a later B02xxxx 2710 and beg, steal or borrow the timebase.
Martin, I'm going to assume you have a 2710 service if you troubleshot the power supply, so locate the corresponding pages for the 100MHz timebase and look at the signals coming from the four outputs (I think it's four, going by memory). Scope them to see what is there advise.
I hate to tell you this but B013xxx and below 2710's using the CFCS are not reliable (memory & PS) or accurate (drift), in comparison to later units. Not saying that it isn't worth the time since there is a learning curve and the early 2710 will certainly give you that experience, but the once the unit is operational you may be disappointed.
Best of luck!
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Re: Fix or Part Out a Tek 475A
On Wed, Nov 25, 2020 at 01:44 AM, David Collier wrote:
Hi all,
Just acquired a 475A via eBay.
All seems to work except the trigger source switch which may just need
adjustment/contact cleaning.
Someone already replaced CR1462 with a larger diode bridge, and the fan motor
is noisy.
However, I need replacement knobs for A & B trigger slope (the outer grey
ones). Can anyone help with these?
I notice the trace is not as fine as that on my trusty HP1740A: maybe the EHT
is too low?
To me, your issue seems an excellent candidate for a new topic, unless you consider parting out your 475A, which I'd recommend against... One important cause of the trace on the Tek 475A being not as fine as that on the HP 1740A is the fact that the 475A, having a 250 MHz bandwidth, shows more noise in the trace. BTW, early 465's (100 MHz, like the 1740A) had a moire noisy trace than later ones. Raymond
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Re: Fix or Part Out a Tek 475A
Congrats on the new scope -- I'm sure you'll enjoy it greatly!
As to trace sharpness, the 465/475 series jugs are sort of infamous for not having the smallest spot size. The expansion mesh gets a lot of blame on the web, but that can't be the whole explanation, as there are many crts with expansion meshes that have smaller spot sizes.
Without seeing your scope's trace with my own eyes (photos tend not to have sufficient fidelity to diagnose this at all well), it's hard to say whether what you're seeing is abnormal. But if it's good and bright, it's unlikely to be an EHT problem.
--Cheers,
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
toggle quoted message
Show quoted text
On 11/24/2020 16:44, David Collier wrote: Hi all,
Just acquired a 475A via eBay.
All seems to work except the trigger source switch which may just need adjustment/contact cleaning.
Someone already replaced CR1462 with a larger diode bridge, and the fan motor is noisy.
However, I need replacement knobs for A & B trigger slope (the outer grey ones). Can anyone help with these?
I notice the trace is not as fine as that on my trusty HP1740A: maybe the EHT is too low?
Regards,
David Collier
Canberra
|
Re: Fix or Part Out a Tek 475A
Hi all,
Just acquired a 475A via eBay.
All seems to work except the trigger source switch which may just need adjustment/contact cleaning.
Someone already replaced CR1462 with a larger diode bridge, and the fan motor is noisy.
However, I need replacement knobs for A & B trigger slope (the outer grey ones). Can anyone help with these?
I notice the trace is not as fine as that on my trusty HP1740A: maybe the EHT is too low?
Regards,
David Collier
Canberra
|
Re: 2710 Spectrum Analyser 'Cannot count VCO, IF' error
Hi guys, 2710's, oh what fun!
For the "Cannot count VCO, IF" I have found that the majority of the time the 100 MHz timebase module has failed or degraded. The absolute quickest way to determine if it has failed is to sub in a know good working one. It will save you hours of troubleshooting. Find a friend with a later B02xxxx 2710 and beg, steal or borrow the timebase.
Martin, I'm going to assume you have a 2710 service if you troubleshot the power supply, so locate the corresponding pages for the 100MHz timebase and look at the signals coming from the four outputs (I think it's four, going by memory). Scope them to see what is there advise.
I hate to tell you this but B013xxx and below 2710's using the CFCS are not reliable (memory & PS) or accurate (drift), in comparison to later units. Not saying that it isn't worth the time since there is a learning curve and the early 2710 will certainly give you that experience, but the once the unit is operational you may be disappointed.
Best of luck!
|
Re: 2710 Spectrum Analyser 'Cannot count VCO, IF' error
I've done some probing and have identified a problem; note that mine is a post B010318 model, so it has the CFCS rather than the CFC board.
I have a very low signal level at J130 on the Phaselock Assembly (beat frequency output to the counter); the manual indicates this should be TTL, but it's about 100mV peak to peak. All of the supply lines are in limits, but I'm not seeing any signal gain between J110 (Phase/ Beat signal input) and the output of U720, with ~150mV p-p signal levels at each stage.
I have noted that there are some mods to the board and I'm not sure if thas has any bearing on it, I spotted that C742 and C747 have been removed and a through hole 220nF fitted instead, so this may be a repair to deal with a damaged track.
If anyone's familiar with this assy, I would appreciate your suggestions.
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Re: LAST CALL for Peter Keller's Book and Current Orders I have
Same thing I've been asking myself. Was busy with health. Came back today
to this :) At least some other people will have a fun book to read. Have
fun!
toggle quoted message
Show quoted text
On Tue, Nov 24, 2020 at 10:52 PM David Kuhn <Daveyk021@...> wrote: I missed out on this; didn't see it. Too Late?
On Thu, Nov 19, 2020 at 5:24 PM Dennis Tillman W7pF <dennis@...>
wrote:
This is a last call for Peter Keller's fabulous book. I will accept orders
until Friday evening my time. At present I have orders for 75 books.
At that time I will publish the final list of people I have received an
order from and I will explain how to make payment.
Below are the people who have been placed on Peter's book order. Please
confirm your name is on this list.
If you have missed all of the excitement here is a summary
Pete Keller (from Tektronix) is prolific writer about cathode ray tubes and
many other kinds of display technologies.
He published a very detailed book on the subject in 1991 which I highly
recommend. The book title is:
"The Cathode Ray Tube, Technology, History, and Applications", Peter A.
Keller. 320 p.
ISBN 0-9631559-0-3;
TK7871.73.K46;
621.3815'42-DC20
I paid $70 for my copy years ago when I bought it from Peter. There is a
copy of his book currently on eBay listed for $650!!!
Peter's book is still available in hard cover and he has copies of it to
sell to us.
Because of recent interest in it from TekScopes members I went out on a
limb
and asked Peter if a discount would be available for our members if we
bought enough books to make it worth his while and if I did all the work
for
him.
He agreed and offered our members a huge discount. The cost will be $30 +
shipping.
I am hoping I can even get him to autograph each copy.
I promised Peter I would keep his effort to an absolute minimum by
collecting the names and addresses, payments which I would send to him in
one lump sum; then when he ships all the books to me I will mail each book
for him.
The cost for a book going anywhere in the US is $30 + $4 Media Rate Postage
+ $3 for supplies and my time. The total will be $37.00.
The cost for orders overseas will be $30 + approximately $35 for Flat Rate
International Priority Mail (this includes tracking).
If you want a copy of Peter's book send your mailing address to me OFF-LIST
at dennis at ridesoft dot com. INCLUDE YOUR ADDRESS.
These are the orders I have as of 2:15PM (UTC-08:00) Coordinated Universal
Time-08.
If your name is not on this list then I missed your order (my apologies)
so
resend it with your address.
UNITED STATES ORDERS
Eric Spendel Fairfield, OH 45014
Dave Daniel Mims, FL 32754
Chuck Azzalina Perkasie, PA 18944
Jean Paul Novato, CA 94947
Kurt Rosenfeld Ossining, NY 10562
Vince Vielhaber K8ZW Oxford, MI 48371
Stan Perkins N6BYU San Diego, CA 92109-2348
Bruce Lane Kent, WA 98030-8803
Mark Huffstutter Seattle, WA 98115
Joe Rigdon Oviedo, FL 32765
Jeffrey S. Dutky Silver Spring, MD 20901
Larry Snyder Springboro, OH 45066-9761
Byron Hayes Jr. WA6ATN Toluca Lake, CA 91602-2914
Michael Drum Fanwood, NJ 07023-1008
Jack Reynolds Howell, MI, 48843
Phil Erickson Clinton, MA 01510
Edward Oscarson New Hartford, CT 06057
Steve Berg Casselberry, FL 32707
Charles Daves Aurora, CO 80015-1422
Chuck Harris Damascus, MD 20872
John Malec IV Northglenn, CO 80234
Marvin Moss Marietta, GA 30064
Tom Norman Escalon, CA 95320
Bill Lavick WA2SMF Edwards, NY 13635
Jeff Frantzen Olathe, KS 66062-3693
Glenn Little Goose Creek, SC 29445
Mark Vincent N. Chesterfield, VA 23236
Lance Lieberman Albertson, NY 11507-1022
Steven Horii Bryn Mawr, PA 19010-1226
Charles Nalley Burien, WA 98166
Carl Miles Rio Rancho, NM 87124
Larry Schneider Otis, ME 04605-7652
Dennis McCreery Bellevue, WA 98008
Tim Laing Lima, OH 45801-4644
Chris Wilkson Detroit, MI 48206
Timothy Koeth Brandywine, MD 20613
John Griessen Albuquerque, NM 87107
Greg Muir Great Falls, MT 59405-3144
Kurt Swanson Wilton, CA 95693-9765
Bruce Gentry KA2IVY Mattydale, NY 13211
Peter Brown Broomfield, CO 80023
Tim Pierce Cottage Grove, OR 97424
Bob Darlington N3XKB Los Alamos, NM 87544
Hugh Vartanian Littleton, MA 01460
Richard Brittingham W4MCD Edenton, NC 27932
Jim Rawlings AF6VF Livermore, CA 94550
Monte Meredith Reno, NV 89511
Chris Loggans Haymarket, VA 20169
Steve Bates Concord, MA 01742
John Glass, O'Brien Electric Dallas, OR 97338
INTERNATIONAL ORDERS
Sigurdur Asgeirsson CANADA
Shaun Merrigan CANADA
Bill Perkins, PEARL, Inc. CANADA
Dan Gajanovic CANADA
Andy Guelzow VA7NNM CANADA
Simon Jarman FRANCE
Christoph F. Bruggaier GERMANY
Heinz Breuer GERMANY
Jan Wuesten GERMANY
Red Dot Finder THE NETHERLANDS
Leo Potjewijd THE NETHERLANDS
Mario Giganti I1CWZ ITALY
Colin Herbert UNITED KINGDOM
Alan Ainslie UNITED KINGDOM
Robert Angell UNITED KINGDOM
Thomas S. Knutsen NORWAY
Jared Cabot JAPAN
Gangyi, Le SINGAPORE
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On Sun, Nov 22, 2020 at 01:51 PM, Jeff Dutky wrote:
Here is the 475 (and 475A) page:
and here is the service manual PDF:
Hi Jeff: Yes, you are correct. I wasn't able to resolve the link's address yesterday (I got repeated D.N.S. errors) but yes it loads for me now. I see that indeed there are no outlines or drawings of the 475A boards, or 475A schematics, in that file. Thank you for the posting the link. Best regards. Roy
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Re: Fix or Part Out a Tek 475A
Hey Jeff,
I was just writing you a reply. We are in sync here! I was just going to share that despite my brave talk this morning, I'm chickening out and not going any further.
I too had some sketchy looking (to me) stuff going on, but now that I've taken a close look I think it's not worth the effort to tear down the transformer and HV wiring that'd be required to get A9 out.
Glad to hear you cleared up the resistor/schematic discrepancy. That's really frustrating when what's in front of you doesn't match the documentation! Documentation bugs are the worst!
Dave
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On Tue, Nov 24, 2020 at 11:28 AM, Colin Herbert wrote:
I can see the 475A Service Manual
Hi Colin: Yes. When I search for "475A" at TekWiki at: the following page comes up: At the right are links (in blue) for the various files associated with the page. The file that I should open is "Tektronix 475A Manual", 070-2162-00? ... which indicates... when opened... that it actually is the "475 service manual." Generally, things are organized, and labelled so, on TekWiki, according to "manual", and "service manual"... so unless someone knew... or opened all the 475A files... they/me would think that is another version of the "user" or "operators" guide? Indeed, it's there.... thus, if one is following the "Fix or Part Out a Tek 475A " thread... why is there any confusion between which parts are in the Z-axis amplifier of a 475A, versus a 475... as the OP of that thread (et. al.) seem to be following a 475 service manual?... at least part of the time. TekWiki for the docs was mentioned several times in the thread.
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On Tue, Nov 24, 2020 at 11:16 PM, Jeff Dutky wrote:
(I assume that there are extension plugins that let you run a plugin outside
the main housing, though I can't find reference to such a thing on TekWiki).
Fixed extender: . Flexible extender: Raymond
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Re: Fix or Part Out a Tek 475A
Simon,
I had a second look at the vertically mounted resistors and I misread the color codes (I read purple as blue), they are marked as 7.5K Ohm, just as the schematics indicate. The resistors still read well out of spec, but this eliminates a big part of the mystery and frustration. The resistors being well out of spec may still be a problem, but at least it looks like I can rely on the schematics.
Also, looking at the board after a night's sleep, I agree that it doesn't look nearly as dire as I was thinking it was.
-- Jeff Dutky
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Dave Peterson
Craig Cramb
Raymond Domp Frank