Test Equipment Anonymous (TEA) group therapy thread

[med6753]

Here's a question for your smart guys...

Background: I have one of those cheap Chinese inverter boards that take 9-12VDC and steps it up over a wide adjustment range up to almost 300VDC. I currently have it set to 190VDC as that is the most common set point used to calibrate the 200V range on most DMM's. And in fact on the 2465 DMM it is an absolute calibration constant requirement. The problem with that board is that it's unregulated and bounces all over. One minute it's 188V and another 192V. So I've been looking for some way to regulate it and I found this which looks promising....

https://www.mouser.com/datasheet/2/268/20005399A-909415.pdf

The trouble is, how do I calculate the values of R1 and R2? It doesn't seem to give enough information other than one example for 5VDC. But I want 190.0V. Maybe I'm missing something. I sure would like to know what resistance values to start with and then tweak it to exactly 190.0V.   

Trying to batter a Chinese upconverter into a stable source of measurement grade high voltage source ? I would say that resistance is futile

What about a proper postregulator ?

It might work. The requirements for the device to regulate is that the input voltage must be 12V or more higher than intended output. If I set the inverter to something like 215V to 220V even if it bounces around it's still above the 12V requirement.

Postregulator? Got some circuit designs that won't break the bank?

[med6753]

Here's a question for your smart guys...

Background: I have one of those cheap Chinese inverter boards that take 9-12VDC and steps it up over a wide adjustment range up to almost 300VDC. I currently have it set to 190VDC as that is the most common set point used to calibrate the 200V range on most DMM's. And in fact on the 2465 DMM it is an absolute calibration constant requirement. The problem with that board is that it's unregulated and bounces all over. One minute it's 188V and another 192V. So I've been looking for some way to regulate it and I found this which looks promising....

https://www.mouser.com/datasheet/2/268/20005399A-909415.pdf

The trouble is, how do I calculate the values of R1 and R2? It doesn't seem to give enough information other than one example for 5VDC. But I want 190.0V. Maybe I'm missing something. I sure would like to know what resistance values to start with and then tweak it to exactly 190.0V.   

Empirical finger in the air approach with casio's excellent solver so you don't even have to do any algebabooble.

Key is hiding in the datasheet fig 3-2.

Vout = 1.2 * (1 + R2 / R1)  + iAdj * R2

iAdj = 10uA
pick R1 around 2.2K (finger in the air estimate - could be totally wrong!), solve for R2 = 364.4k

Bingo. 360k in stock.

360k + 1% = 363.3, a good 1k less than the max.
360k - 1% = 356.4k. Span is about 10k or so potentially here.

Dig in junk box, find 10k multi turn trimmer.

Thus:

R1 = 2.2K
R2 = 360k in series with 10k multi turn pot.

desired output voltage is 200v, min load is 300uA so this is not good enough. Whack a 100k resistor on the output to stop it oscillating.

Great! Thanks! Actually I want 190V, not 200V but at least I can get there with those resistance values as a starting point. 

[Wolfgang]

Here's a question for your smart guys...

Background: I have one of those cheap Chinese inverter boards that take 9-12VDC and steps it up over a wide adjustment range up to almost 300VDC. I currently have it set to 190VDC as that is the most common set point used to calibrate the 200V range on most DMM's. And in fact on the 2465 DMM it is an absolute calibration constant requirement. The problem with that board is that it's unregulated and bounces all over. One minute it's 188V and another 192V. So I've been looking for some way to regulate it and I found this which looks promising....

https://www.mouser.com/datasheet/2/268/20005399A-909415.pdf

The trouble is, how do I calculate the values of R1 and R2? It doesn't seem to give enough information other than one example for 5VDC. But I want 190.0V. Maybe I'm missing something. I sure would like to know what resistance values to start with and then tweak it to exactly 190.0V.   

Trying to batter a Chinese upconverter into a stable source of measurement grade high voltage source ? I would say that resistance is futile

What about a proper postregulator ?

It might work. The requirements for the device to regulate is that the input voltage must be 12V or more higher than intended output. If I set the inverter to something like 215V to 220V even if it bounces around it's still above the 12V requirement.

Postregulator? Got some circuit designs that won't break the bank?

Have a look at some homebrew designs at:

electronicprojectsforfun.wordpress.com/power-supplies/high-voltage-lab-power-supplies/

[Kosmic]

Since we are talking about equipment acquisition.

Got a Lambda LQD-421 for 20$ on ebay. Channel 2 was supposed to be broken. In the end the channel was fine and it was just the switch of the meter that needed a little bit of Deoxit.


Still took the time to disassemble the thing and I had to replace 3 tired electrolytic cap.


I really like Lambda psu. This one is rated at 150uV rms for the ripple and noise.

[bd139]

Oh that's a bit sexy 

[xrunner]

Do you guys ever use security seals on anything you fix for other people (even friends  )?

I sometimes put one on things I fix for others, such as the repeater pre-selector I was working on. It isn't so much to stop someone from opening it up (in this case it would be nice if it did ...), but rather, it tells me if someone did open it up, and it may have been mucked around with. If it's failed and/or mis-adjusted if it comes back to me and it's been opened that's just good information to have (but it doesn't void my warranty).

I've been using these stickers. The plastic backing can easily be pulled off but not without leaving behind remnants especially if put on over non-flat areas. Another way is to put a drop of hard-drying paint on a screw, such as insulating varnish, which will crack off if jacked with.

Yes, there are those readers here skilled in the dark art of removing these without a trace, but I doubt I'll be fixing anything for you anyway LOL. 

[Kosmic]

Normally I put anti-tampering sticker on everything I sell on eBay. Just in case.

[bd139]

I sell everything for parts only with the disclaimer “for parts only due to no returns on old test gear”. Not worth fecking around with seals.

It doesn’t actually affect final value because I don’t do auctions, only fixed price

[bd139]

Bought an 8012a for just over a tenner. Apparently the display is faded. Let’s see what I get for my money

Have done the surgery on those before to put a new display in. Not the most fun job but not too difficult.

Better head over to the old fluke thread now 

[nixiefreqq]

In other TEA news, I, on the spur of the moment, rescued an HP 5321A. It's missing feet and one of the four Nixies doesn't light up, but it's still got its HP badge (can't win 'em all, eh?). I'll let you know how dead it is when I get it.

Sweet.  Those seem to be rather rare.  Good luck with it, and I hope the issue is driver and not Nixie tube related - those use the (also pretty rare) upside-down nixies.  Fingers crossed for you.

Yeah, I'm not quite sure why they're as rare as they are. They're not that good, technically. Perhaps not many were sold. The B model has more functionality and 5 or 6 digits (vs only 4), but originally cost twice as much as the A model. There was a 5321B that recently sold for $200. That's a bit too much moolah for a little old counter.

sorry......am a couple of days behind on this thread.   congratulations on the 5321a.

those drivers are pretty rare too  (and not compatible with standard 74141 or 7441 drivers).  BUT if it turns out you need a couple, PM me with an address and i'll stick these in an envelope.

the upside down nixies...….wow.....now those really are unobtanium. 

[mnementh]

Here's a question for your smart guys...

Background: I have one of those cheap Chinese inverter boards that take 9-12VDC and steps it up over a wide adjustment range up to almost 300VDC. I currently have it set to 190VDC as that is the most common set point used to calibrate the 200V range on most DMM's. And in fact on the 2465 DMM it is an absolute calibration constant requirement. The problem with that board is that it's unregulated and bounces all over. One minute it's 188V and another 192V. So I've been looking for some way to regulate it and I found this which looks promising....

https://www.mouser.com/datasheet/2/268/20005399A-909415.pdf

The trouble is, how do I calculate the values of R1 and R2? It doesn't seem to give enough information other than one example for 5VDC. But I want 190.0V. Maybe I'm missing something. I sure would like to know what resistance values to start with and then tweak it to exactly 190.0V.   

Start with a 25K-ohm-ish 10-turn pot set at 50%/5 turns; ends across VOUT and GND and ADJ to the center tap. Adjust for perfect voltage. Use that as a starting point for fixed resistor selection, or if it is stable enough, pot the shaft and call it a day.

mnem
*Back to the salt mines*

[mnementh]

   Since we are talking about equipment acquisition. Got a Lambda LQD-421 for 20$ on ebay. Channel 2 was supposed to be broken. In the end the channel was fine and it was just the switch of the meter that needed a little bit of Deoxit.   Still took the time to disassemble the thing and I had to replace 3 tired electrolytic cap.

I really like Lambda PSU. This one is rated at 150uV rms for the ripple and noise.

*wibble*

That looks exactly like the one I had that died a fiery death due to my abuse/testing of quadcopter ESCs;    Only difference is mine was rated 0-28V/6.7A or 7.7A or  somesuch, and single output. I loved that PSU like a sibling... it was with me longer than my Fluke 87. But there was nothing left to save once I put out the fire... I still cry a little inside every time I see one like it, as I haven't found another at a price I could afford.

mnem
*Sunday Spring Cleaning*

[mnementh]

@med:  https://www.ebay.com/itm/352504262470

mnem
*Coffee broken*

[URI]

[upcoming voltnuttery]
Edit: there’s an unknown untested HP 3455A on eBay. I was tempted by this as it’s a Bob Pease favourite. But it’s large, noisy and unknown.

Untested -tempting! 
Bob Pease favourite -even more tempting 

Seriosly, don't go that way.
For example, the succeeding HP 3456A is a very fine Voltmeter with excellent performance and little noise.   

If you'd go for the non-classic variant with rubber keys (which many don't like -what makes them less expensive) you'd get the last revision with no errata to work through because it's all in there already. I know because I have two of those.   

The HP 3456A with classic keys comes in different variants of different ages (oldest ones with fan no one needs/wants obviously) and you have to be more careful what you get. Most of the HP 3456A with rubber keys are fully working but yet old enough to have a settled and stable reference. Many of those classic HP keys are faulty -they look classic but they don't feel/work to their look.

BTW, you'll want a quartz for filtering out 50Hz-noise (as most of the 3456As come with one for 60Hz) but you can get them custom made to HP specs for little money...   

[Mr. Scram]

Do you guys ever use security seals on anything you fix for other people (even friends  )?

I sometimes put one on things I fix for others, such as the repeater pre-selector I was working on. It isn't so much to stop someone from opening it up (in this case it would be nice if it did ...), but rather, it tells me if someone did open it up, and it may have been mucked around with. If it's failed and/or mis-adjusted if it comes back to me and it's been opened that's just good information to have (but it doesn't void my warranty).

I've been using these stickers. The plastic backing can easily be pulled off but not without leaving behind remnants especially if put on over non-flat areas. Another way is to put a drop of hard-drying paint on a screw, such as insulating varnish, which will crack off if jacked with.

Yes, there are those readers here skilled in the dark art of removing these without a trace, but I doubt I'll be fixing anything for you anyway LOL. 

.
I honestly wouldn't appreciate people putting stickers on my kit.

[xrunner]

I honestly wouldn't appreciate people putting stickers on my kit.

Well that's part of the deal see - I usually don't charge my friends for labor they only give me what they think it's worth, so if they don't want a sticker they can take it elsewhere. I'd say that's a pretty damn good deal and they so far have all agreed bar none. 

[0culus]

Looking at microwave frequency counters that might go along with my HP 8569B. So far I've found a few examples of the HP 5343A. Anyone got one/used one/know that it's not worth buying, etc?

[bitseeker]

I've been using these stickers. The plastic backing can easily be pulled off but not without leaving behind remnants especially if put on over non-flat areas.

Yes, I've used numbered stickers for stuff I've repaired and resold. Fortunately, I haven't had one come back, yet. I like the ones that you have that will self-destruct, so to speak, when peeled. I'll have to get some after I finish up the rectangular ones I currently have.

Another way is to put a drop of hard-drying paint on a screw, such as insulating varnish, which will crack off if jacked with.

I haven't tried that yet. Sounds like a good idea, especially on equipment that have many points of entry like old HP gear with separate panels.

Yes, there are those readers here skilled in the dark art of removing these without a trace, but I doubt I'll be fixing anything for you anyway LOL. 

Fortunately, not everyone who buys online is similarly skilled.

[bitseeker]

In other TEA news, I, on the spur of the moment, rescued an HP 5321A. It's missing feet and one of the four Nixies doesn't light up, but it's still got its HP badge (can't win 'em all, eh?). I'll let you know how dead it is when I get it.

Sweet.  Those seem to be rather rare.  Good luck with it, and I hope the issue is driver and not Nixie tube related - those use the (also pretty rare) upside-down nixies.  Fingers crossed for you.

Yeah, I'm not quite sure why they're as rare as they are. They're not that good, technically. Perhaps not many were sold. The B model has more functionality and 5 or 6 digits (vs only 4), but originally cost twice as much as the A model. There was a 5321B that recently sold for $200. That's a bit too much moolah for a little old counter.

sorry......am a couple of days behind on this thread.   congratulations on the 5321a.

Thanks, and no worries on getting behind. Sometimes I'm half a dozen pages behind or more.

those drivers are pretty rare too  (and not compatible with standard 74141 or 7441 drivers).  BUT if it turns out you need a couple, PM me with an address and i'll stick these in an envelope.

Many thanks in advance. Hopefully, they'll be operational, but then that might mean the choob is dead  . I will certainly let you know.

the upside down nixies...….wow.....now those really are unobtanium.

Yeah, I saw them listed on Sphere before, but even then they were out of stock. Now I don't even see them listed.

I see you have a 5221B there. Very nice. Does it have the sixth digit option?

[bitseeker]

If you'd go for the non-classic variant with rubber keys (which many don't like -what makes them less expensive) you'd get the last revision with no errata to work through because it's all in there already. I know because I have two of those.   

Interesting. I don't think I've ever seen of these. The ones with the hard buttons and flat spring mechanism are the usual 3456 I run across.

The HP 3456A with classic keys comes in different variants of different ages (oldest ones with fan no one needs/wants obviously) and you have to be more careful what you get. Most of the HP 3456A with rubber keys are fully working but yet old enough to have a settled and stable reference. Many of those classic HP keys are faulty -they look classic but they don't feel/work to their look.

Yeah, one of the reasons I've avoided them is the old key mechanism. So, are these rubber keys like those on the 3478A?

[mnementh]

Jeezus... how does Amazon make profit doing this?

   

I bought from them a metal and bentwood slat bed frame similar to a couple of the Premier Flex bed frames I already have in my home.

I expected similar quality to the ones I have, but what arrived... well, it wasn't even close. The Premier is made of mandrel-bent tubing, so is light and rigid and strong, the Europa is square-cut tubes with a bit of flat steel bracket and plastic tube corners. So I called them and tried to return it, and they told me that due to the weight, it wasn't eligible for return, but since I wasn't happy with the quality, they'd issue me a return and I could dispose of it as I see fit. 

After I got off the phone, I realized it was probably a matter of cost of return shipping being more than the product cost them.

But still... the question I have to wonder is... how in the hell do they make a profit overall doing this shit? I can't be the first to tell them their bed is a POS and want a refund...

mnem
"But hey, Customer Service!!!"

[bitseeker]

The devil's in the data. If they get too many returns, I'm sure they'll can the product. Amazon + analytics = megaprofit. At the scale of an individual buyer, some things they do can seem counterproductive. At the scale that they operate, though, reality can be very different. They're not hurting for profit, that's for sure.

[Berni]

Since we are talking about equipment acquisition.

Got a Lambda LQD-421 for 20$ on ebay. Channel 2 was supposed to be broken. In the end the channel was fine and it was just the switch of the meter that needed a little bit of Deoxit.


Still took the time to disassemble the thing and I had to replace 3 tired electrolytic cap.


I really like Lambda psu. This one is rated at 150uV rms for the ripple and noise.

That PSU looks really nicely built inside, the name Lambda is well known for a reason.

But i already have too many PSUs

[URI]

If you'd go for the non-classic variant with rubber keys (which many don't like -what makes them less expensive) you'd get the last revision with no errata to work through because it's all in there already. I know because I have two of those.   

Interesting. I don't think I've ever seen of these. The ones with the hard buttons and flat spring mechanism are the usual 3456 I run across.

Then you haven't looked especially for those in the past.   
In fact the vast majority of the 3456A sold are the versions with classic keys.

The HP 3456A with classic keys comes in different variants of different ages (oldest ones with fan no one needs/wants obviously) and you have to be more careful what you get. Most of the HP 3456A with rubber keys are fully working but yet old enough to have a settled and stable reference. Many of those classic HP keys are faulty -they look classic but they don't feel/work to their look.

Yeah, one of the reasons I've avoided them is the old key mechanism. So, are these rubber keys like those on the 3478A?

I haven't come across a 3478A physically yet. But I think yes. They are quiet similar to the ones of my 34401A. Just like rubber keys in modern Agilent/Keysight test equipment.
Look here: First example,second example.
The Power switch key is still classical because it's driving the same mechanical switch inside. 
For Europeans the shipping from the US of A is quiet hefty but for that money why should I want anything less than the latest version of a 3456A?

The 3456A is a very good 6 1/2 digit voltmeter. Neither the 3457A (that I also have) nor the 34401A succeeded the 3456A.
Its successor is the 3458A according to Keysight today:


That's no real surprise looking through old Hewlett Packard catalogs: The 3456A was still being sold (until 1992) while the 3457A was on the market (since 1986). And with its noisier input stage the 3457A is clearly performing less well compared to the 3456A.

[bitseeker]

Thanks for the examples! Now I'll know it when I see it.