Author Topic: what's your recent fail?  (Read 7799 times)

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Offline exeTopic starter

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what's your recent fail?
« on: April 20, 2021, 06:27:43 pm »
Hi folks,

I just made a combo fail. One is, I assumed that in complimentary bjts (like 2n3904 and 2n3906) the smaller part number means NPN. Turned out not to be the case in case of 2SD882 (npn) and KSB772 (pnp).

The second is, I installed transistors backwards. That's because I got pinout from my new transistor tester the wrong way. Turned out contacts on the ZIF socket numbered not the way I expected.

What's your recent fail?

PS transistors and my expensive opamp which I have in single quantity (lt1468) survived the abuse thanks to limiting current when I power the circuit. The opamp tried to sink current from the output, got hot, I noticed that and fixed the circuit.
 

Offline harerod

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Re: what's your recent fail?
« Reply #1 on: April 20, 2021, 07:55:20 pm »
Sadly, most likely, your poor, mistreated LT1468 will not match its spec anymore. Better get a invest 12€ in a couple of replacement with the next parts order.
But you knew that already...
« Last Edit: May 03, 2021, 07:56:28 am by harerod »
 

Offline exeTopic starter

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Re: what's your recent fail?
« Reply #2 on: April 20, 2021, 08:02:02 pm »
Yep, measured offset is 15mV. Either it's oscillating (will check tomorrow), or I fried it. I usually buy at least two ICs of each kind to eliminate doubts when things don't work as expected, but Idk why I have only one of it.
 

Offline T3sl4co1l

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Re: what's your recent fail?
« Reply #3 on: April 20, 2021, 08:37:58 pm »
Burned four old RF transistors trying to make a buffer amp with them. Seems they don't like running on the edge of ratings (which I don't have, but based on behavior they're somewhere around 20V 200mA -- TO-39 metal can, and I'd even gone to some trouble to heatsink them well!).

Tim
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Bringing a project to life?  Send me a message!
 

Offline exeTopic starter

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Re: what's your recent fail?
« Reply #4 on: April 21, 2021, 07:12:48 am »
Burned four old RF transistors trying to make a buffer amp with them. Seems they don't like running on the edge of ratings (which I don't have, but based on behavior they're somewhere around 20V 200mA -- TO-39 metal can, and I'd even gone to some trouble to heatsink them well!).

What were their part numbers, if I may ask?
 

Offline DTJ

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Re: what's your recent fail?
« Reply #5 on: April 21, 2021, 08:31:24 am »
Killed yet another DMM fuse by trying to measure voltage with the test leads in the wrong hole.

I guess manufacturers know this is going to happen and then make the fuses expensive!
 

Online PartialDischarge

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Re: what's your recent fail?
« Reply #6 on: April 21, 2021, 09:35:54 am »
Burned four old RF transistors trying to make a buffer amp with them. Seems they don't like running on the edge of ratings (which I don't have, but based on behavior they're somewhere around 20V 200mA -- TO-39 metal can, and I'd even gone to some trouble to heatsink them well!).

Tim

That is completely your fault, next time use a triode and care no more about ratings.

 
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Offline station240

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Re: what's your recent fail?
« Reply #7 on: April 21, 2021, 09:52:40 am »
Measuring waveforms around a circuit I made, and the breadboard test rig I'm using to test it, got very noisy 50V P-P waveforms.
1. Scope probe ground was connected to the wrong ground point (hence the noise).
2. Scope probe had been been bumped out of x10 down to x1 (hence 50V on a 5V circuit)
3. Circuit is more reliable if everything is powered from one 5V source (some of the noise).

So while I suspected I was seeing 50V floating from my isolated 5V supply and changed the setup, it fixed a problem but not the one I had in mind.
The circuit has optoisolators, hence the need to have the scope ground probes on the correct location.

 

Offline Ed.Kloonk

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Re: what's your recent fail?
« Reply #8 on: April 21, 2021, 10:32:21 am »
I forgot to put the charger on a car battery yesterday so a car would be ready for today.

iratus parum formica
 

Offline T3sl4co1l

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Re: what's your recent fail?
« Reply #9 on: April 21, 2021, 12:24:15 pm »
What were their part numbers, if I may ask?

TRW / 201 (top)
PT4578 / 7922 (side)

Not new, as you can see. :)


That is completely your fault, next time use a triode and care no more about ratings.

I would gladly, if I had one that offered even a fraction of the bandwidth and ran on the voltages available in circuit. :(

And not for lack of familiarity, or trying: here's a 6LB6 being pulsed at a cool 3kW or so (1270V into 500 ohms).  But as you can see, it's terribly, terribly slow.  Plate capacitance is just way too much.  (Top: plate, 100x, AC coupled; bottom: grid, 10x.)



Tim
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Bringing a project to life?  Send me a message!
 

Offline nicknails

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Re: what's your recent fail?
« Reply #10 on: April 21, 2021, 12:47:00 pm »
Connected power backwards and damaged 6 IC's  :palm:
 

Offline YurkshireLad

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Re: what's your recent fail?
« Reply #11 on: April 21, 2021, 02:10:12 pm »
I recently got new glasses, I also now need reading glasses. Of course, I decided not to use the new reading glasses and accidentally connected the ground pin of an AHT10 to 5V input. No magic smoke, but poof! Luckily a minor mistake to a minor component. I'm being more careful and I'm using my reading glasses now too!  :palm:
 

Offline Melt-O-Tronic

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Re: what's your recent fail?
« Reply #12 on: April 21, 2021, 03:46:48 pm »
I had been injecting power into a circuit with DMM probes connected to my 66309D power supply.  I had another set of probes plugged into a DMM.  A few hours later, working on a completely separate circuit, I picked up the wrong probes to check for the presence of mains voltage.   :palm:

God was merciful.  It only blew a small fuse on the 66309D's motherboard and I had spares.  Ugh.  This is how I learn bad practices.
 

Offline mindcrime

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Re: what's your recent fail?
« Reply #13 on: April 21, 2021, 05:30:22 pm »
My most recent "D'oh, fail!" moment was a few weeks ago. I was playing around with one of those 4-pin crystal oscillators on a breadboard, and getting a reading of a very weak 60hz signal on the scope, even though the part was supposed to be something like 24mhz or something. It didn't take long to figure out that the oscillator wasn't outputting anything, and that what I was seeing on the scope was just line-noise from the 60hz mains in the room. But why wasn't the oscillator oscillating? :scared: :wtf:

Well... it turns out that sometimes when you are looking at a part bottom-side down on the bread-board, and simultaneously looking at the datasheet on a PC screen that's a couple of feet away, and you're not really paying attention to how the part in the diagram is oriented, you can get crossed up on which pins are which. I had wired the thing up like it was upside-down basically. D'oh.  |O  :palm:

Flipped all the connections around and got my signal as expected.   :-+
« Last Edit: April 21, 2021, 05:32:44 pm by mindcrime »
 

Online David Hess

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Re: what's your recent fail?
« Reply #14 on: April 22, 2021, 12:21:05 am »
I powered up one of my old legacy PCs to copy the BIOS off for someone.  It had been partially disassembled while I decided whether to refurbish it and without the fan noise, I did not realize that I left it on.  By the next day, overheating had apparently damaged it because it no longer starts the POST.
 

Online artag

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Re: what's your recent fail?
« Reply #15 on: April 22, 2021, 03:08:17 pm »
Ordered some SMA right-angled sockets. Didn't notice until I'd soldered them in that they were the reverse sort with a pin where the hole should be. Evil things !
 

Offline mindcrime

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Re: what's your recent fail?
« Reply #16 on: April 22, 2021, 06:20:25 pm »
Last night I was soldering headers on a new Arduino 33 IoT board. Got the first side done fine, then started on the other side. Got down to where I had about 4 more pins to solder when I realized that when I inserted the row of headers I misplaced it by one hole, so the D13 pad was empty, and one of my header pins was sticking through the mounting hole.  :palm:

Luckily I was able to cut the "extra" pin off, and then successfully get it solder in place on D13. I tell ya what though... to me, soldering headers like that is one of the most challenging things I ever do, and that's doing a full row where the thing is supported once you tack a couple in place. But soldering a single header pin by itself like that? ^@#!@#&#$%@@#!!!!!  Not fun. If you guys know the "trick" to doing that, please share.
 

Offline exeTopic starter

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Re: what's your recent fail?
« Reply #17 on: April 22, 2021, 07:33:37 pm »
If you guys know the "trick" to doing that, please share.

I insert headers into the breadboard, this way it's trivial to solder. This also guarantees that after soldering pin headers will fit the breadboard.

It might be difficult to remove the the device after soldering. For this I use IC puller/remover.

If the board is too big to fit the breadboard then I insert only one side, and make a support for the other side.
 
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Offline duckduck

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Re: what's your recent fail?
« Reply #18 on: April 22, 2021, 07:35:52 pm »
Posted my fail (with "after" picture) 5 days before you asked:

https://www.eevblog.com/forum/beginners/should-i-power-a-device-with-the-leads-hooked-up-backwards-on-the-power-supply/msg3549908/#msg3549908

Oh, the replacement signal generator didn't work. Damn cheap crap off of Amazon...
 

Offline exeTopic starter

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Re: what's your recent fail?
« Reply #19 on: April 22, 2021, 08:43:16 pm »
Posted my fail (with "after" picture) 5 days before you asked:

Wow, that's quite some explosion!

while I decided whether to refurbish it

I guess the decision has been made :)


Meanwhile my probe slipped and I shorted poor's lt1468 pins to a power rail. Now it's really dead, huh :(. Ordering four more just in case...
 

Offline mindcrime

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Re: what's your recent fail?
« Reply #20 on: April 22, 2021, 09:10:17 pm »
If you guys know the "trick" to doing that, please share.

I insert headers into the breadboard, this way it's trivial to solder. This also guarantees that after soldering pin headers will fit the breadboard.

It might be difficult to remove the the device after soldering. For this I use IC puller/remover.

If the board is too big to fit the breadboard then I insert only one side, and make a support for the other side.

Oh, that's genius! Can't believe that thought never occurred to me. D'oh. Thanks for sharing. I am totally doing that from now on.  :-+ :-+
 

Offline harerod

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Re: what's your recent fail?
« Reply #21 on: April 23, 2021, 05:10:25 pm »
exe on Yesterday at 20:33:37mindcrime on Yesterday at 19:20:25
If you guys know the "trick" to doing that, please share.

I insert headers into the breadboard, this way it's trivial to solder. This also guarantees that after soldering pin headers will fit the breadboard.

It might be difficult to remove the the device after soldering. For this I use IC puller/remover.

If the board is too big to fit the breadboard then I insert only one side, and make a support for the other side.

Oh, that's genius! Can't believe that thought never occurred to me. D'oh. Thanks for sharing. I am totally doing that from now on.  :-+ :-+
Just make sure to apply lots of heat, otherwise the plastic of the breadboard would melt. >:D
 

Offline mindcrime

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Re: what's your recent fail?
« Reply #22 on: April 24, 2021, 08:43:24 am »
exe on Yesterday at 20:33:37mindcrime on Yesterday at 19:20:25
If you guys know the "trick" to doing that, please share.

I insert headers into the breadboard, this way it's trivial to solder. This also guarantees that after soldering pin headers will fit the breadboard.

It might be difficult to remove the the device after soldering. For this I use IC puller/remover.

If the board is too big to fit the breadboard then I insert only one side, and make a support for the other side.

Oh, that's genius! Can't believe that thought never occurred to me. D'oh. Thanks for sharing. I am totally doing that from now on.  :-+ :-+
Just make sure to apply lots of heat, otherwise the plastic of the breadboard would melt. >:D

FWIW, I was soldering headers on another Arduino Nano tonight and I tried this technique of jamming the headers in the breadboard. The board width wasn't just right for both rows to plug in, so I did one side, and just used a few wads of heat shrink tubing to support the other side. Worked a treat. Much nice than trying to tack them in place with glue or tacky blue loctite goop, etc., and then solder with the board elevated.

I'll definitely be using this in the future when dealing with header pins. Thanks again for sharing the tip, exe!
 

Online Ice-Tea

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Re: what's your recent fail?
« Reply #23 on: April 24, 2021, 09:03:16 am »
Needed a 1kV signal so hooked up my bench DMM to the source to tune it. Turned on the source.

...

The source goes up to 2kV and that was exactly what it was still set to. Hint: the bench DMM goes up to 1kV.
 
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Offline bd139

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Re: what's your recent fail?
« Reply #24 on: April 24, 2021, 09:05:49 am »
 :-DD. Reminds me of the BM22s I tortured a while back



Still works even when it got 2.1KV! Made some unpleasant noises though.
 


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