Date   

Re: Encouraging beginners: What are we accomplishing?

John Crighton
 

Hello Roy,

I am really surprised at you of all people sounding like a wet blanket.

The owner of this tekscope group told you in no uncertain terms if you
want to talk about ESR Meters to go and form your own group. Which
to your credit you did just that. I also did not like the way that the owner
of this group, Dennis Tillman, jumped on Mr Chuck Harris for describing
how to use an oscilloscope with a function generator to check capacitors
for value and ESR. Shutting someone up for describing how to use an
oscilloscope on an oscilloscope group is to me just plain crazy.
Those are rules that you have to obey, like them or not.

Roy, if you are not enjoying reading about the repair of the 475 scope
by a beginner then do not read the thread. It is that simple!

I think it is marvellous that so many people on this group are willing
to help an individul fix his 475 scope. What a great thing to do,
while we are in corona virus lock down.
My fellow countryman Graham VK1GVC, down in Canberra is
doing a great job helping Bruce and so so are all the othere people.
The side benefit for me and no doubt others on this group is that
Bruce is asking basic questions as a beginner that other people
on this group might not dare to ask for fear of looking foolish.

Keep asking questions Bruce. I want you to fix this scope.

Regards,
John Crighton
Sydney

----- Original Message -----
From: "Roy Thistle" <roy.thistle@...>
To: <TekScopes@groups.io>
Sent: Wednesday, May 27, 2020 1:51 PM
Subject: [TekScopes] Encouraging beginners: What are we accomplishing?


Hi all TekScopers:
Reading through a long thread, recently posted, caused me to wonder.. just what are TekScopers accomplishing with threads like this... and why are we encouraging someone who is "... new to electronics..." to dig into a 475?... one of the most complex, and compact, analog instruments ever designed.
I suppose.. in consideration... Michael discouraged the use of a Mr. Carlson super Weller-kluge special, on the 475's pcb(s)... but, ya know... somewhere the thread... the 475 owner hints he paid 20.00 for 475?, and he's also got a nonworking? PM3218 too.
So why didn't someone just recommend/... right off the bat... to take the 475 to someone who knows what they are doing... drop another 100.00 on it... and then he'd have one of the best scopes ever made.
Or alternatively... and better... just start in on the PM3218...itself a very fine instrument, with a double insulated power supply... and way overkill, for a beginner.
Look, I'm not unsympathetic... it's just that...too often.. after parting with some scarce cash... or finding some Tek picked apart in a basement somewhere, where its been languishing for a generation...I've witnessed the havoc wreaked by someone trying to "fix" them.
If you want to call me a dumb ass... for thinking this way... well fine... just PM me to do it. I can't promise I'll reply to that... but, I'll read your message.
Best regards and wishes.
Roy




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Re: 475 questions

ciclista41@...
 

Hi All,

I was just searching "475" in the photos folder and found this one: https://groups.io/g/TekScopes/photo/12901/0?p=Name,,475,20,1,0,0

Those are the neon bulbs I was asking about in my first post. I don't think anyone said anything about them, but I found that by searching "neon bulb oscilloscope", I found this: https://en.wikipedia.org/wiki/Pearson%E2%80%93Anson_effect

So the bulbs are used as an oscillator.

Also, perhaps more of a Friday effect, and inconsequential because the two are identical, the A7 board on the US Army circuit map and the one on the Tektronix manual have the C1091 and C1093 in opposite positions. Both have an associated inductor with the same number part (L1091 and L1093). The Army version switched these two, as well. Since most of these parts have somewhat sequential numbering in their photos/maps/diagrams, I would say that this time it was the Army that had the Friday, because the part numbers are hand written, rather than printed, and they are out of sequence with the surrounding parts when they are in the switched position. Again, it doesn't matter that the inductors are switched, because they are also identical to one another. Just some weirdness, the kind of oddball thing I tend to notice.


On Fri, May 22, 2020 at 09:48 PM, <ciclista41@...> wrote:


Hi Harvey,

So frustrating! I had a reply nearly as long as your post above, but
accidentally hit some button and the entire thing evaporated. Oh well,
maybe
I will be less wordy and more to the point this time.

Thanks for such a thorough set of suggestions and explanations! This sort
of
advice is so valuable to me. I understood the part about the rectifiers
right
away. The part about the linear voltage regulators will take some research
on
my part to get up to speed on that. I think I almost understand the part
about NPN emitter followers, though. I'll be using all of that as well as
everyone else's advice as I figure this thing out. Glad the advice has not
been conflicting! Gives me confidence that I'm headed in the right
direction.

So, tacking a question on to this reply that's meant for anyone following
the
thread, since you've spent so much time already:

How do I know what generic components are best to replace the original
parts?
For instance, the tantalum caps come up a lot, but I assume when folks
replace
them, they don't use the same as the originals. What DO they use? There
are
so many types of capacitor, even in this one scope, and it's more than 37
years old. The large power supply caps are replaced with newer, smaller
electrolytics, but I've heard that some brands are more reliable and last
longer than others. What are some good choices?

I looked up one of the original rectifiers, an MDA960-3. I found a NOS of
it
on Ebay for almost $9 plus shipping. At that rate, this is going to get
expensive very quickly. So what can I use instead? I assume that by
looking
up the specs on each original component that I end up replacing and finding
something that meets or exceeds those specs, I'll probably be okay, but I
could really use the voice of experience here.

I'm aware of Digikey and Mouser. I ordered some diodes from Digikey several
years ago to build a rectifier that I used to convert the power from a hub
generator on my touring bike to charge my phone as I rode. It even worked,
although my buddy said the one I built for him killed his phone. Mine had
some issues that I never resolved. I'm hoping to soon have the ability to
design my own circuit, rather than copying someone else's, and have it be
rock-solid! But, I digress...

Thanks again, Harvey!

Bruce


Re: 475 questions

VK1GVC
 

Bruce, the link to the pics on TekScopes worked for me and that capacitor looks very 1980's tantalum as Michael confirmed in a later 475 manual and the Tek Common Parts manual.  Ceramics of that era were commonly flat circular disks, very different from what you have.

Roger re testing in place - very problematic.  Best to remove them to eliminate any ambiguity and as you have reported success in desoldering then that's the best option while you have access.  BTW I'm curious to know why you *believe* that they are faulty - mere suspicion based on type and age, or something else?

You quoted your post of 22 May to Harvey a few minutes ago in which you sought advice about what can and cannot be substituted when replacing 1982 components in 2020.  Has that qn been answered to your satisfaction or is it still a live issue?  The short answer is: it depends.  The long answer really has to address a specific component in a specific application.  But the laws of physics haven't changed a lot in the last 40 years so there is almost certainly something out there which can be bought/found/made/adapted or cajoled to do the job.  If you need a 1amp 400V rectifier diode then a IN4004 of the 70's or 80's is just the same as one from the factory today.  If you need a very specific high-spec module made for or by Tek for a very challenging application 40 years ago and now out of production ... oh dear, you've got a problem. Fortunately we now have TekScopes, some wikis, eBay and of course the WWW.

Graham

On 27/05/2020 1:24 pm, ciclista41 via groups.io wrote:
Hi Graham,

I posted a photo of the C1091 tantalum, along with the plaque stuck to the back of my scope here:

https://groups.io/g/TekScopes/album?id=247625&p=Created,,,20,2,0,0

Bruce

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Encouraging beginners: What are we accomplishing?

Roy Thistle
 

Hi all TekScopers:
Reading through a long thread, recently posted, caused me to wonder.. just what are TekScopers accomplishing with threads like this... and why are we encouraging someone who is "... new to electronics..." to dig into a 475?... one of the most complex, and compact, analog instruments ever designed.
I suppose.. in consideration... Michael discouraged the use of a Mr. Carlson super Weller-kluge special, on the 475's pcb(s)... but, ya know... somewhere the thread... the 475 owner hints he paid 20.00 for 475?, and he's also got a nonworking? PM3218 too.
So why didn't someone just recommend/... right off the bat... to take the 475 to someone who knows what they are doing... drop another 100.00 on it... and then he'd have one of the best scopes ever made.
Or alternatively... and better... just start in on the PM3218...itself a very fine instrument, with a double insulated power supply... and way overkill, for a beginner.
Look, I'm not unsympathetic... it's just that...too often.. after parting with some scarce cash... or finding some Tek picked apart in a basement somewhere, where its been languishing for a generation...I've witnessed the havoc wreaked by someone trying to "fix" them.
If you want to call me a dumb ass... for thinking this way... well fine... just PM me to do it. I can't promise I'll reply to that... but, I'll read your message.
Best regards and wishes.
Roy


Re: 475 questions

ciclista41@...
 

Hi Harvey,

This is just to say that that post of mine that evaporated...I just found it in a "Drafts" folder on my home page of groups.io! Nice to know that I can look there if it ever happens again. Just wish I knew what I did to make it go away in the first place!

Bruce

On Fri, May 22, 2020 at 09:48 PM, <ciclista41@...> wrote:


Hi Harvey,

So frustrating! I had a reply nearly as long as your post above, but
accidentally hit some button and the entire thing evaporated. Oh well, maybe
I will be less wordy and more to the point this time.

Thanks for such a thorough set of suggestions and explanations! This sort of
advice is so valuable to me. I understood the part about the rectifiers right
away. The part about the linear voltage regulators will take some research on
my part to get up to speed on that. I think I almost understand the part
about NPN emitter followers, though. I'll be using all of that as well as
everyone else's advice as I figure this thing out. Glad the advice has not
been conflicting! Gives me confidence that I'm headed in the right direction.

So, tacking a question on to this reply that's meant for anyone following the
thread, since you've spent so much time already:

How do I know what generic components are best to replace the original parts?
For instance, the tantalum caps come up a lot, but I assume when folks replace
them, they don't use the same as the originals. What DO they use? There are
so many types of capacitor, even in this one scope, and it's more than 37
years old. The large power supply caps are replaced with newer, smaller
electrolytics, but I've heard that some brands are more reliable and last
longer than others. What are some good choices?

I looked up one of the original rectifiers, an MDA960-3. I found a NOS of it
on Ebay for almost $9 plus shipping. At that rate, this is going to get
expensive very quickly. So what can I use instead? I assume that by looking
up the specs on each original component that I end up replacing and finding
something that meets or exceeds those specs, I'll probably be okay, but I
could really use the voice of experience here.

I'm aware of Digikey and Mouser. I ordered some diodes from Digikey several
years ago to build a rectifier that I used to convert the power from a hub
generator on my touring bike to charge my phone as I rode. It even worked,
although my buddy said the one I built for him killed his phone. Mine had
some issues that I never resolved. I'm hoping to soon have the ability to
design my own circuit, rather than copying someone else's, and have it be
rock-solid! But, I digress...

Thanks again, Harvey!

Bruce


Re: 475 questions

ciclista41@...
 

Hi Graham,

No need to apologize for "bad" jokes. That kind of humor is okay with me, as it's less likely to go "over my head." If the cap fits...get it? ;-)

Sorry, tested in place. I'll yank them and try again, since I believe them to be bad, anyway. However, if I replace them, I'll never know what fault they introduced, if any! Too bad.

Two photos posted at https://groups.io/g/TekScopes/album?id=247625&p=Created,,,20,2,0,0!

Bruce

On Tue, May 26, 2020 at 06:30 PM, VK1GVC wrote:


Bruce, I wouldn't be concerned about tolerances on the 2.2uF filter caps
on a power rail - to some extent the more uF the better, within reason. 
Some capacitors for this purpose have tolerances of -20% and +100%
indicating just that.  Anyway others have tracked down better info on
C1091 and C1093 and tantalum makes sense.  For an 8V rail anything over
about 12V rating is fine so 20V or 25V is more than OK, or even more if
you happen to find a 2.2uF cap which fits the space on the PCB.  (If the
cap fits?  Sorry ... bad joke)  BTW did you test these 2 caps out of the
circuit or in place?

I can see that your component knowledge is growing fast with the help of
ppl here and, fortunately, the low voltage DC part of a complex piece of
test eqpt is the easiest place to start fault finding.  The sheer
complexity and design cunning by Tek engineers which went into these
units is amazing and I'm dreading fault-finding in the really tricky
parts of my 2465 if I ever have to do it.

Re pins 14 and 16 of the transformer, if you've tested CR1412 rectifier
out of circuit (good) and the adjacent two capacitors (bad) then there
is no reason to try to disconnect the transformer at this stage. 
Disconnection was only so that you could test CR1412 and as you tested
it by removing it from the PCB then you've got it covered.

If you wish to share photos I understand that the TekScopes photo place
can do it altho' I haven't tried it yet myself.

Graham

On 27/05/2020 10:33 am, ciclista41 via groups.io wrote:
Dan,

Ok, Tektronix Common Parts Catalog. Got it!

Bruce



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Re: 475 questions

ciclista41@...
 

Sure John!

Glad you're enjoying it! So helpful for me.

Bruce

On Tue, May 26, 2020 at 06:21 PM, John Clark wrote:


Hey Bruce,
Can I make a request? Since I also have a 475 I'm enjoying following your
thread via email but would you mind quoting the reply/post that you're
replying to? It makes it helpful in knowing what you are answering or asking.
Otherwise it's just an answer or reply out of context.

Thanks,
John

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of ciclista41 via
groups.io <ciclista41=yahoo.com@groups.io>
Sent: Tuesday, May 26, 2020 8:33 PM
To: TekScopes@groups.io <TekScopes@groups.io>
Subject: Re: [TekScopes] 475 questions

Dan,

Ok, Tektronix Common Parts Catalog. Got it!

Bruce




Re: 475 questions

ciclista41@...
 

Hi Graham,

I posted a photo of the C1091 tantalum, along with the plaque stuck to the back of my scope here:

https://groups.io/g/TekScopes/album?id=247625&p=Created,,,20,2,0,0

Bruce


Re: 475 questions

Mlynch001
 

I am assuming you are testing these two caps out of circuit? If they are still in circuit, then those tests are probably not valid.

--
Michael Lynch
Dardanelle, AR


Re: 475 questions

Mlynch001
 

Like I said a while back, these are filter caps for the -8V and +5V Rails. Yours are definitely no longer capacitors, so they need replacement. The 475A manual I have shows 20V as does the common parts manual. 20V or 25V, either one works when used in that position.

--
Michael Lynch
Dardanelle, AR


Re: 475 questions

VK1GVC
 

Bruce, I wouldn't be concerned about tolerances on the 2.2uF filter caps on a power rail - to some extent the more uF the better, within reason.  Some capacitors for this purpose have tolerances of -20% and +100% indicating just that.  Anyway others have tracked down better info on C1091 and C1093 and tantalum makes sense.  For an 8V rail anything over about 12V rating is fine so 20V or 25V is more than OK, or even more if you happen to find a 2.2uF cap which fits the space on the PCB.  (If the cap fits?  Sorry ... bad joke)  BTW did you test these 2 caps out of the circuit or in place?

I can see that your component knowledge is growing fast with the help of ppl here and, fortunately, the low voltage DC part of a complex piece of test eqpt is the easiest place to start fault finding.  The sheer complexity and design cunning by Tek engineers which went into these units is amazing and I'm dreading fault-finding in the really tricky parts of my 2465 if I ever have to do it.

Re pins 14 and 16 of the transformer, if you've tested CR1412 rectifier out of circuit (good) and the adjacent two capacitors (bad) then there is no reason to try to disconnect the transformer at this stage.  Disconnection was only so that you could test CR1412 and as you tested it by removing it from the PCB then you've got it covered.

If you wish to share photos I understand that the TekScopes photo place can do it altho' I haven't tried it yet myself.

Graham

On 27/05/2020 10:33 am, ciclista41 via groups.io wrote:
Dan,

Ok, Tektronix Common Parts Catalog. Got it!

Bruce

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Re: 475 questions

John Clark
 

Hey Bruce,
Can I make a request? Since I also have a 475 I'm enjoying following your thread via email but would you mind quoting the reply/post that you're replying to? It makes it helpful in knowing what you are answering or asking. Otherwise it's just an answer or reply out of context.

Thanks,
John

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of ciclista41 via groups.io <ciclista41=yahoo.com@groups.io>
Sent: Tuesday, May 26, 2020 8:33 PM
To: TekScopes@groups.io <TekScopes@groups.io>
Subject: Re: [TekScopes] 475 questions

Dan,

Ok, Tektronix Common Parts Catalog. Got it!

Bruce


Re: 475 questions

Mlynch001
 

Search TekWiki: Search term “Common Parts”. In that list it is 1989 Materials Catalog. Lots of great catalog information in that section.

--
Michael Lynch
Dardanelle, AR


Re: 475 questions

ciclista41@...
 

Dan,

Ok, Tektronix Common Parts Catalog. Got it!

Bruce


Re: 475 questions

ciclista41@...
 

Hi Colin,

I show tolerance as 10% when searching for 196D225X9025HA1.

Thanks,

Bruce


Re: 475 questions

ciclista41@...
 

Hi Michael,

I think you're on the right track. I don't know where I got it, but if you search for sjcc002.tmp, you will find a document showing that the Tektronix 475 with options 4 and 7 is known as OS-261 C(v)1/U by the US Army. On the back of my scope is an adhesive plate indicating that this scope is that very scope. On page 57 of that document, the C1091 and C1093 capacitors are identified as 196D225X9025HA1. I discovered that 199D225X9025HA1 is a substitute. Both are Sprague dipped tantalum, 2.2μF 25V (not 20). Guess I'll have to start relying on this document for parts rather than the standard Tektronix 475 document.

Thanks,

Bruce


Re: 475 questions

ciclista41@...
 

Hi Dan,

"Common Design Parts Catalog" sounds like an excellent resource, but it didn't come up when I searched for it. Do you have a link?

Well, although they look fine, the GME-236 made a big fuss with both of them! C1091 measures 34Ω in one direction, 21Ω in the other in circuit with my analog meter. The AVR "transistor tester" does not recognize C1091 as a cap, but as a 43Ω resistor, regardless of polarity. It's very consistent with that measurement, and will not see it as a capacitor. With C1093, I can't get it to recognize it as anything "no, unknown, or damaged part" (40Ω in one direction, 21Ω in the other with analog).

Thanks

Bruce


Re: 475 questions

ciclista41@...
 

Hi Graham,

It sounds as if your philosophy of whether to keep or replace suspect components matches mine. My understanding of what each component is doing in a particular circuit is very weak, so I'm not sure what a suitable replacement would be if not the identical part, and these boards were manufactured in late 1982, so it's not exactly current technology. That can be a good thing, because it was intended to be maintainable, rather than tossing an entire board or worse, an entire device, when something goes bad. So, as several have suggested, I keep asking questions! I try to do my own research, too, but sometimes the explanations on websites are over my head or don't match my question closely enough. You guys have been much better in that respect!

I agree that I shouldn't be trying further diagnosis until my power rails are up and in spec. But when I poke around and see out-of-spec components on a relatively inaccessible board, I'm inclined to replace them if I can figure out what they should be replaced with.

I haven't commented on the attachments debate, but I'm with you for allowing them. There is https://groups.io/g/TekScopes/photos. Is that a good place for me to post?

Bruce


Re: 475 questions

Michael W. Lynch
 

Colin,

You made me look again. I guess it was my "Friday"?? I did read and quote that specification incorrectly. That "6%" that I was "assuming" to be the capacitor tolerance was a specification called "ESR (Ohms) DF % (MAX)". That cap is 20% tolerance, as you correctly stated. In other respects, I was correct in my reading the catalog.

--
Michael Lynch
Dardanelle, Arkansas


Re: 475 questions

ciclista41@...
 

Albert,

That link is going to be a great resource for me!

Damn! When I replied with my musings about where pi/√2 comes from, I had typed something about the integral of the sine function, but thought better of it. Sometimes a lack of confidence is a good thing...sometimes not. I guess I should not be confident about what I touch or connect in a high voltage circuit, but maybe have more confidence in my long-term memory. For sure, my short-term memory took a hit that has not fully recovered since my chemotherapy.

Bruce