EEVblog
ฝัง
- เผยแพร่เมื่อ 27 ส.ค. 2024
- Dave attempts to trace a short "real-time" on the main board of the Lecroy 9384C oscilloscope.
Teardown video is here: • EEVblog #217 - Lecroy ...
Forum Topic: www.eevblog.com...
EEVblog Main Web Site:
www.eevblog.com
EEVblog Amazon Store:
astore.amazon.c...
Donations:
www.eevblog.com...
Projects:
www.eevblog.com...
Electronics Info Wiki:
www.eevblog.com...
One technique I've used is to freeze the whole board until it turns frosty white, and then apply power to low resistance rail while watching which portions board are the first to defrost.
Surely four-wire resistance measurement would have been more reliable here? I don't necessarily mean with a real four-wire multimeter, just feeding 0.1A into the 3.3V rail and finding the component with the lowest voltage at its 3.3V point? This would remove the reliance on sharp leads, and inconsistency due to probing varying oxide thicknesses, as the time variations as various caps charge and discharge in response to the probes.
Dave you need to do that trick WITH the FLIR looking at the board that'd be awesome to see!!!
Hi Dave! I've noticed lots of dust between IC's. I've had once a situation where small piece of metal was mixed with dust causing short in circuit. After applying some air the damn thing just worked fine. Cheers!
Oops. Forgot to add.
When you're cranking in those 11A, measure the voltage across those tantalum capacitors. A low voltage would mean a short nearby.
Dave, instead of a better ohmmeter one can use a millivolt meter. Just connect a current limited supply to the shorted rails.
Soren Kuula watch the video next time. He does that after probing.
Adam Besmer watch the video next time and also read the 1st sentence in Sorens comment.
Yes Dave attached a current limited supply but no he did not use a millivolt meter to find the highest voltage drop.
BTW, he does in part 2.
This gives me great heart knowing that I have not fixed electrical item yet. So even expert like you failing kinda makes me happy!
I love your troubleshooting videos. I learn something new everytime I watch your videos. I am in the electronics repair field and find your videos a invaluable resource for information as well as inspiration for advancing my career. Cheers from Canada
This is where a thermal imaging camera comes in really handy. That's what we use for checking "mystery" boards straight out of manufacturing for layer-to-layer shorts.
I saw a video of a guy finding a short using alcohol, he brushed it over the board and it evaporated first from the hot component. Neat trick. Love your videos. 30+ watts is a lot of energy. Also, my intuition is that if those chips are heating the short might be down circuit from them or they'd have very low voltage.
the problem is, that the psu turns off automatically and with such a delicat device its not a good idea to use that method
Dave,we really enjoy all of your video
I popped the IR filter off a CMOS camera once and could see a soldering iron glow, but yeah, that's still a couple of hundred degrees hotter than you'd need in this application.
You should add this to your “repair” playlist!
This is outragously educational. Thanks for doing this.
12:45 *Melted looking relay towards the bottom of the board.*
13:10 and 13:55 "[No] obviously blown components."
Even if it has nothing to do with the 3.3v rail, still kinda funny XD
Saw that I was like nooo, Look harder!
I was literally screaming at him!
I right away saw this too. Body burned and the relay really sure will not work anymore :D
YAY! I've been waiting quite some time for this video- I love your repair videos, they're very, very interesting- even if you don't quite get it to work!
That static is something out of a horror film. Like a ghost doesn't want you to repair the scope.
I would suggest to feed 0.1-0.5V into 3.3V rail, so that no semiconductors are switching on (they usually start "doing something" after 0.6V) so that only non-semiconductor short is conducting, and measure voltage drop at different points on the PCB.
The point being reading the voltage not the low resistance you don't have to worry about meter lead resistance, the tips to component connection resistance, how hard your pushing on the parts, etc near as much
Fixed or not, this was still a good informative video for diagnosing a bad component.
If you have an IR-thermal camera, you could use that to look at the board as it is being powered to see where the power is being dissipated.
I'll have another go at it tomorrow morning...
Could you try the different way around, heating the board/chips and watch for a increase in resistance of the 3V rail ?
It is a lot of extra power to be dissipated, so I do certainly suspect the heatsunk ASICs in some way.
Thank you for the fantastic lesson. You should do more lessons in fault location and methods. Cheers, again.
For the schematics you can try the schematic of the 9374M I think this units are similary. Here there is the namer of the manual to the manual: LeCroy_9374M-L-TM_Service_Manual.pdf
great i am camerounian and i am watching you are channel step by step it very nice what you are doing
Cameras sensor are sensible to near infrared only, which is the kind that can be used to "see" IR controls and see in the dark (with an IR flashlight), the "thermal" infrared is waay apart from the visible light.
Anyway, if any component gets "red hot", maybe you can see it with your eyes, in the dark.
I really enjoy your repair videos, more of these please :)
One tip is to use an IR (FLIR) camera... faulty circuits pop up like a sore thumb,
have used that method sucessfully several times.
BTW cheapest thermal imaging cameras are like 1500$ (60x60 resolution), which is somewhat affordable - so it's slowly falling out of 'fancy equipped' category.
..and a little while later,I see you tried this method!
(That's what I get for commenting before watching the entire video.)
Don't know if it would work, but cameras are more senstive to IR than we are. Try hooking up to the high power supply, turning out the lights making the room as dark as possible and looking through the camera screen. It's a shot in the dark (pun, sorry!) but might help.
Ever try feeding the shorted buss with a PS limiting the current to a max 1 amp (and 3.33v) and looking for the lowest voltage across the component? The short in this case should limit the voltage to well below what the good ASICs start to turn on. 1 amp .16 ohm .16 volts.
Also I have found shorts like this in the past by spraying a board area with chiller till its really cold and frosts up, Apply power and look for what defrosts first. Those vortex chillers that run on compressed air work well.
The Scope is not a purely resistive load, and the leads and connectors do factor in, too
Few days ago I wondered what had happened to this LeCroy, and was going to make a post on the forum asking about it. Murphy:)
Sorry mate did not mean to offend was kinda joke. To make me feel better about keeping with electronics. I love your show! Keep up good work.
Pretty crazy for sure. Pulling 11 amps when the PS can only supply 6 makes it sure seem like something is wrong and gone to ground. Since the chips all got warm, is there an additional regulator that supplies all of them, or some other common component? Schematic with voltages or resistance measurements sure would be handy right now!
Unless some spike on one of the other rails/or the 3.3V rail triggered it, that is.
I assume they are quite much connected to the same places (just different "port number" for digital stuff), so one fault could possibly have killed them all.
Nice video! thumbs up! I think you will have to remove the heatsinks of these devices and power them up to see which one is the faulty.
every time someone says "murphy's law" i think of my actual friend murphy showing up and breaking things.
You don't thutch with the probe, you just hold close to the device. If there is a dc current the resistance in the probe will go down and you must set the referance on your instrument
No, nothing to do with it. Inadvertent damage during the teardown.
Hi Dave! What strikes me is that the ”blow the crap out of the faulty component” method didn´t work. I dont think that anything that wasn't designed for that could have survived 11Amps. Maybe you should look closer at the power supply! My gut says that the board is ok... :)
I agree, but I just could not resist.
The PSU is where l look. Its rated less then 35amps output given that wire size of 18 or 20ga at the MB connection, if not it would have melted a long time ago. Unless the 3.3 splits the load.
Voltage should drop on a place where short is present.
When you're applying power supply it sinks more current than LeCroy power supply limit due to short.
This will work only if short has 0 Ohm resistance.
An interesting approach could have been to use a thermal imaging camera. You could hook up an external high current 3.3V power supply, turn it on for a second or two and see where the board gets hot. Crude, but it could work if you accept the possibility of blowing up the board.
I have a Kef Kit160 and makes a buzzing sound but had it open and can't find exactly what in the power supply is making the buzzing sound. And just because that is buzzing don't mean it fault could be something using more power than it should.
I agree. I would also like to see Dave dump 11 Amps through other expensive equipment.
The AIM-TTi I-Prober 520 Current Probe might show the route the 11A are following. If you've still got it, that is...
I've got a method to find your short,and possibly even remove the bad part from the board,all at once!
3.3V at 100A.
There can be some unintended casualties though.
(Not afraid to admit,I've actually used this method before,successfully even!)
3.2V at 11A is 0.29 ohms. That's really a really low resistance, even for a short at the end of a trace. You might have a poorly soldered DC socket.
Thats a real tough one with it taking the 11A for an extended duration. The extra 5A has to be going somewhere, so probably not into something small like a cap. Perhaps photonicinduction has a beefy enough power supply to find/pop the short
Nice video! Quite strange that at 3.2V it only draws 11 amps. It doesn't make sense since the resistance is only 0.1 ohms!
"... and went KAPUTT!"
as someone who speaks German I laughed way to hard. :)
Wouldn’t it be better to limit it to 1-2A and use isopropanol to see where it heats up?
Not sure what the test voltage of your DMM is on the low ohms range. I'd be tempted to measure the short in terms of semiconductor junction drop.
The ASIC's may draw that much current if nothing is clocking.
11:10 Between the two P63AD chips, directly in line with the PSU connector, there is a surface-mount component that looks like it sprayed brown gunk toward the PSU connector, covering some traces on the PCB. Maybe that component went "sizzle-pop" and the gunk shorted?
Hi, after 30min I'm thinking PSU on it and some IR visual, and controlled current increasing to see where does it go to pinpoint. And then you said it yourself. Maybe it is not so complicated to do after all. And IR camera like that can help you in your next troubleshooting. You said also that your PSU can deliver 20 some Amps, but the board "only" draws about 10. You measured 0.15 Ohm. With 3.2V I would expect 21 Amps.
Why don't you power the whole thing up with the 3.3V rail working with the high current supply and all the other rails with the main supply. Something could have daisy chained down all those ASICs and killed something in them. The scope might still work but with a certain function going wrong.
That does seem to be a bit hot. The asics might be using all of the power. There should be an extra 15 - 20 watts being burned and a cap would be smoking if it was burning that much power.
Maybe 10-11 amps is it's normal current consumption? Seems high but not too unreasonable considering there's 4 ASICs on it. Check if the PSU is dead or if it's indeed current limiting and shutting down the 3.3v rail.
The relay may be an unrelated issue. Something blew the ass out of the relay on channel 1
I had 2 Stratix IV's on a 0.9V rail, that read way
Nothing like measuring the leakage of 0.1billion low voltage mosfets in parallel. Gets you every time :) Good story, I ran into that very thing once as well. Had to pause and think it through.
what happens if you bypass the 3.3v rail on the main power supply, then use the high amperage power supply to power that rail (I have pulled 15 amps from a 12 amp 12V rail on a computer power supply). Or if possible, power the 3.3V rail then use the fluxgate magnetometer to see if any of those components that you were concerned about are behaving differently as compared to all of the others. (the short point should have different characteristics)
Ha, I was wondering the other day what you did with it. I couldn't recal a repair.
Just an FYI; it's not babysitting if it's your own child. That's just parenting.
SWEEET! 43mins of awsome! :D
All these comments about what was obviously wrong and no one mentioned that it was 240 degrees C on the bench?
There is the possibility of power supply failure that damaged all the components on the 3.3V rail...
Why not pump 3.2V / 11A through the board and measure the voltage at the solder pads? No contact resistance problems and low voltages are measurable even with crappy multimeters to worry about. The only drawback is that accidently shorting points on the board is severely punished ;-9
Why not try to boot it with your heavy duty psu + the original one, 3.3 from the high power and the rest from the normal. To see if it does boot or not ?
Best possible Sunday night entertainment.
The current through the short should have been a lot higher than 11,5 amps by Ohm's law. Can this be used to narrow down the types of possible broken components?
I'm not too familiar with Lecroy scope internals, but would the damage to the large brown package in the analog front end on the left-most channel (with BNC's facing forward) have something to do with it? Can be seen in video at 12:37 to 12:50 as others noted.
I would have thought it might cause some problems with that channel even if it's not the cause of the short.
loved it dave
Hook up the 3.3 V and look for a minimum voltage.
do you say "kaputt"? :D This is funny, as I am german, and it's the german word for broken :)
It's just one of those fun sounding words that English speakers like to use!
Ha! We have same word "капут" in russian language, so it's likely came to us from german - never thought about, funny!
VileVermin историю в школе прогуливать не надо было )))
It’s been borrowed from German, actually
I thought it was better to power it at a low constant current to see what gets warm, rather than blasting it full power right away to see what blows up. If you burn it out completely, you might not be able to find it.
Could you feed in the 11amps then use the non-contact current probe thingy you reviewed a while back to find where all that current is going?
thermal camera Dave, see it you can get one used, broken or something like that
Use the amp probe on the 3.3 volt, see if the PS is the fault or the board.
Fantastic! I have a very similar short on a 12 volt rail on a layered board. Your video helped me realize that my meter doesn't measure low enough resistance to help me find a problem like this one. Are you going to make another video showing that you finally found the short? I also need a better power supply that will go over 10 amps. Confused as to why the short is not heating up, same as my board.
Looking at the layer marks on the PCB, is there any significance to the two being inverted?
You have 4 large, sinked ASICs drawing 35 watts. Guess what? It is not the board. The power supply is probably no longer able to handle the designed draw. I would check the current sense on the supply.
saw a relay package with melted hole at about 13min...anything to do with that!!
The probe detect "big" dc current. You set the threshold.
I have BWD POWERSCOPE 881A (McVan Instruments) please can you tell me where to get its repair manual please its urgent.
Would suggest Upgrade to the new Metrix Power scope from Chauvin Arnoux.
In India Cyronics in Pune can help you. rahulcyronics@gmail.com
Normal 3.3V system rails do not measure 0.1ohms in both directions with a multimeter. I smell a rat.
Oops, I should have watched the whole video before commenting.
Well at least you tried.
Have you noticed that one broken (open) relais housing?? i would not expect the big fail cioming from it, but its STRANGE anyways.
that looks suspiciously like an normal ATX power connector from the PSU....
IR camera is the trick
Would a current probe be able to trace out a short like this in a multilayer board?
why dont you use the AIM-TTi I-Prober 520 to find out where the current goes?
I found this page knowing only what I could remember from my Physics II course I took 3 years ago. Now every day I try to research more and more about electronics so I can better understand your videos. Any books or other material you can recommend for me besides simply searching the internet for more info?
With that much current, it might be a short on one of the connectors?
Is it possible the 3v3 rail is ok, and the psu internally is not giving a 3v3 rail. The 11A draw looks about right for all those high current flash converters, as they have multiple parallel resistor parts inside. I would suspect the power supply if the asics are all getting toasty, but all are same temp. 11A on a 3v3 rail is not that much, I see them on servers capable of 40A or more and it is needed. Dying cap in the psu can time?
One of the maroon boxes appears to have a hole melted in it