Test Equipment Anonymous (TEA) group therapy thread

[Saskia]

argl.
Trip to Reichelt 2 days ago, pulled a portable Scopemeter, but alas it is not booting.
did take a bloody zbox PC along, should not have done it, but, ...

and did have a water leak in the house with the flat that I just sold.
I'm still responsible for that, as I still carry the risk until transfer of ownership is complete.

FML ...
 

[TERRA Operative]

The Tek AWG510 Arbitrary Waveform Generator turned up today, it boots ok so far.
I'll update the software tonight and have a play with it. Might stick a couple CF cards in to replace the clockwork disk and the MASSIVE 10Mb (yes, 10 Megabyte.....) SSD for more and faster storage.

I'll keep this one until a higher spec unit (like a 600 or maybe a 700 series unit) pops up.

[med6753]

Around these parts that's considered a "starter" set. I have 12 Flukes. 3 are frequency counters, the balance DMM's. 25 pieces of Tektronix gear and that doesn't include plug-in units. I'm a little light on hp gear. Only 4. I need to step up my game here.

So yes, you don't have a problem. 

It’s only been a few months and it was winter time which is kinda lean for me. I have a side gig where I can make a bunch of mad money from spring to late fall. The pile will grow.

Well don't be a stranger. We're always interested in new members and their gear and purchases. 

[Ice-Tea]

argl.
Trip to Reichelt 2 days ago, pulled a portable Scopemeter, but alas it is not booting.
did take a bloody zbox PC along, should not have done it, but, ...

and did have a water leak in the house with the flat that I just sold.
I'm still responsible for that, as I still carry the risk until transfer of ownership is complete.

FML ...
 

Which one? I have some experience. 

[Peter_O]

Tried to find the analog remote control connector fitting into the 7-Pin socket on the right side of the large output connector.
The manuals seem to give no spec or source.

Any hint is welcome.
Same for the 4pin digital connector above.

Looks like Phoenix Contact MSTB series connectors.

Yeah, deffo Phoenix Contact. I'm not going to confirm or deny your suggested part numbers because digging through PC's website/catalogues gives me headaches.

I will however suggest finding the HP service manual for it because sometimes you get lucky and they have a real manufacturer's part number as well as the internal HP part number.

We have the same series psu at work, I had the service manual available from keysights website, to hand. It only shows a HP part number no manufacturer p/n, so the RS or phoenix part is an educated guess

Thx for the input. Yes I checked all the manuals and there is no info about the original part.
I found an even cheaper source. Anyhow, it will be <20 Euros incl. shipment for some of these. I will just give it a try and come back. Will take some time, as I will wait for the shopping list to get longer. :-)

[Vince]

So I must replace them. Tempco wise, should not be a problem, as schematic reads 1,050 ppm... which is... atrociously crap ?!

1,000ppm when any cheap metal film is 50ppm ? I guess in th '60s 1,000ppm was good, and the Allen Bradley carbon composition were even worse ?...

In the 1k-10k value range even the old carbon composition resistors didn't have temperature coefficients that bad. However, higher value composition resistors >100k did have temperature coefficients of that order.

It could be that these resistors are specified as having a certain temperature coefficient as part of a temperature compensation scheme. The fact the designer took the trouble to annotate the temperature coefficient on the schematic indicates that it was considered a critical parameter and not just a side effect of using cheap resistors.

Hmmm OK. So they are not low tempco... they are custom tuned tempco, it's much worse... that means I will never be able to buy / find suitable replacements ! 

So I would have to design a complete new replacement board to produce that 4.000V Vref 

[TERRA Operative]

So I must replace them. Tempco wise, should not be a problem, as schematic reads 1,050 ppm... which is... atrociously crap ?!

1,000ppm when any cheap metal film is 50ppm ? I guess in th '60s 1,000ppm was good, and the Allen Bradley carbon composition were even worse ?...

In the 1k-10k value range even the old carbon composition resistors didn't have temperature coefficients that bad. However, higher value composition resistors >100k did have temperature coefficients of that order.

It could be that these resistors are specified as having a certain temperature coefficient as part of a temperature compensation scheme. The fact the designer took the trouble to annotate the temperature coefficient on the schematic indicates that it was considered a critical parameter and not just a side effect of using cheap resistors.

Hmmm OK. So they are not low tempco... they are custom tuned tempco, it's much worse... that means I will never be able to buy / find suitable replacements ! 

So I would have to design a complete new replacement board to produce that 4.000V Vref 

LM317... 

[Messtechniker]

I remember having seen a circuit somewhere
for a variable tempco resistance.
Cannot find it at this moment.

[Vince]

I remember having seen a circuit somewhere
for a variable tempco resistance.
Cannot find it at this moment.

Wow, that's an interesting concept ! I am curious to see that... maybe with some Googling...

[Vince]

So I must replace them. Tempco wise, should not be a problem, as schematic reads 1,050 ppm... which is... atrociously crap ?!

1,000ppm when any cheap metal film is 50ppm ? I guess in th '60s 1,000ppm was good, and the Allen Bradley carbon composition were even worse ?...

In the 1k-10k value range even the old carbon composition resistors didn't have temperature coefficients that bad. However, higher value composition resistors >100k did have temperature coefficients of that order.

It could be that these resistors are specified as having a certain temperature coefficient as part of a temperature compensation scheme. The fact the designer took the trouble to annotate the temperature coefficient on the schematic indicates that it was considered a critical parameter and not just a side effect of using cheap resistors.

Hmmm OK. So they are not low tempco... they are custom tuned tempco, it's much worse... that means I will never be able to buy / find suitable replacements ! 

So I would have to design a complete new replacement board to produce that 4.000V Vref 

LM317... 

So much for the tempco ! 

I guess a modern adjustable Zener diode, a mid-range Vref chip ... accuracy is irrelevant as it will be trimmed/adjusted anyway. Only the tempco is relevant I think...

Zero experience designing that kind of stuff.. I guess now is the time 

EDIT : Oh, that must have been sarcasm on your part for sure, sorry .... 

[Messtechniker]

Maybe this is a starting point::
https://www.electronicdesign.com/technologies/components/article/21764866/whats-all-this-tempco-stuff-anyhow

A bit more here, for the sake of completness: simply search for
"Dial-a-Tempco Exponential Converter"

[TERRA Operative]

EDIT : Oh, that must have been sarcasm on your part for sure, sorry .... 

  

Yeah, an LM317 would give you 4V, but the stability would be questionable.

[BU508A]

EDIT : Oh, that must have been sarcasm on your part for sure, sorry .... 

  

Yeah, an LM317 would give you 4V, but the stability would be questionable.

a LM399 on the other hand¹ ...

 

¹together with a high precision and stable resistor divider network

[med6753]

EDIT : Oh, that must have been sarcasm on your part for sure, sorry .... 

  

Yeah, an LM317 would give you 4V, but the stability would be questionable.

Don't laugh. An LM317 might get you real close with a precision divider and a 10 turn trim pot to set the voltage. Yea, stability might be an issue until it warms up and settles. Might be worth a try. Would be cheap and easy. 

Edit...or how about a high stability LM723?

[TERRA Operative]

Would get the meter working for a couple dollars at least, and if it does prove to be stable enough with the limited number of digits and all, well, there's nothing more permanent than a temporary fix that works.

I vote to try it for the fun of it. 

[AVGresponding]

EDIT : Oh, that must have been sarcasm on your part for sure, sorry .... 

  

Yeah, an LM317 would give you 4V, but the stability would be questionable.

Don't laugh. An LM317 might get you real close with a precision divider and a 10 turn trim pot to set the voltage. Yea, stability might be an issue until it warms up and settles. Might be worth a try. Would be cheap and easy. 

Edit...or how about a high stability LM723?

Cue my first project with the multiturn pots and knobs...

[Vince]

OK I have made up my mind.

Trying to recreate a resistor with the same weird tempco is too difficult to get right. I would never be sure that it restored proper operation of the original design, because I am not competent enough.

I think it's easier to start from a blank sheet and do an entire new replacement board with a modern Vref. This way I control everything, use known parts with knows specs, available datasheet etc.
It's also a marvelous excuse/opportunity to do a little bit of design, use a Vref which I have never done before, and of course give me some more training on Kicad, which I need. Every opportunity to do design little boards on Kicad is good to take here. Plus, it will look cleaner/tidy once done, that trying to Frankenstein the old board.
Plus, I find it cool to go the extra mile and design custom stuff to save an old TE. It's my way of showing it some love and respect...

So... new board it will be, with a "modern" little Vref chip.  Don't know much about them... luckily Dave Jones recently did a video on these : "Jelly bean Vref ".

While this is being sorted out, I can get the meter going as you said with any cheap and dirty solution. Hell I could simply replace these two resistors with regular modern carbon resistor and call it a day, should "work". Bye bye tempco, but at least it would allow that board to produce a voltage of appropriate value. Stable it won't be, but still, it's gonna be good enough to test the meter, allow to fully troubleshoot / repair it, etc.

Hell I could even just shove two wires in the meter and supply the Vref using my external lab power supply !

Yeah..... this meter is becoming more and more of a project !  It's a time to make its own thread before I am too far into it ! 

[mnementh]

Or you could try repairing the existing resistors, unless you butchered the bobbins too badly... 



mnem
Or you could take the easy route and hack your Cheap Chinese Voltage Standard... 

[Vince]

Yes butchered it has been. coils got cut when I cut the yellow "jacket", sadly.

Chinese Vref well yes I guess I could add a pot to it and use that as an external ref for the meter, why not...

[Ice-Tea]

EDIT : Oh, that must have been sarcasm on your part for sure, sorry .... 

  

Yeah, an LM317 would give you 4V, but the stability would be questionable.

Don't laugh. An LM317 might get you real close with a precision divider and a 10 turn trim pot to set the voltage. Yea, stability might be an issue until it warms up and settles. Might be worth a try. Would be cheap and easy. 

Edit...or how about a high stability LM723?

Cue my first project with the multiturn pots and knobs...

Don't laugh with the LM317. It's pretty much the only high(er) voltage LDO that is available for space projects.

[mnementh]

What do you mean I have a problem? I don’t have a problem. You’re the one with a problem.

I only had the MD78 in December. This is just the Fluke meters I own. Doesn’t include some other equipment.

I’ve held off buying vintage stuff. Only because I’m in the process of moving. Once I’m settled in though I’m going old school analog Fluke equipment.

So... this is just what you keep in your road bag, right RoadDog...? 

Oh, and welcome to the nuthouse! We look forward to seeing your collection grow enabling you.

mnem

[med6753]

Vince, here's another alternative. Use your AD584-M set to 10V and divide it down to 4.000V.

This is a circuit I built up to check 3.5 and 4.5 digit DMM's that require 190mV, 1.9V, and 19V as their calibration sources. I had to use two AD584-M's in series because I needed 19V. You could take one of the basic circuits and play with the resistor values to get exactly 4.000V. The trim pots are 25 turn and the resistors are 0.1%.



 

[Neper]

Looks very much like the connectors which were common on electric kettles & "electric jugs" in Oz, prior to adoption of the modern type IEC connector.

Vince's connector was originally developed in Germany where it was known as a Kaltgeraetestecker, literally a cold appliance plug.

The variety for kettles and waffle irons was about twice as big, had a ceramic portion at the front and looks like this:

[Vince]

Vince, here's another alternative. Use your AD584-M set to 10V and divide it down to 4.000V.

Yes ! That's exactly what we have discussed a second ago with Dwagon above ! 

TEA is such a fast paced thread, these things happen ! 

Thanks for the schematic though.

[mnementh]

Yes butchered it has been. coils got cut when I cut the yellow "jacket", sadly.

Chinese Vref well yes I guess I could add a pot to it and use that as an external ref for the meter, why not...

Well, my point was why reinvent the wheel. Make a circuit that works using the Cheap & Cheerful China-Direct™ Vref, then once you have your meter working, or at least functional enuf that you know you're gonna stick with it til it does, then you can start shopping some AD584s and design your PCB based on the VRef, which is doubtless directly based on the dev example circuits in the AD584 datasheet.

Have fun!

mnem