Date   

Re: This message has not been downloaded from the server.

Vince Vielhaber
 

Are you getting this when reading with your web browser or an email client?

Vince.

On 05/23/2020 08:02 PM, Craig Cramb wrote:
Dennis

Why do I get this error in some of the feeds on topics?

“This message has not been downloaded from the server”.

I will see several Post but randomly thru the conversation posts don’t show up.

Craig


Re: 475 questions

VK1GVC
 

Bruce, I think your next investment should be a good multimeter as those AC measurements are just plain NUTS!  It's fair to say that the RS Micronta is not the cutting edge of 2020 technology, and wasn't 30 years ago either, but if it's still good for troubleshooting DC vehicle electrics and other similar tasks then it still has its uses.  For measuring 'pure' AC voltages, ie an AC voltage without any DC bias, then it might be OK as well but I would urge you to check it - more below.  As for a better meter I'll leave that to USA members to advise as you will have different choices from us in AUS.  I have two Flukes and love them, and they're bombproof, but there's heaps of choice these days.  If you haven't got a meter which can measure capacitance then that would be useful too.

I searched for a schematic for your meter without success but I did find this one for a different model Micronta:
http://ansteckend.org.uk/info/micronta/Micronta_22-204A_range_doubler_multimeter_instructions.pdf

The schematic doesn't show any blocking capacitor in the AC volts measurement circuit and I suspect your meter may not have one either.  Here's a simple test to find out: Select a suitable low AC volts measurement range on your Micronta and measure the voltage of a battery such as 6V or 12V or whatever you have nearby.  If the meter has a blocking capacitor then it should read zero, if no blocking capacitor then it might read 1.3 to 1.5 times the expected DC voltage.

As an aside it might be worth CAREFULLY measuring your household AC mains with the Micronta on a suitable AC volts range and if the meter reads about 110V or 120V or whatever it should be, then at least that AC measurement range should be OK.

Another aside: ohms per volt.  A meter must(*) draw some current from the circuit being measured and in general the lower this current, the better, so it doesn't affect the measurements you are doing.  The 20,000Ω/V DC figure for your meter means that if for example you select the 10V DC range then the meter has a resistance of 10 x 20,000Ω = 200,000Ω across the measuring probes.  For measuring low voltage DC power supplies this is just fine; if you were measuring voltages in circuits where the currents are small and resistances are high then the meter could significantly affect the circuit you are trying to measure.  In general the more ohms per volt, the better.

Returning to the DC voltages you have measured on the capacitors and test points, and ignoring the AC measurements, I reckon that the 'raw' or unregulated DC voltages on all on the filter capacitors of all supplies exc the 50V are about right.  These are a bit higher than the intended regulated output voltage and that is entirely normal.  As others have pointed out, all the low voltage regulators use the reg +50V DC as a reference and if that's not correct then it will affect all of the others.  If I can distill a few key measurements you have reported:

+50V (UNREG) is 40V
+50V test point is at 37.5V
DC across C1414 ~ 45V

So there is something very wrong with 45V (or 40V?) across C1414 as this voltage must be higher than 50V for the 50V regulator to be able to work.  Why is it so?  My guess would be a faulty rectifier CR1412, cap C1414, or less likely C1412 or even T1400 (ouch).  The circuit around the 50V area is a cunning design to get two voltages out of one transformer winding (typical Tek!) so it's a bit harder to understand.

Also I suggest one more important voltage to measure: the AC voltage on the transformer across terminals 14 and 16 of T1400.  This should be about 40V AC so that when rectified by CR1412 there is, say 55V, across C1414.  If the AC voltage into the rectifier is low then there's more head-scratching to do.  If it's about 40V then I reckon that rectifier CR1412 and/or C1414 are most likely faulty.  But first it would checking your meter on one or more AC volts ranges so that you have confidence in what you measure.

Graham

(*) Yes there are ways of measuring voltages with bridges and nil current drawn but that's for another day.

On 24/05/2020 10:34 am, ciclista41 via groups.io wrote:
Graham,

Yeah, those readings made no sense to me, and when the AC was consistently between 2.2 and 2.3 times the DC, I figured something wasn't kosher.

I've got an old Radio Shack Micronta 22-291U, It says 20,000Ω/V DC and 10,000Ω/V AC. Not sure if that helps. I think it's at least 30 years old. Nothing in the manual about a blocking capacitor.

Open to suggestions for a better DMM. I'd like a good compromise between top-of-the-heap and price, but not leaning too heavily on price if the compromise is going to have me disappointed and needing yet a better one down the road. I get the impression that the Flukes tend to be more idiot proof, but there sure is a premium to be paid for that. I'd be open to a bench meter if that saved me some money, because I can do pretty well with what I've got when it comes to portability. You know, troubleshooting vehicle electrical problems and such.

Bruce

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Re: Tek power cables, older equipment

 

Hi Raymond,
It is a 3 prong MALE plug sticking out the rear of the instrument with a plastic shroud around it to prevent you from touching a hot connector.
There may be pictures of the connector on the back of the instruments Sean mentioned up on TekWiki so you could see for yourself what they look like. They were not un-common until the mid-1960s where the danger was more appreciated and where we switched to worldwide 3 prong power cords that adhered to standards like the IEC 60320 or NEMA power plugs which are also used in the US.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Raymond Cote
Sent: Saturday, May 23, 2020 3:21 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek power cables, older equipment

I dint have those types if scopes. What do they look like ? Picture would be nice

In matters of style, float with the current. In matters of Principle, stand like a rock. “. — Thomas Jefferson —

On May 23, 2020, at 12:07, "sdturne@q.com" <sdturne@q.com> wrote:

For instruments like the 114 pulse generator, 184 time mark generator, and more. Does anyone know of a good place to either get these power cables? I have one, that came with my Type 114. With a 184 on the way, I'd like to find another.

Thanks!

Sean







--
Dennis Tillman W7pF
TekScopes Moderator


Re: 475 questions

Harvey White
 

Ebay, unless they sell name branded (and known) parts, is likely to sell Chinese (not sure of the quality) parts.  In the case of a scope or older test equipment, I'd recommend going with known parts of known quality, which should postpone replacing the "ebay" parts when they fail.

All parts have a lifetime.  It depends on the stress the part is under and the kind of part.  Capacitors in power supplies have an AC current flowing through them due to the ripple in the supply. There's a spec for that.  Capacitors that run hot (even if just near hot components) have a reduced life.  Capacitors can be bought in various lifetimes:  1000 hours at 105 degrees C, 2000 hours, 4000 hours.  The more reliable, the more expensive.  Reduce the temperature and the lifetime goes up.  Since you don't know the environment in the scope, most will overbuy just to keep from replacing the part again.

I'd steer clear of ebay parts.  They are typically (if not a brand name) of lesser quality.  If a brand name, they may be forgeries.  I do use some connectors from amazon.com.  (ribbon connectors and jumpers).  They are of acceptable quality, but not the same quality as US made connectors.  For semiconductors, I stick to the vendors I have mentioned, although there are other industrial grade suppliers that are good.

I've done a bit of plumbing, but it's not my field.

An ESR tester is a good thing, it does point you at failed capacitors.  In circuit and out of circuit, though, are two different circumstances.

Harvey

I have used your offline composition method before. I just got lazy. Have been composing offline for any lengthy posts since losing that one.

Yes! I like plumbing analogies, as I have (too much) experience with plumbing, having almost replaced the entire plumbing system in my house this spring, both fresh water and drains. I moved to a 1970 house from a 1954 house, and had far less trouble with the 1954 plumbing in 18 years than the 1970 plumbing in two.

I'm still making my way through the manual and the electronics book. Maybe I should do more of that and less time on the forum, but this is more fun.

Your comments on component substitutions are just what I needed! Very helpful, thank you!

And thanks, also, for the additional sources for components. Ebay has selections of 500 caps of various values for under $15, but I don't know if I'd use most of them. For now, I'll order what I need with at least a few to spare, keeping in mind the higher quantity price advantage. And I'll familiarize myself with the older devices I have around here and decide which to attempt to fix and which to cannibalize. I assume most components will still be good, and I can test them more reliably as I pull them, but I'm less confident of older caps. I do have an ESR tester, though, so should be able to tell how bad they might be in spite of having capacitance within spec.

I am going to watch for surplus from local universities and colleges. I'm also still trying to find local Facebook groups that might become a similar resource.

Thanks again! I'll be referring back to your post!

Bruce




Re: OT Deoxit performance on extremely low level switches? OFF-list only

 

Hi Dave,
When you click on a post to read it (assuming you receive each post in a
separate email) you will see this line at the top like the one at the top of
your post as I was reading it just now:
TekScopes@groups.io; on behalf of; Daveolla <grobbins@netflash.net>

Sometimes, as in your case it is obvious what your address is. Other times
you have to do a little bit of guesswork.

This was what was at the top of Ed Breya's original post:
to:TekScopes@groups.io; on behalf of; Ed Breya via groups.io
<edbreya=yahoo.com@groups.io>

In this case you can guess what his email address is by simply removing the
equal sign Groups.io put in it to confuse bots.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Daveolla
Sent: Saturday, May 23, 2020 4:50 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] OT Deoxit performance on extremely low level
switches? OFF-list only

Sorry Ed this is on list, I couldn't find your email addy in your post. Dont
know if it mentions Deoxit but may be useful.
A google should find this,
What Designers Need to Know About Low Voltage Contacts.pdf
by Samuel Garte 1.415KB
If you cant find it I can send it you.

Dave

At 01:28 PM 5/23/2020, you wrote:
First, please respond directly to me only OFF-list, and only with
relevant info. I don't want to get off on another huge Deoxit
good/bad/whatever discussion, which has been covered many times. I
would just like any feedback or experience info on whether Deoxit would
help to improve mechanical switch contact performance used in very low
level circuits.

One of my projects involves boxing up some special transformers and a
switching system, for isolating and dividing down AC signals by large
factors (E-3 to E-6), down as far as the 1 nV RMS region. A fair number
of switching elements are needed to route and select various
transformer output taps to send to the single output connection. There
are two transformers to cover two frequency bands
10 Hz-1 kHz, and 1 kHz-100 kHz, and each has four outputs for the
decade dividing. The switching elements need to have as low an on
resistance (<< 1 ohm) as possible, and function well at extremely low
levels. Since this is an AC system, I'm not worried about Seebeck
effects, just the low level contacting ability. The primary sides of
the transformers are at more normal levels, so the switches there are
not critical.


I have all sorts of nice low level regular and Hg reed relays that
would do the job, but since the output side is to be isolated, to
minimize interference, it would be much better to do all the switching
passively with mechanical switches. This would avoid needing
electricity, and the proximity problems of having relay coils and
capacitance in the low level environment, and power supply and line
noise and ground loops (no power cord), or messing with battery power.
Especially, there would be no power transformer emissions to worry
about.

I have lots of mechanical switches of all sorts. I'd like to go with a
rotary wafer type to select the transformer taps and frequency ranges.
I have mostly standard Ag plated type contact ones and some Au ones. I
can usually build a switch from pieces for almost any arrangement.

Another, but quite complicated option is to use low level reeds
actuated by a mechanically driven magnet, but doing that would be a big
project in itself, so scratch that, unless a simple way pops up.
Another way is to make heavy analog switches with big MOSFETs, but
that's a lot of parts, a battery, and issues with capacitance and
crosstalk. So, good old mechanical switching seems the best way to go -
if only it can actually be done.

The big question then, is how to get a regular, environmentally exposed
contact to be usable in the nV region. Wetting the contacts with Deoxit
is the only practical thing I can picture so far. There is another
class of contact "protectors" based on synthetic oils, but I think I
need chemical action too, so these may not work - I'll have to
investigate that too.

So anyway, does anyone have experience or knowledge of how Deoxit would
behave for low level contacts? It may boil down to a "try it and see"
scenario, but it would be nice to have some info in
advance. OFF-list only, please.

Ed







--
Dennis Tillman W7pF
TekScopes Moderator


Re: 475 questions

Harvey White
 

If there is any voltage on the points being measured for ohms, you'll get some very odd readings.  If there's DC, you could even get a negative resistance.  If there's AC, the reading will not be stable and will vary above and below a mythical value.  If you're measuring a capacitor charging, the resistance will start low and then increase.

If you measure across a resistor and a semiconductor junction, the resistance may measure differently depending on whether or not the meter (and old analog meters likely do....) uses more than 0.6 volts to measure resistance.

In one case, you measure the forward conducting diode in parallel with the resistor.  In another, you measure the reverse biased diode in parallel with the resistor.

If you can use a voltage less than the forward drop of the diode, you're likely to get just the resistor since the diode isn't turned on.

Harvey

On 5/23/2020 7:53 PM, ciclista41 via groups.io wrote:
Albert,

R1478 which should be 3.6 ohms measures 3.2 on analog, 3.6 on digital.

R1468 which should be 0.6 ohms measures 0.7 on analog, 0.7 on digital.

So not far off. I do trust my analog more because it doesn't bounce around like the digital. In fact, I measured again just now with the digital, and could not get a reading above zero on either resistor, while the analog repeated the earlier readings. Pfft! I probably need a better DMM, but used Fluke 87 III's are about $100. Any suggestions?

Thanks,

Bruce



Re: This message has not been downloaded from the server.

 

Hi Craig,
I have no idea. I have never heard that anyone else gest this.
I will ask Groups.io if they can explain it. It may take a few days for an answer because of the holiday.
Dennis

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Craig Cramb
Sent: Saturday, May 23, 2020 5:03 PM
To: TekScopes@groups.io
Subject: [TekScopes] This message has not been downloaded from the server.

Dennis

Why do I get this error in some of the feeds on topics?

“This message has not been downloaded from the server”.

I will see several Post but randomly thru the conversation posts don’t show up.

Craig





--
Dennis Tillman W7pF
TekScopes Moderator


Re: 475 questions

ciclista41@...
 

Michael,

Yes, I'll be digging deeper with the suggested references. I will download the 465 manual. I think it may be time to get a hard copy of the manual for this thing. I can blow the diagrams up on the computer, but my attempts to print them out have not been reliably readable. I don't like being restricted to 8 1/2 x 11" paper and having to literally cut and paste to get a useful scale.

Ace Hardware is handy and they sell brass rod in various diameters. When I get these caps out, I'll have an idea of proper diameter and I'll either upset the short pieces to make them snug (wish I had a metalworking lathe, but I don't), and drill the lead hole with my drill press. I may need to find a Dremel drill press and Dremel, as I have done much more woodworking than electronics, and so my tools are much larger than the optimum.

I am a former bicycle racer--one of the best in Arizona in the mid 70's- early 80's. I competed around the US, Canada (BC only), northern Mexico, and New Zealand. Some thought that since I wasn't good enough to make a living at it, it was a waste of time. Some 40 years later, I don't regret it a bit! I developed the ability to suffer both mentally and physically. I learned that what one does today may not pay off tomorrow, but it will pay off in weeks or months. I discovered that it can be both fun and rewarding to push oneself past perceived limits toward actual limits far beyond, and even to expand beyond the initial actual limits. It helped get me though surgery, chemotherapy, and radiation treatments five years ago that were hellish. So yeah, I think I can handle some struggles with teaching this old dog some new tricks even though I'm well past my prime physically and at least some past my prime mentally. The encouragement and well wishes are always welcome, though!

Bruce


Re: 475 questions

ciclista41@...
 

Graham,

Yeah, those readings made no sense to me, and when the AC was consistently between 2.2 and 2.3 times the DC, I figured something wasn't kosher.

I've got an old Radio Shack Micronta 22-291U, It says 20,000Ω/V DC and 10,000Ω/V AC. Not sure if that helps. I think it's at least 30 years old. Nothing in the manual about a blocking capacitor.

Open to suggestions for a better DMM. I'd like a good compromise between top-of-the-heap and price, but not leaning too heavily on price if the compromise is going to have me disappointed and needing yet a better one down the road. I get the impression that the Flukes tend to be more idiot proof, but there sure is a premium to be paid for that. I'd be open to a bench meter if that saved me some money, because I can do pretty well with what I've got when it comes to portability. You know, troubleshooting vehicle electrical problems and such.

Bruce


Re: 475 questions

Leanna L Erickson <lle@...>
 

50 volts must be spot on before further trouble shooting.

On May 23, 2020, at 6:15 PM, ciclista41 via groups.io <ciclista41=yahoo.com@groups.io> wrote:

Hi again, Dave.

Here are the readings I just took across the test points:

DCV, then ACV

110 = 87 225

50 = 37.5 90

15 = 12 22.5

5 = 3.5 4.2

-15 = -14.2 32.5

-8 = -5.7 18.5

UNREG 50 = 40 102.5

105 = 7.5 20.5

Either I am measuring incorrectly or something is WAY off from expected, but from these readings, I'm not seeing evidence of which rectifier to focus on. Also, I thought AC measurements were supposed to be taken in series with the thing being tested, not parallel to them.

Bruce



Re: 475 questions

ciclista41@...
 

Harvey,

I have used your offline composition method before. I just got lazy. Have been composing offline for any lengthy posts since losing that one.

Yes! I like plumbing analogies, as I have (too much) experience with plumbing, having almost replaced the entire plumbing system in my house this spring, both fresh water and drains. I moved to a 1970 house from a 1954 house, and had far less trouble with the 1954 plumbing in 18 years than the 1970 plumbing in two.

I'm still making my way through the manual and the electronics book. Maybe I should do more of that and less time on the forum, but this is more fun.

Your comments on component substitutions are just what I needed! Very helpful, thank you!

And thanks, also, for the additional sources for components. Ebay has selections of 500 caps of various values for under $15, but I don't know if I'd use most of them. For now, I'll order what I need with at least a few to spare, keeping in mind the higher quantity price advantage. And I'll familiarize myself with the older devices I have around here and decide which to attempt to fix and which to cannibalize. I assume most components will still be good, and I can test them more reliably as I pull them, but I'm less confident of older caps. I do have an ESR tester, though, so should be able to tell how bad they might be in spite of having capacitance within spec.

I am going to watch for surplus from local universities and colleges. I'm also still trying to find local Facebook groups that might become a similar resource.

Thanks again! I'll be referring back to your post!

Bruce


Re: TM50X transistors

Michael W. Lynch
 

Dennis,
Ah!  That makes perfect sense now that you explained it like that.  My TM506 Rackmount did not have those type of holes.  It would have been nice if it did.

Thanks for the detailed explanation.

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

On Friday, May 22, 2020, 7:19:15 PM CDT, Dennis Tillman W7pF <dennis@ridesoft.com> wrote:

Hi Michael,
I should have been clearer. I was referring to the mainframes where the pass transistors were mounted on a PC Board of some kind. In some mainframes they were mounted on part of the chassis and a little 3 wire lead set was used to connect the transistor over to the PC Board. Those chassis mounted ones weren't a problem because the leads could go into the PCB in whatever order they needed to be in.

The later TM5xx PCBoards where the transistor leads were soldered directly into the board had 3 holes for the transistor leads. About 1/4" away was another set of 3 holes parallel to the first 3 holes. You could not miss a PCB that had this special arrangement of holes to accommodate whatever order the transistor's leads were in.. Those other 3 holes went to the all the other places the pass transistor had to go to. There was no connection between the first set of holes and the second set of holes until you inserted short jumpers between them. If your transistor's leads were in the right order you inserted 3 jumpers straight across from one set of holes to the other set. If you transistors leads were in a different order you inserted jumpers so they shuffled the leads into the correct order needed.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Michael W. Lynch via groups.io
Sent: Friday, May 22, 2020 12:53 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] TM50X transistors

On Fri, May 22, 2020 at 02:26 PM, Dennis Tillman W7pF wrote:

The pin out of the pass transistors changed when that happened. At one point Tek realized this would probably happen again and they modified their PC Boards with extra pads on the board so wire jumpers could be installed to adjust for >any orientation of the pins during manufacturing.<<
Dennis,

Any Idea when TEK might have started adding these pads that you speak of? I installed some new pass transistors in my RM506 and had to do some "creative" adaptations of the transistors that I was able to buy,  Perhaps I was simply not seeing these pads on my unit?  Or are these pads simply too obvious to overlook?

Thanks!

--
Michael Lynch
Dardanelle, Arkansas





--
Dennis Tillman W7pF
TekScopes Moderator


Re: 475 questions

VK1GVC
 

Bruce, I'll comment in a bit more detail later (if others don't beat me
to it) but your AC voltage readings are wayyyy off what I'd expect, off
the planet almost.  At a guess I'd expect a few volts, no more.  There
are also some subtleties about how AC voltmeters will read peak-to-peak
volts but that qn can wait for now.

I can't think of any fault in your 475 which could cause these readings
without a lot of smoke and mess so the next task is to work out why you
are getting these readings so let's start at the start: could you pls
tell the group the exact make and model of the meter you are using?  To
read AC ripple voltage your meter must have a blocking capacitor in
series with it and normally this cap will be switched in when you select
the AC volts range.  High readings suggest that this may not be the case
which is kinda odd, so best we look first at your meter.  Apologies if
you have posted this info earlier and I missed it.

Graham

I would have asked you to attach a pic of your meter ... if attachments
where permitted :)

On 24/05/2020 8:56 am, ciclista41 via groups.io wrote:
Hi Graham!

Thanks for your contributions and supportive words! Yes, what I have learned has mostly been internet sourced, including the book available at allaboutcircuits.com, but I am only at Chapter 6 of volume 1. I am picking up more from eevblog, various youtubers, and both TekScopes and TekScopes2. I did take both semesters of the University Physics intro (weed-out) course and passed them both, although I tried to do them in summer school, which worked for the first semester, but not the second, which was mostly on electromagnetism. I did okay in the calculus parts, but the fact that this was more than two decades after a weak foundation in both high school electronics and physics along with a full-time load as a half-time parent meant that my grasp was barely enough to pass the class the following fall semester. I was shocked that I was given a C, as I think I only got about 40% on the final exam. I did get an A in the one-credit-hour lab, which was the hardest I ever worked for a single credit in my life. As I mentioned in an earlier post, this new hobby is partly about fixing that less-than-satisfying part of my life.

Thanks for the advice about checking out other Tek 4xx manuals. I will try that. I am still struggling to get through the 475 explanations, but I did download "Troubleshooting Your Oscilloscope--Getting Down to Basics" from Tektronics last night. I expect it will be helpful in giving me a more systematic approach.

Your explanation of the full wave rectifier confirmed my correct understanding of that circuitry! That felt good, as I had not much clue about that a couple of weeks ago.

I have found no sign of overheating on any components, except for smoke residue on components under the "Warning High Voltage" aluminum shield, though no sign of any of them being bad. One exception: the two neon bulbs (still no idea what these are doing there) next to each other, DS1382 and DS1383 do not glow when the power is on.

Another observation I made last night was that after running the board for several minutes, I shut it off. I shorted the big caps for safety, but while C1462 gave me a good "snap" and C1472 gave me an even louder one, none of the other four held any detectable residual charge when shorting them. Neither did any of the caps under the aluminum shield.

Yes, you are right that I am confidently running the scope directly plugged into the wall, because nothing bad seems to happen. With the scope running, I get the following measurements:

DC across +50 to ground ~ 39V AC across the same ~ 87V

DC across C1412 ~ 65V AC across C1412 ~ 150V

DC across C1414 ~ 45V AC across C1414 ~ 103V

DC across C1442 ~ 20.5V AC across C1442 ~ 47V

DC across C1452 ~ 9.5V AC across C1452 ~ 21V

DC across C1462 ~ 12V AC across C1462 ~ 27V

DC across C1472 ~ 22.5V AC across C1472 ~ 51V

Each AC reading seems to be about 2.2 to 2.3 times the DC one. Not sure if that's what should be happening, but it was consistent, so the readings are probably correct even if the information isn't useful. Am I doing something wrong here? This doesn't seem to distinguish any of these sub circuits as being a culprit.

Sorry, no infrared camera available.

Bruce



--
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https://www.avast.com/antivirus


This message has not been downloaded from the server.

Craig Cramb
 

Dennis

Why do I get this error in some of the feeds on topics?

“This message has not been downloaded from the server”.

I will see several Post but randomly thru the conversation posts don’t show up.

Craig


Re: 475 questions

ciclista41@...
 

Albert,

R1478 which should be 3.6 ohms measures 3.2 on analog, 3.6 on digital.

R1468 which should be 0.6 ohms measures 0.7 on analog, 0.7 on digital.

So not far off. I do trust my analog more because it doesn't bounce around like the digital. In fact, I measured again just now with the digital, and could not get a reading above zero on either resistor, while the analog repeated the earlier readings. Pfft! I probably need a better DMM, but used Fluke 87 III's are about $100. Any suggestions?

Thanks,

Bruce


Re: 475 questions

ciclista41@...
 

Very interesting, Albert. I do have a variable switching power supply that will put out either constant voltage or constant amperage with 0-30V and 0-10A. I'll have to try that!
Bruce


Re: 475 questions

ciclista41@...
 

Hi again, Dave.

Here are the readings I just took across the test points:

DCV, then ACV

110 = 87 225

50 = 37.5 90

15 = 12 22.5

5 = 3.5 4.2

-15 = -14.2 32.5

-8 = -5.7 18.5

UNREG 50 = 40 102.5

105 = 7.5 20.5

Either I am measuring incorrectly or something is WAY off from expected, but from these readings, I'm not seeing evidence of which rectifier to focus on. Also, I thought AC measurements were supposed to be taken in series with the thing being tested, not parallel to them.

Bruce


Re: 475 questions

ciclista41@...
 

Hi Graham!

Thanks for your contributions and supportive words! Yes, what I have learned has mostly been internet sourced, including the book available at allaboutcircuits.com, but I am only at Chapter 6 of volume 1. I am picking up more from eevblog, various youtubers, and both TekScopes and TekScopes2. I did take both semesters of the University Physics intro (weed-out) course and passed them both, although I tried to do them in summer school, which worked for the first semester, but not the second, which was mostly on electromagnetism. I did okay in the calculus parts, but the fact that this was more than two decades after a weak foundation in both high school electronics and physics along with a full-time load as a half-time parent meant that my grasp was barely enough to pass the class the following fall semester. I was shocked that I was given a C, as I think I only got about 40% on the final exam. I did get an A in the one-credit-hour lab, which was the hardest I ever worked for a single credit in my life. As I mentioned in an earlier post, this new hobby is partly about fixing that less-than-satisfying part of my life.

Thanks for the advice about checking out other Tek 4xx manuals. I will try that. I am still struggling to get through the 475 explanations, but I did download "Troubleshooting Your Oscilloscope--Getting Down to Basics" from Tektronics last night. I expect it will be helpful in giving me a more systematic approach.

Your explanation of the full wave rectifier confirmed my correct understanding of that circuitry! That felt good, as I had not much clue about that a couple of weeks ago.

I have found no sign of overheating on any components, except for smoke residue on components under the "Warning High Voltage" aluminum shield, though no sign of any of them being bad. One exception: the two neon bulbs (still no idea what these are doing there) next to each other, DS1382 and DS1383 do not glow when the power is on.

Another observation I made last night was that after running the board for several minutes, I shut it off. I shorted the big caps for safety, but while C1462 gave me a good "snap" and C1472 gave me an even louder one, none of the other four held any detectable residual charge when shorting them. Neither did any of the caps under the aluminum shield.

Yes, you are right that I am confidently running the scope directly plugged into the wall, because nothing bad seems to happen. With the scope running, I get the following measurements:

DC across +50 to ground ~ 39V AC across the same ~ 87V

DC across C1412 ~ 65V AC across C1412 ~ 150V

DC across C1414 ~ 45V AC across C1414 ~ 103V

DC across C1442 ~ 20.5V AC across C1442 ~ 47V

DC across C1452 ~ 9.5V AC across C1452 ~ 21V

DC across C1462 ~ 12V AC across C1462 ~ 27V

DC across C1472 ~ 22.5V AC across C1472 ~ 51V

Each AC reading seems to be about 2.2 to 2.3 times the DC one. Not sure if that's what should be happening, but it was consistent, so the readings are probably correct even if the information isn't useful. Am I doing something wrong here? This doesn't seem to distinguish any of these sub circuits as being a culprit.

Sorry, no infrared camera available.

Bruce


Re: OT Deoxit performance on extremely low level switches? OFF-list only

Daveolla
 

Sorry Ed this is on list, I couldn't find your email addy in your post. Dont know if it mentions Deoxit but may be useful.
A google should find this,
What Designers Need to Know About Low Voltage Contacts.pdf
by Samuel Garte 1.415KB
If you cant find it I can send it you.

Dave

At 01:28 PM 5/23/2020, you wrote:
First, please respond directly to me only OFF-list, and only with relevant info. I don't want to get off on another huge Deoxit good/bad/whatever discussion, which has been covered many times. I would just like any feedback or experience info on whether Deoxit would help to improve mechanical switch contact performance used in very low level circuits.

One of my projects involves boxing up some special transformers and a switching system, for isolating and dividing down AC signals by large factors (E-3 to E-6), down as far as the 1 nV RMS region. A fair number of switching elements are needed to route and select various transformer output taps to send to the single output connection. There are two transformers to cover two frequency bands 10 Hz-1 kHz, and 1 kHz-100 kHz, and each has four outputs for the decade dividing. The switching elements need to have as low an on resistance (<< 1 ohm) as possible, and function well at extremely low levels. Since this is an AC system, I'm not worried about Seebeck effects, just the low level contacting ability. The primary sides of the transformers are at more normal levels, so the switches there are not critical.


I have all sorts of nice low level regular and Hg reed relays that would do the job, but since the output side is to be isolated, to minimize interference, it would be much better to do all the switching passively with mechanical switches. This would avoid needing electricity, and the proximity problems of having relay coils and capacitance in the low level environment, and power supply and line noise and ground loops (no power cord), or messing with battery power. Especially, there would be no power transformer emissions to worry about.

I have lots of mechanical switches of all sorts. I'd like to go with a rotary wafer type to select the transformer taps and frequency ranges. I have mostly standard Ag plated type contact ones and some Au ones. I can usually build a switch from pieces for almost any arrangement.

Another, but quite complicated option is to use low level reeds actuated by a mechanically driven magnet, but doing that would be a big project in itself, so scratch that, unless a simple way pops up. Another way is to make heavy analog switches with big MOSFETs, but that's a lot of parts, a battery, and issues with capacitance and crosstalk. So, good old mechanical switching seems the best way to go - if only it can actually be done.

The big question then, is how to get a regular, environmentally exposed contact to be usable in the nV region. Wetting the contacts with Deoxit is the only practical thing I can picture so far. There is another class of contact "protectors" based on synthetic oils, but I think I need chemical action too, so these may not work - I'll have to investigate that too.

So anyway, does anyone have experience or knowledge of how Deoxit would behave for low level contacts? It may boil down to a "try it and see" scenario, but it would be nice to have some info in advance. OFF-list only, please.

Ed


Re: Tek power cables, older equipment

Raymond Cote
 

I dint have those types if scopes. What do they look like ? Picture would be nice

In matters of style, float with the current. In matters of Principle, stand like a rock. “. — Thomas Jefferson —

On May 23, 2020, at 12:07, "sdturne@q.com" <sdturne@q.com> wrote:

For instruments like the 114 pulse generator, 184 time mark generator, and more. Does anyone know of a good place to either get these power cables? I have one, that came with my Type 114. With a 184 on the way, I'd like to find another.

Thanks!

Sean


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