Test Equipment Anonymous (TEA) group therapy thread

[Vince]

so I guess..... oh no... I guess I have now officially a new TE to fix ?!!     

No schematics no nothing and zero knowledge of how these things work at all    ... wish me luck

At this point, I'm going to offer one bit of sage advice given by grand-dad that has served me well, and that I have suffered a time or two for ignoring it:

Always be a one-handed electrician. 

mnem
In other words, make sure you are never the shortest path to ground.

Yes I always probe one handed. I stick the ground test lead to the chassis, move my right hand away from the instrument and use my left hand to probe around.
I am 6'6", so I am never the shortest path ! 

That said, it's all low voltage in there. Any SMPS in any modern device is 400Vdc ! And all my glowing Tek scopes hav 500Vdc all over the place exposed. This 3 phase supply pales in comparison, and is way less dangerous the way it's put together  / constructed. All wires are insulated, very little is exposed. compared to a glowing scope.

Bottom line is, I am alwyas careful, so does not matter how "dangerous" the device is... if you are careful you will be fine regardless of the TE, but if your are not then even with a lower risk TE, you can get burned...
So, just be in a careful mindset no matter what you do, and you shall live long and prosper ! 

[25 CPS]

Yes I always probe one handed. I stick the ground test lead to the chassis, move my right hand away from the instrument and use my left hand to probe around.
I am 6'6", so I am never the shortest path ! 

That said, it's all low voltage in there. Any SMPS in any modern device is 400Vdc ! And all my glowing Tek scopes hav 500Vdc all over the place exposed. This 3 phase supply pales in comparison, and is way less dangerous the way it's put together  / constructed. All wires are insulated, very little is exposed. compared to a glowing scope.

Bottom line is, I am alwyas careful, so does not matter how "dangerous" the device is... if you are careful you will be fine regardless of the TE, but if your are not then even with a lower risk TE, you can get burned...
So, just be in a careful mindset no matter what you do, and you shall live long and prosper ! 

Live long?  Hopefully.  Prosper?  These days?

[med6753]

The genuine, no bullshit, correctly spaced and certified connectors for the lady in waiting have shown up.

Saskia, PM me.

[Vince]

Vince,

[...]  Note that it should also measure 115V to the common (neutral) connection.

What do you get when measuring (Use a DMM here! This is where the ScopeMeter style scopes shine.) between the phases?

One b0rkened phase sounds like you're having a blown output. All fuses OK?

"slightly over 150V PtP" is not that far from

TO answer questions.

Yes all 3 fuses are good, it's first thing I checked before even powereing it up. They are all good and the proper rating, no cave man butchered that part.

Voltage measurements, with the Fluke 11, pseudo "RMS" then.. but well we know we are working with a clean sine wave and only at 400Hz so should be good for that meter...

First I adjusted the 200V from the front panel. I got it at 199V. Well at 200V spot on just before doing the measurements, but then once I had done the measurements I checked it again and it was down to 199V    So not the most stable thing in the world.

Phase 1 to ground : 4.2V
Phase 2 to ground : 90.5V
Phase 3 to ground : 99.5V
Between Ph2 and Ph3 : 199V.

So a 10% difference between Ph2 and 3, hmmm...

[Vince]

Yes I always probe one handed. I stick the ground test lead to the chassis, move my right hand away from the instrument and use my left hand to probe around.
I am 6'6", so I am never the shortest path ! 

That said, it's all low voltage in there. Any SMPS in any modern device is 400Vdc ! And all my glowing Tek scopes hav 500Vdc all over the place exposed. This 3 phase supply pales in comparison, and is way less dangerous the way it's put together  / constructed. All wires are insulated, very little is exposed. compared to a glowing scope.

Bottom line is, I am alwyas careful, so does not matter how "dangerous" the device is... if you are careful you will be fine regardless of the TE, but if your are not then even with a lower risk TE, you can get burned...
So, just be in a careful mindset no matter what you do, and you shall live long and prosper ! 

Live long?  Hopefully.  Prosper?  These days?

Yes you are right, slip of the tongue... the old saying does not hold water anymore indeed !!!!  When you have to decide between buying food or buying petrol for the car to go to work, something is severely screwed up 

[mnementh]

   This pleases me.

   This...   ehhhh...

These Horror Fraught Little Red Boxes of Damifino™ have been lurking in the forgotten corners of my junk for at least a decade and 3 moves (Since I lived in San Damntonio, IIRC); there were a even dozen, so I guess there has been some attrition since I usedta collect them as the free goodie whenever I went there and bought something I needed just to have them to give away (usually along with a quick lesson on how to measure a battery or continuity) to noob RC pilots who had nothing.

Now...  do I do widdem...? If I open them up, I know I'll feel obligated to clean up after the 9V leak-bomb inside... 

But chunking them just feels wrong. An affront to the tool gods.

mnem
What is the best multimeter in the world...? The one you have when you need it.

[med6753]

   This pleases me.

   This...   ehhhh...

These Horror Fraught Little Red Boxes of Damifino™ have been lurking in the forgotten corners of my junk for at least a decade and 3 moves (Since I lived in San Damntonio, IIRC); there were a even dozen, so I guess there has been some attrition since I usedta collect them as the free goodie whenever I went there and bought something I needed just to have them to give away (usually along with a quick lesson on how to measure a battery or continuity) to noob RC pilots who had nothing.

Now...  do I do widdem...? If I open them up, I know I'll feel obligated to clean up after the 9V leak-bomb inside... 

But chunking them just feels wrong. An affront to the tool gods.

mnem
What is the best multimeter in the world...? The one you have when you need it.

Those DMM's are excellent candidates for HV smoke tests. 

[Vince]

Matra 400Hz 3 Phase PSU repair update

OK after only  5 minutes probing around, I might found something....

I think that one of the 3 heat sinks / 2N3055 pairs, the one located at the back half of the chassis, is for the PSU part of things. It's un marked.

The other two H/S however are "strangely" marked 'A' and the other 'B'... just like the Amp boards are labeled A and B ! Hmmm !!! 

So I make the reasonable assumption that that's how it is. Only two H/S, one for each of the two amps. Only two amps not 3.

so since I have two working phases and one down... I will make the assumption that one of the amps is working fine (fine "enough" at least, for our immediate troubleshooting needs..), and the other is not.
Also, the two amps looks strictly identical, judging by the looks of theuir respective boards. It's also would make sense that they are identical, in any case, doesn't it..

So I will make the assumption that I can compare voltages on both amps, and that they ought to be identical.

so, I probed the voltage on the metal case of their 2 TO3 2N3055 tranistors.

On one amp, one 2N3055 reads about 40V and the other about 20V. Which makes sense since these are the two voltages I see when I measure all the filter caps in the PSU section. Also makes sense because the two PSU boards are marked 40V for one, and 15V for the other. 15, 20... close enough.

SOOO when I measured on the OTHEr amp.... one of the 2N3055 reads 40V, fine, but the other reads only 6.6V !!!  Hey..... getting somewhere.

So I meaured the voltage across all the (six) filter caps .. again. Again I find them at 40 or 20V  heu... hold a minute, THIS ONE reads only 7 Volts now ?! 

So maybe the cap is bad and overloading the transformer and voltage drops a lot. I guess the transformer is not happy at all and that might why it makes that horrible noise at power up ?! Hmmm...

OK so I will investigate in that direction. I guess I could desolder the wires from that cap, to see if the voltage at the wires goes back up to 20V or so as it should I think...

Stay tuned !!! 

[mnementh]

The genuine, no bullshit, correctly spaced and certified connectors for the lady in waiting have shown up.

Saskia, PM me.   

Oh shit... they have the A-word on them. Hide 'em quick before Vince sees!!! 

mnem
*poking frogs for fun & profit since nineteen mumblety-mumble*

[med6753]

The genuine, no bullshit, correctly spaced and certified connectors for the lady in waiting have shown up.

Saskia, PM me.   

Oh shit... they have the A-word on them. Hide 'em quick before Vince sees!!! 

mnem
*poking frogs for fun & profit since nineteen mumblety-mumble*

Que? Clue me. 

[med6753]

Matra 400Hz 3 Phase PSU repair update

OK after only  5 minutes probing around, I might found something....

I think that one of the 3 heat sinks / 2N3055 pairs, the one located at the back half of the chassis, is for the PSU part of things. It's un marked.

The other two H/S however are "strangely" marked 'A' and the other 'B'... just like the Amp boards are labeled A and B ! Hmmm !!! 

So I make the reasonable assumption that that's how it is. Only two H/S, one for each of the two amps. Only two amps not 3.

so since I have two working phases and one down... I will make the assumption that one of the amps is working fine (fine "enough" at least, for our immediate troubleshooting needs..), and the other is not.
Also, the two amps looks strictly identical, judging by the looks of theuir respective boards. It's also would make sense that they are identical, in any case, doesn't it..

So I will make the assumption that I can compare voltages on both amps, and that they ought to be identical.

so, I probed the voltage on the metal case of their 2 TO3 2N3055 tranistors.

On one amp, one 2N3055 reads about 40V and the other about 20V. Which makes sense since these are the two voltages I see when I measure all the filter caps in the PSU section. Also makes sense because the two PSU boards are marked 40V for one, and 15V for the other. 15, 20... close enough.

SOOO when I measured on the OTHEr amp.... one of the 2N3055 reads 40V, fine, but the other reads only 6.6V !!!  Hey..... getting somewhere.

So I meaured the voltage across all the (six) filter caps .. again. Again I find them at 40 or 20V  heu... hold a minute, THIS ONE reads only 7 Volts now ?! 

So maybe the cap is bad and overloading the transformer and voltage drops a lot. I guess the transformer is not happy at all and that might why it makes that horrible noise at power up ?! Hmmm...

OK so I will investigate in that direction. I guess I could desolder the wires from that cap, to see if the voltage at the wires goes back up to 20V or so as it should I think...

Stay tuned !!! 

Why not just check the capacitors for shorts/ESR?

[mnementh]

   This...   ehhhh...

Those DMM's are excellent candidates for HV smoke tests. 

They're tougher than you think. I've seen 1200VDC on one of them measuring the wrong place inside a microwave oven. I was a 0-handed electrician on that one. 

Besides which, they're still as accurate as pretty much any wiggle-meter... and certainly good enough to give away to some noob doesn't have anything.

Or to use as your "perfect henchman" meter like above... so you don't risk a decent meter when you wanna do somethin' stoopit.

mnem

"Still better'n 'iss..."

[mnementh]

Oh shit... they have the A-word on them. Hide 'em quick before Vince sees!!! 

mnem
*poking frogs for fun & profit since nineteen mumblety-mumble*

Que? Clue me. 

I'm poking fun at V again for turning his nose up at that MegaZoom 54621D for 50 quid cuz "Agilent! Yuckyputz!".

mnem
*agitating-ily*

[Saskia]

Ok, had a not so nice day, returned from the doctor, and finally got around to fixing a few things.

Made some photos of the Uni-T DMM (UT8802E),  but did not take it apart as I still want to flip it.

Nothing fancy ...

It does have a USB port on the back tho.

[mnementh]

It does have a USB port on the back tho.

That's just so you can play MP3s off a thumbdrive. 

mnem
Seriously tho... hope you feel better soon. I hate being poked and prodded by MDs too.

[Saskia]

actually I seem to have caught something flu-like.
Spent Saturday mostly in bed (except for the quick discord session), had nasty limbs pain (as in when you have a real flu) which caused problems when walking. This slowly got better and finally subsided sometime around the afternoon.
So I did manage to unpack another 2 or so moving boxes, put together that zbox that I bought by mistake (yes, it passes selftest) and managed to make a couple of photos of that Uni-T. Also managed to check the probes for my R+S RTC1002 (they work, ye gods, those are stoopeedly expensive), clarified with the notary that they finally got their act together so that they can tell the buyer or my apartment to actually pay up. Did play vault (safe) tetris and now am preparing for sack time.

[Vince]

Matra 400Hz 3 Phase PSU repair update

Why not just check the capacitors for shorts/ESR?

Well, I precisely just said I was gonna check that cap, didn't I  ?! 

Me : I will check that cap.
Smurf : why don't you just check the caps ?! 

   I love you Papa Smurf ! 

OK so I removed a metal plate from the bottom of the PSU so I could get access to the bolts holding that cap to the chassis.

Pulled it out of the instrument, enough slack in the wiring for that, great.Desoldered a wire, called the chinese meter. It said capacitance spot on, and ESR only 2 or 3 ohms, for an old 100uF 50V cap that's OK to me. I replaced the cap with a couple 2,200uF 50V in series, gotta do with what you have. ESR same as the old cap, and capacitance spot on too.
Fire up... still 7 Volts. OK so the old cap is not at fault. Better : if I put NO cap at all.. I STILL get 7Vdc and no ripple !   
SO there must be another filter cap somewhere...  but one one of the boards. The big filter caps in the PSU area are either 20V or 40 and one is 60V, the biggest  and tallest one in the middle, that's not blue. This one goes to the two 2N3055 on the PSU related H/S.

Oh, while the cap was disconnected, I measured the resistance of that rail. A few kilo-ohms, so no short there.

So next  logical step is... this 7V must go to the bad amplifier board, and there must be another, small cap locally that filter that rail as well, presumably. There is no short so even that smaller local cap might not b that bad, and instead it's some other component that's clamping the rail to 7V instead of 20.

So next step is to identify which of the two amplifier boards is the bad one, pull it out, and inspect it, look for caps.... stay tuned ! 

[Robert763]

@Vince
There is a possibility that thes 4 small electrolytics are not filter capacitors. They could be DC blocks on the output of the amplifiers. There appears to be only one larger capacitor so possibly a single supply rather than a split one.
Assuming you have checked all four of the smaller electrolytics I'd check two things next.
1/ The two signals on the coaxial connectors are thr same amplitude and 90 deg ot of phase. I presume this is the drive to the amplifier.
2/ The output transistors on the faulty side

[Vince]

Thanks for the suggestions about these caps... yes that's interesting and probably true... The biggest cap is 60V and serves as you say most likely the only power rail. Then (5 not 4) blule smaller caps, that read either 20 or 40V, go tot eh ampllfier boards.

... I have just confirmed that, se picture below. I probed the board connections at the back of the socket underneath the chassis, on both amplifier boards, to see what voltages I would find, and compare the two boards.

Indeed we see only 40 and 20V on these boards. Voltage wise, we see one pin that carries 40V (first from the top). That's good on both boards. However the next 4 pints carry 20V on onre board... and same pins on the other boars all read 6+  or 7votls ! Here is my 7V again....

I am getting somewhere it looks like.

Will check these 2N3055 of course indeed, easy and well, power semi conductors like to fail after all...

Stay tuned.... 

[Vince]

No don't stay tuned.... at least not tonight. I am tired, time to go to bed.... will resume work on it tomorrow.

Did you see how lovely the wiring is ? 99.99% of the wires are white ? That makes it so easy to trace wires eh ?!   

I guess someone at Matra ordered by mistake a palette of white wires instead of just one spool, and the supplier refused to take the excess back. So Matra said oh boy what are we gonna do to use up all that white wire ! Hmmm.... what about making some of these 400Hz 3Ph PSU for that missile contract we just got the other day !!! 

[Cerebus]

I guess someone at Matra ordered by mistake a palette of white wires instead of just one spool, and the supplier refused to take the excess back. So Matra said oh boy what are we gonna do to use up all that white wire ! Hmmm.... what about making some of these 400Hz 3Ph PSU for that missile contract we just got the other day !!! 

Or the military procurement order specified it because someone with more scrambled eggs on their uniform than good sense decide that it was "good security" that a spy couldn't snap a photograph of their super secret power supply and identify what it did using the wiring colours as a clue.  (I have actually heard this kind of thinking from senior figures in both civilian and non-civilian life.)

[mnementh]

Hmmm... 16000 posts. Time for a change. While it was fun playing surf-potato mnem for a while, honestly... Carpe' mnem just... fits.

mnem

    Thanks, neomys!

[mnementh]

Something small... but a first.

      

This is my first part printed in TPU with my CR6-SE; actually my first time printing TPU on any printer I own. It's a replacement for missing rubber snubbers in the drawer glides in my big effing toolbox.

As always, full details and 3DP nerd stats can be seen over on the 3DP thread:

https://www.eevblog.com/forum/3d-printing/3d-printer-yet/msg4165885/#msg4165885

mnem
*toddles off to sort some tools*

[cyclin_al]

400Hz? I'd say something used in an airplane.

Or anti-airplane. The Bloodhound system used 400Hz mains for all ground equipment. From time to time, one of the Scania 200+ KVA gensets used with Bloodhound here in Sweden turns up and people are confused...

I figured that would still be airplane equipment.  It would however fall in the "forced-landing gear" category... 

[capt bullshot]

No don't stay tuned.... at least not tonight. I am tired, time to go to bed.... will resume work on it tomorrow.

Did you see how lovely the wiring is ? 99.99% of the wires are white ? That makes it so easy to trace wires eh ?!   

I guess someone at Matra ordered by mistake a palette of white wires instead of just one spool, and the supplier refused to take the excess back. So Matra said oh boy what are we gonna do to use up all that white wire ! Hmmm.... what about making some of these 400Hz 3Ph PSU for that missile contract we just got the other day !!! 

Nothing wrong with that, no stupid manager or scrambled eggs general involved. These wire looms are made according to a carefully planned layout, as you can see, the person who had to solder the wires to the pins can identify the wires by their position. Just like a PC Board, all the traces got the same colour on a PCB, too, don't they?