Test Equipment Anonymous (TEA) group therapy thread

[med6753]

Type 105: Successful power up. No smoke. But we do have some issues.

First issue. The critical -150V reference won't go any lower than about -160V. Line voltage related? Not sure yet. It's wired for 117V and my line voltage is typically 123V and higher. There's no wiring option for 125V. It could be something else and I'll check into it.

   

We do have a square wave and it looks decent. Until you go below approx 1kHz then it looks like crap. But it does look decent up to it's limit of 1MHz. But not worried about this until I solve the -150V reference issue.




The fan motor also has sloppy bearings and the shaft is pumping back and forth making a racket. I need to add some sort of sleeve.

Gonna let it cook for a while.

[tggzzz]

That's probably because you've never been rich enough to own Lemo connectors. Strictly not for the proles or Les Bourgeoisie, aristocrats only need apply. I've virtually only heard of them. I believe a rich gentleman once permitted me to touch one, for a minute.

With Lemo connectors, there is a certain tactile and visual pleasure of engineering being just right.

[tggzzz]

Have you seen the prices for Fischer connectors? Like the ones used in those Solartron DMMs?

And if that doesn't put you off, look at the minimum order value.

Group buys are definitely indicated!

[tggzzz]

We do have a square wave and it looks decent. Until you go below approx 1kHz then it looks like crap. But it does look decent up to it's limit of 1MHz.

Looks like CH1 is AC coupled

[ch_scr]

(...)

We do have a square wave and it looks decent. Until you go below approx 1kHz then it looks like crap. But it does look decent up to it's limit of 1MHz. But not worried about this until I solve the -150V reference issue.
(...)
Gonna let it cook for a while.

Looks good!
To bias the fan in one direction, sometimes a magnet with a small gap towards one face of the fan shaft is used.
Regarding the "tilting" of the square wave below 1kHz, have you tried to DC couple the scope input to exclude its influence?

[med6753]

(...)

We do have a square wave and it looks decent. Until you go below approx 1kHz then it looks like crap. But it does look decent up to it's limit of 1MHz. But not worried about this until I solve the -150V reference issue.
(...)
Gonna let it cook for a while.

Looks good!
To bias the fan in one direction, sometimes a magnet with a small gap towards one face of the fan shaft is used.
Regarding the "tilting" of the square wave below 1kHz, have you tried to DC couple the scope input to exclude its influence?

You know what? I am an idiot. Both you and tggzzz are correct. The scope was AC coupled.

 D'OH

DC coupled no more tilt. 

[david77]

That's probably because you've never been rich enough to own Lemo connectors. Strictly not for the proles or Les Bourgeoisie, aristocrats only need apply. I've virtually only heard of them. I believe a rich gentleman once permitted me to touch one, for a minute.

With Lemo connectors, there is a certain tactile and visual pleasure of engineering being just right.

Definitively. Same goes for other niche connector manufacturers. Spinner, Rosenberger, Souriau. All very nice. But if you have to ask the price, you can not afford them.

[Vince]

Type 105: Successful power up. No smoke. But we do have some issues.

First issue. The critical -150V reference won't go any lower than about -160V. Line voltage related? Not sure yet. It's wired for 117V and my line voltage is typically 123V and higher. There's no wiring option for 125V. It could be something else and I'll check into it.

Looking good so far ! 

However I don't understand why you are complaining that the ref voltage won't go lower than -160V ?! It's not supposed to go lower than that, or even get as low as -160V to begin with, it's supposed to HIGHER Med, HIGHER , at -150V !! 
If it can go as far as -160V then why can't you adjust it -150V ?

[med6753]

Spot check of the frequency meter against this 1912A. It is surprising accurate. There are individual adjustments for each range so it can be tweaked.






The reference has settled at -158.6V. I'm wondering if I should leave it as is and try to perform a calibration. 

[Vince]

Heating the outer sheath of a cable and stretching it is very bad practice.
I puts stresses ito the cable and can cause the inner conductor insulation to be pulled back over time resulting in exposed conductors. It's a complete bodge don't do it.

Interesting... perhaps you should tell Leviton this, as this process (aside from adding the heat-shrink when possible; that was mine) was their recommended practice with the hospital-grade plugs which were the only kind we were allowed to use to "fix" a power cord in the ISD AV lab where I got my start. This was literally taken from a flyer sent with the catalogs we ordered from.

If you're going with the "appeal to authority" argument it's traditional with respect to cabling to cite a NASA document or similar, not material that marketing stuffed in with a product catalogue. 

NASA ? Really ? The same NASA whose Engineers crashed a fancy expensive probe or rover on Mars because they can't freaking tell the difference between Metric and Imperial units ?! 

SURELY you need to come up with a better authority than that !!! 

If NASA told me to strip the wires by one cm.... I would forever wonder : "yeah that's what they wrote but... maybe they really meant to strip an inch not a cm... ".   

[med6753]

Type 105: Successful power up. No smoke. But we do have some issues.

First issue. The critical -150V reference won't go any lower than about -160V. Line voltage related? Not sure yet. It's wired for 117V and my line voltage is typically 123V and higher. There's no wiring option for 125V. It could be something else and I'll check into it.

Looking good so far ! 

However I don't understand why you are complaining that the ref voltage won't go lower than -160V ?! It's not supposed to go lower than that, or even get as low as -160V to begin with, it's supposed to HIGHER Med, HIGHER , at -150V !! 
If it can go as far as -160V then why can't you adjust it -150V ?

It's a matter of perspective. Even though it's a minus voltage I regard -160V "higher" than -150V. The adj pot is maxed out. If I turn it the voltage goes even "higher" upwards of -170V.

[ch_scr]

You know what? I am an idiot. Both you and tggzzz are correct. The scope was AC coupled.

 D'OH

DC coupled no more tilt. 

Everyone working alone has done stuff like this. If they say they don't, they lie.
Don't fret, you're not an idiot for it, its just the usual "missing the forest for the trees", it happens to everyone once in a while.
An colleague of an colleague once debugged one channel of a stereo-set for a better part of the day, until someone randomly walked by and put the fader back on center...

Edit:
They say an expert is someone who once already made all the errors in particular field 

[Vince]

The reference has settled at -158.6V. I'm wondering if I should leave it as is and try to perform a calibration.

Hmm.... I would try to fix that first, because it does not seem quite right. Your line voltage is not THAT far off compared to the transformer configuration, you should be able to easily adjust it to -150V regardless, I would think !  Maybe a tired tube or drifted resistor in the PSU section... have a look.

I mean, all my Tek  scopes run at at 245V instead of 220V and I always had plenty of adjustment range to set them to -150V.

[Vince]

Type 105: Successful power up. No smoke. But we do have some issues.

First issue. The critical -150V reference won't go any lower than about -160V. Line voltage related? Not sure yet. It's wired for 117V and my line voltage is typically 123V and higher. There's no wiring option for 125V. It could be something else and I'll check into it.

Looking good so far ! 

However I don't understand why you are complaining that the ref voltage won't go lower than -160V ?! It's not supposed to go lower than that, or even get as low as -160V to begin with, it's supposed to HIGHER Med, HIGHER , at -150V !! 
If it can go as far as -160V then why can't you adjust it -150V ?

It's a matter of perspective. Even though it's a minus voltage I regard -160V "higher" than -150V. The adj pot is maxed out. If I turn it the voltage goes even "higher" upwards of -170V.

Yeah I figured that's what you meant, but I am in a cheeky monkey mood right now ! 
OK I will behave now...

[Cerebus]

NASA ? Really ? The same NASA whose Engineers crashed a fancy expensive probe or rover on Mars because they can't freaking tell the difference between Metric and Imperial units ?! 

Hey, at least they got as far as Mars in the first place. How long was it after launch that Ariane 5 (principal designer - "Centre national d'études spatiales") exploded? Oh yes, 37 seconds due to a software fault. It's not only NASA that has experience in turning lots of money into lots of burning fragments.

[Vince]

TE time.

My WaveTek DM27XT  has developped a problem in the past months... the LCD is almost dead. Turning it on, would give a couple very faint segments to see... and that was on a good day.
Twisting the case firmly in the right direction would make the LCD come to life again, as good as new so... opened it up, and as I was removing the 4 screws that hold the LCD bezel onto the circuit board I realized hey wait a minute, one for the screws is MISSING ?! 

I guess it must have happened when I took it apart to show it to you when I got it 9 months ago. 

All my fault then. Found a screw in my 2.2kg screw box that I have not sorted yet... a long painful process then...

Now all fixed up and looking good. 

I love this little meter, well worn out cosmetic wise, but I don't care... I would have killed to have this puppy when I was a boy !
Plus... it's also the only piece of TE I have that can measure inductance ! So it's precious to me if just for that... below measuring an EMI coil marked at 2x49mH. It measures it at 51mH, good enough for me... it's not like coils are super accurate things anyway.. it probably is indeed closer to 51mH than the rated 49mH I bet !   Plus, there is 2 meters worth of test leads so maybe that adds some inductance as well...
I will trust my little meter more than the tolerance on an EMI coil ! 

So to sum it up :

1) Losing tiny screws when taking TE apart sucks....
2) Be super careful not to lose tiny screws when you take stuff apart that you care about....
3) Searching for a tiny screw in a 2.2kg box of screws is not fun --> I MUST sort this screw box ! 

I mean, they are all different so it's not about spending a life time characterizing each of them and give them each their own dedicated little box... that's unrealistic and silly.
No but... there must be a compromise to be found somewhere... Like say, sort them into broad categories. Broad enough that it does not require spending 2 years sorting nor end up using 154 different boxes, but narrow enough that it speeds up search time considerably, to a sane level.

I don't know, could start by sorting between machine screws and self tapers. Then subdivide by size : big, medium, small. Then a "miscellaneous" category to gather all the uncommon types, specific looking screws.  Then maybe another category for countersunk screws.
That would be a good beginning I think... any kind of sorting is better than no sorting at all I think ! 

[Vince]

NASA ? Really ? The same NASA whose Engineers crashed a fancy expensive probe or rover on Mars because they can't freaking tell the difference between Metric and Imperial units ?! 

Hey, at least they got as far as Mars in the first place. How long was it after launch that Ariane 5 (principal designer - "Centre national d'études spatiales") exploded? Oh yes, 37 seconds due to a software fault. It's not only NASA that has experience in turning lots of money into lots of burning fragments.

WHAT ?! Did I manage to trigger C !   

OK let's reply, I am in Dwagon mood right now ! 

At least the French didn't kill astronauts because they can't freaking figure out that the o-ring in challenger would shrink when cold, leak and badaboom !!

.. or kill more astronauts because they can't freaking be bothered to fix a heat shield on the Shuttle before re-entry : "yeah guys, it's gonna be fine, don't worry, we are NASA after all right ! 


But I hear you.... these tragedies could not possibly happen to us because well, we never had a shuttle to begin with 


But I don't care anyway, I am not into patriot BS at all, shit happens all the time to every body everywhere, it's just life ! 

[mansaxel]

If you think that is bad you have obviously never wired a high density LEMO or Hirose connector 

Given that I have not even ever heard these names you mention, I will have to trust you 

That's probably because you've never been rich enough to own Lemo connectors. Strictly not for the proles or Les Bourgeoisie, aristocrats only need apply. I've virtually only heard of them. I believe a rich gentleman once permitted me to touch one, for a minute.

"fischer" connectors want a word with you, Cerebus.

Especially the triaxial ones for TV camera work; easily 150+ EUR a piece 20 years ago, and required specialist tooling, of course. The assembly is more like plumbing, where several different wrenches are required to clamp the two isolated screens in, maintaining not only insulation between them, but also IP68 enclusure levels. 

Most people managed to fit one in about 45 minutes. My personal record is about 15 minutes, but that was after a grueling weekend in which we made 10 off 300m camera cables that were due to go out on a rental gig. 11mm cable, not the easy 8mm one. Luckily it was not the 14mm "bedea" direct-burial type that infested the Hahnenkammrennen slopes and similar places before SMPTE Lemo optical camera cable became the new standard:




I do think I've got an old electrickal Lemo here, yes, a 6-pin one, from a headset-equipped desktop phone made by Ericsson, to which a Sennheiser headset had been fitted. Hiroses are not even close in price or quality, but very finicky to solder, especially if you're supposed to shove a resistor and a small cap in them too, as is not uncommon when interfacing lavalier mikes to beltpack transmitters.

[tggzzz]

(...)

We do have a square wave and it looks decent. Until you go below approx 1kHz then it looks like crap. But it does look decent up to it's limit of 1MHz. But not worried about this until I solve the -150V reference issue.
(...)
Gonna let it cook for a while.

Looks good!
To bias the fan in one direction, sometimes a magnet with a small gap towards one face of the fan shaft is used.
Regarding the "tilting" of the square wave below 1kHz, have you tried to DC couple the scope input to exclude its influence?

You know what? I am an idiot. Both you and tggzzz are correct. The scope was AC coupled.

D'OH

DC coupled no more tilt. 

Been there, done that, got the T-shirt. As has every practicing electronic engineer.

[Ice-Tea]

Have you seen the prices for Fischer connectors? Like the ones used in those Solartron DMMs?

Why, yes. Turns out jamming a piece of wire in the socket is good enough for testing, thank you very much. Next up: triax.

[capt bullshot]

Got a few left overs of them, too:



Though not as sophisticated ones as Mansaxel has shown

[med6753]

I'll never see this again in my lifetime. Genuine OE Honda parts cheaper than aftermarket. Front brake rotors and pads. And best of all the rotors are made in USA, not in some cheap Chinese foundry.

[mnementh]

Wow... didn't think one could write so much about a 3 wire plug !     I don't understand half of it, will need to read it 3 or 4 times I guess.... yes pics would help here.. while you search for them, I will do my own research to figure out what the hell is this " polyolefin " that you are talking about...

Hey, buddy... we don't mind when you get all anal about our knobs, lovingly hand-crafted of PLA and hand-painted to the finest detail we can muster... now you get to hear it about how you fab cables. 

I couldn't find the pics I was thinking of... but I have a extra-long 90° IEC cord that I need but has the GND lug borked off, so here's how I do mine. I'll try and be as detailed as I can, so you can understand not only the technique, but the thought process as well.




PVC vs Polyolefin Heat-Shrink Tubing

There are two common types of heat-shrink tubing; PVC and polyolefin. Yes, there are oodles of specialty formulations, but when you're shopping heat-shrink tubing, most of the time the manufacturer will list these two primary product lines. PVC is the stiff, shiny, crunchy kind usually used to build battery packs. Polyolefin is the soft, flexible kind with a satin finish usually used for cable fab.




Getting Started

Here's the IEC cable I'm going to reterminate; I'll do the whole deal, as if I were color-coding as well. This "hospital-grade" plug is not best quality; probably why it has languished at the bottom of my Bin o' Cords for years. But it will do for this example. Note the order of the conductors on the cut end; they match the order of the terminals on the plug. I have seen molded plugs assembled to the end of the cable where the black and white are reverse order: Obviously, when your cable comes by the kilometer, you're going to assemble from the end the manufacturer gives you on the reel. 




Laid Out

Here I've laid out the heat-shrink and the outer housing. Note that I've moved everything a little extra far from the end to allow for "adjusting" the sheathing.




Skinning the Cable Safely

There are more ways to skin a cable than there are to skin a rabbit; this is how I prefer to do it when I have the time & tools and want to make extra-sure I don't nick the insulation on the inner conductors. I fully expect to get roasted on this one; I'm putting on my flame-proof jammies right now. 




Assembled Connector

Here the plug end is assembled; this one is relatively easy to keep the inner conductor tails properly short and still able to work with them. On this particular plug, the clamp is plenty far away that the tails could be even longer than this and still have proper contact area between clamp and sheathing.

What's important is to ensure that when you hold the plug and wiggle the wire, there is sufficient radius (it only needs to be a few mm) that it bends in the middle, not right where the copper wire clamps under the screw.

Next comes "adjusting the sheathing" using the process I described earlier; I'm just going to cut/paste here.

Once you've connected the wires, pull the cable through the housing such that you have ~500-1000mm to work with. Using your heat gun, heat the outer sheathing of the cable at the connector end such that it is hot to the touch, but not hot enough you that it starts to melt and you can leave fingerprints in it.

Now, grip the cable with the cold part in one hand (get a right proper "wanking for all yer worth" grip here  ) and the heated part of the cable in the other, then pull/slide that hand down the length of the hot part of the cable towards the just-finished connector. It usually does not take much force to make the outer sheathing walk down the individual wires such that your "too much too long tails" are again covered in the sheathing, and all nice and tidy again. Lay the cable out flat on your bench, and wait for the sheathing to cool completely.

If you've done your prep work correctly, the difference between "tails just long enough to work with" and "sheathing exactly where it needs to be for the clamp to work" is literally just a few millimeters. Do your best to learn to work with tails absolutely as short as you can deal with. 




First Layer of Heat-Shrink

Here I've applied the first layer of heat-shrink; I've "adjusted" the sheathing a little too far, so when I reheat for the 2nd layer of heat-shrink, I'm going to very gently adjust it back a few mm.




2nd Layer of Heat-Shrink

Here I've applied the 2nd layer of clear polyolefin heat-shrink and "adjusted" the sheathing back a bit just to where the wire bends in the middle of the radius again. As you can see, the conductor and insulation on the tails is not harmed; but net "adjustment" of the sheathing is probably at most ~2mm.




Tightening the Clamp

    This is a pet peeve of mine... so many times I'll see this kind of plug end where the clamp has been tightened down too far... sometimes even to the point of stripping out the plastic screw holes.  This runs the risk of crushing the cable to the point that conductors can cross... Just DON'T!




Finished

Here's my finished IEC cable. You can see the double heat-shrink strain-relief, and you can see the matching color-coding at the other end.

You may now critique to your heart's content.

mnem
 

[Cerebus]

"fischer" connectors want a word with you, Cerebus.

Tell them to bring money, lots of it, otherwise the butler will be saying "Sir, is not at home"*.

*OK, the cat will meow at them, but it's the same thing. And she has a tuxedo, ish.

[ch_scr]

(...)

You may now critique to your heart's content.

mnem
 

I guess it's more of a critique on the style of plug and less of your technique...
but: in Germany a properly terminated plug is made in such a way, that when excessive force pulls the conductors out from under the screws, the earth wire comes out last, because it is left a bit longer. Seems like in your plugs there isn't even space for that  Apart from that, I especially like the dual heatshrink strain relief and advice on how much to tighten the clamp. 
Edit: Also a professional would use crimped ferrules on stranded wire, but it's the US I guess