EEVblog #405 - Lecroy 9384C Oscilloscope Repair - Part 3

[M. András]

I wish Dave would at least cut the 3 other chips off to show the short going away.

and the short still exist and it was all along under the metal can

[cengland0]

Something being "worth" depends a lot on how much money one has.

...

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).

I 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.

[TheWelly888]

"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!

[SeanB]

Yes, every time I try to rate a thread I get an error that I am not allowed to do so..........

[max-bit]

Now, it's (definitely) will not work
But I laughed, with the drill - grinder
  good job, Dave!

[Rick]

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.

[max-bit]

Which IC (diode or capacitor?) Is broken? not verifiable ....
The damage can be any item, and this multi-layer PCB
I do not know how to run a (paths) supply
In 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 ....

[AndyC_772]

Dave

Did 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?!)

[SeanB]

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.

[EEVBFan]

I am still curious to beat up against this snag, and hope to get a Part4

To 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 not

Therefore i think it is a "short" between the copper planes 3V3 and GND
the copper (power) planes are very large and therefore all contribute to dissipate this huge power loss therefore the board still looks cool  under heat detection camera

I 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 snag
if the short has gone we know the short has to be at the piece of a half pcb

regards

[Nermash]

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 psu
Followed by the new HD scope of course...

[tom66]

I doubt they even have parts for these models any more.

[grumpydoc]

I doubt they even have parts for these models any more.

They 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.

[bminish]

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 Knife
Brendan   

[ejeffrey]

[quote author=EEVBFan link=topic=13083.msg177673#msg177673
Therefore i think it is a "short" between the copper planes 3V3 and GND
the copper (power) planes are very large and therefore all contribute to dissipate this huge power loss therefore the board still looks cool  under heat detection camera
[/quote]

No 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.

[electronics man]

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?