Date   

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
 

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@...@gmail.commlynch003@...

On Friday, May 22, 2020, 7:19:15 PM CDT, Dennis Tillman W7pF <@Dennis_Tillman_W7pF> 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



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



Re: Update on my 7854 diagnostics project

 

Hi Ke-Fong-Lin,

I think Holger's solution of having them done by a PCB house was quite clever and it is inexpensive as well.

There are a lot of franchise stores that make inexpensive signs. A simple Google search I just made for "low cost signs" found thousands of them.
Most of these places might be surprised if you asked them if they could do holes or holes for individual keys.
But it might be worth searching for this capability since it will probably come in handy sooner or later.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Holger Lübben
Sent: Saturday, May 23, 2020 8:07 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Update on my 7854 diagnostics project

Hi!

The trick is: In this case the front panel is also a pcb ;-)

This board is 0.8mm thick, white soldermask and black silk screen.
Here is a closeup of one of my red & white ones:

http://w140.com/tekwiki/images/7/77/P7001_program_overlay_card.jpg

If you look closely you can see the copper borders under the silkscreen

There a two downsides:
1) You can't get inner holes with sharp corners - usually you have to deal with 3mm corners. Thats the reason why my 7854 keyboard overlay card has a big hole per keyboard row - compared to individual holes for each key on the original card
2) I've tried a local pcb manufacturer and one of those cheap chinese ones and both reuqire at least one pad on the pcb. Thats the reason for the two pads on my panels.

But beside from that: They are great and look even better in real world.

If you want to have professional front panels you can also use services like www.schaeffer-ag.de. That's one of the local german ones, but I think you'll find such a company in every country.

Holger






--
Dennis Tillman W7pF
TekScopes Moderator


Re: Tek power cables, older equipment

 

Hi Sean,
David Holland beat me to the punch. The air conditioner extension cords sold by Lowes are a perfect solution once you shave off the little nubbin on the female end next to where the D-shaped earth connector is. They come in many different lengths, they are inexpensive, and you can buy them in almost any hardware store beside Lowes.

I wish everything was this easy to replace on Tek equipment.

Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of David Holland
Sent: Saturday, May 23, 2020 10:14 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek power cables, older equipment

https://www.lowes.com/pd/PRIME-6-ft-3-Prong-Gray-Air-Conditioner-Appliance-Power-Cord/1002462146


Something like that works on my 184 & 106....

May have to trim off the little nubbin on the female end, but it works well enough...

David


On Sat, May 23, 2020 at 1:07 PM <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: Tek 7K flex extenders available again

 

It is great that we have members who are able to provide so many things that make maintaining our collections easier.

Hi Etienne, and anyone else who may want one of John's flexible extenders,
Please conduct these transactions directly with John.

Hi John,
If you can remember in the future, please contact interested parties off line even when you are contacted through TekScopes like Etienne did.

Thanks, Dennis Tillman W7pF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of John Griessen
Sent: Saturday, May 23, 2020 8:00 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 7K flex extenders available again

On 5/23/20 6:50 AM, evdsp39 wrote:
HI John,

I am very interesting to buy the 7k flex extender so plese tell me the cost included the shipping at this address :

COLISEXPAT - ref.276174
10, rue Eugène Hénaff
93000 - BOBIGNY
FRANCE
tel: 01.84.74.03.75 Mob : 06.76.40.32.22

I will pay by PAYPAL or AMEX card

Thank you for answer.

Etienne.
I sent you a paypal invoice.

--
John Griessen






--
Dennis Tillman W7pF
TekScopes Moderator


Re: 475 questions

Albert Otten
 

On Sat, May 23, 2020 at 10:39 PM, <ciclista41@...> wrote:


Are "low-homic" current sensing resistors different from any other resistor of
the same rating?
Oh no, not at all. Since you are a beginner with 'scopes I thought too quickly that you might also not have small value resistors handy.
BTW I don't have a 475 myself and I sold my 465 long ago. For fun I measured the +12V and -12V in my 454 (an earlier analog 'scope than the 465) and found 10-11 ohms at both supply lines. A near zero value is really strange.
BTW in case you don't have one yet, a stabilized variable DC power supply with variable current limiting is very useful. Not just as power source but also in fault seeking. For instance, you can feed one of the big filter caps with a few volts DC and measure (or read) the (leakage?) current drawn.

Albert


Re: 475 questions

ciclista41@...
 

Hi Albert,

Are "low-homic" current sensing resistors different from any other resistor of the same rating?

I checked my vast supply of components and found four 47K ohm resistors. By the way, that is my entire collection of components, unless you count various non-working or old devices on boards taken out of service before they quit working. I still have quite a few even though I took a load of that sort of thing to the city's special collection day for all sorts of recyclables when we moved from Tempe to Mesa about three years ago. Rather than buying new computers when better ones became available, I would hand the older motherboards down to my son, who would get an upgrade from his previous hand-me-down, and I would get the best I could of approximately 2-year-old technology at sale prices. That way, I could afford to "keep up." So, I have several motherboards from computers that my son no longer used, as well as the occasional computer power supply that no longer had the proper connectors for the new boards I got. Then, of course there are various obsolete routers, low baud dial-up modems, and some non-computer boards from appliances that quit or were replaced with improved ones. One of the reasons I ordered a powered solder sucker was to make cannibalizing these old boards for devices with which to build or repair new stuff. I'll see if I can find some low-homic resistors unless you tell me what you prescribe is something different.

Bruce


Re: Tek power cables, older equipment

@0culus
 

Thanks for the suggestions everyone! I think either the air conditioner cord or one of the adapters will be perfect for what I want.

Sean


Re: Tek power cables, older equipment

Eric
 

I make my own. The Leviton No. 5269 fit the frames with no modification. They fit, barely but it is not a force fit

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of sdturne@q.com
Sent: Saturday, May 23, 2020 1:08 PM
To: TekScopes@groups.io
Subject: [TekScopes] Tek power cables, older equipment

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