Author Topic: Test Equipment Anonymous (TEA) group therapy thread  (Read 1539418 times)

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Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10625 on: May 13, 2018, 06:39:52 pm »
Problem being of course is that it would need it to be calibrated first once you repaired it

From mobile device so predictive text might have struck again
Just calibrate it comparing it to your DMM, then use it to calibrate the DMM again. Problem solved.
Haha, save the time and money and just believe that your DMM is displaying the correct value, that's job done

From mobile device so predictive text might have struck again
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Offline Ero-Shan

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10626 on: May 13, 2018, 07:41:00 pm »
So this is probably the last episode in the PM2421 series. You may skip it if you're easily bored.

Let's go back for a moment to the first, small problem: the knackered power switch (left one in the picture). It shouldn't be too hard to replace, should it? I have switches a plenty ...


As you can see, the key in the thread is on top. The middle switch would be almost perfect, but the lever would then point down in the ON position (this is a clear no-go for me). And, even worse, the solder lugs would point down and interfere with a PCB. So I went for the right one (it has another set of lugs on the bottom). I snapped the down-pointing lugs off and had a not exactly pretty, but working solution.


Now the PSU with that resistor-cum-lamp. To get easier access I removed the whole back panel. What I had already seen but simply ignored so far became too obvious to be ignored any longer. Something strange must have happened to that DMM. All around the mains transformer there was a deposit very much reminiscent of the corrosive spilling of batteries. But there surely never was any battery. This is even more mystifying as the transformer itself or the PCBs don't show traces of the crystalline stuff. It's also on the bar (girder?) of the case, on both sides! But nothing on the top cover immediately above it!




If anyone has a reasonable explanation, I'm all ears.

To not make matters worse, I tested the PSU with resistors as load. The service manual says the +/- 15 volts shall be loaded with 100 mA, the 5 V I loaded with about 500 mA (my own guess). The +15 volts is also the main reference voltage for the ADC, it's allowed to stray 15 mV. +14.993 V it was, -15 V were a little farther off,  but both well within spec. 5 volts were fine, too.


Still wary about the overload at the 5 volts, I used my lab supply for that and the orinal PSU for the rest. About half an ampere current, the thing works as before. Switching the 5 volts also to its own PSU doesn't make a difference. So no explanation whatsoever for the overload, too. Grrr.

So I continued looking for the main problem: the display shows some random number, mostly static, sometimes changing. I replaced the comparator with that of the DIVO, and suddenly the display changed constantly, but didn't show anything resembling the voltage at its inputs.
It was then that Roger Dimwit finally had an idea (why did it take so long? you ask; first bouts of dementia I guess). The input to the ADC is a voltage between -7 V and +7 V, why not just circumvent the pre-amp and apply this directly? But that didn't help much. Still, with the error persisting, there was a chance that the pre-amp with that Photochopper made of pure unobtanium might be healthy after all. To make a very long story short, I eventually came across this:

(A) The inputs of the NAND were both high, but the output was 1.6 volts. About .3 volts diode drop - might be consistent with the small current. But I pulled the cathode out of the PCB. The NAND's output now read 0. :wtf: This made no sense at all, but I put another diode in.
(B) This looks much better. And, I just couldn't believe it, the display was stable with numbers that were consistent with the voltage I had set at the ADC input.
So I connected the pre-amp to the ADC again, and I was able to measure DC volts, DC amps and ohms (didn't try AC). Not exactly dead-on, but should be adjustable.

The exaltation didn't last long. With the next power-up, the DMM had returned to its alter ego - a random number generator. Finally I recognized the smell that should have registered from the very beginning: the stink of a case full of red herrings! There actually was an explanation for the 1.6 volts at the NAND's output: a bad ground connection. 40 years ago I had learned to knock on PCBs so they showed bad connections. Now that I did that, I could see a definite response. I really deserve no better! So I got out the board once more (not to easy, as the rigid cable harness is in the way - you have to remove the back or front first). Looking at the solder joints with my best loupe, however, revealed no obvious culprit. But I resoldered all those that looked the least bit suspect (somehow I can't get myself to just resolder all of them - doing it on an obviously perfect solder joint is ridiculous).
That seems to have done the job. I'm more than a little embarrassed about that.

Still needs the adjustment (input is 10 volts), but that can wait.


Why do I tell you all this? To show off my ignorance? I don't know.
 

Offline Ero-Shan

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10627 on: May 13, 2018, 07:45:47 pm »
Talking of TEA things that tempt me but I'm not going to bite on, there's a FLUKE 5440B Direct Voltage Calibrator going as a buy it now for £450 on ebay UK if anybody's interested. Start your own home cal lab!

If I lived in the UK I'd made an offer already. This is the thing I'm sorely missing! £450 isn't really much if it works.
Problem being of course is that it would need it to be calibrated first once you repaired it

From mobile device so predictive text might have struck again
I was under the impression that the calibrator is in working condition.
My Knick allows me to generate up to 150 volts DC, but above that I have nothing, and I also have no stable AC source.
The Fluke may not be calibrated, but it might generate stable voltages over a wide range.
 

Offline tautech

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10628 on: May 13, 2018, 08:05:54 pm »
 :)
Ero-Shan
I once volunteered to fix a misbehaving MIG welder... I can fix anything, right ?  :palm:
Much did I live to regret it for a good six months or more .....would work fine then NOT.  :wtf:
Bloody thing drove me nuts for a good while, the initial repair was simple enough, it had been dropped !  :o
A PCB mount transformer IIRC 20VA had cheerfully ripped one of it's PCB TH mounting pins from the encapsulation and the very fine primary winding. Replace transformer....simple fix.
But get this, the bloody thing was mounted approaching the middle of the PCB and well away from the PCB fixings but looking back now that probably saved the PCB from breaking when it was dropped.

Getting back to the ongoing faults.....a couple of cracked solder fillets on SMD components was deemed to be the problem.....reflowed, so they must have been.
Well back the bloody thing came, probably for the fourth time and I WASN'T to be beat !  :rant:

Then a EE buddy said; flex the PCB and listen for clicking. Well you couldn't see any cracks in the solder no matter how good the magnification or lighting was.....but the bugger still clicked !  :rant:

Reflowed every joint by hand, probably ~200 and haven't seen the thing since.  :-DD
The little tricks we learn.  ;D
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Online bd139

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10629 on: May 13, 2018, 08:07:05 pm »
Ero-Shan. That corrosion looks like typical stuff you get on steel/aluminium joints. It does it all by itself. I had a Land Rover that basically looked like that all over.
 

Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10630 on: May 13, 2018, 08:22:20 pm »
Ero-Shan. That corrosion looks like typical stuff you get on steel/aluminium joints. It does it all by itself. I had a Land Rover that basically looked like that all over.
Yes its the reaction of 2 dissimilar metals in direct contact with each other that will cause that kind of corrosion if they become subjected to moisture so its possible that it might have had some liquid spilled on it or has been in a damp environment for a time.
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Offline Ero-Shan

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10631 on: May 13, 2018, 09:05:07 pm »
Ero-Shan. That corrosion looks like typical stuff you get on steel/aluminium joints. It does it all by itself. I had a Land Rover that basically looked like that all over.
Yes its the reaction of 2 dissimilar metals in direct contact with each other that will cause that kind of corrosion if they become subjected to moisture so its possible that it might have had some liquid spilled on it or has been in a damp environment for a time.
The main corrosion appears far from where the 2 metals are joined. This is just weird. Whatever, I removed all the powdery stuff. And from the outside it can't be seen.  ;D
 

Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10632 on: May 13, 2018, 09:20:12 pm »
Could it be perhaps that maybe a screw, washer or a nut or other such similar think like a shield might have laid there for a while and corroded away and your left with the residue?
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Offline factory

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10633 on: May 13, 2018, 11:17:21 pm »
Talking of TEA things that tempt me but I'm not going to bite on, there's a FLUKE 5440B Direct Voltage Calibrator going as a buy it now for £450 on ebay UK if anybody's interested. Start your own home cal lab!



If I lived in the UK I'd made an offer already. This is the thing I'm sorely missing! £450 isn't really much if it works.
Problem being of course is that it would need it to be calibrated first once you repaired it

From mobile device so predictive text might have struck again
I was under the impression that the calibrator is in working condition.
My Knick allows me to generate up to 150 volts DC, but above that I have nothing, and I also have no stable AC source.
The Fluke may not be calibrated, but it might generate stable voltages over a wide range.

If it is working, why couldn't they be bothered to show it powered up? Then again the seller seems to be one of those places that lists/sells the items for you.
Hopefully they haven't tried sticking 240V into it given the label showing it set for 115V supply voltage, also the box it's pictured in would probably cause the item to get damaged in shipping as there is no room for proper packing.

David
 

Offline Ero-Shan

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10634 on: May 13, 2018, 11:19:24 pm »
Could it be perhaps that maybe a screw, washer or a nut or other such similar think like a shield might have laid there for a while and corroded away and your left with the residue?
I frankly don't know. Whatever caused this didn't damage the electronics, though. That's the main thing, so I'm content.
 

Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10635 on: May 13, 2018, 11:28:53 pm »
Talking of TEA things that tempt me but I'm not going to bite on, there's a FLUKE 5440B Direct Voltage Calibrator going as a buy it now for £450 on ebay UK if anybody's interested. Start your own home cal lab!
I was going to say about it being set for 115v and that if they've connected it to 240v then it will almost certainly require a lot of fixing. For something that cost the best part $14,000 new it doesn't look like its been cared for much either. It does however seem to be attracting plenty of watchers, it had 10 at the last check.



If I lived in the UK I'd made an offer already. This is the thing I'm sorely missing! £450 isn't really much if it works.
Problem being of course is that it would need it to be calibrated first once you repaired it

From mobile device so predictive text might have struck again
I was under the impression that the calibrator is in working condition.
My Knick allows me to generate up to 150 volts DC, but above that I have nothing, and I also have no stable AC source.
The Fluke may not be calibrated, but it might generate stable voltages over a wide range.

If it is working, why couldn't they be bothered to show it powered up? Then again the seller seems to be one of those places that lists/sells the items for you.
Hopefully they haven't tried sticking 240V into it given the label showing it set for 115V supply voltage, also the box it's pictured in would probably cause the item to get damaged in shipping as there is no room for proper packing.

David
Who let Murphy in?
 

Offline GerryBags

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10636 on: May 14, 2018, 06:39:19 am »
Ero-Shan - that looks to me exactly like the corrosion you get in a coastal environment.
 

Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10637 on: May 14, 2018, 07:48:56 am »
Ero-Shan - that looks to me exactly like the corrosion you get in a coastal environment.
Could be, especially if the metal was scratched?
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Offline GerryBags

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10638 on: May 14, 2018, 08:12:29 am »
I had some amazing corrosion formations around the stern glands on my old boat. They were electrically connected to the earth system of the boat to stop galvanic corrosion of the wood around the bronze glands (the propellor-shafts being the connection with the water to ground), or steel around the bronze in the case of a steel hull, but it's that dissimilar materials thing again. On the inside of the hull, down in the bilges it is always wet and salty and with the constant use of a liveaboard you get these huge green and white masses building up on hose-clamps, bolts, anything connected to the glands. It's a more extreme version of what happens inside any electrical gadget, like the VHF radio, but it can also happen much further away from the water in areas where winter storms are common.

It ends up looking like this:
 

Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10639 on: May 14, 2018, 03:30:23 pm »
Oh FFS... yer all on about a effing thirdhand Euro-version of American Idol THE GONG SHOW ?!?

*cough* Thirdhand? The Eurovision song contest was first broadcast in 1956, the Gong Show was first broadcast in 1976. We produce this rubbish, then your countrymen copy it and lap it up. Oh, and of course American Idol (2002) was based on the UK's Pop Idol (2001) and produced by the same Brit, Simon Fuller.

Hardly surprising this whole thing, it's not as if your countrymen don't have previous form: "New Amsterdam", "New York". If you fancy a change again you could try "New Stevenage".  :)

Actually, The Gong Show was based on "Opportunity Knocks" which started on BBC Radio in the '40s; so your show is still a knock-off. As for stealing names for towns, y'all have no room to talk either; there are towns all over your little island whose names are pilfered from the Roman empire.

None of that really matters anyways; where I was going with my comment was "It's a flupping talent show! Who cares?" (And that's a correct answer, BTW) They're always best enjoyed at the end of the season, when you get the "Reader's Digest" condensed version.  :-DD


mnem
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Offline mnementh

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10640 on: May 14, 2018, 03:34:13 pm »
Ero-Shan. That corrosion looks like typical stuff you get on steel/aluminium joints. It does it all by itself. I had a Land Rover that basically looked like that all over.
Yes its the reaction of 2 dissimilar metals in direct contact with each other that will cause that kind of corrosion if they become subjected to moisture so its possible that it might have had some liquid spilled on it or has been in a damp environment for a time.
The main corrosion appears far from where the 2 metals are joined. This is just weird. Whatever, I removed all the powdery stuff. And from the outside it can't be seen.  ;D

Hmmm... what are the chances it was caused by electrolyte from an exploded cap someone replaced ages ago but never bothered to clean up?


Just a random thought...


Congrats on resurrecting it, BTW. That one looks like it was a real head-scratcher.  :-+


mnem
*Toddles off to ded*
 

Offline tautech

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10641 on: May 14, 2018, 05:11:31 pm »
Saved myself from a TEA session today by simply setting a limit on what I was prepared to shell out for a Tek 465 that wouldn't light up.  :phew:
https://www.trademe.co.nz/Browse/Listing.aspx?id=1625234115&archive=1

They're not that common here and only occasionally come up for sale.
Looked pretty straight and tidy so hopefully the buyer knows what their doing and gets it up and running again.
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Online bd139

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10642 on: May 14, 2018, 05:22:28 pm »
That’s not a bad price (£45 UK). Almost certainly a shorted tant and blown fuse. Probably ten minutes fix.

Add some turd polish and you’ve got a £100 profit at least here in the U.K. 
 

Offline Brumby

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10643 on: May 14, 2018, 05:29:00 pm »
If it was this side of the ditch and somewhere within driving distance, I might have gone to $100.  There is some front panel illumination, but no trace.

After checking the settings, if that didn't bear fruit, I'd be hoping for an easy HT/EHT fix ... something obvious and inexpensive.
 

Online med6753

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10644 on: May 14, 2018, 05:34:21 pm »
About $60 USD. Fair price. I agree with bd139 on the fix. I really doubt the CRT is dead as the seller indicated.
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Offline tautech

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10645 on: May 14, 2018, 05:41:45 pm »
That’s not a bad price (£45 UK). Almost certainly a shorted tant and blown fuse. Probably ten minutes fix.

Add some turd polish and you’ve got a £100 profit at least here in the U.K.
That's what I figured it'd be something simple as I'd asked the owner if he'd been inside it and he hadn't.
Hadn't decided whether to flick it or keep it if I'd won it but most likely keep it as some icon to a past age.
I always liked the probe cal fixture on these as you used them for sanity checks for current probes too, something I reckon is sadly missing on modern scopes. The Telequipment models had a current spec for probe cal to gnd for the same purpose.
Was never to bothered about making a buck from it.
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Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10646 on: May 15, 2018, 07:56:15 am »
That Fluke 5440B has just relisted https://www.ebay.co.uk/itm/JOHN-FLUKE-5440B-Direct-Volt-Calibrator-Voltage-IEEE-488-5205-5220-Digital-Out-/362319105716?_trksid=p2385738.m4383.l4275.c10

Haha I think everyone has noticed the 115V has been selected on the back and with them claiming it is working (what on 240V into 115v tappings  :o ) Of course, it could be correctly set up internally, noway of finding out without seeing inside.

I did think about lobbing a very low offer in last night, then I remembered, I don't have that much space free for it, but it could have turned out to be the catch of the century if a low offer was accepted and it did work  :-+
Who let Murphy in?
 

Online bd139

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10647 on: May 15, 2018, 08:10:06 am »
Hooky as anything. Address of registered business is a private residence which means they’re running a crap shifting outfit from a storage unit somewhere. Also it’s not shown working.
 

Offline Specmaster

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10648 on: May 15, 2018, 08:25:57 am »
If its wired internally for 115V they can't show it working  :-DD I must admit, it does seem strange and thats why I never tried a low offer, and of course the limited space, although I have sold a scope and a few other bits but that is in preparation for the newer stuff coming in soon hopefully.

Nothing wrong selling from a private residence as a registered business, plenty of people run a business from home. I know of someone who sells  shit loads of packaging materials on Ebay, Amazon etc. I wanted some some plastic bags urgently and as they are just round the corner from me, said I'd collect them as I knew where they were. The guy asked me where that was and when I told him, he said that was his home and registered office and directed me to a farm just out of town, when I got there, it was an industrial estate that I never knew existed seeing as it was nearly 2 miles off the main road and down a private road. They occupied 3 massive warehouses on that site and were having a fourth built, the moral of the story is, you can't judge purely on the registered or declared address, they may have warehouses in the area that are geared up for mail orders only.
« Last Edit: May 15, 2018, 04:41:48 pm by Specmaster »
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Offline bitseeker

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Re: Test Equipment Anonymous (TEA) group therapy thread
« Reply #10649 on: May 15, 2018, 02:39:26 pm »
Sooooo when do we get to see it unclad?  :-DD

There you go, also opened the rectangle steel can to peek what is under it.  :P

Cool. Added to the POI index. :-+
I TEA.
 


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