Test Equipment Anonymous (TEA) group therapy thread

[Specmaster]

Look like there's more where it came from. The seller listed some more at 150$

https://www.ebay.com/itm/393592090990

Anybody know the lowest offer he's going to accept ?

I paid $140 plus shipping. They did not respond to a $100 offer, not even by turning them down. Granted, the offer was made over a weekend, so if they're a commercial operation might not reply then anyway. And I got a Syndrome relapse and bought it anyway. It IS a good deal, even at list, because the condition as verified is essentially brand new.

Besides, who needs more than 3 ¹/₂ digits anyway?   

Truth be told, not very many, in reality. Yes, there are occasions when you could do with more resolution. I think for most people, it is more about bragging rights and or peer pressure, something akin to the top speed and or BHP of a car, when does the average driver use the full performance of their cars in normal day-to-day driving?

I know that someone will challenge me on the above points, but I'll admit right at the outset that I fall into that category seeing as my car has a top speed of 132mph and a 170BHP, also most of my bench meters are either 4.5 or 5.5 digits as are my handhelds. Do I need them to have that amount of resolution, no, not in the repairing of gear which is an activity that most of us are involved in.

[Specmaster]

I didn't think it was a problem over there as we are supposed to be waving the incoming lorries through AFAIK, is that not the case?

There were times when the traffic from France to the UK was just as badly affected and there were tailbacks from Calais all the way back to the Belgian border.

Was that when the ports were either blockaded, weather too bad for shipping, or just since the UK left the EU?

[med6753]

On my local CL. Very tempting but no. Both tube testers are run of mill emissions testers. If they were MU testers I'd jump on it. And the vast majority of the tubes are series string odd ball filament value TV tubes. The audiophools don't even want those. And neither do I. 

[tggzzz]

Look like there's more where it came from. The seller listed some more at 150$

https://www.ebay.com/itm/393592090990

Anybody know the lowest offer he's going to accept ?

I paid $140 plus shipping. They did not respond to a $100 offer, not even by turning them down. Granted, the offer was made over a weekend, so if they're a commercial operation might not reply then anyway. And I got a Syndrome relapse and bought it anyway. It IS a good deal, even at list, because the condition as verified is essentially brand new.

Besides, who needs more than 3 ¹/₂ digits anyway?   

You are almost convincing me to buy one. That price is damn good especially including the HV probes. And only $12 shipping for me. But I already have a HV probe and Fluke 87 is just about as tough although I don't think I should pound nails with it. 

Well the 27 is waterroof (IP67) and the 87 is only IP30. Of course a sitution where you need IP67 AND  HV probe is 

The 25 - and therefore the 27 - is gas proof in that it can be operated in explosive atmospheres. I got mine (and quite a few others) a few years ago, before their quality was recognised.

[bd139]

That makes me think of this for some reason. Probably because I never grew up when I got to 12 

[tggzzz]

Look like there's more where it came from. The seller listed some more at 150$

https://www.ebay.com/itm/393592090990

Anybody know the lowest offer he's going to accept ?

I paid $140 plus shipping. They did not respond to a $100 offer, not even by turning them down. Granted, the offer was made over a weekend, so if they're a commercial operation might not reply then anyway. And I got a Syndrome relapse and bought it anyway. It IS a good deal, even at list, because the condition as verified is essentially brand new.

Besides, who needs more than 3 ¹/₂ digits anyway?   

Truth be told, not very many, in reality. Yes, there are occasions when you could do with more resolution. I think for most people, it is more about bragging rights and or peer pressure, something akin to the top speed and or BHP of a car, when does the average driver use the full performance of their cars in normal day-to-day driving?

The main use-cases for "everyday" use are when observing small changes. Examples: cell voltage over time, temperature (etc) sensitivity of a UUT, tracing current along conductors to find the short circuit.

Of course for those the stability is more important than the accuracy/precision.

[tggzzz]

Went to the local hamfest, not expecting much. Too many people weren't wearing masks.

Nearest to something interesting was a tiny Simpson DMM, but I've more interesting things in the queue ATM.

[nixiefreqq]

Look like there's more where it came from. The seller listed some more at 150$

https://www.ebay.com/itm/393592090990

Anybody know the lowest offer he's going to accept ?

I paid $140 plus shipping. They did not respond to a $100 offer, not even by turning them down. Granted, the offer was made over a weekend, so if they're a commercial operation might not reply then anyway. And I got a Syndrome relapse and bought it anyway. It IS a good deal, even at list, because the condition as verified is essentially brand new.

Besides, who needs more than 3 ¹/₂ digits anyway?   

You are almost convincing me to buy one. That price is damn good especially including the HV probes. And only $12 shipping for me. But I already have a HV probe and Fluke 87 is just about as tough although I don't think I should pound nails with it. 

YOU are not allowed to buy one of these.

i forbid it.

[Neper]

I didn't think it was a problem over there as we are supposed to be waving the incoming lorries through AFAIK, is that not the case?

There were times when the traffic from France to the UK was just as badly affected and there were tailbacks from Calais all the way back to the Belgian border.

Was that when the ports were either blockaded, weather too bad for shipping, or just since the UK left the EU?

Various combinations of all three. Bad weather usually only affects the port of Dover. Calais and Dunkirk are less problematic in this regard.

The greatest problem was an enormous surge in goods traffic towards the UK in the weeks before Brexit, made still worse by strikes of the customs agents complaining about the increased workload through all the red tape.

Mind you, all the paperwork in connection with Brexit is already in place. As I understand it, the temporary open border policy of the UK only concerns a waiver on import checks for meat, fruit and vegetables.

[Neper]

On my local CL. Very tempting but no. Both tube testers are run of mill emissions testers. If they were MU testers I'd jump on it. And the vast majority of the tubes are series string odd ball filament value TV tubes. The audiophools don't even want those. And neither do I. 

If they were MU testers you wouldn't get them for 100 bucks.

I have the Precision 910 and it's far better than no tube tester at all. Good at detecting short circuits and does all I need. Plus it can be used to detect ringing in tubes and to check for leaky capacitors.

BTW, I have the complete docs of the 910 plus a long list of additional tube settings in Word or PDF format.

[Vince]

Hey what do you know, just after I bought my Metrix 232 Wobulator.... same local website ANOTHER pops up ! The same.

https://www.leboncoin.fr/bricolage/2046259422.htm

Paid mine 60 Euros, and seller was OK to ship. This new one seller wants.... 280 Euros for it ! 
And he refuses to ship AND takes NO OFFER either !

Looks like there is money to be made here ! I am starting to look strange at my Wobulator... I hope he can't sense it or he might run away and hide !

Need to get mine working first ! On his he managed to display something, looks like a spectrum analyzer pattern with a large peak at the center, and
smaller peaks, symmetrical on the sides...

So I looked at how he wired his 232, the position of the switches etc, set mine up the same way and hey... it does display something ! Nothing as cool as his though. I can get peaks to display, but all the same height, and very unstable, picture is blurry. Tried the two frequency fine tuning controls I have at my disposal but no joy. They can make the signal disappear completely, but they won't make it any less unstable sadly.

I also note that I was wrong... the scope must internally wired to the instrument as guy didn't use the external scope input yet he did get a signal on the screen ! So...

The feeling I get is that the HF / Main generator is 100% kaput, probably a dead tube obviously... and as for the LF / modulation part, I would guess it's kinda working but very sick. So maybe a dying tube as well. Not dead just yet... just on the verge.

Don't have a tube tester... with some luck the tubes used in this thing are also present in my Tek scopes so I can just swap them, that would cost me nothing.

[xrunner]

Need to get mine working first ! On his he managed to display something, looks like a spectrum analyzer pattern with a large peak at the center, and
smaller peaks, symmetrical on the sides...

So I looked at how he wired his 232, the position of the switches etc, set mine up the same way and hey... it does display something ! Nothing as cool as his though. I can get peaks to display, but all the same height, and very unstable, picture is blurry. Tried the two frequency fine tuning controls I have at my disposal but no joy. They can make the signal disappear completely, but they won't make it any less unstable sadly.

I also note that I was wrong... the scope must internally wired to the instrument as guy didn't use the external scope input yet he did get a signal on the screen ! So...

Well I'm sure you realize what I'm about to say, but you didn't exactly write it ... just because it displays "something" doesn't mean it's working right. 

[Neper]

On his he managed to display something, looks like a spectrum analyzer pattern with a large peak at the center, and smaller peaks, symmetrical on the sides...

...suggesting that the DUT is a filter or a resonant circuit.

[Vince]

Well so you mean his Wobulator is Kaput too ?

But at least he can get a stable picture on the CRT, and his comb pattern looks more plausible than the crap I get from mine...

He seems to kinda know what he is talking about, or if he is not then he is a good actor AND has balls as he said he would demonstrate that the unit works before any cash is handed...

But well if you say his doesn't work, you know better than I do ! 

Need to search for the user manual. Waht I am hoping, is that it's possible to set up the instrument to bypass all the wobulator specific stuff, and simply display the output of the HF generator. If I can display a clean and stable sine wave on the CRT it will help for the sale...

[Neper]

You might want to do a Google search for the basic principle of a wobulator.

[med6753]

Look like there's more where it came from. The seller listed some more at 150$

https://www.ebay.com/itm/393592090990

Anybody know the lowest offer he's going to accept ?

I paid $140 plus shipping. They did not respond to a $100 offer, not even by turning them down. Granted, the offer was made over a weekend, so if they're a commercial operation might not reply then anyway. And I got a Syndrome relapse and bought it anyway. It IS a good deal, even at list, because the condition as verified is essentially brand new.

Besides, who needs more than 3 ¹/₂ digits anyway?   

You are almost convincing me to buy one. That price is damn good especially including the HV probes. And only $12 shipping for me. But I already have a HV probe and Fluke 87 is just about as tough although I don't think I should pound nails with it. 

YOU are not allowed to buy one of these.

i forbid it.

I'm on to you. Reverse psychology will not work.     

[Cerebus]

Truth be told, not very many, in reality. Yes, there are occasions when you could do with more resolution. I think for most people, it is more about bragging rights and or peer pressure, something akin to the top speed and or BHP of a car, when does the average driver use the full performance of their cars in normal day-to-day driving?

I know that someone will challenge me on the above points, but I'll admit right at the outset that I fall into that category seeing as my car has a top speed of 132mph and a 170BHP, also most of my bench meters are either 4.5 or 5.5 digits as are my handhelds. Do I need them to have that amount of resolution, no, not in the repairing of gear which is an activity that most of us are involved in.

The place where you need the resolution in the real world is when you need a long scale along with the resolution. During prototyping of the GPSDO I needed to confirm that the 16 bit DAC was doing what I was telling it to and correlate it with the output from the OCXO.

The DAC has a range of 0-5V and a 70uV LSB step size and there's also 10nV/sqrt(Hz) reference noise (6 uV p-p in 0.1-10Hz) to be taken into consideration. To measure that meaningfully I had to have a meter with significantly better than 16 bit resolution (5 digits). My Keithley 197 (5 ¹/₂ digits) would have to be on the 20V range to cover 0-5V, so would have been on 100uV resolution for the bottom digit, the 34461A (6 ¹/₂ digits) has a 10V range with 10uV resolution so was suitable, but that still only gives 7 counts to cover that 70uV step size, 5 counts if you take the claimed noise into account. Having 5 counts that mean something out of a range of 5V in 10uV steps (500,000 counts) requires not just high resolution but also good linearity (both INL and DNL).

That sort of small difference to be measured in the middle of a much larger continuum of possible values crops up all the time in design verification work.

[Cerebus]

You might want to do a Google search for the basic principle of a wobulator.

Or you could whack the dragon with a 2x4 and watch him throw a wobbly. 

[Robert763]

Truth be told, not very many, in reality. Yes, there are occasions when you could do with more resolution. I think for most people, it is more about bragging rights and or peer pressure, something akin to the top speed and or BHP of a car, when does the average driver use the full performance of their cars in normal day-to-day driving?

I know that someone will challenge me on the above points, but I'll admit right at the outset that I fall into that category seeing as my car has a top speed of 132mph and a 170BHP, also most of my bench meters are either 4.5 or 5.5 digits as are my handhelds. Do I need them to have that amount of resolution, no, not in the repairing of gear which is an activity that most of us are involved in.

The place where you need the resolution in the real world is when you need a long scale along with the resolution. During prototyping of the GPSDO I needed to confirm that the 16 bit DAC was doing what I was telling it to and correlate it with the output from the OCXO.

The DAC has a range of 0-5V and a 70uV LSB step size and there's also 10nV/sqrt(Hz) reference noise (6 uV p-p in 0.1-10Hz) to be taken into consideration. To measure that meaningfully I had to have a meter with significantly better than 16 bit resolution (5 digits). My Keithley 197 (5 ¹/₂ digits) would have to be on the 20V range to cover 0-5V, so would have been on 100uV resolution for the bottom digit, the 34461A (6 ¹/₂ digits) has a 10V range with 10uV resolution so was suitable, but that still only gives 7 counts to cover that 70uV step size, 5 counts if you take the claimed noise into account. Having 5 counts that mean something out of a range of 5V in 10uV steps (500,000 counts) requires not just high resolution but also good linearity (both INL and DNL).

That sort of small difference to be measured in the middle of a much larger continuum of possible values crops up all the time in design verification work.

This is when a stable adjustable voltage source is useful. It can be connected between common and the meter negative. It is then used to off-set most of the DAC output so you can use a lower range on the meter and see the small steps.

[Specmaster]

Truth be told, not very many, in reality. Yes, there are occasions when you could do with more resolution. I think for most people, it is more about bragging rights and or peer pressure, something akin to the top speed and or BHP of a car, when does the average driver use the full performance of their cars in normal day-to-day driving?

I know that someone will challenge me on the above points, but I'll admit right at the outset that I fall into that category seeing as my car has a top speed of 132mph and a 170BHP, also most of my bench meters are either 4.5 or 5.5 digits as are my handhelds. Do I need them to have that amount of resolution, no, not in the repairing of gear which is an activity that most of us are involved in.

The place where you need the resolution in the real world is when you need a long scale along with the resolution. During prototyping of the GPSDO I needed to confirm that the 16 bit DAC was doing what I was telling it to and correlate it with the output from the OCXO.

The DAC has a range of 0-5V and a 70uV LSB step size and there's also 10nV/sqrt(Hz) reference noise (6 uV p-p in 0.1-10Hz) to be taken into consideration. To measure that meaningfully I had to have a meter with significantly better than 16 bit resolution (5 digits). My Keithley 197 (5 ¹/₂ digits) would have to be on the 20V range to cover 0-5V, so would have been on 100uV resolution for the bottom digit, the 34461A (6 ¹/₂ digits) has a 10V range with 10uV resolution so was suitable, but that still only gives 7 counts to cover that 70uV step size, 5 counts if you take the claimed noise into account. Having 5 counts that mean something out of a range of 5V in 10uV steps (500,000 counts) requires not just high resolution but also good linearity (both INL and DNL).

That sort of small difference to be measured in the middle of a much larger continuum of possible values crops up all the time in design verification work.

Which is precisely what I said "Yes, there are occasions when you could do with more resolution." and another place the extra resolution is useful is tracking down a short circuit to ground on a PCB where the closer you probe to the actual short location, the resistance reading will also drop slightly.

And of course, as you stated, "That sort of small difference to be measured in the middle of a much larger continuum of possible values crops up all the time in design verification work." But not everyone is involved in design work, there are many of us who are only involved in the repair process, of old equipment that we are trying to keep out of becoming landfill and a large part of that old equipment would very likely have been designed and tested using devices with wobbly pointers on them and also denoted in many service manuals under the test equipment required to service the equipment. In fact, on some equipment, even a 2.5digit DMM will present the user with false readings unless care is taken to allow for the variation in circuit loadings and their effects on voltage readings.

These are all "Gotcha's" that can and will catch people out.

[capt bullshot]

And now for something completely different:

https://www.eevblog.com/forum/repair/yokogawa-ta520-time-interval-analyzer/

This is a copy of the post in the repair thread:

So I've got this nice instrument for some timenuttery acticities.
The TA520 is a time interval analyzer that can do gapless period width or time delay measurements of signals of more than 10MHz

The unit works nicely as I received it from a seller of used equipment, except when it was operated for more than one or two hours. Then it started to display really strange results:



And the built-in self test reported various failures:



Sometimes it's the Multiplexer Board only, sometimes Multiplexer Board and Aquisition board 2, sometimes Measurement board and Multiplexer board. Turning the unit off, letting it cool down fully restored the normal operation, so this is pointing to some thermally induced failure, like a broken bond wire inside a chip package, bad solder joint, ...

This is a view of the Multiplexer board, I started to diagnose here because this board failed always, the other boards only sometimes.



As there's no service manual of this instrument, the only hint is this block diagram from the user manual:



So, there's four time-to-voltage converters that are driven by the multiplexer and fractional pulse generators. Additionally, in this list view, one can see every fourth measurement is wrong. This gives some hints, one of the four T/V channels might have failed.



I started investigating the multiplexer board, there's just some "standard" ECL chips, none of them ran hot nor was susceptible to thermal shocks (I've used freezer spray on them).
Then I've checked the analog output of the T/V converters and found them all operating. After some more thermal testing (heating or cooling the multiplexer and measurement board and watching the results) I've ruled out measurement and multiplexer as the cause of this failure. There was no obvious correlation between cooling or heating these boards and the occurrence of the failure.

Moving on to the next board in the signal chain, this is the acquisition board 2. It has a set of four large chips, most probably multiplexing and storing the ADC results into the acquisition RAM. The RAM is a bunch of four static RAMs near each large chip. I've started measuring and comparing the RAM signals (data, address, control signals) - and there it is: The RAM chips have the CE2 input unused, and the board designer tied this pin to 5V through a 10k pull-up resistor, one resistor for each group of four RAMs.




Three of the four groups of RAMs had the CE2 pin at high, with some capacitively coupled noise:



At the fourth group, the signal looked different:



Here's the signal at the adjacent pin, A15.



Note the similarity of the waveform, though the amplitude is different. Measuring with a DMM, I found there's a resistance from16k (cold) to 12k (warm) from Pin CE2 to Pin A15 on this group of RAM chips. Now it's quite visible what is the cause for the thermally dependent failure mode: When the instrument is turned on in cold state, the 10k pull-up is enough to keep the level at CE2 just above the "high" input level, and the RAMs are operating. When the unit slowly warms up, this resistance falls to about 12k, the signal level reaches "low" level territory and the RAMs start to act randomly, sometimes storing the acquired values, sometimes not. A perfect match to the symptoms I've observed. A quick test by shorting the pull-up confirmed this.

Now it's about time to locate the offender: Desoldering the RAM chips until the offender is found:



I was lucky at the second chip, so now the root cause was identified.



As I don't have these RAMs in stock, I put the chip back in place for now, and added a 1k resistor in parallel to the 10k pullup. That's sufficient to keep the level at the CE2 pin at "high", so the unit can be used further until a proper replacement is found and ordered.

It's an interesting mode of failure, there must be a resistive path between these two adjacent pins inside the packaging. No external contamination was found.

[Cerebus]

This is when a stable adjustable voltage source is useful. It can be connected between common and the meter negative. It is then used to off-set most of the DAC output so you can use a lower range on the meter and see the small steps.

Which of course is the principle of the good old fashioned differential voltmeter. Just for fun I once set up two brand new identical 9V batteries, connected the negatives together and slapped the Keithley (which was the best meter I had at the time) across the two positive poles on its 200mV range (giving 1 uV resolution) and watched the voltage slide back and forth as I briefly touched first one battery and then the other.

I have a hankering to own one of the old Fluke differential voltmeters, but whenever I spot one in time it's either overpriced, in suspect condition, or 'over there' (i.e. the US). 

[tggzzz]

This is when a stable adjustable voltage source is useful. It can be connected between common and the meter negative. It is then used to off-set most of the DAC output so you can use a lower range on the meter and see the small steps.

Which of course is the principle of the good old fashioned differential voltmeter. Just for fun I once set up two brand new identical 9V batteries, connected the negatives together and slapped the Keithley (which was the best meter I had at the time) across the two positive poles on its 200mV range (giving 1 uV resolution) and watched the voltage slide back and forth as I briefly touched first one battery and then the other.

I have a hankering to own one of the old Fluke differential voltmeters, but whenever I spot one in time it's either overpriced, in suspect condition, or 'over there' (i.e. the US). 

Use "separates", and eschew "pre-packaged instruments".

All you need are a "decent" voltage source driving a "decent" KVD, plus a nice low-current moving coil meter. If you only want 3digit resolution, use 1m of resistance wire and a 1m steel rule instead of the KVD:)

[Cerebus]

Use "separates", and eschew "pre-packaged instruments".

All you need are a "decent" voltage source driving a "decent" KVD, plus a nice low-current moving coil meter. If you only want 3digit resolution, use 1m of resistance wire and a 1m steel rule instead of the KVD:)

And how pray am I to do that whenever a decent KVD crops up cheap somewhere you make off with it? Or if not you then I have Robert as a secondary suspect. 

[Specmaster]

Use "separates", and eschew "pre-packaged instruments".

All you need are a "decent" voltage source driving a "decent" KVD, plus a nice low-current moving coil meter. If you only want 3digit resolution, use 1m of resistance wire and a 1m steel rule instead of the KVD:)

And how pray am I to do that whenever a decent KVD crops up cheap somewhere you make off with it? Or if not you then I have Robert as a secondary suspect. 

Just have to be a bit nimbler on your feet, I guess