Test Equipment Anonymous (TEA) group therapy thread

[Zenith]

Izzat the "across the pond" equivalent of dis guy...? Not sure bd would be willin' ta shave 'is head like I do... 

mnem
 

Along those lines - the very embodiment of cleaning.

He was an old fashioned pilot cartoon character with a handlebar moustache who flew about cleaning things.



The products were OK but they didn't work quite like that.

[Cerebus]

...You seem to have this unfounded belief that the English criminal law is something handed down from on high by the elite to oppress the huddled masses. It isn't, most criminal law in England and Wales evolved as Common Law, based on precedents set in the trials of ordinary people for the actions they took towards other ordinary people who had brought the matter before the courts for adjudication.

I probably didn't explain my thinking very well; sorry. 

Not English criminal law specifically; but the change in direction of lawmaking in general over my lifetime. I'm pretty sure you've noticed the resumed tendency for laws in general to reinforce the Golden Rule rather than any real form of social equity. Also the general trend towards an ever-tightening net of laws which as an aggregate tend to criminalize poverty.

I guess I thought it was only so egregious over here; examples like these show to me that this isn't just a "Corporate States of America" problem but rather a "Human beings and Humanity" problem.

At least, that's where my thinking was going.

mnem
At this point I'm going to drop the subject, as it is definitely dipping toes in the Politics mudpuddle.

The Criminal Damage Act 1971 (you can read the whole thing here, it's short) is actually an example of how to make good law. It tackles a simple principle not some huge raft of various acts that the government or people who "think something must be done" would like to see criminalised, it's universally applicable, it's short, there are no more special cases than absolutely necessary (i.e. arson), it's in plain English, and it removed a lot of the cruft and special cases that did exist in previous existing law (Malicious Damage Act 1861). Modern legislators could learn a lot in principle from reading it and following its example.

The original including schedules of repeals etc ran to 10 pages in the small sparse format HMSO used to use for Acts of Parliament, the two most recents Acts of Parliament, both relatively transient things, run to 26 and 84 pages respectively, the most recent Act passed with Criminal Law as the subject ran to 353 pages.

[mnementh]

Thanks, that mostly made sense even to a lay-person like myself. Certainly not a representative example of much of what has been passed in the nearly half-century since, I fear. 

mnem
Hell, my tax returns have less clarity... even the short form.

[Cerebus]

Main tools used were a microfibre cloth and some kitchen spray 

Change your avatar to Mr Sheen.

Izzat the "across the pond" equivalent of dis guy...? Not sure bd would be willin' ta shave 'is head like I do... 

mnem
 

He looks like the first words out of his lips are gonna be "You're not from around here are you boy?".

Mr. Sheen was somewhat friendlier:

[Specmaster]

That's about it, it's like, at least in the UK, it is not illegal for someone to park their car on your driveway, but it is illegal for you to remove it or damage it in any way 

Wrong in almost every important respect. It is unlawful for someone to park on your driveway(tort), it is not unlawful to have said vehicle moved on private property, but becomes illegal the moment on is on public property unless one is properly licensed to do so or is a bailiff acting under court order, or anyone acting under the directions of a police constable or traffic warden (RTA), it is unlawful to damage it in so doing (tort), but recent precedent shows that it is not illegal to damage it in doing so (https://www.bbc.co.uk/news/uk-england-tees-60260155). It is illegal to clamp or otherwise immobilise a vehicle on private property except by closing a gate or barrier that was present but not closed when the vehicle was parked (Protection of Freedoms Act 2012 S.54).

That's about it, it's like, at least in the UK, it is not illegal for someone to park their car on your driveway, but it is illegal for you to remove it or damage it in any way 

Wrong in almost every important respect. It is unlawful for someone to park on your driveway(tort), it is not unlawful to have said vehicle moved on private property, but becomes illegal the moment on is on public property unless one is properly licensed to do so or is a bailiff acting under court order, or anyone acting under the directions of a police constable or traffic warden (RTA), it is unlawful to damage it in so doing (tort), but recent precedent shows that it is not illegal to damage it in doing so (https://www.bbc.co.uk/news/uk-england-tees-60260155). It is illegal to clamp or otherwise immobilise a vehicle on private property except by closing a gate or barrier that was present but not closed when the vehicle was parked (Protection of Freedoms Act 2012 S.54).

Well, that is what I was told by a serving police officer, who was on duty at the time and was attending an incident when that actually happened to me a neighbour who was being a right entitled idiot because he had his family had 5 vehicles to park 

[med6753]

More Datron 1071

As I said in my last post about this meter, there's no such thing as a perfect one when you're talking about something from the mid '70s.
Mine was no exception, and although the meter powered up straight away when I received it and seemed to give plausible results when
reading a few voltage references and precision resistors, it was obvious that the meter wasn't entirely happy. First task was to check the
infamous Philips blue electrolytics.



Sure enough, with one end freed from the PCB, they measured:

Des.        Printed    Actual         ESR
               Value       Value
C45        47μF        34μF           8.1Ω        (Furthest away in the photo)
C46        47μF        34μF           6.4Ω
C47        33μF        28μF           8.1Ω
C48        33μF        25μF           10.2Ω
C49        10μF        9.7μF          4.5Ω
C50        10μF        9.4μF          7.6Ω

The replacements from Kemet and Vishay were a bit of a squeeze, but had rather better parameters:

Des.  New        New
         Value       ESR
C45   50μF       0.22Ω
C46   49.7μF    0.22Ω
C47   32.2μF    1.38Ω
C48   31.5μF    1.44Ω
C49   11.7μF    0.55Ω
C50   11.7μF    0.55Ω



I then checked the various power rails and found out of tolerance voltages and excessive ripple,
so it was time to turn my attention to that area of the meter. This is where the fun starts!

The power supply is implemented on the board that runs across the rear of the meter. Between that and the
rear of the case, Datron also crammed in all of the boards that handle the optional outputs, the front/rear
relays and the two stacked toroid transformers. It's kind of packed in there as you can see from
the photo below.


The only way I could easily work on the power supply was to separate the rear of the case with all its
boards from the rear PCB and remove the analogue, digital and current boards so that I had clear access to the
solder side of the PSU. I wasn't keen on my chances of being able to put it all back together again without
extensive photo documentation of what plug went where - there are no identifying labels on any of the plugs
that connect everything together, so I took my time and took many photos along the way. Finally, the rear
of the case was free!



continues in next post (which will be after I've eaten some strawberries and cream )...

Philips CRAPacitors are also very common in Fluke equipment and are to be shot on sight without trial. 

[Robert763]

New TEA
What could it be?

It's a General Radio 2220 Bug Hound. Used for tracing shorts and opens in PCBs and wiring. also good for genearl circuit tracing.
Unlike similar tools like ToneOhm and the HPP current tracer probe it uses AC signals and a phase sensitive detector. I'm looking forward to using it in anger.

So non-contact, or just very tiny current so as not to blow up stuff like the ShortSqweek and Huntrons?

mnem
 

Both.
Non-contact probe with LEDs to show current direction and contact with +- 50uV or 500uV

Ooooooh... does indeed sound like the PCB debugging Holy Grail. I can see why you're so pleased to find one. 

*adds another "must-have" to his watchlist... and slides it right up to the top*

mnem
Damn you Robert! Damn you to... New Jersey!!!

Already been to New Jersey, more than once. I lived and worked in (old) Jersey Channel Islands for a while.

Just to annoy you more I paid £21.37 including shipping for it ($25.35 US)

[mnementh]

My condolences and *shakes my fist*  You lucky bastard!

mnem
 

[mnementh]

That's about it, it's like, at least in the UK, it is not illegal for someone to park their car on your driveway, but it is illegal for you to remove it or damage it in any way 

Wrong in almost every important respect. It is unlawful for someone to park on your driveway(tort), it is not unlawful to have said vehicle moved on private property, but becomes illegal the moment on is on public property unless one is properly licensed to do so or is a bailiff acting under court order, or anyone acting under the directions of a police constable or traffic warden (RTA), it is unlawful to damage it in so doing (tort), but recent precedent shows that it is not illegal to damage it in doing so (https://www.bbc.co.uk/news/uk-england-tees-60260155). It is illegal to clamp or otherwise immobilise a vehicle on private property except by closing a gate or barrier that was present but not closed when the vehicle was parked (Protection of Freedoms Act 2012 S.54).

Well, that is what I was told by a serving police officer, who was on duty at the time and was attending an incident when that actually happened to me a neighbour who was being a right entitled idiot because he had his family had 5 vehicles to park 

Part of me wants to say "Take it out of gear and release the parking brake, then let nature take its course..." but no doubt it would be A) seen by witlesses and 2) the driveway would either be too flat for the car to roll the way intended without being pushed the entire way or worse, would slope the wrong way and the car would crash into your house. 

(Yes, for the purpose of this self-indulgent fantasy I am ignoring the prevalence of gearshift and steering wheel interlocks.)

mnem
*toddles off to get some urethane*

[Cerebus]

Well, that is what I was told by a serving police officer, who was on duty at the time and was attending an incident when that actually happened to me a neighbour who was being a right entitled idiot because he had his family had 5 vehicles to park 

Relying on a serving police officer as a reliable, accurate source of legal knowledge is perhaps not the best course of action, especially as what they tell you is usually dictated by "What should I say to get this plonk arrested/out of my hair as quickly as possible?".

The Police and Criminal Evidence Act 1984 actually requires a person who isn't "a constable" to have a better knowledge of what is and isn't a criminal offence and what kind it is than "a constable" to effect a lawful arrest (section 24 versus section 24A arrests). It's damning when the law formally expects a layman to be better legally educated than a policeman. 

[mnementh]

Philips CRAPacitors are also very common in Fluke equipment and are to be shot on sight without trial. 

Absolutely not!

They shall be condemned to death by electrocution with extreme prejudice.   

mnem
using as high and inverse a voltage as one can muster!

[tggzzz]

Ok on way back from hamfest now.

That absolute turd arrived at 08:30 and emptied it again 

Did manage to grab a manky tek 465, a solartron 7150, some 10 turn pots, TO18 heat sinks and a book to sell. And I still have change from £25 

Is the turd a dealer?

Yes. Same one I mentioned to you last time. He waltzed off with a pile of kit and left the trash for everyone else. Turns up as a seller but doesn't set up, goes round and empties everything off and that's it.

There are no rules around this? In any case, if he's a known quantity and you can learn what vehicle he uses, it should be possible to run interference and stop him from getting there early, if you can organise a few people for joint action.

Do they just leave straight after, or do they eventually set up their stall? I guess the organisers shouldn't let them in early if they arrive with nothing to sell. 

David

Or of course, they could just make a rule that nobody buys/sells anything until the fest is officially open to the members and public, but that would scupper BD's plans as well 

Having rules and enforcing rules are orthogonal.  But you knew that.

Well, what I thought I knew was, BD getting there early, convincing the organizers to let him in early so that he can beat the turd, perhaps his hyper miling style of driving cost him precious moments today 

Some hamfests where I've sold stuff have an explicit "no trading before door open for public" rule. It is ignored, and I don't see how it can reasonably be enforced on the day.

My best suggestion would be to warn hamfest organisers that there is such an individual, along the lines of "you may like to keep an eye on a trader driving a green Ferrari, and see whether he stays around until the end". Then next year the organisers might decline to book him again. Very imperfect, of course.

[mnementh]

Well, that is what I was told by a serving police officer, who was on duty at the time and was attending an incident when that actually happened to me a neighbour who was being a right entitled idiot because he had his family had 5 vehicles to park 

Relying on a serving police officer as a reliable, accurate source of legal knowledge is perhaps not the best course of action, especially as what they tell you is usually dictated by "What should I say to get this plonk arrested/out of my hair as quickly as possible?".

The Police and Criminal Evidence Act 1984 actually requires a person who isn't "a constable" to have a better knowledge of what is and isn't a criminal offence and what kind it is than "a constable" to effect a lawful arrest (section 24 versus section 24A arrests). It's damning when the law formally expects a layman to be better legally educated than a policeman. 

mnem
does this mean a knowledgeable citizen can effect a citizen's arrest on a ignorant police officer and make it stick...?

[Zenith]

Well, that is what I was told by a serving police officer, who was on duty at the time and was attending an incident when that actually happened to me a neighbour who was being a right entitled idiot because he had his family had 5 vehicles to park 

There's a difference between unlawful and illegal. If someone parks a car on your driveway without your permission, you could sue them as a civil matter. But, who wants to to go to the expense and risk of raising a lawsuit over a car parked on the driveway of a private house for an evening, and attempt to assess damages?

[bd139]

Well, that is what I was told by a serving police officer, who was on duty at the time and was attending an incident when that actually happened to me a neighbour who was being a right entitled idiot because he had his family had 5 vehicles to park 

There's a difference between unlawful and illegal. If someone parks a car on your driveway without your permission, you could sue them as a civil matter. But, who wants to to go to the expense and risk of raising a lawsuit over a car parked on the driveway of a private house for an evening, and attempt to assess damages?

No you tow it out onto the road with your Land Rover and phone the police and tell them it has been abandoned.

Have some experience with that 

[Zenith]

No you tow it out onto the road with your Land Rover and phone the police and tell them it has been abandoned.

Have some experience with that 

I'm sure that in almost all cases, you'd get away with it and nothing more would be heard. The police would have no interest in the matter, unless it was damaged or caused an accident or something, but I believe it is illegal to do that off your own bat.

[Cerebus]

Already been to New Jersey, more than once. I lived and worked in (old) Jersey Channel Islands for a while.

Ah the Channel Islands, where you really learn what a car horn is for. (For those who haven't been there, most roads have 20-30 yards visibility to the next bend and high walls and hedges that mean you can see nothing around them.)

I had a adult cousin with a farm on Guernsey and two uncles who owned and ran the [then] biggest department store in St. Peter Port so I spent a lot of summer holidays over there in my youth while my Father caught up with that part of the family. This had the odd side effect that I'd go back to school each year in new school trousers with fancy French labels that had come gratis from the Gent's Outfitters section of Uncle Bill's store, and lots of hand-me-downs from Uncle Jack's sons who were just the right 'little bit older' than me to have grown out of something at just the right time.

[bd139]

No you tow it out onto the road with your Land Rover and phone the police and tell them it has been abandoned.

Have some experience with that 

I'm sure that in almost all cases, you'd get away with it and nothing more would be heard. The police would have no interest in the matter, unless it was damaged or caused an accident or something, but I believe it is illegal to do that off your own bat.

Probably is.

I try and break the law at least once a day.

[mnementh]

Yeah, C addressed that idea directly with the bit about the instant it hits a public street the moving agent, be it vehicle or person, had better be a police officer or acting as a deputy of the court (how they do it over here for wreckers towing illegally parked cars) or it is illegal; hence my little Dr. Dorian daydream aboot just releasing the parking brake and letting the car roll out into traffic... 

mnem
Why am I still here?

[Cerebus]

I try and break the law at least once a day.

it's your patriotic duty as an Englishman to resist all that Norman and Roman rubbish! 

[Zenith]

Probably is.

I try and break the law at least once a day.

But it's as well to know when you are breaking the law, so you can calculate the risks and minimise them. In this case it's a good idea not to be seen doing it if you can help it, and I'd say that phoning the police and telling them about an abandoned vehicle, needlessly draws their attention to the matter and puts you in the picture.

[Neper]

But it's as well to know when you are breaking the law, so you can calculate the risks and minimise them.

Aka the 11th commandment.

[grizewald]

Datron 1071 - A very strange problem

After fixing the PSU and putting everything back together again, I started testing the meter in earnest to see how accurate and
stable it was. Sadly, I rapidly discovered that it was neither accurate or stable. 

The first thing I noticed was that when turned on from cold, there was a huge offset on the voltage ranges. For example, on the
10V range, there was a -700µV zero offset with the input terminals shorted. As the meter warmed up, this would decrease and
sometimes go all the way to a few tens of µV positive, but not always. Once the meter had warmed up, I could use the input zero
key to tune out the offset, but if I connected up a voltage reference for a few minutes and then switched back to a short again, the
zero offset would again be way off. Or sometimes not!

I noticed some white powdery deposits on the analogue board which looked like the result of poor cleaning after the repairs that
had previously been performed, so I took the analogue board out, taped over all the pots to stop anything getting into them and
did the job properly this time. This made absolutely no difference whatsoever. The meter still couldn't establish and hold a stable
zero. In desperation, I powered up the meter, threw a winter coat over it and gave it a thorough roasting in case the instability was
caused by moisture which had infiltrated it. Again, this proved to be a pointless endeavour.   

Utterly frustrated, I put the meter away in a corner and forgot about it for a year.

...

The pressure from work had started to abate and I could feel the Datron mocking me from the corner of room. I started again by
studying the service manual's functional description and circuit diagrams in detail. At some point, a lightbulb came on while I was
looking at this part of the analogue board's circuit diagram:



This jogged my memory about an excellent article by a gentleman named Karlheinz on amplifier.cd where he discussed his
experiences repairing a Datron 1061A. (https://amplifier.cd/Test_Equipment/other/Datron1061/Datron_1061.html)

The circuit in the diagram deals with input bias current compensation. Specifically, when calibrating the meter, one step of the
process consists of connecting a shielded box containing a 10MΩ resistor in parallel with a 1nF capacitor to the input terminals
and pressing the "Ib" calibration button. When you do this, the meter measures the input bias current, calculates a correction
and stores that in the calibration memory.

When a voltage or resistance range is subsequently selected, the digital board fetches the Ib correction value and transfers it
to the analogue board over the opto isolators which implement the isolation barrier between the boards. The value itself is an 8 bit
number which the analogue board then latches into buffers which function as the input to a D-A converter which is implemented
in discrete components on the analogue board.

The voltage generated by the converter enters the circuit pictured above on the Ib Comp line and is applied to the inverting input of
op-amp M3. This causes the op-amp to drive current through the diode and resistor to the M23 opto isolator's LEDs and the right-hand
transistor to sink current so that the voltage over R198 matches the input voltage on Ib Comp. The other transistor acts as a current
mirror referenced to the negative bootstrap voltage (-BS) and effectively floats the Ib correction onto the bootstrap supply. This
mechanism ensures that no cross current can flow and ensures that the DC isolator remains isolated from the correction voltage.

If there's anything wrong with the M23 opto isolator, this circuit won't work properly and could well cause the kind of problems I was
seeing. It wouldn't be the first time a faulty opto isolator has been identified as the cause of a problem in these meters and when you
consider how this opto isolator is being used, both LED/transistor pairs need to have matched characteristics for the correction to be
faithfully reproduced - this particular opto isolator is a specially selected part and is marked with an orange dot.

Here is the relevant part of the analogue board:



The opto isolator M23 is the 8 pin part with the orange dot at the lower left of the photo and the op-amp M3 is in the TO-99 package
at the top of the picture to the right of the flatflex cable.

Armed with the location of the components involved, I fired up my oscilloscope and prepared to start probing!

The diode and resistor that pin 6 of the op-amp is connected to are just behind that red film capacitor next to the op-amp. You won't
believe what I saw when I looked behind that capacitor...





 

Whoever built the PCB in Datron's factory had obviously twisted the component leads of the diode and resistor together in preparation
for soldering them but had gone to lunch or been otherwise distracted before they completed the final step! And so the board remained
for some 35 years before the connection between the two components deteriorated to the point that it started to cause a problem!

Due to them being hidden behind the film capacitor, I never noticed and neither did anyone else. I'm sure the connection was perfectly
OK during QA testing and calibration, so it just sat there like a little time bomb waiting to trigger decades later.

I gave the leads a gentle scraping with a scalpel and used plenty of flux when I finally completed the forgotten assembly step so I could
be sure that the connection would be good after soldering. I then constructed the suggested "Ib source" required and performed the
calibration step. The meter's zero offset immediately dropped to zero. After turning the meter off and allowing it to cool down before powering
up again, the initial zero offset was within a few tens of microvolts and once the meter had fully warmed up, it was very close to zero without
needing the use the "Input Zero" button.

Since correcting this problem, the meter has proved to be exceptionally quiet, stable and accurate. Noise on the 10V range is around +/- 2.1µV
which beats my Solartron 7061 (at +/- 12µV) by miles. Both meters agree within a few PPM on any reading which is excellent considering that
I paid to have the Solartron properly calibrated couple of years ago.

And finally, it's just a great looking meter!

[med6753]

 

[tautech]

@grizewald
Did you follow any of Defpom's vids on Datron repairs ?
https://www.youtube.com/playlist?list=PL2z3V9RkHQE3JrgdtFlmEC6LDbg-5Ah00