Date   

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


Re: 475 questions

ciclista41@...
 

Albert,

Thanks for that link!

Sorry, what's "exp" in the second equation? I understand the basic idea. Measure the time to discharge the capacitor given a known initial charge and the known rate of discharge for a healthy capacitor. If the time is too low, the capacitor is unable to properly acquire or hold a change, and needs to be replaced.

Bruce


Re: TM500 Tester

Errick
 

Thanks for the update! I can't wait to see all of the details of the unit and see one on my bench working.


Re: 475 questions

ciclista41@...
 

Well, I pulled the CR1412 rectifier from the board--piece of cake with the ZD-985. I don't know what precipitated the failed caps, or if they just went bad on their own. But with the negative probe of my diode tester on the Tacklife on the positive pin of the rectifier, I got .445V on each of the center pins and .885V on the negative pin from the positive probe. Comparing that to another good rectifier I had out of circuit (values were about half of what I got on the CR1412) I got similar results. So the rectifier tests as good and I don't know how it could have precipitated the cap failure.

I have not figured out how to get to pins 14 and 16 of the transformer. They really packed things in tight on this scope!


Re: Tek 2710 SA error: Unable to delete files at startup

WB6GHK
 

alfa beta,

Google is reporting the links you provided are pointing to "file is in owner's trash"
Could you please bring them back to life/

Thank you!


Re: 576 collector supply issues

Eric
 

And If not the breaker check the Variac. The collector supply is wall -> Breaker -> Variac - > T300 after T300 it gets a little weird also be very careful in there the 1500V is exposed when you have 115 on T300.

On 5/26/2020 3:55 PM, Martin Whybrow wrote:
I'm repairing my newly acquired 576, it doesn't have any voltage on the collector supply whatever settings I use. I've checked and repaired the interlock switch on the safety box, but still no luck. I'm now starting near the beginning and have checked T300 and there is no 115V supply on it. I need to go back to K323 which enables the supply to the transformer, but I can't locate it; the manual is not one of Tek's finest and it doesn't appear to show the location of several major parts! Can anyone tell me where it's located?


Re: 576 collector supply issues

Ed Breya
 

Before digging too deep, check the circuit breaker button to make sure it's not popped, and reset it if it is. It's on the deck, right above the variac. If you just got it, it's possible someone before may have overloaded it.

Ed


Re: 576 collector supply issues

Bob Koller <testtech@...>
 

Remove the bottom cover, there are relays accessible from there.


576 collector supply issues

Martin Whybrow
 

I'm repairing my newly acquired 576, it doesn't have any voltage on the collector supply whatever settings I use. I've checked and repaired the interlock switch on the safety box, but still no luck. I'm now starting near the beginning and have checked T300 and there is no 115V supply on it. I need to go back to K323 which enables the supply to the transformer, but I can't locate it; the manual is not one of Tek's finest and it doesn't appear to show the location of several major parts! Can anyone tell me where it's located?


Re: 475 questions

Colin Herbert
 

Well, someone was having a "Friday afternoon" time when all this was done, because my 475A manual (070-2162-00, Rev. D, Sept 1979, if any of that is significant) shows the tolerance of 290-0523-00 as 20%. That would fit in with an aluminium electrolytic, I think. Maybe the 6% tolerance is more typical of a tantalum cap? Dunno, it beats me.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Michael W. Lynch via groups.io
Sent: 26 May 2020 17:09
To: TekScopes@groups.io
Subject: Re: [TekScopes] 475 questions

Probably a dipped Tantalum cap? Cannot verify, since I do not have my 475A opened up at the moment.<
Curiosity got the best of me, so I went to the TEK Common Parts Manual for Capacitors and confirmed my statements above,

Here is what TEK shows for the specifications of 290-0523-00:

"ELECTROLYTIC, TANTALUM (Dry)"

2.2uF 20V 6% .175" dia x .375" Long x .155" Lead spacing (radial cap) and it is a dipped style cap (Type 1).

Ref. Pg 13-16 of the Common parts Catalog.

--
Michael Lynch
Dardanelle, Arkansas


Re: TM500 Tester

Michael W. Lynch
 

Bob,
This is great.  Another project for me to build. 

Michael Lynch 479-226-0126 Home Phone479-477-1115 Cell Phonemlynch001@excite.commlynch002@gmail.commlynch003@yahoo.com

On Tuesday, May 26, 2020, 11:01:47 AM CDT, robeughaas@gmail.com <robeughaas@gmail.com> wrote:

I am working to finish the firmware and hope to have it out in a couple of weeks. The vintageTEK Museum will publish the circuit board layouts and schematics in KiCad and the firmware source code. We will also make programmed processors available. The design is entirely contained in a single-wide TM500 module -- no external load resistors. A "teaser" video is here:  https://youtu.be/YLdaMePWttI   This version has a 16x2 display. I have since changed over to a 20x4 display.

--
Bob Haas


Re: TM500 Tester

Eric
 

Bob,

    This is great I cant wait for these to be available. Looking forward to this one.


Eric

On 5/26/2020 12:00 PM, robeughaas@gmail.com wrote:
I am working to finish the firmware and hope to have it out in a couple of weeks. The vintageTEK Museum will publish the circuit board layouts and schematics in KiCad and the firmware source code. We will also make programmed processors available. The design is entirely contained in a single-wide TM500 module -- no external load resistors. A "teaser" video is here: https://youtu.be/YLdaMePWttI This version has a 16x2 display. I have since changed over to a 20x4 display.


Re: 475 questions

Michael W. Lynch
 

Probably a dipped Tantalum cap? Cannot verify, since I do not have my 475A opened up at the moment.<
Curiosity got the best of me, so I went to the TEK Common Parts Manual for Capacitors and confirmed my statements above,

Here is what TEK shows for the specifications of 290-0523-00:

"ELECTROLYTIC, TANTALUM (Dry)"

2.2uF 20V 6% .175" dia x .375" Long x .155" Lead spacing (radial cap) and it is a dipped style cap (Type 1).

Ref. Pg 13-16 of the Common parts Catalog.

--
Michael Lynch
Dardanelle, Arkansas


Re: TM500 Tester

 

I am working to finish the firmware and hope to have it out in a couple of weeks. The vintageTEK Museum will publish the circuit board layouts and schematics in KiCad and the firmware source code. We will also make programmed processors available. The design is entirely contained in a single-wide TM500 module -- no external load resistors. A "teaser" video is here: https://youtu.be/YLdaMePWttI This version has a 16x2 display. I have since changed over to a 20x4 display.

--
Bob Haas


Re: 475 questions

Michael W. Lynch
 

All:

I am betting that the 475 manual is in error stating that these are ceramic caps, I have 475 and 475A manuals open side by side. Both manuals show C1091 and C1093. Both manuals show the same part number for both items.

C1091 and C1093 = TEK P/N 290-0523-00

The 475A manual additionally calls this part out correctly as a 2.2 uF 20v Electrolytic capacitor, manufactured by SPRAGUE with a MPN of 196D225X0020HA1. If you look at the SPRAGUE part number, it is clear that this is a 20V part not 350V part.

Looking at the schematic for the 475, there would be no reason to use a 350V cap on the -8V or the +5 V supply rails. These two (C1091 and C1093) are definitely polarized caps for decoupling or filtering those supply rails at the board.

Since the 475 and 475A are identical in this area of the circuit, I am confident that the 475 manual shows the wrong Voltage and Type for that cap. The 475A manual calls out the correct part.

Probably a dipped Tantalum cap? Cannot verify, since I do not have my 475A opened up at the moment.

Sincerely,

--
Michael Lynch
Dardanelle, Arkansas


Re: 475 questions

VK1GVC
 

Bruce, don't be shy about replacing suspect components while you have
access, think of it as insurance.

As for lack of trace, I agree that there could easily be more faults yet
to be found elsewhere but no point in even thinking about that until you
have all power supply rails present and correct within specification. 
So once you knock the +50V fault on the head, read through the alignment
procedure until you find where it specifies exactly what these voltages
should be and adjust accordingly.  That will be a big step for progress.

My copy of the 475 manual shows C1091 and C1093 (p6-7 of elec parts
list) as 2.2uF, ceramic, 350V and the schematic of A7 shows them as
2.2uF and polarised.  I'll stick my neck out and invite correction by wiser persons than I, but I don't ever recall seeing a polarised ceramic
capacitor so that's a bit odd, as is the 350V rating. Clearly their
purpose is filtering those 2 incoming supplies to the A7 board and 2.2uF
is reasonable for that and it might not even matter much if these
capacitors were ceramic or tantalum.  If you were able to take a
close-up pic of these caps and post a link to the image in a future
email then I'm sure someone will be able to identify it.  (Now wouldn't
attachments be useful for that?? ;-))  Anywayzez, Dan's analysis of
these earlier is comprehensive and provides guidance for testing.  And
if in doubt, swap 'em out!

Graham

On 26/05/2020 2:42 pm, ciclista41 via groups.io wrote:
Hi Graham,

Very encouraging! Thank you! I'll cross my fingers that your reasons 1, 2. and 3 hold true and I'll be finished when the caps go back in.

Since I have not seen any trace on this scope, I have no idea if there are issues beyond the power supply. However, I'm fairly certain the C1091 and C1093 caps are bad. Since they are only accessible when the A9 board is off, as it is now, I think now's the time to change those. Still confused as to whether those are ceramic (as my manual says), or tantalums, as I thought those were the common culprit for so many issues. When I search for tantalum capacitor and click on images, what comes up is just what these look like--glossy, bright colors, looking dipped! A similar search for ceramic capacitors shows a few that look somewhat similar, but most look more like rubber covered disks. So could my manual be wrong, or did Tektronix later change the specs to ceramics from tantalums? Or vice versa? My copy of the manual is a scan of a paper one that shows updates through Ser. #B070000, while mine's B287863. I could not find a single reference to a tantalum capacitor in the entire manual.

Bruce



--
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Re: Tek 4041 GPIB Controller

Monty McGraw
 

Dennis,

I added a Tektronix 4041 photo album with photos of my 4041 running the System Verification tape.

https://groups.io/g/TekScopes/photo/247590/5?p=Created,,,20,2,0,0

Monty


Re: 475 questions

Albert Otten
 

Hi Bruce,

I was teasing you when I only gave the mathematical expression. You're right about the sine wave background but a calculus approach is more straightforward than a geometrical approach. It's all about the ratio of average absolute value and rms (root-mean square) value. In AC mode the multimeter responds to the average absolute value but has to display the rms value. Some derivations are here https://www.electronics-tutorials.ws/accircuits/average-voltage.html and in their rms tutorial.

When you still want to test those big caps you can also use mathematics. Suppose you have a 5000 uF cap, hook your voltmeter across the terminals, charge the cap to 9 V with a battery and then discharge the cap via a 2 k resistor. The voltage should decrease rather slow with a time constant RC = 0.005*2000 s = 10 s; v(t) = v(0)*exp(-t/10s). After ln(2)*10 s = 7 s the voltage should read 4.5 V.
If the decay is (much) faster then likely the capacitance is insufficient, or there is a too large leakage current.

Albert

On Tue, May 26, 2020 at 02:32 AM, <ciclista41@yahoo.com> wrote:


Hi Albert,

Yup, 2.22 is ~ pi/√ 2! And I did not know that, but I thought the
consistancy of the ratios between those measurements on each rail might
indicate something to somebody, and you were the one! Very interesting
observation.

My trigonometry is rusty, but maybe I'll look into the math behind this more
deeply when I don't have such a steep learning curve going, anyway. My guess
is that this has something to do with the sine wave and the fact that pi is
derived from the circumference of a circle and 1/√ 2 is the sine of the unit
circle at 45° (1/(4pi) radians). Since the sine wave is what we use to
describe the oscillation of voltage with respect to time in AC and is also the
graph of the values of the sine of an angle as it goes through the 360° (2pi
radians) of a full circle (1 Hz), it has to make sense there, somewhere! My
calculus is incalculably rustier than my trigonometry, given that I never had
the opportunity to teach calculus in my entire career, but it could also
derive from the derivative of the sine function. ;-)

Bruce


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