Martin,
??? Unfortunatly I can answer that. I have the tube in question it is weak. It is doing a double ramp but this one is slightly weak. I have a second tube as well that is VERY weak. I have not looked in to rejuvination of these or rebuild yet let me know if you are interested They came to me at cost of shipping and I am more then happy to pass them on for cost of shipping.
Eric
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On 5/28/2020 5:35 AM, Martin Whybrow wrote: Ryan, has that CRT been taken? If not, I would be interested, does the screen appear burned? My 576 works, but has a completely dead spot where the intensity was left too high with a static spot displayed.
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I agree. I recently grabbed a P6139A out of Raytheon Technologies (RTX, my day job) e-waste bin and found that it works well with my 400 MHz HP 54504A scope (also an RTX rescue). I was able to adjust the probe to get a nice flat response when connected to the calibrator on the 54504A. Fortunately it also looked flat with the calibrator on my Tek 7904.
So, yes, for most purposes a properly adjusted 500 MHz probe will work with a 400 MHz scope. If you're testing pulses up near the limit (handy rule of thumb is pulse rise/fall time is 0.35/3 dB bandwidth), say 0.9 ns (about 400 MHz 3 dB BW), then no, you won't get an accurate picture unless you use the probe specifically designed for the scope. Also handy to remember 1 ns rise or fall time is equivalent to 350 MHz 3 dB BW, and 1 GHz BW is equivalent to 0.35 ns rise or fall time.
And I'd check the input capacitance of the scope (7 pF in the case of the 54504A) versus the output capacitance of the probe (8 pF in the case of the P6139A), and if they are close, you will probably get good results when you connect the probe to the calibrator and adjust it for flatness. Sometimes you can even find the range of capacitance of the probe. The HP 10430A probes I have with the 54504A scope say "1 Megohm||6.5 pF for 1 Megohm||6-9 pF inputs" on them. Also check to see what probe(s) go with what Tek scopes.
There's more, but it's probably covered in those references Raymond mentioned.
Good luck!
Jim Ford
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------ Original Message ------ From: "Raymond Domp Frank" <hewpatek@...> To: [email protected]Sent: 5/28/2020 4:49:56 AM Subject: Re: [TekScopes] probe. On Thu, May 28, 2020 at 07:40 AM, James Theonas wrote:
Is this probe a good match for my scope?
It would be insofar as bandwidth is concerned. The transient response however is not matched to the input characteristics of the 2465B. It'll work but signal fidelity will not be optimal, resulting in visible step response artifacts. For the 2465B, Tek recommended the P6137. With the right tools and equipment, you could optimize the behavior of the probe with its high-frequency adjustments.
Raymond
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James,
Maybe my earlier response was a bit terse and therefore limited.
The general answer to your question "Is this probe a good match for my scope?" should be "no". Chuck's answer and mine show you why:
You will not in practice achieve the "promised" 400 MHz bandwidth with that combination. But, neither will you with the Tek-specified P6137. That does not mean there's no observable difference between the two under any circumstances. Under specific test circumstances the difference is clear.
If you purchase a P6139A with the intention to observe and measure over the full bandwidth (bw) of the 2465B 'scope, you'll be disappointed. In fact, *no* high-impedance passive probe will do, as Chuck explained. One might add that the source impedance used for specifying scope bw is 25 (!) Ohm. Not many real-life signal sources fit that requirement!
At frequencies below 100 MHz or edge speeds slower than ca. 15ns the P6139A will provide acceptable fidelity. Most people use their 'scopes in that range and it makes no real difference if you use a P6139A, P6139B or a P6137.
Remember that for looking at edges, it's not the frequency but the edge speed that determines the speed requirements. For faster speeds either a fast FET probe or a Lo-Z probe with 50, 500 or 500 Ohm is a better choice. Get a copy of Tek's "ABC of Probes" or Doug Ford's "The Secret World of Oscilloscope Probes" and read all about it.
As said, for things like audio, Arduino projects, shortwave Ham and the like, a P6139A or almost any other "HF" quality passive probe will make you happy. That's where Chuck's P6105, 6, 7 choice comes in. They can often be had at low prices. If you get one of those, try and get a low-inductance ground clip/wire, unless you only do audio. The standard ground wire (4 - 6 inches) produces huge ringing, even at frequencies below 100 MHz. And choose an attenuation of 1:10, *not* 1:1. If you want to know why, read the publications mentioned above.
For anything faster, go Lo-Z (cheap/very cheap (DIY possible)) or (Hi-Z) FET.
Raymond
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On 2020-05-27 11:20 PM, Mlynch001 wrote: ... Many Tantalum caps do not have a voltage designator band. This one is supposed to be 50V, according to the parts list. That Voltage Value can usually be derived indirectly from the known operating voltage of the circuit. In this case, common sense tells us this cannot be a 16V cap, since it is operating in a circuit using a higher voltage than 16V. You would want to replace this with one of at least the same or greater voltage rating.
If you're going to the trouble of ordering new ones and replacing, I believe it's also now understood to be good practice to de-rate tantalums by *at least* 2 x the operating voltage. (In these lists I've heard a lot of cases where the originals were barely de-rated and thereby producing unnecessary failures -- even in Tek gear, perhaps moreso the newer SMT.) --Toby
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Tektronix tweaked the probes meant for the 2465B to match
the response of the inputs on the 2465B, so for specified
performance, only a p6137 will do.
But, likely you will never notice the difference.
The 10M, probe tip, frequency response of these scopes was
simply bragging rights for tektronix.
The parallel capacitive reactance at the probe tip swamps
the probe's 10M resistance long before you get to 400MHz.
It even swamps most circuits where you might think you would
like to make a measurement using a 10M probe...
Amuse your date, calculate Xc for the probe at 400MHz.
P6135,6,7 probes are pretty easily damaged. Often it is
better to get a much slower P6105,6,7 100MHz probe, and
enjoy its near indestructibility.
It is unlikely you will ever be bothered by its frequency
response.
-Chuck Harris
James Theonas via groups.io wrote:
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A quick question for the group. I have a 2465b and have found a p6139a locally in good condition. Is this probe a good match for my scope?
Dimitris Theonas
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Hi Bruce,
Okay - I was thinking the 475's caps were the same as the 465 but perhaps not.
It's a custom board I designed and had manufactured. BTW, if you notice, the board shown has a trace that had to be removed for that version of the board (I made a mistake...). I had another batch made where that wasn't necessary.
Thanks,
Barry - N4BUQ
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----- Original Message ----- From: "ciclista41 via groups.io" <ciclista41@...>
To: [email protected]
Sent: Thursday, May 28, 2020 2:22:48 AM
Subject: Re: [TekScopes] 475 questions
Hi Barry,
That certainly looks like a neat way to handle it! I've already order the
disc-shaped ones for this board. As far as I know, there isn't a similar
set-up available for the 475, but I like the single board with stand-offs.
My 475 has six large caps there, rather than five, although I read
somewhere that two of these are in parallel, so can be replaced with a
single cap. Was that solution a custom job, or purchased ready made?
Bruce
On Wed, May 27, 2020 at 08:03 AM, n4buq wrote:
I have hesitated to mention this as a possible approach to the filter caps
in
the 475 because:
1. I don't know for sure whether the layouts between the 465 and 475 are
identical
2. The design is, well, a bit kludgy (if I do say so myself)
However, I thought I'd pass it along.
Pictured in this album is an implementation of a separate circuit board
that
provides that ability to use common snap-in caps as replacements. My
intent
for this was to make it possible to replace those caps again (should it
every
become necessary) without further desoldering/soldering on the main board.
/g/TekScopes/album?id=64929
There are small disc adapters that do somewhat the same thing (I have
some);
however, if a future cap replacement becomes necessary, I'm not sure it is
possible to do that without removing the disc which, of course, involves
solder work on the main board.
Maybe one day I'll afford a snazzy desoldering tool which would probably
(certainly?) make that part much easier for me but, for those large can
connections, it's not fun with a 25-year-old Radio Shack solder sucker.
The
can, itself, is a rather large heat sink/spreader which further complicates
that process.
Anyway, FYI.
Thanks,
Barry - N4BUQ
----- Original Message -----
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.
|
Re: Encouraging beginners: What are we accomplishing?
Many enthusiastic youngsters had comparable experiences with instrument companies in the 1960s. General Electric and to a lesser degree RCA were also very kind to young hams and experimenters. I spent my youth in a place where one huge chemical plant dominated the local industries. They had an extensive outreach to youngsters showing interest in science and especially technology, it paid off for them by providing an abundance of techie kids applying for employment after graduation. This was the company that invented super glue, at the time it was still under patent and only available from them. Their recruiters always came prepared with lots of it that didn't quite measure up but was still very usable. An occasional Tektronix, General Radio, or Hewlett Packard manual would also be in their bag. None of us with "pump gas-cut grass-throw papers" money could afford anything Tektronix unless we were exceptionally lucky and it for some reason showed up at the local scrapyard that took in from many regional industries. While some of us had driver's licenses, most of us got there on bicycles or walked. One testament to the quality of equipment was how well it survived a few miles in a bicycle trailer or cart.
Bruce Gentry, KA2IVY
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On 5/27/20 10:36 PM, stevenhorii wrote: My experience with Tektronix began far before I had a Tek scope. I was
about 11 years old and saw advertisements in Scientific American for
Tektronix oscilloscopes. I wanted a catalog to learn more about them. I
wrote a letter to Tektronix (I believe it was to the HQ in Beaverton)
asking for a catalog. Whoever received it must have figured out I was a kid
- no company name or address and clearly a home address. Best regards and wishes.
Roy
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Re: Tek 4041 GPIB Controller
Stephen,
I think it would be pretty simple to put an Arduino board inside the 4041 case - connected to the internal keyboard header, plus my resistor mod so the Arduino could direct drive serial into the 4041.
It might be easier to not worry about how long the 4041 takes to boot and just install an Arduino reset button on the back of the 4041. Press the Arduino reset button and the Arduino program would output the SET DRIVER and SET CONSOLE commands - which would require that the 4041 had the Program Development ROMs.
Does everyone on this thread already have those ROMs in their ROM Carrier?
Otherwise - the 4041 will only auto load an AUTOLD.IT program from tape - as the Program Development ROMs are required to run ASCII BASIC commands like SET DRIVER and SET CONSOLE.
Or someone needs to disassemble the Utility ROM and figure out how to make a PROM that would hold the AUTOLD.IT program to do the serial commands.
When I look at the 16-bit binary image of the Utility ROM, it looks organized similar to the Tektronix 4050 ROM packs, with a header, followed by ROM call names, each followed by the entry point address for that ROM call.
In addition the last 1024 bytes of the Utility ROM look like a template for the PROM image:
Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
00003C00 30 2B 00 20 47 F3 00 20 2B 4B 00 24 60 AA 4E 75 0+. Gó. +K.$`?Nu
00003C10 00 00 00 00 00 06 00 10 46 4F 52 84 00 08 41 53 ........FOR?..AS
00003C20 43 FF 00 00 49 54 45 FF 01 00 45 4F 4D 01 01 11 C?..ITE?..EOM...
00003C30 45 4F 55 01 01 10 45 4F 41 01 01 0F 45 4F 48 01 EOU...EOA...EOH.
00003C40 01 0E 00 00 00 00 46 69 6C 65 20 20 54 79 70 65 ......File Type
00003C50 20 20 53 69 7A 65 20 20 20 20 43 72 65 61 74 69 Size Creati
00003C60 6F 6E 20 44 61 74 65 20 20 5F 5F 5F 5F 20 20 5F on Date ____ _
00003C70 5F 5F 5F 20 20 5F 5F 5F 5F 20 5F 5F 5F 5F 5F 5F ___ ____ ______
00003C80 5F 5F 5F 5F 5F 5F 5F 5F 5F 5F 5F 5F 00 00 00 00 ____________....
00003C90 00 05 50 52 4F 4D 3A 00 00 00 00 00 00 00 00 00 ..PROM:.........
00003CA0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003CB0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003CC0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003CD0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003CE0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003CF0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003D00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003D10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003D20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003D30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003D40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003D50 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003D60 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003D70 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003D80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003D90 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003DA0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003DB0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003DC0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003DD0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003DE0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003DF0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003E00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003E10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003E20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003E30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003E40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003E50 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003E60 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003E70 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003E80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003E90 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003EA0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003EB0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003EC0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003ED0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003EE0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003EF0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003F00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003F10 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003F20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003F30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003F40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003F50 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003F60 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003F70 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003F80 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003F90 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003FA0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003FB0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003FC0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003FD0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003FE0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00003FF0 FF FF FF FF 22 22 21 22 01 01 FE FE 3D 0F F4 20 ????""!"..??=.?
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On Thu, May 28, 2020 at 07:40 AM, James Theonas wrote:
Is this probe a good match for my scope?
It would be insofar as bandwidth is concerned. The transient response however is not matched to the input characteristics of the 2465B. It'll work but signal fidelity will not be optimal, resulting in visible step response artifacts. For the 2465B, Tek recommended the P6137. With the right tools and equipment, you could optimize the behavior of the probe with its high-frequency adjustments. Raymond
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Ryan, has that CRT been taken? If not, I would be interested, does the screen appear burned? My 576 works, but has a completely dead spot where the intensity was left too high with a static spot displayed.
|
Re: 576 collector supply issues
Wiring restored to original and now it's working. Going to go through the full test and cal procedures to see how it's behaving now.
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This is intended for use with some TDS scopes and has a 500MHz bandwidth. So probably ok with a 400MHz scope. They also have a problem which can render them scrap. See:
I don't have either a 2465B or a P6139A, so you can take this with a pinch of salt, except for the mentioned problem.
Colin.
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of James Theonas via groups.io Sent: 28 May 2020 06:40 To: TekScopes Mail List (New: groups.io) Subject: [TekScopes] probe. A quick question for the group. I have a 2465b and have found a p6139a locally in good condition. Is this probe a good match for my scope? Dimitris Theonas
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Re: Tek 4041 GPIB Controller
Monty,
Good to see you have now established communication with the keyboard port. You are correct that the COMM0 port description is required for a 4041 with the dual RS232 port option.
I use the same technique since my tape drive doesn't work and I have to manually enter those commands every time the 4041 is powered up to redirect the console. I been thinking of automating the process by building a small microcontroller board that emulates the keyboard and outputs the necessary commands every time the 4041 is powered on. I haven't progressed this yet as I need to do some experiments to figure out when the 4041 has completed its power-up sequence and is ready to accept keyboard commands and how fast it can process those commands.
Stephen
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Re: Encouraging beginners: What are we accomplishing?
Hello Dennis,
Denis Cobley was his name, I spelt it incorrectly.
If you look up the old messages you will find him.
In regards to test equipment repairs, Magic flowed
from his hands and he had an encyclopdiac knowledge of Tektronix scopes of that era.
The little company, "TrioSmartcal", where he was the service manager changed its name as it merged
and got absorbed by other companies. Over the years
all the people that I once knew have drifted away so I
do not know where Denis Cobley is today. One of the most helpful men I have ever known, I learnt a
lot from him.
More than a decade ago, thanks to this group, I met Denis Cobley and got a job when I needed one. That is something more than just luck!
Regards,
John Crighton
Sydney
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----- Original Message ----- From: "Dennis Tillman W7pF" <dennis@...> To: < [email protected]> Sent: Thursday, May 28, 2020 2:17 PM Subject: Re: [TekScopes] Encouraging beginners: What are we accomplishing? Hi John Thanks for the reply and the very interesting story. I feel like I know Denis Cobly from somewhere. I did a search of my email but didn't fine anything. Would you ask him if he recognizes my name, and if so, from where, Thanks, Dennis --- This email has been checked for viruses by AVG.
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Hi All, I may have done this, but I don't think so: /g/TekScopes/photo/247625/0?p=Created,,,20,2,0,0. Note the cap and resistor are supposed to be soldered to one another, but the joint was broken. I soldered the leads back together, but I think I need a cylindrical crimp fitting to reduce the chance that the joint will break there again. Bruce
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Hi Barry,
That certainly looks like a neat way to handle it! I've already order the disc-shaped ones for this board. As far as I know, there isn't a similar set-up available for the 475, but I like the single board with stand-offs. My 475 has six large caps there, rather than five, although I read somewhere that two of these are in parallel, so can be replaced with a single cap. Was that solution a custom job, or purchased ready made?
Bruce
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Show quoted text
On Wed, May 27, 2020 at 08:03 AM, n4buq wrote:
I have hesitated to mention this as a possible approach to the filter caps in
the 475 because:
1. I don't know for sure whether the layouts between the 465 and 475 are
identical
2. The design is, well, a bit kludgy (if I do say so myself)
However, I thought I'd pass it along.
Pictured in this album is an implementation of a separate circuit board that
provides that ability to use common snap-in caps as replacements. My intent
for this was to make it possible to replace those caps again (should it every
become necessary) without further desoldering/soldering on the main board.
/g/TekScopes/album?id=64929
There are small disc adapters that do somewhat the same thing (I have some);
however, if a future cap replacement becomes necessary, I'm not sure it is
possible to do that without removing the disc which, of course, involves
solder work on the main board.
Maybe one day I'll afford a snazzy desoldering tool which would probably
(certainly?) make that part much easier for me but, for those large can
connections, it's not fun with a 25-year-old Radio Shack solder sucker. The
can, itself, is a rather large heat sink/spreader which further complicates
that process.
Anyway, FYI.
Thanks,
Barry - N4BUQ
----- Original Message -----
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
--
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|
Hi Michael,
I had noticed that page of the manual in passing, but did not study it, as I assumed it would be following the same standard used elsewhere. Thank you for pointing out that that is not the case. I now have that page printed for easier reference in the future and have verified the correct cap rating using it as you describe. The diagram also shows the vertical stripe as indicating the positive lead. However, as you indicated, the voltage rating corresponding to the gray color of the vertical stripe is not designated in the chart. If we call it silver, rather than gray, the chart remains ambiguous as to voltage rating. I assume that since the C1304 is supposed to be 50V ±20 that that is what it is. As you said, no way to tell by looking at the capacitor, itself, though.
How did you know what voltage is being used by the circuit on the A7 board?
Bruce
|
Hi Michael,
Very good to hear that Tek has that convention, as it confirms what I thought about how these were oriented before I took them out. Experience is so very valuable when it comes to this kind of thing. Thank you very much for sharing yours!
Bruce
toggle quoted message
Show quoted text
On Wed, May 27, 2020 at 07:24 PM, Mlynch001 wrote:
Bruce,
The square pad is TEKs way of designating the positive side of any polarized
device. So Yes, square pad is + side of the Capacitor. This also applies to
diodes as well. Sometimes Tek will use the square pad to designate the number
one pin of an IC, however, this is not universally true. The number one pin
can also be designated by a small round dot on the PC board, adjacent to the
pad. The number one pad is sometimes not identified in any manner. My
experience is working many of these 4xx Series as well as other contemporary
Tektronix instruments. This holds true on almost all the instruments that I
have personally repaired. I do not always depend on the color codes on these
caps, I tend to rely on the values stated in the schematics and in the parts
list. One thing that I try to do is take a picture of the area of the board
where I am working, BEFORE I make any changes and I try to document exactly
these sort of markings for later reference.
--
Michael Lynch
Dardanelle, AR
|
Hi Graham,
I've taken several photos, particularly of the A8 board that I removed to get at the large caps. Forgot to do that with the A7 board, but I noted that the printing on the cap was facing the front of the scope before removal, so got away with the oversight this time.
Yes, that colorful sleeping dog will remain undisturbed!
Bruce
toggle quoted message
Show quoted text
On Wed, May 27, 2020 at 06:59 PM, VK1GVC wrote:
Bruce, the + sign is unambiguous, that lead is definitely the postive
lead.? The 'bent knee' lead may be the + lead but I am not aware of that
as a convention so trust the markings.? Likewise the square solder pad
may be a Tek convention (can other readers comment?) but I am not aware
of it so I wouldn't rely on it.? Not having access to a 475 I can't get
a good look at the A7 board and the image of the PCB layout, Fig 7-16 in
the manual is very grainy and I can't see the shape of these pads.? The
best way to confirm which way around these tantalums should be is by
looking at the pics you took of the board before you removed them!? Yes
I forget to do that too, but it's very helpful in these circumstances.?
I did refer to the pic of C1091 you posted but the focus is a bit off
where it's needed.? I *think* the + is on the left as that looks like
the 'bent knee' lead but I'm not certain.
The next best way is to identify nearby components and find which
connects to which, and the schematic shows those two ferrite bead
inductors L1091 and L1093 and they tell the story.? Note that supply
rail to L1091 and C1091 is negative and the other L and C are on a
postive supply rail so the capacitor polarity will reflect that.
As for the colourful tantalum on the A9 board, I worked out the colour
code as you did and I can't explain the difference with the parts list.?
That could be a wild goose chase all of its own so unless you have
reason so suspect its motives, I think the sleeping dog principle applies.
Graham
On 28/05/2020 9:43 am, ciclista41 via groups.io wrote:
Hi Graham,
I try to treat people that way, too. After my brief adventure with C1091 and C1093, I'm doing the same with tantalum caps in this scope.
The leads on this tantalum are not symmetrical to the body. If you look at
them as legs on a body, one seems to have a knee bent out to the side rather
than dropping straight to the floor. There is a + sign printed closer to that
leg. I'm guessing that's the positive lead. The through holes they came out
of have a square trace pad and a round trace pad. I'm guessing these are to
guide polarity. I think the positive leg went to the square, while the
negative went to the round, but I'm not absolutely sure of that.
Confirmation? Is this a standardized thing?
At /g/TekScopes/photo/247625/0?p=Created,,,20,2,0,0, you'll
see an even more colorful one I found on my A9 board. Who knew these scopes
were wearing jewelry when no one was looking?
According to this chart:
, that's
a Red=2, Violet=7, Grey=.01 multiplier, Green = 16V.
So that's .27μF, right? But the manual says this is a 196D275X9050JA1 or a 290-0573-00. The latter is listed in the Tektronix Common Parts Catalog as
2.7μF, 50V. What am I not getting?
Bruce
On Wed, May 27, 2020 at 07:40 AM, VK1GVC wrote:
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.
|
A quick question for the group. I have a 2465b and have found a p6139a locally in good condition. Is this probe a good match for my scope?
Dimitris Theonas
|
Raymond Domp Frank