Design a New Precision LCR Tweezers with Much Lower Cost 【Shannon Tweezers ST42】

[tautech]

I ordered a ST42 I am interested in being able to somewhat qualify/gauge the "fried or not ?" status of some capacitors, in-circuit, without always needing to desolder them.
I and my friends & family often have some items or appliances which always seems to fry due to corners cut on the BoM.

Like, on multiple cheap electric heaters bought at the same manufacturer, a capacitor after some diode bridge rectifier, had been choose by the manufacturer at a rating of 275 V (our mains AC is 230V +/- 10%), of no-name or similar quality. I replaced those 275 V caps by 350/375 V+, and they work again...

The capacitor was used to power the very very small PCB handling the controls and the small monochrome LCD.
The appliance is powered on by a "soft" button, I think it maybe has some implications to forcibly always being powering some IC.

At the time on some forums, some people said that if we were "unlucky" to "power on" the heater at "the wrong time" of the AC sinusoidal (which happens 100 times per second...), the capacitor which is rated too low would suddenly charge (it's a cap!) at a high current, at high rectified DC.

Well anyway, it was just for the anecdocte ;
- A LNK304GN fried during storm & lightning
- a remote parking lot door that the building maintenance company says it doesn't work anymore due to being too old, which I suspect they have in fact fraudulently removed from the associated rolling codes
- a pool robot which card has taken some water, and may be salvaged
- an air conditionner PCB which sometimes shut off after some minutes
- a remotely controlled garage door where one of the two motors door aren't anymore powered (motors work), so it's the relay or whatever which I didn't yet identified

Some stuff to diagnose !

Welcome to the forum.

Few devices offer full reliability for 'in-circuit' tests however with some circuit understanding we can identify when a measurement seems correct or not.
Never discount the skills gained from removing components for accurate tests.

[folays]

Few devices offer full reliability for 'in-circuit' tests however with some circuit understanding we can identify when a measurement seems correct or not.
Never discount the skills gained from removing components for accurate tests.

Yes, I don't mind removing the presumably-failed component, and test it with my BM869s, especially if it is indeed the failed one, and I aim to resolder a replacement.

But for 5+ capacitors, if the ST42 is able to correctly "hint" the first which should undergo the "desolder" treatment, that's a good thing

[tautech]

Few devices offer full reliability for 'in-circuit' tests however with some circuit understanding we can identify when a measurement seems correct or not.
Never discount the skills gained from removing components for accurate tests.

Yes, I don't mind removing the presumably-failed component, and test it with my BM869s, especially if it is indeed the failed one, and I aim to resolder a replacement.

But for 5+ capacitors, if the ST42 is able to correctly "hint" the first which should undergo the "desolder" treatment, that's a good thing

This is where your experience dominates.....I've been using SMD smart tweezers for nearing 2 decades and will only blindly trust out of circuit tests. 
Still, ST42 is the best SMD tweezer I have used.

[DaneLaw]

This is where your experience dominates.....I've been using SMD smart tweezers for nearing 2 decades and will only blindly trust out of circuit tests. 
Still, ST42 is the best SMD tweezer I have used.

What other "Smart" SMD tweezers have you tried over these last 2 decades?

[snorlax212]

Hi guys. I accidentally applied 12v dc to my Shannon tweezers via type-c, so one IC is burnt (I hope its the only one). Can you please help me to identify this IC?

[ceut]

Hi guys. I accidentally applied 12v dc to my Shannon tweezers via type-c, so one IC is burnt (I hope its the only one). Can you please help me to identify this IC?

I give you a photo of mine I have done when I was fixing my CH340e problem 
Best thing to do => PM Shannon to ask him 

Also, it seems that it is the well-know IC Charger LTC4054-LTH7 which has burned on yours (with 12V on the input: it would be somewhat logical)

[snorlax212]

Hi guys. I accidentally applied 12v dc to my Shannon tweezers via type-c, so one IC is burnt (I hope its the only one). Can you please help me to identify this IC?

Also, it seems that it is the well-know IC Charger LTC4054-LTH7 which has burned on yours (with 12V on the input: it would be somewhat logical)

Thanks to you and @nAyPDJ (for https://www.eevblog.com/forum/testgear/design-a-new-precision-lcr-tweezers/msg4775666/#msg4775666).
Its indeed LTH7, I replaced it with TP4054 (chinese equivalent), and now charging works (trace under LTH7 was "welded" to burnt IC, so I cut it and replaced with wire).
However, tweezers not detecting when connected to pc in bootloader mode, so something else is broken.
As device use ch340 IC (340ED02 chip labeled on pic.), I can assume that this IC is burnt too.
Does it make sense to replace it? I ask because I have mediocre soldering skills to desolder this IC with common soldering iron (cannot use hot air due to display).

Offtop:

Best thing to do => PM Shannon to ask him 

I did it at first, but after sent PM I had no messages in "Sent items", I did it again and still no data, looks like forum issue (and I spammed Shannon's with PMs abit
Also hes not often visit the forum

[Kean]

Its indeed LTH7, I replaced it with TP4054 (chinese equivalent), and now charging works (trace under LTH7 was "welded" to burnt IC, so I cut it and replaced with wire).
However, tweezers not detecting when connected to pc in bootloader mode, so something else is broken.
As device use ch340 IC (340ED02 chip labeled on pic.), I can assume that this IC is burnt too.
Does it make sense to replace it? I ask because I have mediocre soldering skills to desolder this IC with common soldering iron (cannot use hot air due to display).

Well done.
It does make sense that the CH340 would also be powered off the USB power, so it is indeed likely damaged.
I would recommend cutting the pins with sharp side cutters to remove it.  You could use a knife, but it is very easy to damage PCB traces that way.  Then use the soldering iron to remove the pins left behind.

When soldering the new part, just tack solder one corner pin, make sure it is properly centred on all pads, then tack solder the opposite corner.  Finally drag solder all the pins using extra flux.
With these finer pitch parts, I find it good to drag outwards (along the pins/traces) with minimal solder to avoid bridges.  Do not press too hard, just use flux and a tiny bit of solder on the iron tip.

[snorlax212]

Its indeed LTH7, I replaced it with TP4054 (chinese equivalent), and now charging works (trace under LTH7 was "welded" to burnt IC, so I cut it and replaced with wire).
However, tweezers not detecting when connected to pc in bootloader mode, so something else is broken.
As device use ch340 IC (340ED02 chip labeled on pic.), I can assume that this IC is burnt too.
Does it make sense to replace it? I ask because I have mediocre soldering skills to desolder this IC with common soldering iron (cannot use hot air due to display).

Well done.
It does make sense that the CH340 would also be powered off the USB power, so it is indeed likely damaged.
I would recommend cutting the pins with sharp side cutters to remove it.  You could use a knife, but it is very easy to damage PCB traces that way.  Then use the soldering iron to remove the pins left behind.

When soldering the new part, just tack solder one corner pin, make sure it is properly centred on all pads, then tack solder the opposite corner.  Finally drag solder all the pins using extra flux.
With these finer pitch parts, I find it good to drag outwards (along the pins/traces) with minimal solder to avoid bridges.  Do not press too hard, just use flux and a tiny bit of solder on the iron tip.

Thanks, I will try to replace it.

[ceut]

Thanks, I will try to replace it.

Here are some links of mine, may help you swap the chip  :
https://www.eevblog.com/forum/testgear/design-a-new-precision-lcr-tweezers/msg5349764/#msg5349764
https://www.eevblog.com/forum/testgear/design-a-new-precision-lcr-tweezers/msg5392076/#msg5392076

I have done all with my Anondstar AD206 Microscope and my TS-100
(no need to use Hot Air as there is no big thermal pad under this very low-power communcation IC).

[KungFuJosh]

Does it make sense to replace it? I ask because I have mediocre soldering skills to desolder this IC with common soldering iron (cannot use hot air due to display).

Yes, replace it, but get the right tools for the job. Something like "Chip Quick SMD remover" will make removal easy: https://www.amazon.com/dp/B015RV4NBS/

Just be careful to clean up really well with IPA before installing the new part.

Thanks,
Josh

[Kean]

Just be careful to clean up really well with IPA before installing the new part.

The ChipQuik low temperature alloy is great for removing parts with many pins.  I've used it many times myself, but it is a bit pricey and has a limited shelf life.
Don't just clean up with IPA though, I'd suggest you first want to use solder wick to get rid of the majority of any remaining alloy.
Maybe I just use too much of it...

[KungFuJosh]

it is a bit pricey and has a limited shelf life.

I think the $10 is worth it considering how well it works. How long did yours last that shelf life was an issue? I have two tubes of it that have been inside a pencil box for a couple years without issue.

You certainly don't need a lot of the stuff, but it can make a mess either way. 😉

[Kean]

it is a bit pricey and has a limited shelf life.

I think the $10 is worth it considering how well it works. How long did yours last that shelf life was an issue? I have two tubes of it that have been inside a pencil box for a couple years without issue.

You certainly don't need a lot of the stuff, but it can make a mess either way. 😉

Down under I think it costs about 3x what you would pay in the USA.  Yay...

It may have just been certain batches that were a problem, or some bad storage.  There was a discussion some time ago so it wasn't just me.
https://www.eevblog.com/forum/manufacture/crusty-chipquick/

I just checked, and the bulk pack I bought in 2017 still looks nice and shiny, but my two older packs look terrible.  So based on that, I should probably "retract" the shelf life thing - but it is something to watch out for especially if buying in bulk.

[snorlax212]

Its indeed LTH7, I replaced it with TP4054 (chinese equivalent), and now charging works (trace under LTH7 was "welded" to burnt IC, so I cut it and replaced with wire).
However, tweezers not detecting when connected to pc in bootloader mode, so something else is broken.
As device use ch340 IC (340ED02 chip labeled on pic.), I can assume that this IC is burnt too.
Does it make sense to replace it? I ask because I have mediocre soldering skills to desolder this IC with common soldering iron (cannot use hot air due to display).

Well done.
It does make sense that the CH340 would also be powered off the USB power, so it is indeed likely damaged.
I would recommend cutting the pins with sharp side cutters to remove it.  You could use a knife, but it is very easy to damage PCB traces that way.  Then use the soldering iron to remove the pins left behind.

When soldering the new part, just tack solder one corner pin, make sure it is properly centred on all pads, then tack solder the opposite corner.  Finally drag solder all the pins using extra flux.
With these finer pitch parts, I find it good to drag outwards (along the pins/traces) with minimal solder to avoid bridges.  Do not press too hard, just use flux and a tiny bit of solder on the iron tip.

Thanks, I will try to replace it.

I replaced ch340e and successfully upgraded to ver. 1.5.7! At first glance, everything works fine. Thanks to all!

[ceut]

I replaced ch340e and successfully upgraded to ver. 1.5.7! At first glance, everything works fine. Thanks to all!

Well done 

- CH340e problems (mine+USB overvoltage): fixed
- LTH7 problem (USB overvoltage): fixed

We can tell for now that the ST42 seems to be a fixable tool and it is a great news! 

Don't remember if someone has damaged (then fixed) his ST42 with inputing voltage on the tweezer tips ?

[Kean]

I replaced ch340e and successfully upgraded to ver. 1.5.7! At first glance, everything works fine. Thanks to all!

Looks very nice, just like a bought one.

[Shannon]

Don't remember if someone has damaged (then fixed) his ST42 with inputing voltage on the tweezer tips ?

Never let the ST42 input end overvoltage, it will cause irreparable damage

High-precision LCR, input overvoltage protection is not easy to design, we have tried in this regard.
Desktop LCR uses a diode bridge for some protection, and the size of those diodes is large enough.

By the way, how high voltage protection do you think is reasonable? Too high voltage will be more difficult to implement. Maybe 30V?

When repairing circuit boards with voltages exceeding 30V, people are generally more cautious.
For example, when repairing air conditioner circuit boards, always have a thick screwdriver ready to discharge the charge of the capacitor.

[ceut]

Never let the ST42 input end overvoltage, it will cause irreparable damage

High-precision LCR, input overvoltage protection is not easy to design, we have tried in this regard.
Desktop LCR uses a diode bridge for some protection, and the size of those diodes is large enough.

By the way, how high voltage protection do you think is reasonable? Too high voltage will be more difficult to implement. Maybe 30V?

When repairing circuit boards with voltages exceeding 30V, people are generally more cautious.
For example, when repairing air conditioner circuit boards, always have a thick screwdriver ready to discharge the charge of the capacitor.

Hello Shannon 
No problem, I know that very well, and I use my ST42 with care when, for example, I check capacitor 

=>I was just wondering if someone here has inadvertently put voltage on the ST42 and has to fixed it ? 

[Martin72]

For example, when repairing air conditioner circuit boards, always have a thick screwdriver ready to discharge the charge of the capacitor.

 

I wouldn't do that...
Using this method, you can damage the capacitors, because a large current flows at that moment.
Better:
use a discharge resistor, which then also limits the current.

[KungFuJosh]

use a discharge resistor, which then also limits the current.

Exactly! I made the attached with a mediocre probe connected to an alligator clip with an inline discharge resistor for discharging caps.

[ceut]

I use tweezers for my part 

Its name is "discharge capacitor pen", lowcost so great for me 
(I found a teardown with a guy who has done the schematic, don't remember where    )

And never shortcut a capacitor, see here a great japanase guy who made many experiments/explanations and great teardown of Nichicon Caps 

[Shannon]

I use tweezers for my part 

Its name is "discharge capacitor pen", lowcost so great for me 
(I found a teardown with a guy who has done the schematic, don't remember where    )

And never shortcut a capacitor, see here a great japanase guy who made many experiments/explanations and great teardown of Nichicon Caps 

This one looks like it's specially made for st42, because it has the same tweezer tip width as st42, and both have the problem of insufficient distance for large capacitors

And I found this one 1000V supported as well, which could adjust the tips distance, but looks quite dangerous.

[Phil1977]

I blew up two of these devices with small caps that were just filled with 600V.

Better to use a simple resistor with voltage that high.

[folays]

Hi, I found a display/convenience bug when using left-handed display mode;

The tweezer "measuring diode" icon is in the wrong direction in left-handed mode. And display the "found" direction in the wrong direction.

For low-voltage diodes (1.2V), the tweezer automatically test both directions, and even displays the "found" forward direction.
But in letf-handed mode, it display the "found" forward direction the wrong way.

For high-voltage diode (3V), the tweer works only in one direction, so we should pay attention to the diode "icon" to known in which direction to test the DUT diode.
But this "icon" suggestion the forward direction is in the wrong direction (when in left-handed mode), so since the Tweezer only test one direction, it "fails" if we do not remember that we have to test the DUT diode in REVERSE-suggested direction.

Confirmed with an Atlas DCS75 Pro to be sure of which terminal is the Anode/Cathode, and tested on the test board sold with the Tweezer.

Best Regards,