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From: "VK1GVC" <vk1gvc@...>
To: [email protected]
Sent: Wednesday, May 27, 2020 9:40:45 AM
Subject: Re: [TekScopes] 475 questions

Bruce, I treat tantalums like I treat people - assume they have good
intentions unless I learn otherwise.? If you remove lots of them without
reasonable suspicion then you'll probably do more damage than good as
Eric has warned.? As tantalums usually fail to a short circuit, a
failed/shorted tantalum will pull down the voltage at that point to
close to zero and this will/should be straighforward to find - later.
At this stage, if I haven't missed any key points, you've found 2
sick/dead capacitors in the +50V supply which MAY be the cause of all
the wrong voltages you've measured in the low voltage power supply
section.? So replace those caps first, then adjust all of the LV power
supply to meet calibrations specs and see what happens.? You might have
a working scope if luck is very much with you, or you might be one step
on a long journey towards that goal.

And when you replace the tantalum which lost a leg, make sure you
install the new one with the right polarity.? Tantalums don't like
reverse voltage and they can get hot, emit smoke and explode.? I've seen
it happen when a workmate powered up some newly assembled eqpt for the
first time and heard a hissing sound so he bent down for a better look.
A cylindrical metal tube type tantalum then exploded and flew off the
PCB, burning itself onto the side of his neck. Very painful ... and the
language was terrible.? And very lucky he didn't get hit in an eye.

BTW here's a different type of tantalum which I don't think has been
mentioned yet - see the colourful little blob in the lower left of the
picture at this link:
/g/TekScopes/photo/12901/22?p=Name,,475,20,1,0,0

It has a black top, brown middle and green bottom ... the colours are a
derivative of the resistor colour code and I think there's a spot on one
side too.? Much better dressed than a plain boring tantalum!

Graham

On 27/05/2020 3:28 pm, ciclista41 via groups.io wrote:

Graham,

Well, my scope is peppered with the kind in the photo. Maybe they
re-spec'ed the caps later in production, or maybe the US Army bought
enough in their contract with Tek that they were able to spec what they
wanted. Mine is from November of 1982, if the date code on the AC power
cord box inside the case just above the transformer is original.

I went ahead and pulled the two tantalums out of the circuit to measure
them. I broke a lead off the first one, pulling too hard. Because I only
have access from the top of this A7 board unless I remove it, which I
don't want to do, my solder sucker wasn't able to slide over the clipped
end of the leads, and I had to just use a sharp tip on my iron. Did much
better on the second one, which came out easily by that second method. I
then used the sucker to remove the remaining solder from the holes in the
board for when I replace the broken one.

Yes, you were right to question my belief that they were bad. Out of
circuit, they both tested well within the green on my ESR tester. So much
for being able to reliably test capacitors in circuit with that thing.
They weren't even close to being in spec when tested with it in circuit.
I was thinking that these dipped tantalums were generally bad in boards
this old based on numerous threads in this forum and others saying how
often these were bad. Some said they routinely replace them all when they
see them in a scope of this era. I have tested dozens on this board and
only found about a handful that this tester considered bad. So,
considering that these two were among the worst that I tested in circuit,
I decided to pull them, as they'd be less easily accessible later when the
A8 board is back in place.

So this makes me question whether the tantalums in this board are among the
infamous ones. I hope not, obviously. Your statement that my photo
showed what looked like a very '80's tantalum made me think maybe the
infamous ones are some earlier 60's or 70's version. How can I know,
other than pulling them all? At this point, I don't see the point of
pulling any of them unless they show up as faulty later, when there is a
trace on the scope and I can run it through its paces and make sure it's
working as it should.

Speaking of working as it should, Tektronics calls for several specialized
calibration tools in the manual. If the scope is running well, with no
serious issues other than calibration, can it be calibrated without
resorting to the purchase of such tools? I briefly noted some shops
wanting a couple of hundred dollars to calibrate a scope. Definitely
don't want to do that! If I thought I had to have someone else calibrate
it, I probably wouldn't have taken on the project and just invested in a
new digital scope.

Bruce

On Tue, May 26, 2020 at 09:09 PM, VK1GVC wrote:

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:

/g/TekScopes/album?id=247625&p=Created,,,20,2,0,0

Bruce

--
This email has been checked for viruses by Avast antivirus software.

I will put in my 2 cents worth here.? I have a 465, and it had been in storage for about 2 years.? It wasn't working when I got it out to use.? Have owned it for about 7 years using in my trouble shooting and repair work.? The scope's case never been off.? I am a complete novice when it comes to SS electronics.? I have been a ham for a long time and have used, repaired, and home brewed tube type transmitters, receivers, and accessories.? With the help I got on TekScopes2, I was able to quickly locate and fix the problem with my scope.? I always welcome knowledgeable help from anyone.

David
KW4DH

On 5/27/2020 1:14 AM, Jim Ford wrote:

I agree with you, John.? At first I was dismayed at Bruce's many posts, but then I thought, hey, I have no experience with the 475 and no interest in one, so I'll just delete the darn posts! Simple as that!

Bruce, knock yourself out!? Post as much as you need to to get the information you need to fix your scope.? Good luck!

Jim Ford

In answer to your question, ANY time you bring in fresh blood, it's
better for everyone. Every time. No exceptions. A rising tide floats all boats.

Right now, Harley Davidson is facing 'massive restructuring'. Why?
Their rider base is literally dying off.
I'm involved in several other hobbies and pursuits where young blood
is not entering. They are dying. And with it comes a similar
intellectual cannibalism.

As any discipline dies, like analog scopes, the entry price will be
lower and lower. Soon, for rummage sale prices, the once-crown-jewel
pieces become affordable. In 1983, how many 60s fastback Mustangs
were parked behind gas station garages (remember those?) and could be
had for a couple hundred? Many were chopped and otherwise brutalized
in ways I can't describe. But such is the price. Today, they're
worth more than most people's financials.

There were many thousands of units produced of scopes and cars and
organs and everything else. Some will live nice lives and some will
die horrible deaths and grownups understand this. I've been the
careless kid and the fastidious curator, but at both extremes I remembered the Prime Directive:
this thing is MINE, not yours. If you're worried about it, you can
buy it from me and store it away. If not, tough.

If we want a growing following, then we have to let the newbs make
their mistakes and learn as we did - yes, even on top tier equipment.
If it grows enough, someday my old junk might be worth as much as I
think it is now. If not, someone will speak poorly of me as they
shovel it all out into a dumpster after my demise.

Besides, if it tracks like everything else, one day some others will
join your song and these units will skyrocket - at least temporarily.
I own a Hammond console. In 1988, it was dumpster fodder. By 2010, it was $10K.
Today, it's maybe $4k. These things have a cycle and scopes are
certainly no exception.

Anyway, help every newb you can. If they want to try their hand, the
answer is NEVER "let someone else do it". They're gonna do it wrong.
Just as wrong as you and I used to do stuff. The sooner they learn to
do it right, the sooner everything gets better.

L.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Roy Thistle
Sent: Tuesday, May 26, 2020 10:52 PM
To: [email protected]
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

Graham,

Well, my scope is peppered with the kind in the photo. Maybe they re-spec'ed the caps later in production, or maybe the US Army bought enough in their contract with Tek that they were able to spec what they wanted. Mine is from November of 1982, if the date code on the AC power cord box inside the case just above the transformer is original.

I went ahead and pulled the two tantalums out of the circuit to measure them. I broke a lead off the first one, pulling too hard. Because I only have access from the top of this A7 board unless I remove it, which I don't want to do, my solder sucker wasn't able to slide over the clipped end of the leads, and I had to just use a sharp tip on my iron. Did much better on the second one, which came out easily by that second method. I then used the sucker to remove the remaining solder from the holes in the board for when I replace the broken one.

Yes, you were right to question my belief that they were bad. Out of circuit, they both tested well within the green on my ESR tester. So much for being able to reliably test capacitors in circuit with that thing. They weren't even close to being in spec when tested with it in circuit. I was thinking that these dipped tantalums were generally bad in boards this old based on numerous threads in this forum and others saying how often these were bad. Some said they routinely replace them all when they see them in a scope of this era. I have tested dozens on this board and only found about a handful that this tester considered bad. So, considering that these two were among the worst that I tested in circuit, I decided to pull them, as they'd be less easily accessible later when the A8 board is back in place.

So this makes me question whether the tantalums in this board are among the infamous ones. I hope not, obviously. Your statement that my photo showed what looked like a very '80's tantalum made me think maybe the infamous ones are some earlier 60's or 70's version. How can I know, other than pulling them all? At this point, I don't see the point of pulling any of them unless they show up as faulty later, when there is a trace on the scope and I can run it through its paces and make sure it's working as it should.

Speaking of working as it should, Tektronics calls for several specialized calibration tools in the manual. If the scope is running well, with no serious issues other than calibration, can it be calibrated without resorting to the purchase of such tools? I briefly noted some shops wanting a couple of hundred dollars to calibrate a scope. Definitely don't want to do that! If I thought I had to have someone else calibrate it, I probably wouldn't have taken on the project and just invested in a new digital scope.

Bruce

On Tue, May 26, 2020 at 09:09 PM, VK1GVC wrote:

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:

/g/TekScopes/album?id=247625&p=Created,,,20,2,0,0

Bruce

--
This email has been checked for viruses by Avast antivirus software.

I agree with you, John.? At first I was dismayed at Bruce's many posts, but then I thought, hey, I have no experience with the 475 and no interest in one, so I'll just delete the darn posts! Simple as that!

Bruce, knock yourself out!? Post as much as you need to to get the information you need to fix your scope.? Good luck!

Jim Ford

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.

In answer to your question, ANY time you bring in fresh blood, it's better
for everyone. Every time. No exceptions. A rising tide floats all boats.

Right now, Harley Davidson is facing 'massive restructuring'. Why? Their
rider base is literally dying off.
I'm involved in several other hobbies and pursuits where young blood is
not entering. They are dying. And with it comes a similar intellectual
cannibalism.

As any discipline dies, like analog scopes, the entry price will be lower
and lower. Soon, for rummage sale prices, the once-crown-jewel pieces
become affordable. In 1983, how many 60s fastback Mustangs were parked
behind gas station garages (remember those?) and could be had for a couple
hundred? Many were chopped and otherwise brutalized in ways I can't
describe. But such is the price. Today, they're worth more than most
people's financials.

There were many thousands of units produced of scopes and cars and organs
and everything else. Some will live nice lives and some will die horrible
deaths and grownups understand this. I've been the careless kid and the
fastidious curator, but at both extremes I remembered the Prime Directive:
this thing is MINE, not yours. If you're worried about it, you can buy it
from me and store it away. If not, tough.

If we want a growing following, then we have to let the newbs make their
mistakes and learn as we did - yes, even on top tier equipment. If it
grows enough, someday my old junk might be worth as much as I think it is
now. If not, someone will speak poorly of me as they shovel it all out
into a dumpster after my demise.

Besides, if it tracks like everything else, one day some others will join
your song and these units will skyrocket - at least temporarily. I own a
Hammond console. In 1988, it was dumpster fodder. By 2010, it was $10K.
Today, it's maybe $4k. These things have a cycle and scopes are certainly
no exception.

Anyway, help every newb you can. If they want to try their hand, the
answer is NEVER "let someone else do it". They're gonna do it wrong. Just
as wrong as you and I used to do stuff. The sooner they learn to do it
right, the sooner everything gets better.

L.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Roy
Thistle
Sent: Tuesday, May 26, 2020 10:52 PM
To: [email protected]
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

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

I found that by searching "neon bulb oscilloscope", I found this:
So the bulbs are used as an oscillator

I don't believe so. IIRC the neons in the 475 are in the EHT supply circuit and are effectively over-voltage spark gaps.

To add to this discussion - replace nothing until you know it is causing a fault especially if you have limited soldering skills.

David

On Tue, May 26, 2020 at 10:05 PM, John Crighton wrote:

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

Hi John:
Yes!... if you do not like the topic... then don't read it. What then, I ask, is the logical consequence of that claim?
And, just for the record... I think all this ESR stuff is 95% foolishness... I don't even have one Topic about ESR meters on TekScopes... if one post even.
And, Dennis didn't tell me to do anything about ESR meters. That's something you are making up.
About Chuck... I don't know: in my estimation Chuck can look after himself... pretty good really.
Yes we can celebrate the marvelous-ness of generosity, that of national solidarity in the time of crisis, and of wonderful serendipity, among other things; but, I broached none of that in my post... none of it.
And, a particularly incoherent response, relative to the questions that I did raise, does nothing to address them... nor shows those questions were directed towards anyone in particular, or about anyone in particular. They are not.
What I posted was my opinion, based on my experience, and I stand by it.
Best regards and wishes.
All the best.
Roy.