Test Equipment Anonymous (TEA) group therapy thread

[bitseeker]

While you guys have been standing around the water cooler debating the merits of one short finding technique vs another I've been working.  And after hours of tracing and dealing with schematics that DON'T match the board (How many times have I had THAT happen) I have FINALLY found the source of the +15V short. 

I present to you bastard 15uf tant. Reads 0.20 ohms. 



It's going to take me at least an hour to restore all the pulled parts on the supply board then install it. Then apply power and see what happens. If I get power up that's great but I'm definitely going order replacement caps for the PSU and do a total recap.

Yay! That was quite the bug hunt. TANTS!

[Kosmic]

3. There is NO WAY in hell am I EVER going to use lighter fluid on a circuit board.  That is just plain dumb and I don't care who's done it. They are asking for trouble. Besides, I don't have any.

How do you clean the board from flux after soldering? I'm using for this IPA.

I tried IPA once but the results were really mediocre. Leave thin brown film and a strong smell.

I think I used this one:




P.S: Sorry for the bad joke I couldn't resist 

[BU508A]

    

[mnementh]

For those of you wondering why I didn't use many of suggestions for finding this shorted tant on the 485 let me give you a quick synopsis as to why:

1. I don't own any thermal imaging devices.

2. None of my power supplies have current limiting. So if it WAS a board short I ran the risk of burning the board and permanently damaging it.

3. There is NO WAY in hell am I EVER going to use lighter fluid on a circuit board.  That is just plain dumb and I don't care who's done it. They are asking for trouble. Besides, I don't have any.

4. Having a schematic that matched the board would have cut the troubleshooting time. Seems I run into this often because Tek is always making updates and improvements during a product run.

 

Yeh, in one video the person wound up his power supply to max which was in my view pretty dangerous as you said, runs the risk of burning out tracks etc  so it makes perfect sense to limit the current and let the voltage collapse to almost zero in the event of a real major short. I'd have no qualms about using lighter fuel or IPA because you do not use a lot of it and you only do small areas at a time and both will evaporate pretty damn quickly so is not an issue (with current limiting ignition is almost impossible) If anything was getting hot enough to cause ignition then it would have been visible before so no need to do liquid testing.

The practise does indeed seem to be pretty wide spread in the professional sphere as I have seen it done before by professional engineers but it is of course done with care, you certainly do not apply the power within the vicinity of the liquid for obvious reasons and I've never seen it used for anything above 19v.

Yes, this is one of those "dirty little secret" techniques which people who know what they're doing use but should NOT share with the ignorant fApple (L)using masses. There's a LOT of that sort of thing out there in the wide, wicked world; starting with use of unprotected LiPo cells as we do in the RC Modeling hobby and a dozen really dangerous practices commonly discussed in the 3DP hobby. Unfortunately, there are lots of those ignorant masses who lurk in here; Every. Freaking. Day.

Just like RC Modeling and 3DP, even experienced users fuck up and burn their houses down. NEVER forget that.

mnem
Don't do this at home, kids!!!

[med6753]

3. There is NO WAY in hell am I EVER going to use lighter fluid on a circuit board.  That is just plain dumb and I don't care who's done it. They are asking for trouble. Besides, I don't have any.

How do you clean the board from flux after soldering? I'm using for this IPA.

I use 100% IPA. I have NO issues with using IPA. I have a big bottle here and also a spray bottle. I DO have an issue with using lighter fluid. I think it's dangerous and can cause damage to some parts.

[bd139]

Yeah lighter fluid is pretty shit for some stuff. Best use for it is writing your name on the ground when you're drunk and lighting it 

Crawled back into normal existence. Temperature hit 38.2 oC! Burned off like that for an hour, got the fluids in and now I feel bloody amazing. Probably a shorted tant in me somewhere 

Now antenna parts shopping 

[mnementh]

There's a big difference between washing your board with alcohol under controlled conditions and applying it (or naphtha and mineral spirits) to an energized but short-circuited PCB which is little more than a potentially arcing electrified heating element. This is by definition the OPPOSITE of "controlled conditions".

mnem
 

 

[BU508A]

I use 100% IPA. I have NO issues with using IPA. I have a big bottle here and also a spray bottle. I DO have an issue with using lighter fluid. I think it's dangerous and can cause damage to some parts.

Ah, now I understand. Lighter fluid, is this Propane/Butane mixture? Yes, this is quite dangerous.
I will stay away from that, too. But since some time I have this Flir One for my Android phone,
which is very handy for such cases. But it is a pain in the neck using it with my phone (Sony Xperia Z3),
which has the micro USB connector on it's left upper side. Have to use a cable with a rectangle plug
to get the Flir One connected. 

[tautech]

Crawled back into normal existence. Temperature hit 38.2 oC! Burned off like that for an hour, got the fluids in and now I feel bloody amazing. Probably a shorted tant in me somewhere 

Overclocked ?
Normal transmission should return soon. 
Or you'll flake out ! 

[mnementh]

I use 100% IPA. I have NO issues with using IPA. I have a big bottle here and also a spray bottle. I DO have an issue with using lighter fluid. I think it's dangerous and can cause damage to some parts.

Ah, now I understand. Lighter fluid, is this Propane/Butane mixture? Yes, this is quite dangerous. (SNIP)

Zippo lighter fuel/BBQ Starter. A mixture of naphtha and mineral spirits. Bloody poisonous and perniciously eyebrow-seeking accelerant.   

mnem
Also doom for your hotdogs... https://youtu.be/RIP80IvFK5Y?t=71

[bd139]

Yep. When I was a kid we had zippos. None of us smoked. Usually for casual arson  . Deadly dangerous things.

[Cubdriver]

Sorry Pat, as I couldn't find much of interest in the UK I was searching on ePay.com for digital counters & voltmeters and that is how I found the Dana, I'm looking forward to the teardown too.

I did end up buying this reversible counter though.   

(Attachment Link)

David

Whoops!! I'm afraid I wound up costing you about $25, then - I took a crack at that one, too, as I'd never seen that model listed before.  That's the danger of a bunch of us having similar interests.  Sorry!  I'd been watching it for months (he previously had it listed at $199 for a loooooong time).  I'd like to see the inside of it when it gets to you, and it's nice to know it will be going to a good home.

-Pat

[med6753]

Yep. When I was a kid we had zippos. None of us smoked. Usually for casual arson  . Deadly dangerous things.

Holy shit....now THAT's dumbass.  Darwin almost caught him.   

[BU508A]

Yep. When I was a kid we had zippos. None of us smoked. Usually for casual arson  . Deadly dangerous things.

    Please tell me this is a fake.       

[bd139]

Perfectly normal with zippo ownership. I remember my grandfather had one. Also had pretty bad parkinsons so was juddering away filling one up. Goes to light up his roll up afterwards and the arm of the chair goes up in flames. He stands up rather slowly, grabs the table cloth off and beats the flames away, then sits down like nothing had happened and carries on the exact point his story was left 

Edit: major flashback then to when I was about 14 and we were camping in the woods. Smell of sterno, zippo fuel and out of date MRE packs from Army surplus 

Edit 2:  https://www.amazon.co.uk/dp/B01M9G16ZS/

[mnementh]

Yeah, perfectly normal...  and so is chemical burns on the front of your leg under the jeans pocket where you keep the damned thing. 

mnem
Another "joy of Zippos" is knowing how long it takes for your eyebrows to grow back.

[tggzzz]

For those of you wondering why I didn't use many of suggestions for finding this shorted tant on the 485 let me give you a quick synopsis as to why:

2. None of my power supplies have current limiting. So if it WAS a board short I ran the risk of burning the board and permanently damaging it.

Currently limiting is very valuable, as you now know

In the absence of that, a series resistor and a low voltage would suffice to limit the current.

[Specmaster]

3. There is NO WAY in hell am I EVER going to use lighter fluid on a circuit board.  That is just plain dumb and I don't care who's done it. They are asking for trouble. Besides, I don't have any.

How do you clean the board from flux after soldering? I'm using for this IPA.

The way I see it, both have their hazards but surprisingly almost every electronics engineer will have at their disposal  some IPA  but very few will have lighter fuel such as Zippo lighter fluid yet both have their unique properties and plenty of uses within the electronic world.

Now it strikes me as some people are horrified at the thought of using lighter fluid in any context what so ever let alone use it to detect short circuits on PCB's and I assume this is because of the flammability aspect?

The plain truth here is that using IPA poses considerably greater fire risk as well as other health risks, but lighter fluid is in fact less volatile and carries almost zero other heath risks.

I attach 2 PDF files that give the data for Zippo petrol (lighter fluid) and for 99% IPA, so in conclusion, Zippo is by far the safer of the 2 fluids and is also the more difficult of the 2 to burn and this fact even surprised me I must say.

[mnementh]

Cigarette lighter fuel contains naphtha. Much more volatile than the base mineral spirits it uses or common household 91% alcohol, which is more than pure enough for 99% of our purposes. Also, the shit makes your workspace stink for days after you use it, whatever you use it for. Common universal household sprayer with adjustable nozzle screwed onto pint bottle of 91% alcohol FTW to minimize damage potential. Hang from wire shelving for convenience and tip-over safety.

For those of you wondering why I didn't use many of suggestions for finding this shorted tant on the 485 let me give you a quick synopsis as to why:

2. None of my power supplies have current limiting. So if it WAS a board short I ran the risk of burning the board and permanently damaging it.

Currently limiting is very valuable, as you now know

In the absence of that, a series resistor and a low voltage would suffice to limit the current.

mnem
I prepared Explosive Runes today.

[Specmaster]

There's a big difference between washing your board with alcohol under controlled conditions and applying it (or naphtha and mineral spirits) to an energized but short-circuited PCB which is little more than a potentially arcing electrified heating element. This is by definition the OPPOSITE of "controlled conditions".

mnem
 

 

This is why you are supposed to use a current limited PSU, so the short cannot pull arcs because the voltage collapses to virtually zero so the actual power dissipated is extremely low. 1A at 19.2V is 19.2W but 1A at say 100mV is way way smaller and is extremely unlikely to cause a spark so ignition is almost zero possibility?  You would have to be some sort of numpty to use a PSU with zero current limiting, which precisely the theory employed in equipment for hazardous areas, extremely low voltages and current.

[Specmaster]

Yep. When I was a kid we had zippos. None of us smoked. Usually for casual arson  . Deadly dangerous things.

Holy shit....now THAT's dumbass.  Darwin almost caught him.   

Agreed, the idiot is supposed to let the fluid drip into the wadding in the main body of the lighter, and then only a few drips at that, always the RTFM   

[bd139]

I’ve been on fire a couple of times worse than that for ref. It looks pretty bad but nothing to worry about mostly. As long as you put it out quick. Most injuries from chemical fires only happen due to the panic when something goes woosh which makes the problem 10x worse.

IPA is pretty nasty stuff if it goes up. Can’t see the flames and the vapour settles on surfaces. You don’t know it’s on fire until your skin starts peeling off or you feel the heat from a distance. Flash point is pretty low too.

[Neomys Sapiens]

For those of you wondering why I didn't use many of suggestions for finding this shorted tant on the 485 let me give you a quick synopsis as to why:

1. I don't own any thermal imaging devices.

2. None of my power supplies have current limiting. So if it WAS a board short I ran the risk of burning the board and permanently damaging it.

3. There is NO WAY in hell am I EVER going to use lighter fluid on a circuit board.  That is just plain dumb and I don't care who's done it. They are asking for trouble. Besides, I don't have any.

4. Having a schematic that matched the board would have cut the troubleshooting time. Seems I run into this often because Tek is always making updates and improvements during a product run.

Yes, it was also a good reason to spare you the hint that a board like yours seemed to be the perfect application for the GenRad GR2220 BugHound, as you would have surely used it if you had one.

[mnementh]

There's a big difference between washing your board with alcohol under controlled conditions and applying it (or naphtha and mineral spirits) to an energized but short-circuited PCB which is little more than a potentially arcing electrified heating element. This is by definition the OPPOSITE of "controlled conditions".

mnem
 

This is why you are supposed to use a current limited PSU, so the short cannot pull arcs because the voltage collapses to virtually zero so the actual power dissipated is extremely low. 1A at 19.2V is 19.2W but 1A at say 100mV is way way smaller and is extremely unlikely to cause a spark so ignition is almost zero possibility?  You would have to be some sort of numpty to use a PSU with zero current limiting, which precisely the theory employed in equipment for hazardous areas, extremely low voltages and current.

Dude... we're dealing with PCBs loaded with inductors and capacitors. are you really going to suggest that if you have an intermittent connection, as would be very possible with a ancient cracked tant, that you couldn't have a spark as you flex the board even limited at say... 200mA?

I know for a fact otherwise; ESPECIALLY where MLCC caps and tants cohabitate on the same PCB.

Also still not willing to live with the stink of lighter fluid. Shit is just plain unfit for civilized spaces. 

mnem
*tzzzt*

[Neomys Sapiens]

Here's something some of you might be able to answer: I have a nice set of Teledyne drafting tools. Unfortunately, the foam in their case badly deteriorated and created some kind of chemical reaction with the metal that was touching it, causing pitting. I've removed the instruments and cleaned them as best I can, but I'd like to replace the foam with something modern, but it needs to be easy to cut so the nice little spots for the instruments can be recreated. Any recommendations? It appears the foam in the bottom of the case is about 0.6" (1.524 cm) thick, while the top is about 0.4" (1.016 cm) thick.

I was much enlightened when I learned how such form-fitting inserts are made. They basically use two different techniques.
One is built up from sheets/plates of one or even of two different materials. That is close to how the so-called 'shadow trays', which outline every tool's position brightly, are made. But it can use more layers. The side walls of any position are vertical or slightly stepped in this case.

The other method translates the desired shapes into metal 2d stencils and corresponding pressures. The foam part is placed onto the stencil and pressure is applied. Then, all material that is standing out on the other side is cut off by a straight blade, almost like a shave. If the form is complex, they use different stencil/pressure combinations consecutively.

So when one sees a gradually rounded recess for the fingertips, this is not cut with a curved spoon-like tool, but it is a oval cut-out in the stencil, which, combined with the specific flexibility of the foam, allows such a shape to be made.