Test Equipment Anonymous (TEA) group therapy thread

[beanflying]

Re: Electronic loads: After having the parts to build one on the shelf for like 5 years I bought one of those:



CV, CC, CP and CR, 220V/20A/150W, color display, bluetooth, app. 25 eurobucks, No idea how they make money on this 

Looks like one of these that have only one transistor to dissipate the load, and their spec equals the transistors spec @25°C. Doesn't take much effort to toast them.
The KP184 at least has 6 transistors to dissipate 400W, so I'd expect it to stand longer ...

It is a fat FET under the hood not sure of the case size or number without lifting the cooler on mine but I have run it at 100+W for extended periods without a Temperature issue. Not sure if the dual fan cooler is available with the current lot but I brought this one at the time because of it over the single downdraught one. If anyone is really keen I can lift the cooler tomorrow.

[tautech]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

Easy with a new toy like capt bullshot has got....a VNA ! 

To spot that difference, one must have $$$ cal kit and cables, too ...

Only for accurate measurement as you will still see the differences. 

What does the "distortion" actually look like, if it is only the connector that is 75 ohm and the rest of the circuit is 50 ohm?  Does it reflect energy at higher frequencies, or something like that?

Mine's packed away so I'll leave it as an exercise for capt bullshot to learn more about VNA mode in his new toy.

Gunna do like menm so off to ded and will check how he's getting on with it tomorrow.

[VK5RC]

More Rifa Madness!
In my last test run I forgot an old HP battery inverter 85901A, the 20Ahr 12V sealed lead acid battery needed a good charge. About an hour in, that lovely smell, a crack and a bit of smoke arose. One of the weird things was as they died, (they took out the mains fuse - not unexpectedly) but sent little spitballs of molten metal with the lovely tarry rifa residue over an area of about 4 square inches of the pcb. Photos below - cleaned up OK - two new X caps and a new fuse and all is happy 👍
Edit - I have not seen the little metal balls before re rifa 'accidents'

[Brumby]

That reminds me ... gotta get some replacements for a few RIFAs - before I discover this for myself.

[capt bullshot]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

Easy with a new toy like capt bullshot has got....a VNA ! 

To spot that difference, one must have $$$ cal kit and cables, too ...

Only for accurate measurement as you will still see the differences. 

Yes, that's true, one can see differences. Anyway, using a TDR (like the 1502C I've got), it's easier to interpret.

Otherwise VNA (or SA with TG) is an easy way to identify unknown components:

[Ice-Tea]

So, I figured I'd turn this on and do a quick check.

Seems I need to doctorate in physics to properly operate this thing 

[capt bullshot]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

Easy with a new toy like capt bullshot has got....a VNA ! 

To spot that difference, one must have $$$ cal kit and cables, too ...

Only for accurate measurement as you will still see the differences. 

What does the "distortion" actually look like, if it is only the connector that is 75 ohm and the rest of the circuit is 50 ohm?  Does it reflect energy at higher frequencies, or something like that?

I don't have a 75Ohm cable with a 50Ohm connector fitter (or vice versa), so I can't show that.
I've compared two BNC tees using a very simple (and non-calibrated) setup here. The VNA shows the "open" response, which ideally should be just a flat line at 0dB):

It's one of the "better" 50 Ohm cables (checked using the 1502 TDR), connected to an 50Ohm tee and a 75Ohm tee (by the looks, don't have any specs of them).
So the result isn't totally as expected, as the 50Ohm tee looks worse than the 75Ohm one hat higher (some GHz) frequencies. Normally, one would expect the 50Ohm one to look better in a 50Ohm setup

Comparing the tees at the TDR does judge the 75Ohm "better" than the 50Ohm tee in a 50Ohm setup, too ...

[Saskia]

ok, the zotac 3090 that I got as replacement for the doa 3090 works as designed. Still waiting for a bloody refund from alternate.

[capt bullshot]

ok, the zotac 3090 that I got as replacement for the doa 3090 works as designed. Still waiting for a bloody refund from alternate.

Guess you'd need patience and insistence with them, waiting alone might not be enough ...

[PA0PBZ]

Since we're talking aircraft engine failures now, this happened yesterday when a 747 took off at Maastricht Aachen Airport.
People commented "It was raining knives"

[bd139]

OMG I just watched a Hermes driver trying to get a fishing pole through someone’s letterbox 

[tggzzz]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

Easy with a new toy like capt bullshot has got....a VNA ! 

To spot that difference, one must have $$$ cal kit and cables, too ...

Only for accurate measurement as you will still see the differences. 

What does the "distortion" actually look like, if it is only the connector that is 75 ohm and the rest of the circuit is 50 ohm?  Does it reflect energy at higher frequencies, or something like that?

See standard transmission line theory.

Frequency domain: a series of nulls, where the depth depends on the degree of mismatch and the frequencies depends on the cable length.

Time domain: a series of steps where the height depends on mismatch and the time delay depends on length.

[Saskia]

ok, the zotac 3090 that I got as replacement for the doa 3090 works as designed. Still waiting for a bloody refund from alternate.

Guess you'd need patience and insistence with them, waiting alone might not be enough ...

escalate via paypal ...

[bd139]

Anyone want 2x HP 400E’s that require some work?

https://www.ebay.co.uk/itm/184674196350

[Robert763]

What you don't want to see on your United Airlines flight 328 from Denver to Honolulu:



(It landed safely.)

You're not kidding, I bet there was a few soiled pants on that flight when it landed.

Yes of course as the public have no idea how hard pilots need train for these types of failures and as it can be seen there's no apparent damage to the airframe or control surfaces and therefore a 777 is perfectly safe to operate with just one engine however landing distances become greatly increased without the full reverse thrust that 2 engines can generate.

looks identical to the failure on UA1175 in 2018 (same aircraft and engine (PW4000) types). That was over the sea so no falling debris issues. Cause was fan blade due to  crack in blade. Inspection (a new thermo- acoustic imaging technque) had previously shown indications of a crack but inspector put it down as a paint defect.
Pratt and Whitney are going to have some hard quetion to answer. 

[Robert763]

Sort of TEA related (has a voltmeter built in), I posted a pic of my shed radio (a Danish made Sailor 16T) a while ago and someone on here was interested in seeing inside it, well I've finally had enough of the voltmeter under-reading and decided to adjust it.

A quick teardown, this radio uses a lot of those Mullard/Philips AF11x series transistors that have a bad reputation of failing with tin-whisker related shorts, despite this I haven't had any trouble with them yet.



Here is the problem I have, with an external supply set for 9V I get a reading of approx 8V of the built in meter.

<BIG SNIP>

All back together with fresh set of 6 D sized leak-tubes. 


David

I have never before come across a radio which has NW on its dial and range switch, WTF is that then?

NW is "Navigation Wave" it's a expansion / extenstion of Long Wave to cover low frequency non-directional beacon transmitters. Akin to ADF on aircraft. It's used with a (in this case manual) directional loop antenna. Thi could be mouned on the bridge roof or for small craft, a hand-held ferrite "loopstick" on a cable.

[Robert763]

[...]
The flames are bad enough but what is more alarming is the severe vibration.

If I was looking out the window at that engine I would be thinking that it's going to fall off at any moment.

The vibrations are likely why everything fell apart in the first place.  Wonder if there is an "engine vibration monitor" in the cockpit?

Normally yes on larger aircraft. I don't knw for sure on the PW4000 777 though.  They are intended to detect low level vibrations as an early warning. Not needed in this case as vibration and damage was obvious.
The early 737 vibration indicators were unreliable and when a BA crew on a later 737 had an engine issue their perception of this caused them not to use them in determining which engine was faulty. This contributed to a chain of events that resulted in the working engine being shut down and the aircraft crashing at Kegworth.

[AVGresponding]

Sort of TEA related (has a voltmeter built in), I posted a pic of my shed radio (a Danish made Sailor 16T) a while ago and someone on here was interested in seeing inside it, well I've finally had enough of the voltmeter under-reading and decided to adjust it.

A quick teardown, this radio uses a lot of those Mullard/Philips AF11x series transistors that have a bad reputation of failing with tin-whisker related shorts, despite this I haven't had any trouble with them yet.



Here is the problem I have, with an external supply set for 9V I get a reading of approx 8V of the built in meter.

<BIG SNIP>

All back together with fresh set of 6 D sized leak-tubes. 


David

I have never before come across a radio which has NW on its dial and range switch, WTF is that then?

NW is "Navigation Wave" it's a expansion / extenstion of Long Wave to cover low frequency non-directional beacon transmitters. Akin to ADF on aircraft. It's used with a (in this case manual) directional loop antenna. Thi could be mouned on the bridge roof or for small craft, a hand-held ferrite "loopstick" on a cable.

Yes, I was about to post something similar.

The clue is the "D.F Aerial" on the NW range.

[Robert763]

What you don't want to see on your United Airlines flight 328 from Denver to Honolulu:



(It landed safely.)

Much nicer to see something like that just after takeoff, instead of in mid-Pacific!

On the subject of looking out the window & being a bit disturbed, I recall, back in 1968, looking out the window at the wing of a Viscount & being a bit worried that the riveted panels seemed to have largish gaps, rather than sitting flush.

I put it down to a jaundiced view of the Viscount, compared to the Fokker F27 I had been travelling in previously, which had a short take off distance & a fairly spectacular climb rate for an airliner.

With the much bigger & older beast, I was surprised by how long it took to reach operating height.
About when the flight attendants were normally handing out "munchies" & pouring coffee in the F27,the Viscount was still groaning & moaning to gain height.

With nothing else to do, I returned to gazing out the window, & apart from the rough looking constuction of the panels, compared to the Fokker, noted a large amount of wing flex.

"Don't be sillly!", I told myself, it just looks different, not necessarily worse!

Sadly, a couple of months later, on the same route, that aircraft "fell out of the sky"--------& yes, a wing fell off!

Wow, that no mechanic caught the signs when the rivets are literally popping out...

I imagine some techies are sweating now, about answering questions about an engine vibrating itself to death after they just gave it the All Clear...

I flew as a passenger on Viscounts a few times in the seventies. it was interesting in turbulance to se the wing flexand twist so much that the inboard engine pointing down and outboard pointing up The lone nacelles (due to the Darts being lighter than the radial engines originally designed for) made it look worse.

[AVGresponding]

Have you been changing out lots of them because they are really unreliable or something?

David

No, this is just as part of a scheduled rewire/refit, which is invariably a blunt instrument here, and can bag you some nice fittings from time to time. The ones I took out are identical to the one you pictured, with the possible exception of the battery; these are a slightly older 3S sub-C Ni-Cd pack, and newer ones will have 1S Li-ion packs.

However, during my time on the maintenance side, doing the fire alarm and EL testing I did notice that the cheaper LED fittings (even when from well known manufacturers) are appallingly unreliable, way more so than older fluo jobbies.

Odd this one still uses Ni-Cd, the new 3V LDO sorted it out and it's now back with it's owner.


Those square LED ceiling panels seem to be utter crap at work, so many have died in the toilet block leaving some areas in complete darkness, last failure took out about half a dozen of them, took maintenance several days to sort that mess out. They are extra annoying as the whole panel fails too, something which was very rare with the quad tube based panels they replaced. 

David

Probably quite a lot of the failures are thermal issues.

As we all know, modern LED lighting is run way harder than it should be, in order to ensure an MTBF that keeps the factories in work.
There is information for the installer in the fitting instructions that tells you not to cover the top side, and how much air space is needed above it, but they are frequently installed by people that can't be arsed to read these things, either because "I've been an electrician for (insert suitable number) years, and I don't need to be told how to fit a light", or the younger ones who just don't give a toss.

I found Big Clive's recent vid on the "Dubai LED lamps" quite interesting. For sure when they start to sell them here, they will a) charge a premium, and b) find another way to bring the MTBF down.

[Robert763]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

Easy with a new toy like capt bullshot has got....a VNA ! 

To spot that difference, one must have $$$ cal kit and cables, too ...

Only for accurate measurement as you will still see the differences. 

What does the "distortion" actually look like, if it is only the connector that is 75 ohm and the rest of the circuit is 50 ohm?  Does it reflect energy at higher frequencies, or something like that?

Mine's packed away so I'll leave it as an exercise for capt bullshot to learn more about VNA mode in his new toy.

Gunna do like menm so off to ded and will check how he's getting on with it tomorrow.

To be honest a Time Domain Reflectometer (TDR) is better for spotting wrong impedance connectors and crimped cables than a basic VNA. VNAs don't natively show distance. The modern ones have a "Distance to Fault" function that provides a TDR like display by applying a FFT.

[Robert763]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

Easy with a new toy like capt bullshot has got....a VNA ! 

To spot that difference, one must have $$$ cal kit and cables, too ...

Only for accurate measurement as you will still see the differences. 

What does the "distortion" actually look like, if it is only the connector that is 75 ohm and the rest of the circuit is 50 ohm?  Does it reflect energy at higher frequencies, or something like that?

I don't have a 75Ohm cable with a 50Ohm connector fitter (or vice versa), so I can't show that.
I've compared two BNC tees using a very simple (and non-calibrated) setup here. The VNA shows the "open" response, which ideally should be just a flat line at 0dB):

It's one of the "better" 50 Ohm cables (checked using the 1502 TDR), connected to an 50Ohm tee and a 75Ohm tee (by the looks, don't have any specs of them).
So the result isn't totally as expected, as the 50Ohm tee looks worse than the 75Ohm one hat higher (some GHz) frequencies. Normally, one would expect the 50Ohm one to look better in a 50Ohm setup

Comparing the tees at the TDR does judge the 75Ohm "better" than the 50Ohm tee in a 50Ohm setup, too ...

Two 75R "stubs" in parallel closer to 50R than two 50R in parallel?

[Specmaster]

Larry Major (older larrikin son in Perth) sent a pic of his spa pool pump motor that kept eating impellers as it occasionally ran in reverse rotation ........pretty obvious why. 

OUCH

[bd139]

I still reckon it was something like that which caused the Greenfell fire. https://en.wikipedia.org/wiki/Grenfell_Tower_fire#Initial_fire_(00:50–01:15)

[Specmaster]

Would someone like to explain to a thicko (me) what is the actual difference between a 75 and 50 BNC and would I tell them apart?

Easy with a new toy like capt bullshot has got....a VNA ! 

To spot that difference, one must have $$$ cal kit and cables, too ...

Only for accurate measurement as you will still see the differences. 

What does the "distortion" actually look like, if it is only the connector that is 75 ohm and the rest of the circuit is 50 ohm?  Does it reflect energy at higher frequencies, or something like that?

I don't have a 75Ohm cable with a 50Ohm connector fitter (or vice versa), so I can't show that.
I've compared two BNC tees using a very simple (and non-calibrated) setup here. The VNA shows the "open" response, which ideally should be just a flat line at 0dB):

It's one of the "better" 50 Ohm cables (checked using the 1502 TDR), connected to an 50Ohm tee and a 75Ohm tee (by the looks, don't have any specs of them).
So the result isn't totally as expected, as the 50Ohm tee looks worse than the 75Ohm one hat higher (some GHz) frequencies. Normally, one would expect the 50Ohm one to look better in a 50Ohm setup

Comparing the tees at the TDR does judge the 75Ohm "better" than the 50Ohm tee in a 50Ohm setup, too ...

Well that is certainly not what I expected as everyone seems to think 75 Ohm is inferior. Just a  thought, you're certain that the traces have not been incorrectly titled