EEVblog #405 - Lecroy 9384C Oscilloscope Repair - Part 3 - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: December 30, 2012, 07:52:44 am
content: Dave.

author: Pentium100
author_rank: Frequent Contributor
timestamp: December 30, 2012, 08:30:54 am
content: Something being "worth" depends a lot on how much money one has. I for example repair broken ATX power supplies, because this lets me save a little bit of money (and since I replace the caps with good quality ones the repaired power supply will probably last longer than a new one).Actually, I try to repair everything before giving up and buying a new device. If I can do it, I save some money (because the replacement parts do not cost as much as the new device).That scope maybe has protection against bad power supply - without 4 rails the CPU might not have displayed anything at all. Or the power to the CRT may be provided by one of the dead rails.

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 30, 2012, 08:42:11 am
content: This video makes me sad, it's odd, I had a pet dog (it was in a state of ill health, 17 years old) put down earlier this week and it didn't make me feel this sad :S Dammit weird electronics people

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: December 30, 2012, 08:46:40 am
content: It's kindof a downer that it's dead, but if it's dead, what can you do? It's too bad pumping several amps into it doesn't set the thing on fire...

author: JoannaK
author_rank: Frequent Contributor
timestamp: December 30, 2012, 08:47:27 am
content: Ah well.. Sometimes it just happen.

author: firewalker
author_rank: Super Contributor
timestamp: December 30, 2012, 09:08:09 am
content: Just juice it up with 40 amps!Alexander.

author: ftransform
author_rank: Frequent Contributor
timestamp: December 30, 2012, 09:24:20 am
content: send it to photonic induction

author: Ketturi
author_rank: Regular Contributor
timestamp: December 30, 2012, 10:12:33 am
content: Even greatest people can't always succeed. Especially in electronics, where n+1 things can go wrong. Sad to see that scope is hopelessly dead, but there wasn't really high expectation after 1st or 2nd video. But hey, now Dave have time to something better, maybe it is just good that this thing is left rest in peace.Btw, I would my self take that CRT display and it's circuitry and try to reverse-engineer it, I love those old amber/green mono displays, and actually I have one working unit under my nightstand xD

author: SeanB
author_rank: Super Contributor
timestamp: December 30, 2012, 10:16:31 am
content: Better to lift it with the Quadcopter and release it from a height, at least it will make for a nice bang...........

author: obsoletemac
author_rank: Newbie
timestamp: December 30, 2012, 11:45:27 am
content: Hi (My first post)Would it be possible to get that little heatsink off to see what that ASIC-ish IC is?//c

author: RoelA
author_rank: Contributor
timestamp: December 30, 2012, 11:57:21 am
content: @obsoletemac , Dave said that it would be very hard and you need chemicals that he doesn't have to remove the glue / thermal stuff..Probably easier just to look it up in the schematics in the other thread

author: SeanB
author_rank: Super Contributor
timestamp: December 30, 2012, 12:07:10 pm
content: Now it is off you just use a heat gun and cook till well done ( and a little smoky as well) then the chip will basically fall off the cooked epoxy.

author: ftransform
author_rank: Frequent Contributor
timestamp: December 30, 2012, 12:15:59 pm
content: does anyone else think it might be the second asic? It did get 2 degrees hotter after all.

author: SeanB
author_rank: Super Contributor
timestamp: December 30, 2012, 12:22:17 pm
content: Probably all 4 are CBB inside from the power supply failing and dumping the 5V rail onto the 3V3 rail before the internal fuse popped. I have seen many ATX supplied die this way, though generally the 5V line protection operates and kills the supply.

author: CarlG
author_rank: Regular Contributor
timestamp: December 30, 2012, 12:43:24 pm
content: @obsoletemac@SeanBAs RoelA said: much easier to check the manual. At least for the one who does the job. Why ask Dave to do something that you might as well do yourself?It's an MDX622 demultiplexer + peak detect monolithic IC======================Excuse me for being rude but please RTM

author: jancumps
author_rank: Unknown
timestamp: December 30, 2012, 12:49:29 pm
content: Auction it for charity.

author: Winston
author_rank: Regular Contributor
timestamp: December 30, 2012, 01:27:26 pm
content: Yep, time to give up on this thing. It is now officially a boat anchor. If even one of the ASICs is bad, it is not economically worthwhile to repair. The process of troubleshooting was very interesting though.

author: tinhead
author_rank: Super Contributor
timestamp: December 30, 2012, 01:42:24 pm
content: Quote from: Pentium100 on December 30, 2012, 08:30:54 amhmm, i think you wrong. It depends on how much money you could get in the same time if you wouldsimply work during this time instead of "wasting for repair".Each every "free" hour we have can be calculated back to money, each time you don't go to work(because you wish to have your free time just because you wasted it before by doing your hobby)you can count that money.Of course not every have a job, or not everybody really care about the free time (e.g. while writing thisi wasted time anyway, so it could be sometimes to "use it" more useful instead of typing ugly long text)Quote from: Pentium100 on December 30, 2012, 08:30:54 amyeah, i still remember my Yokogawa Signal Gen repair. Due the moisture (actually i think it was cup of coffe and an idiot)one of the PCBs was complettly broken and another one partially. I had to restore many digital and analog traces - andparts as well. I got the Gen dirt cheap, so i spend only "time" and parts. Finally, after i counted only the parts i wasalready over the "used gear" price, not funny eh. And of course, i spend a week!, to restore the PCB.So finally i spend, with work hours and parts, about 3k USD. For that money i could nearly buy a new one.But yeah, i does not means that i gived up and not repairing things anymore, sure i do it still. Howeverfor most thigns - unless it's just really unique or really cool thing - i'm calculating the time and money i wishto invest, and if i'm over the limit then i'm simply stopping (and selling such things for few bucks to compensate a bit).In Dave's case, in ym opinion, he reached the limit already.Quote from: jancumps on December 30, 2012, 12:49:29 pmyeah, good idea

author: G7PSK
author_rank: Super Contributor
timestamp: December 30, 2012, 01:53:18 pm
content: Looks like the LeCroy is as dead as the Monty python parrot, time to take it out and give it a decent send offhttps://www.eevblog.com/forum/Smileys/default/smiliey_scope_broke.gif

author: IanJ
author_rank: Unknown
timestamp: December 30, 2012, 06:01:31 pm
content: Quote from: G7PSK on December 30, 2012, 01:53:18 pmAbsolutely!..................Would love to see Dave set fire to the LeCroy.......it's job is done.Ian.

author: ZekeD
author_rank: Newbie
timestamp: December 30, 2012, 10:50:56 pm
content: Thanks for the excellent troubleshooting, and proper evaluation on when to say enough is enough.While the scope is beyond hope, the amount of knowledge passed on in the process made this a massive success. Happy new year.

author: robrenz
author_rank: Super Contributor
timestamp: December 30, 2012, 11:57:02 pm
content: +1

author: krenzo
author_rank: Regular Contributor
timestamp: December 31, 2012, 03:19:25 am
content: I wish Dave would at least cut the 3 other chips off to show the short going away.

author: McMonster
author_rank: Frequent Contributor
timestamp: December 31, 2012, 03:30:30 am
content: While I am curious about the real cause of the short and failure I also think we've had enough of this scope already. There's just nothing interesting more to do with it. Time for a different video.Wel, actually there is something that could be interesting, but it would have to include destruction of the board, preferably photonicinduction style.

author: gazza666
author_rank: Newbie
timestamp: December 31, 2012, 09:30:47 am
content: I would remove the other three ASIC-ish IC to see if the short was gonethe board would be nice and clean then in case somebody donated four new chipsyou never know

author: M. András
author_rank: Super Contributor
timestamp: December 31, 2012, 10:42:30 am
content: Quote from: krenzo on December 31, 2012, 03:19:25 amand the short still exist and it was all along under the metal can

author: cengland0
author_rank: Contributor
timestamp: December 31, 2012, 03:30:03 pm
content: Quote from: Pentium100 on December 30, 2012, 08:30:54 amI have a different opinion. If it takes you 2 hours to fix a product that you could purchase for less than your hourly wage, it doesn't make much sense to fix it. Just do some overtime or work a couple extra hours and buy a new one.Edit: Looks like tinhead already said the same thing.

author: TheWelly888
author_rank: Frequent Contributor
timestamp: December 31, 2012, 04:33:51 pm
content: "One sick puppy" now put to sleep...Still it was interesting to watch Dave investigate the fault and I learned one or two tips for faultfinding electronic gear so it wasn't a complete waste of time - Thanks Dave.Some of the posts on this thread makes me regret the lack of a "Like This Post" button on this forum!

author: SeanB
author_rank: Super Contributor
timestamp: December 31, 2012, 04:44:10 pm
content: Yes, every time I try to rate a thread I get an error that I am not allowed to do so..........

author: max-bit
author_rank: Frequent Contributor
timestamp: December 31, 2012, 05:03:49 pm
content: Now, it's (definitely) will not workBut I laughed, with the drill - grindergood job, Dave!

author: Rick
author_rank: Frequent Contributor
timestamp: December 31, 2012, 05:13:22 pm
content: To make sure that it's the ASIC's that are faulty, aren't there specific signal levels that you can measure on their pins to pinpoint the fault, rather than to make assumptions. I am only asking the question.

author: max-bit
author_rank: Frequent Contributor
timestamp: December 31, 2012, 05:13:46 pm
content: Which IC (diode or capacitor?) Is broken? not verifiable ....The damage can be any item, and this multi-layer PCBI do not know how to run a (paths) supplyIn practice, the service, to replace the entire motherboard goes.Dave good try ... but unfortunately the damage probably somewhere in a hybrid system .... and they probably be GaAsFet technology ....

author: AndyC_772
author_rank: Super Contributor
timestamp: December 31, 2012, 06:32:12 pm
content: DaveDid you every try figuring out which are the 3.3V and GND pins on that ASIC, and probing the chip itself to see if you can measure the fault?(How sickening would it be at this stage to measure the power pins and find evidence of a perfectly normal, working power supply structure in there?!)

author: SeanB
author_rank: Super Contributor
timestamp: December 31, 2012, 06:46:58 pm
content: Considering that probably 40 or more pins are supply and ground around that package it will be hard to check, they often are not all connected internally, or have a high resistance between them. Often you find digital, analogue and io supply and ground rails, and application of voltage between them with others not connected can cause the chip to latch up.

author: EEVBFan
author_rank: Newbie
timestamp: January 03, 2013, 09:53:36 pm
content: I am still curious to beat up against this snag, and hope to get a Part4To certain sure the Asic are not involved scratch off the other two due the power pins story at the reply above here,yeah we must have seen a temperature rise by scratching off the first one which was notTherefore i think it is a "short" between the copper planes 3V3 and GNDthe copper (power) planes are very large and therefore all contribute to dissipate this huge power loss therefore the board still looks coolunder heat detection cameraI think in one of the via(s) like mounting hole or other one(s) a tiny is short exist between the copper planes 3V3 and GND, Maybe it is possible to pick up the flow current by some probe at an scope to see where current is flowing,other wise 3V3 trace can be cut to see if the short disapears and if there are none 3V3 traces only a 3V3 copper plane cut the pcb into half with a hack saw to catch and trace location of this snagif the short has gone we know the short has to be at the piece of a half pcbregards

author: Nermash
author_rank: Frequent Contributor
timestamp: January 03, 2013, 10:28:24 pm
content: Just a thought, Dave probably created more media coverage on Youtube for LeCroy than all their other videos.If I were somebody really smart in LeCroy, I sure would send him 4 new Asics and a new psuFollowed by the new HD scope of course...

author: tom66
author_rank: Super Contributor
timestamp: January 04, 2013, 10:28:03 pm
content: I doubt they even have parts for these models any more.

author: grumpydoc
author_rank: Super Contributor
timestamp: January 04, 2013, 10:55:40 pm
content: QuoteThey do, in fact, have some spares available (though I very much doubt that includes a motherboard or ASICs) - I enquired about buying a new front panel for a 9354 I acquired which had some broken encoders and they did still have them.Admittedly the reason that the still have them is probably that they wanted more than twice what I paid for the 'scope so I declined. But if I'd had deep enough pockets I could have bought one.

author: bminish
author_rank: Newbie
timestamp: January 05, 2013, 02:30:03 am
content: It's a bit of bodge but I have in the past successfully unsolderd chips like this by threading thin(ish) enamelled wire behind each row of pins in turn and pulling forwards as I reheat with a meaty soldering iron. As the wire slips out it lifts the pins.You have a somewhat better chnace of having a chip you can reuse than if you use the Xacto KnifeBrendan

author: ejeffrey
author_rank: Super Contributor
timestamp: January 08, 2013, 01:09:54 am
content: [quote author=EEVBFan link=topic=13083.msg177673#msg177673Therefore i think it is a "short" between the copper planes 3V3 and GNDthe copper (power) planes are very large and therefore all contribute to dissipate this huge power loss therefore the board still looks coolunder heat detection cameraNo way. You would easily see a plane-to-plane short under the thermal camera. Once Dave looked with the IR camera and the only major hotspots were the ASIC heatsinks it was game over. It was obvious that they were the culprit and all 4 were blown. Other components may be damaged as well, but those asics are dead dead dead.

author: electronics man
author_rank: Frequent Contributor
timestamp: April 15, 2014, 02:38:57 pm
content: I know this is an old thread, but i cant stop thinking it is something under that metel can, surely it would have been worth desoldering it to be sure?