Author Topic: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2  (Read 29974 times)

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Offline EEVblog

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EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« on: December 21, 2012, 01:33:52 am »


Dave.
 

Offline albertr

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #1 on: December 21, 2012, 03:09:24 am »
Dave, good show, man! But why not to put everything together (main board, CRT board, CPU board and memory boards) and try to fire it up while powering 3.3V rail externally? I know you mentioned that it already went kaput, so there's nothing to lose?

-albertr
 

Offline Psi

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #2 on: December 21, 2012, 03:52:19 am »
Seconded.

Just because it has a short doesn't mean it wont work.
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Offline kbs1

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #3 on: December 21, 2012, 04:07:54 am »
that's what I was wondering as well. Does it work?:D
 

Offline HardBoot

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #4 on: December 21, 2012, 04:37:54 am »
When you have a short all of that current is just going straight to ground instead of powering anything...

I wonder if the thing works with that hot chip completely ripped off and the 3v powered... if the firmware is smart enough it'll at least give an error, if you had the right firmware for the 2 channel version it'd then work... if that chip is for the extra channels and not the primary channels...
« Last Edit: December 21, 2012, 04:49:18 am by HardBoot »
 

Offline Psi

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #5 on: December 21, 2012, 04:47:28 am »
When you have a short all of that current is just going straight to ground instead of powering anything...

In this case the short isn't too bad. It's only drawing a few amps more at rated voltage.
(9A vs the normal 6A)
So it's not a dead short, It's a bit of semiconductor somewhere which is eating up power and producing heat.
There will be a voltage drop but it should be possible to overcome that by providing 3.4 or 3.5V instead of 3.3V.
The chips will run from that just fine.

« Last Edit: December 21, 2012, 04:49:09 am by Psi »
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Offline EEVblog

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #6 on: December 21, 2012, 06:16:26 am »
Anyone know a nice way to get those heatsinks off?

Dave.
 

Offline free_electron

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #7 on: December 21, 2012, 06:48:16 am »
Thermal epoxy... Dissolves in MEK Methyl Ethylene Ketone... Nasty stuff... Do it outside. It stinks up the whole place.
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Offline Psi

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #8 on: December 21, 2012, 06:53:08 am »
i once tried to pull/pry off a heatsink epoxied to a BGA chip.
The epoxy pulled the die right out of the IC :palm:
It wasn't anything important so i just laughed :)


hehe, i just had a look and found the PCB still in my junk draw.
Pretty sure there is supposed to be a die in the center :P


« Last Edit: December 21, 2012, 06:59:23 am by Psi »
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Offline kyndal

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #9 on: December 21, 2012, 06:58:07 am »
i second the idea of hooking it back together
and "give it" the 10 amps it wants.

and hell.. might work just fine

might give some indications as to where the failure is located
(maby channel "second chip" is debunked ?)  snip off the 3.3v pins
and you have yourself a handicapped but functional scope ?

/Kyndal
 

Offline nitro2k01

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #10 on: December 21, 2012, 07:32:25 am »
I think the "chip 2" theory may be a red herring. I think it may just be that that chip happens to be opportunistically closer to the current return path when you're using the screw hole as the negative voltage supply. 3.2 V * 8.6 A = ballpark 30 W. This is what you got when connecting the external and original power supply in the same time, or ballpark 8 W per chip. This doesn't seem all that off for that kind of heatsink. The short when measuring with a multimeter would indeed indicate a dead short, probably inside the chips, but it can't hurt to reassemble it and try it with an external 3.3V supply. Worst thing that can happen is that it doesn't work at which point you can say OH WELL and chuck it in the recycling bin.
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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #11 on: December 21, 2012, 09:36:13 am »
Anyone know a nice way to get those heatsinks off?

Dave.

Machine them off on a mill. The only "safe" option that comes to mind  :-//
 

Offline M0BSW

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #12 on: December 21, 2012, 11:09:30 am »
 I thought it was a brilliant Video, helping me to pick this up, learning loads of stuff,I like the IR thermonitor, you can buy those fairly cheap, the flir , I think its called , that's way to expensive for a hobbyist, I have seen one of those been used buy a ghost hunter, with way to much money, back to the real world,I guess the IR therm just gives you a good indication if something is way to hot
« Last Edit: December 21, 2012, 12:17:37 pm by M0BSW »
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Offline robrenz

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #13 on: December 21, 2012, 12:24:48 pm »
Both videos are great. Seeing troubleshooting techniques in action and then all the forum commentary is quite an education. ( at least for me)

Offline DeepSubMicron

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #14 on: December 21, 2012, 01:45:23 pm »
Hi I am just a wannabe lab rat. I followed the two thrilling repair videos.
My impression is that you tried in the second video to show it is not repair able rather than actually trying to repair it. For example, you have successfully narrowed down the search area to the 4 ASICs. But then you didn't go deeper into the rabbit hole and analyzed the hot spots in more detail.
I was most disappointed about the TTI current probe. If this is not the perfect use case then such a probe is completely pointless.
You are probably right with the conclusion it is not repair able but it is hard to accept that.
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #15 on: December 21, 2012, 01:47:10 pm »
hey Dace.....
i had a little time and went trough the Service Manual of 9374 cause was easy to find:
https://www.google.gr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CDcQFjAB&url=http%3A%2F%2Fwww.ko4bb.com%2Fmanuals%2Findex.php%3Fdir%3DLeCroy&ei=m2jUUK7IFo3s0gX904GIDA&usg=AFQjCNGw2RFNWNshbCCT1cmM1D94s2fStw&bvm=bv.1355534169,d.d2k

this is VERY SIMILAR to the 9384 topology go and look at PCB layout

there are 2 custom chips (ASICs):
HSH423 ___> the ADC-Buffer ASIC from the fronted
MDX416___> the SRAM ASIC driver connected to the HSH423 ASIC  <--------the 4 ASICs shorted to ground

well ..... the 3.3V power is not powering the ASICs....it is the floating ground controlled by the 2pins cable feedback to the power supply !!!!

so maybe there is no problem with a short and it is a power supply failure on reading the feedback from the 2cable feedback connector from the main board
page 294

also there are (SMD , 3 of them) some regulators with reverse protection diodes over IN-OUT that they provide all the floating-to-the-ground power to the chips

so my theory is this:
the regulators provide the Vcc...Power Supply control over the floating ground with the 3.3V rail

....maybe i am wrong , but should take a look of that 2 pins  feedback to the power Supply or the Power Supply itself  ???
....so maybe there is nothing wrong with that ASICs  :-//

George
« Last Edit: December 21, 2012, 01:51:23 pm by pir »
 

Offline M0BSW

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #16 on: December 21, 2012, 02:08:31 pm »
Anyone know a nice way to get those heatsinks off?

Dave.

Machine them off on a mill. The only "safe" option that comes to mind  :-//
Are they that well stuck on then.
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Offline vaualbus

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #17 on: December 21, 2012, 02:36:32 pm »
I don't belive that the asics are broken. In fact How the problem on the trigger of the oscilloscope, as we can see on the teardown, can affect the asics?
For me probably some components are partial demage, and cause the short.
Probably the best way is to try first to resolder the components and change all the bypass capicitor and than try to remove one by one.
Another think How I capicitor can became hot?
Than you could try to replace the hot chip.
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #18 on: December 21, 2012, 02:50:07 pm »

well ..... the 3.3V power is not powering the ASICs....it is the floating ground controlled by the 2pins cable feedback to the power supply !!!!

....maybe i am wrong , but should take a look of that 2 pins  feedback to the power Supply or the Power Supply itself  ???
....so maybe there is nothing wrong with that ASICs  :-//

George


just watch the video #1 @2:10
 

Offline Classicmacintosh

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #19 on: December 21, 2012, 02:56:15 pm »
G'day Dave & others,
I've gotta hand it to ya Dave, you have at least 543% more patience than I do :D
I would have just stuffed 30v at god knows how many amps through the blighter by now!
On a more serious note have you tried to give the PCB a *bloody* good whack or two? I suspect yanking the second ASIC won't do anything really useful sadly.
The damage to the scope housing must have been the result of a nasty fall though.. could have caused an internal power plane short.

-Ed
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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #20 on: December 21, 2012, 03:01:22 pm »
maybe the short is +V pin of the second chip.... Don't know... it should be helpful excluding some part of circuit such as the 4 chips whit heatsink and see if the current change or is still in the 10A range...
 

Offline opablo

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #21 on: December 21, 2012, 03:24:06 pm »
I would love to see what happens if you assemble it back together and start feeding as much juice as it wants to the 3.3 rail with your external PSU.

And start cranking it up until you are able to overcome the voltage drop produced by your short... 3.4, 3.5, 3.6, etc.

Maybe it works !...

Or maybe the chips are really and deeply dead and nothing happen....
 

Offline cengland0

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #22 on: December 21, 2012, 03:28:25 pm »
I think it was misunderstood how to use the FLIR.  The heat you thought you saw coming from the BNC connectors was not heat.  In fact, you can look at the screen and see the heat scale on the right hand side.  Notice that the maximum temperature on the scale is much less than when you have it pointed at one of the heatsinks.
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #23 on: December 21, 2012, 04:07:33 pm »
The 3.3V is the Floating Ground of the DAC<---->SRAM<--->CPU
The ASICs are OK...DO NOT REMOVE THEM
THE PIN-1 of 3.3V is the SRAM Vcc..that is why it is not shorted to ground
THE PIN-2,PIN-3 is the FLOATING GROUND..and the circuitry related to that  has the problem...the feedback to PS?
THAT CHIP THAT WENT TO 100'C ....is fried because from 15V-3.3V=11.7V .. got 15V+

did anyone bother to go through an "allmost the same scope" schematic except me ?  :-//

VEE is the 3.3V floating ground of pin2,pin3
see pics
 

Offline gszo123

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #24 on: December 21, 2012, 05:00:20 pm »
I think it was misunderstood how to use the FLIR.  The heat you thought you saw coming from the BNC connectors was not heat.  In fact, you can look at the screen and see the heat scale on the right hand side.  Notice that the maximum temperature on the scale is much less than when you have it pointed at one of the heatsinks.

Actually I think Dave was right. There are several factors to consider when using IR camera. First is of course the scaling of colors you mentioned.

Second is that FLIR doesn't measure temperature direcly but IR radiation that can be subject to phenomena any radiation is, namely: transmission and reflection, so measuring temp of shiny surfaces can be tricky (the same is when you are trying to take a photo of a mirror, you not only take photo of mirror itself but also of objects reflecting from its surface). And this happened there on BNC. Camera was showing effect of combined radiation from the BNC itself as well as radiation reflected from eg. Dave's hand.

Third factor is that different materials have different emmissivity coefficients (dependent on color, roughness, etc), so that when measuring its temp you should first set proper coefficient in the camera to make accurate measurements. Thats why, probably, absolute values measured in the video were somewhat off. But in this case it was all about relative temp not absolute.

See more info here: http://assets.fluke.com/manuals/Ti30____umeng0000.pdf


BTW, hello from Poland NOT Holland :)
« Last Edit: December 21, 2012, 05:08:43 pm by gszo123 »
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #25 on: December 21, 2012, 05:33:36 pm »
Hey Dave...
what do you measure on OFF and ON situation from the PS over that 2pin cable?
if it is -2V ~ -3V BINGO!!!

possible combinations inside that PS and output over that 2 pins:
12V-15V=-3V
5V-7V=-2V

THERE IS YOUR FLOATING GROUND  ;D
..and maybe that short is inside the PS
please measure the "3.3V pin2,pin3" over that 2pin plug for pass through...
please measure the "3.3V,pin1" over the "3.3Vpin2,pin3"
please measure the "3.3V pin2,pin3" to other pins of that plug (coupled with a feedback controlled -3.3V PS out)

p.s. i told my shelf to just take a look over a Leroy schematic for a minute and i am doing it all day...  ::)
..and going over the videos again i thought that this 2pin cable is way too fat to be a feedback to PS....
why there are 2 headers of this kind? what is the second one ?

<Edit>
the 9374 is different from 9384 in that 2pin header and the floating is done with some regulators.
the 9384 service manual from the link i posted , does not have the pages of the 3.3V and the diagrams are hard to read

"i want to see that old horse running again"
<Edit>


<Edit>
that 2pin header is actually a 3pin header , red-black-white
<Edit>

<Edit>
i see a -3.3V or what?
damn...totally unreadable
see pic
<Edit>
« Last Edit: December 21, 2012, 07:48:51 pm by pir »
 

Offline bpn1028

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #26 on: December 21, 2012, 06:17:29 pm »
Is it possible that it is no longer shorted and the original short was vaporized by the current applied?   I don't recall seeing it tested again with the Ohm meter after all that current was applied for a long time.  I know it is drawing more current than expected, but is it really still shorted?
 

Offline cengland0

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #27 on: December 21, 2012, 06:58:37 pm »
Actually I think Dave was right. There are several factors to consider when using IR camera. First is of course the scaling of colors you mentioned.

Second is that FLIR doesn't measure temperature direcly but IR radiation that can be subject to phenomena any radiation is, namely: transmission and reflection, so measuring temp of shiny surfaces can be tricky (the same is when you are trying to take a photo of a mirror, you not only take photo of mirror itself but also of objects reflecting from its surface). And this happened there on BNC. Camera was showing effect of combined radiation from the BNC itself as well as radiation reflected from eg. Dave's hand.

Third factor is that different materials have different emmissivity coefficients (dependent on color, roughness, etc), so that when measuring its temp you should first set proper coefficient in the camera to make accurate measurements. Thats why, probably, absolute values measured in the video were somewhat off. But in this case it was all about relative temp not absolute.

What you're saying can happen; however, in the case of this troubleshooting video, I respectfully disagree with you.  If you look at the video at 31:05, you can clearly see that the scale is at 26.2 max and 22.2 min.  The Flir will automatically detect the hottest items within that range and colorize them accordingly.  The rest of the video toward the end it appears Dave figured out how to fix the scale to 89.5 max and 25.7 min and that's when you do not see the heat coming from those BNC connectors.

In the video, at 7:24 he tests the bench temperature and it's 24-25 degrees.  So you're only looking at a 1.2 degree difference from the bench to the maximum of the Flir scale.  The Flir is sensitive enough to pick up that temperature difference in the 22.2 to 26.2 range and show you that the BNC connectors are warmer.

For your homework today,  :), try this.  Heat up a shiny piece of metal to 100 degrees that is extremely reflective.  Then, using a temperature probe of that metal while it is angled toward a block of ice, what temperature would it read?  I remember the Mythbusters getting past an IR alarm sensor by using a piece of glass because the unit couldn't "see" behind that glass.  They used a similar visual IR heat detection device as well and it was completely the temp of the glass and not what was behind it.  So even though I haven't performed this test myself, I would guess the temp it would read is close to the 100 degree side instead of the 0 degree side.
 

Offline lewis

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #28 on: December 21, 2012, 08:18:51 pm »
Actually I think Dave was right. There are several factors to consider when using IR camera. First is of course the scaling of colors you mentioned.

Second is that FLIR doesn't measure temperature direcly but IR radiation that can be subject to phenomena any radiation is, namely: transmission and reflection, so measuring temp of shiny surfaces can be tricky (the same is when you are trying to take a photo of a mirror, you not only take photo of mirror itself but also of objects reflecting from its surface). And this happened there on BNC. Camera was showing effect of combined radiation from the BNC itself as well as radiation reflected from eg. Dave's hand.

Third factor is that different materials have different emmissivity coefficients (dependent on color, roughness, etc), so that when measuring its temp you should first set proper coefficient in the camera to make accurate measurements. Thats why, probably, absolute values measured in the video were somewhat off. But in this case it was all about relative temp not absolute.

What you're saying can happen; however, in the case of this troubleshooting video, I respectfully disagree with you.  If you look at the video at 31:05, you can clearly see that the scale is at 26.2 max and 22.2 min.  The Flir will automatically detect the hottest items within that range and colorize them accordingly.  The rest of the video toward the end it appears Dave figured out how to fix the scale to 89.5 max and 25.7 min and that's when you do not see the heat coming from those BNC connectors.

In the video, at 7:24 he tests the bench temperature and it's 24-25 degrees.  So you're only looking at a 1.2 degree difference from the bench to the maximum of the Flir scale.  The Flir is sensitive enough to pick up that temperature difference in the 22.2 to 26.2 range and show you that the BNC connectors are warmer.

For your homework today,  :), try this.  Heat up a shiny piece of metal to 100 degrees that is extremely reflective.  Then, using a temperature probe of that metal while it is angled toward a block of ice, what temperature would it read?  I remember the Mythbusters getting past an IR alarm sensor by using a piece of glass because the unit couldn't "see" behind that glass.  They used a similar visual IR heat detection device as well and it was completely the temp of the glass and not what was behind it.  So even though I haven't performed this test myself, I would guess the temp it would read is close to the 100 degree side instead of the 0 degree side.

I'm afraid gszo123 is bang on. IR emissivity and surface reflections are serious problems when trying to make accurate measurements with a thermal imaging camera. Those BNCs were not warm, it was reflected body heat.

Just for fun, I'd thought I'd try your experiment:

Here's the setup using a saucepan, boiling water, ice, a tub of CarPlan four seasons screenwash and a Fluke Ti10 thermal imaging camera. (Yes, ABELtronics Limited is winding down for Christmas). The highly polished stainless steel saucepan is boiling on my workshop hob. An ice pack rests against the screenwash tub facing the saucepan:




Different angle:




A closeup reveals you can see the reflection of the ice pack in the side of the saucepan:




The water in the saucepan is boiling:




Here's a thermal image of the side of the saucepan. The temperature shown on the right (35.7C) is the temperature of the crosshair in the middle of the image. Note it's a lot colder than it should be (100C) because of the poor IR emissivity of the polished stainless. (The ghostly lighter blue bit right under the crosshair is a thermal reflection of me taking the image):




Moving the crosshair over the reflection of the ice shows the TI camera thinks the saucepan is apparently 15.9C at the point where the ice is reflecting. You can see the reflection of the kettle slightly to the left. Remember the saucepan is at 100C:




The ice pack is showing as -0.6C (the warm kettle can be seen in the background):




With the pan lid off the TI camera thinks the water is 93C, but the side of the saucepan is considerably colder:





So in answer to your comment, even with a polished bit of metal at 100C reflecting off ice, the TI camera still errs towards the colder end.

Thermal reflections are a problem and definitely are a trap for young players!





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Offline gazza666

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #29 on: December 21, 2012, 09:08:45 pm »
Dont Give up Dave
Great Stuff
 

Offline c_francof

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #30 on: December 21, 2012, 09:46:25 pm »
Isn't it better to use the external 11 Amp font and with the multimeter going testing different 3.3v rail points and detect where is the less Volt drop in the rail, I mean , with 11Amp flowing in 3.3V track you can detect where is 0.16ohm short. Sorry because of my bad english and the fact I am not a "repair-man" just hardware engineer , so im not so used to repair stuff. :-+
 

Offline vaualbus

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #31 on: December 21, 2012, 10:17:29 pm »
I don't belive that the asics are broken. In fact How the problem on the trigger of the oscilloscope, as we can see on the teardown, can affect the asics?
For me probably some components are partial demage, and cause the short.
Probably the best way is to try first to resolder the components and change all the bypass capicitor and than try to remove one by one.
Another think How I capicitor can became hot?
Than you could try to replace the hot chip.
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #32 on: December 21, 2012, 10:43:37 pm »
<UPDATE>

the main board is OK!
the ASICs are OK!
70'C is normal (see the biiiiiiiiiiiig heatshinks) (forget the 100'C little chip....cause it is missing the floating)
Not normal for the ASICs could be ....say 110'C
the thermal scan is OK!

there are 3 pins on 3.3V
pin1 is the Vcc for the SRAMs , partially ACISs ....and others
pin2 is A FLOUTING 3.3V to a -3.3V for a part of the circuitry (float GND..say for the A-B channels)
pin3 is a  FLOUTING 3.3V to a -3.3V for an other part of the circuitry (float GND..say for C-D channels)

i bet that if Dave powers it up with the 3.3V_pin1 connected only and the 5V rail...the ASICs will fire up !

there is a 3-pin-plug feedback to the PS ...i suspect from the service manuals (can't see...schematics are unreadable) that this is the +15V,-15V feedback and has something to do with a -9.2V , a -5V , a -3.3V internally ...into the PS
i see into the manuals some fets controlling a "test-diagnostic" circuit over that +15V,-15V feedback

all seems ok ...what is missing?
the -3.3V to get a float !!!
in that big power connector should be a -3.3V deference opposing the +3.3V_pin2,pin3 ...and everybody is happy.....

so to conclude .... a rail of the PS is sorted internally....witch is powering opposing -3.3V to that +3.3V (pin2,pin3)
this can be done by a "pure" -3.3V to that big plug....or with a combination of other rails to get the -3.3V
when this got a runaway... the +3.3V is grounded....and fried...



p.s.
i declare it solved
 

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #33 on: December 21, 2012, 10:51:19 pm »
 

Offline The_Penguin

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #34 on: December 22, 2012, 12:25:43 am »
Both videos are great. Seeing troubleshooting techniques in action and then all the forum commentary is quite an education. ( at least for me)

Agreed. Unfortunate that we still don't know for sure what the problem is, but it's always interesting seeing how other people go about troubleshooting a problem.
 

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #35 on: December 22, 2012, 01:00:37 am »
Both videos are great. Seeing troubleshooting techniques in action and then all the forum commentary is quite an education. ( at least for me)

Agreed. Unfortunate that we still don't know for sure what the problem is, but it's always interesting seeing how other people go about troubleshooting a problem.

 :-+

the man told it @ the start: "i don't know if i'll fix it"
because i know what he was actually talking about he should said:"this puppy is so complicated and that type of hardware is veeeeery hard to fix without a service manual and walking in the dark"

a certified "EE repair man" would go through 6months on seminars....to be able to repair that hardware...and with special equipment also
but any way..... :-+ to Dave...he is my EE Guru

In electronics you'll have 1milion fails...but this 1 time you'll get something working........damn is satisfaction !

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Offline EEVblog

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #36 on: December 22, 2012, 01:20:47 am »
the main board is OK!
the ASICs are OK!
70'C is normal (see the biiiiiiiiiiiig heatshinks) (forget the 100'C little chip....cause it is missing the floating)
Not normal for the ASICs could be ....say 110'C
the thermal scan is OK!

there are 3 pins on 3.3V
pin1 is the Vcc for the SRAMs , partially ACISs ....and others
pin2 is A FLOUTING 3.3V to a -3.3V for a part of the circuitry (float GND..say for the A-B channels)
pin3 is a  FLOUTING 3.3V to a -3.3V for an other part of the circuitry (float GND..say for C-D channels)

Your theory does not add up.
It fails to explain the 0.1ohms on the main 2 pin 3.3V rail, which is directly connected to the ASICs and ground. As verified by continuity measurement on all the decoupling caps.
There is nothing "floating" about the main 3.3V rail, it goes directly to several dozen bypass caps under the ASICs, and is ground referenced.
Sam has verified that the 3.3V rail measures over 1 ohm, and draws less than 6A.

Granted, I have not looked at the 9374 schematics, as I have a 9384C.

Dave.
 

Offline NiHaoMike

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #37 on: December 22, 2012, 05:17:55 am »
Maybe only one chip was bad to begin with but then you violated the rail sequencing and damaged the rest? At work, someone messed up the rail sequencing on a test board and the result was smoke, a lot of it in fact.
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Offline Psi

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #38 on: December 22, 2012, 06:42:35 am »
Possibly.

I came across a plasma display driver IC many years back that would smoke itself if you powered it without a clock signal for more than a few seconds.
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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #39 on: December 22, 2012, 10:32:55 am »
I just watched the video on the Flir camera, I thought Dave was going to say " let's tear it apart"  :palm: I'm glad to say he didn't,  :phew:, there are just somethings that are to expensive to take apart.
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Offline ftransform

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #40 on: December 22, 2012, 12:14:48 pm »
Just a thought but is it not a good idea to replace the entire power supply system with your own power supplies? I.e. run the 3.3/5/12/whatever rails all from individual power supplies.

Not in this case, but in general for trouble shooting. At least after the lack of shorts is confirmed. Or does alot of equipment have the main board run some kind of self check on the PSU?

curious.

And another idea: Is it possible that the low resistance is some kind of protection feature? I.E. perhaps the sequence of startup goes:
(controlled by a power supply sequencer or w/e)
1) Enable 12 volt supply
2) wait 100 ms
3) turn on 3.3 volt supply

Lets say that that perhaps if the 3.3 V supply was turned on prior to the 12 volt supply some kind of catastrophic failure would ensue, wrecking the device.
So as a safeguard against the failure of the PSU startup sequencer the designers made the 3.3 volt is shorted to ground through some kind of component that goes into a high impedance state only when the power is applied to the 12 volt rail, ensuring that if the power supply sequencer failed the device would be rendered nonfunctional but easy to repair (i.e. 4 asics are not fried)

Is this an insane idea? :scared:
« Last Edit: December 22, 2012, 12:21:20 pm by ftransform »
 

Offline ftransform

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #41 on: December 22, 2012, 12:26:50 pm »
Or perhaps it is even more complicated then that.

Maybe it goes like this:
1) turn on 5V rail
2) Have MCU verify something or another
3) have MCU turn off the short on the 3.3 volt rail if whatever thing got verified.

Maybe by shorting the rail to ground rather then controlling the power supply offers greater reliability?


or maybe I have been up for too long..... :scared:
 

Offline cengland0

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #42 on: December 22, 2012, 01:23:29 pm »
I'm afraid gszo123 is bang on. IR emissivity and surface reflections are serious problems when trying to make accurate measurements with a thermal imaging camera. Those BNCs were not warm, it was reflected body heat.

Just for fun, I'd thought I'd try your experiment:

I see your experiment and still have doubts.  The pan you use is round so it is not possible for it to reflect the icepack in every spot of that pan.  Additionally, things such as the lid were also not reflecting the icepack but were represented by the same color in your tests. This proves to me that it is something other than reflection that is causing it to show a lower temperature. 

Perhaps you could have taken a temperature reading of the pan with the fluke instead of the water inside it.  The bottom of pans are designed to transfer as much of the stove heat with as little loss as possible.  Expensive kitchen equipment try to do this as evenly as possible.  The sides of the pan are sometimes made of different material and do not transfer the heat in the same way as the bottom. I'm still surprised at these results.  I would have thought you would get more heat transfer from the water inside to the outside of the pan.

I bet you could have removed the ice pack and received the same results because it's not the temperature of the ice pack you're seeing -- the so called "reflected heat"

Notice you had to remove the lid to see the temperature of the water inside.  Why do you suppose that is?  It appears to be a glass top so if you can see through it, the visual probe should have been able to also see the temperature inside but it cannot.  This is what was proven by the experiments with the Mythbusters. 
 

Offline SeanB

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #43 on: December 22, 2012, 01:30:20 pm »
I did the same a week ago, there was a difference of around 5C between a plain anodised aluminium block and the same block that has a non stick coating on it. The 2 points are adjacent to each other (2cm) on the same heated thermal mass heater. You can see where the field of view of the sensor moves from the coating to the anodised surface.
 

Offline LaurenceW

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #44 on: December 22, 2012, 03:15:33 pm »
But, FTransform, what sort of unpowered circuit (without a relay on board, of which there is no sign) could create a 0.1R resistance, particularly to the low voltage of a multimeter? And would it be good design practice for one piece of electronics to CROWBAR a power supply rail in this way?  A series switch that only enables one power supply line after another is established would surely be a better approach. If indeed it was really a requirement.  That doesn't seem right to me I'm afraid.

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Offline cengland0

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #45 on: December 22, 2012, 03:32:57 pm »
I did the same a week ago, there was a difference of around 5C between a plain anodised aluminium block and the same block that has a non stick coating on it. The 2 points are adjacent to each other (2cm) on the same heated thermal mass heater. You can see where the field of view of the sensor moves from the coating to the anodised surface.
Come on guys.  My point was that Dave did not notice the scale changed and that's why those BNC connectors looked hot -- not because of the reflective values.  I agree different materials will show differences in a Flir IR measurement but that's not what caused the problem.  It's all about the scale.

I understand Dave's hand is around 37c degrees (98.6f) and radiates heat nearby and that can cause things near your hand to appear hotter but that is not what the problem is.  If the scale was set properly, you would not have seen any reaction when his hand was nearby the BNC connectors.
 

Offline gszo123

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #46 on: December 22, 2012, 03:53:20 pm »


Perhaps you could have taken a temperature reading of the pan with the fluke instead of the water inside it.  The bottom of pans are designed to transfer as much of the stove heat with as little loss as possible.  Expensive kitchen equipment try to do this as evenly as possible.  The sides of the pan are sometimes made of different material and do not transfer the heat in the same way as the bottom. I'm still surprised at these results.  I would have thought you would get more heat transfer from the water inside to the outside of the pan.

Actually with thermocouple measurement you would get around 100C because it uses different principle of measurement - heat is transfered by conductivity - you can simulate the same kind of measurement when you touch the pan. I am pretty sure you would feel the heat. But IR camera bases its measurement on radiated heat which is very low for the polished metal. When you place your finger close to the pan without touching, you wouldn't burn yourself, would you?



Notice you had to remove the lid to see the temperature of the water inside.  Why do you suppose that is?  It appears to be a glass top so if you can see through it, the visual probe should have been able to also see the temperature inside but it cannot.  This is what was proven by the experiments with the Mythbusters.

Glass is transparent to visible light and is opaque to wavelengths IR camera measures, that is why you cannot see heat through glass. It is not visual probe because visual radiation is what your eyes can see. And you cannot see heat. One can imagine opposite situation, when you place your hand inside plastic bag you cannot see your hand with your eyes, but thermal camera can.

Please see an example below. There is person holding piece of glass that is reflecting heat of other people in the room, but you cannot see heat of the holder through glass.



Dave meant that there appear to be hotspots on the BNCs, NOT that whole BNCs are hot. And those hotspots are from reflection and not from the temperature itself.



Anyway I don't know how opacity of glass to far infrared proves that BNC cannot reflect heat?
« Last Edit: December 22, 2012, 04:02:54 pm by gszo123 »
 

Offline KD0CAC John

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #47 on: December 22, 2012, 04:37:02 pm »
I wandered if the 3 wires for the 3v supply , with 2 of them being hot and 1 not .
What about running the test voltage to just the 2 wires that were heating up ?
 

Offline johan

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #48 on: December 22, 2012, 06:14:56 pm »
I did the same a week ago, there was a difference of around 5C between a plain anodised aluminium block and the same block that has a non stick coating on it. The 2 points are adjacent to each other (2cm) on the same heated thermal mass heater. You can see where the field of view of the sensor moves from the coating to the anodised surface.
Come on guys.  My point was that Dave did not notice the scale changed and that's why those BNC connectors looked hot -- not because of the reflective values.  I agree different materials will show differences in a Flir IR measurement but that's not what caused the problem.  It's all about the scale.

I understand Dave's hand is around 37c degrees (98.6f) and radiates heat nearby and that can cause things near your hand to appear hotter but that is not what the problem is.  If the scale was set properly, you would not have seen any reaction when his hand was nearby the BNC connectors.
I agree. One can easily get fooled or distracted by the dynamic scale. When I do this kind of troubleshooting I always set the scales to manual and between room temperature and for example 100 degrees celcius. I also start by taking one image where the whole board is visible, one image for each side. I usually print the images and look at them closely, it's easier than you think to miss something when scanning around as Dave does in the video...
 

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #49 on: December 22, 2012, 08:02:20 pm »
I wandered if the 3 wires for the 3v supply , with 2 of them being hot and 1 not .
What about running the test voltage to just the 2 wires that were heating up ?

I think he early established that one of the pins in the socket was not connected. So he was effectively connecting the test voltage to only the wires that were heating up because of this. The third wire remained cold because no current at all was flowing through it.
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Offline vaualbus

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #50 on: December 22, 2012, 08:08:08 pm »
I've a idea the Why the short can't be  under the metallic cover?
 You've never checked under there.
 

Offline ftransform

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #51 on: December 22, 2012, 10:39:54 pm »
But, FTransform, what sort of unpowered circuit (without a relay on board, of which there is no sign) could create a 0.1R resistance, particularly to the low voltage of a multimeter? And would it be good design practice for one piece of electronics to CROWBAR a power supply rail in this way?  A series switch that only enables one power supply line after another is established would surely be a better approach. If indeed it was really a requirement.  That doesn't seem right to me I'm afraid.

It is still a puzzle!
I'm guessing JFETS have higher resistance then 0.1 ohms. :(
 

Offline lewis

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #52 on: December 23, 2012, 02:32:13 am »
I'm afraid gszo123 is bang on. IR emissivity and surface reflections are serious problems when trying to make accurate measurements with a thermal imaging camera. Those BNCs were not warm, it was reflected body heat.

Just for fun, I'd thought I'd try your experiment:

I see your experiment and still have doubts.  The pan you use is round so it is not possible for it to reflect the icepack in every spot of that pan.  Additionally, things such as the lid were also not reflecting the icepack but were represented by the same color in your tests. This proves to me that it is something other than reflection that is causing it to show a lower temperature. 

Perhaps you could have taken a temperature reading of the pan with the fluke instead of the water inside it.  The bottom of pans are designed to transfer as much of the stove heat with as little loss as possible.  Expensive kitchen equipment try to do this as evenly as possible.  The sides of the pan are sometimes made of different material and do not transfer the heat in the same way as the bottom. I'm still surprised at these results.  I would have thought you would get more heat transfer from the water inside to the outside of the pan.

I bet you could have removed the ice pack and received the same results because it's not the temperature of the ice pack you're seeing -- the so called "reflected heat"

Notice you had to remove the lid to see the temperature of the water inside.  Why do you suppose that is?  It appears to be a glass top so if you can see through it, the visual probe should have been able to also see the temperature inside but it cannot.  This is what was proven by the experiments with the Mythbusters.

Trust me. It is the ice reflecting in the side of the pan. It's a good job you're not a betting man, removing the ice pack did indeed get rid of the darker reflection. I know it seems counter-intuitive. Regarding lid reflection - on the contrary, you can see a darker colour on the rim of the lid, above the ice reflection on the pan's side, in the previous images.

The pan was full of boiling water for 10 mins or so, the steel is about 0.8mm thick. It's going to be the same temperature as the water within a degree. The reason the TI camera thinks the temperature is significantly lower is because the pan is a poor emitter (but good reflector) of infrared, not because there is poor heat transfer between the water and the outside of the pan. If it was painted black it would register much hotter, even though it's still at 100C.

Here's the thermal image with the lid on:

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Offline lewis

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #53 on: December 23, 2012, 02:32:57 am »
Sorry, I'm getting off-topic and will shut up now...
« Last Edit: December 23, 2012, 02:44:59 am by lewis »
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pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #54 on: December 23, 2012, 05:40:57 am »
i repeat it once again.....  simple test....

DOES THE ASICS FIREUP WITH THE PIN1 3.3V and 5V?

as simple as that....  :-//

<Edit>
there are trims between ADC ans SRAM management
....for float ground triming?
...if so there is your 0.100 to 1Ohm
<Edit>
« Last Edit: December 23, 2012, 05:46:52 am by pir »
 

Offline Monkeh

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #55 on: December 23, 2012, 06:52:36 am »
i repeat it once again.....  simple test....

DOES THE ASICS FIREUP WITH THE PIN1 3.3V and 5V?

as simple as that....  :-//

<Edit>
there are trims between ADC ans SRAM management
....for float ground triming?
...if so there is your 0.100 to 1Ohm
<Edit>

Your theory does not add up with the rest of the evidence.

If those pins are for some reason floating grounds connected back to the PSU, why are they directly connected to each other and why are they the same colour wire?

And why is the PSU rated to provide 13A when a single wire isn't capable of carrying it at 3.3V without significant volt drop?

You're making a similar error to Dave and making assumptions based on a schematic for a different device.
 

Offline EEVblog

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #56 on: December 23, 2012, 10:53:47 am »
You're making a similar error to Dave and making assumptions based on a schematic for a different device.

What error am I making?
I have it confirmed from a Lecroy service engineer that the 3.3V rail in the 9384 is specified at 6A, and it is also mentioned in a 9384 manual block diagram.

Dave.
 

Offline Monkeh

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #57 on: December 23, 2012, 11:29:33 am »
You're making a similar error to Dave and making assumptions based on a schematic for a different device.

What error am I making?
I have it confirmed from a Lecroy service engineer that the 3.3V rail in the 9384 is specified at 6A, and it is also mentioned in a 9384 manual block diagram.

Dave.

And that's the first you've told us of it. Until now, we've been operating on the basis of a note in a manual for a different device.

And I'll note there's the still unresolved matter of a label which seems to say +3.2V 13A.
 

Offline Electr0nicus

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #58 on: December 23, 2012, 01:52:31 pm »

And that's the first you've told us of it. Until now, we've been operating on the basis of a note in a manual for a different device.

And I'll note there's the still unresolved matter of a label which seems to say +3.2V 13A.

Just watch the video at 16:35.
 

Offline Monkeh

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #59 on: December 23, 2012, 02:55:01 pm »

And that's the first you've told us of it. Until now, we've been operating on the basis of a note in a manual for a different device.

And I'll note there's the still unresolved matter of a label which seems to say +3.2V 13A.

Just watch the video at 16:35.

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pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #60 on: December 23, 2012, 03:03:51 pm »
i repeat it once again.....  simple test....

DOES THE ASICS FIREUP WITH THE PIN1 3.3V and 5V?

as simple as that....  :-//

<Edit>
there are trims between ADC ans SRAM management
....for float ground triming?
...if so there is your 0.100 to 1Ohm
<Edit>

Your theory does not add up with the rest of the evidence.

If those pins are for some reason floating grounds connected back to the PSU, why are they directly connected to each other and why are they the same colour wire?

And why is the PSU rated to provide 13A when a single wire isn't capable of carrying it at 3.3V without significant volt drop?

You're making a similar error to Dave and making assumptions based on a schematic for a different device.

you are wrong about reading  a schematic for a different device...
all 9384 are the same (board No F9384-3)... and the letter after it is the Memory size and the options
all 93X4 have common PCB.....the 9374 have some unpopulated comps
just
 

Offline Monkeh

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #61 on: December 23, 2012, 03:07:15 pm »
you are wrong about reading  a schematic for a different device...
all 9384 are the same (board No F9384-3)... and the letter after it is the Memory size and the options
all 93X4 have common PCB.....the 9374 have some unpopulated comps
just

And you, apparently, are wrong about your floating ground idea, because the very images you just posted show pins 10, 11, and 12 as being +3.3V.

E: That also makes it clearer that I was probably seeing one of the 5.2V supplies on the label. Ahh, blurry images. The pinout doesn't seem to match the PSU label, though.
« Last Edit: December 23, 2012, 03:11:57 pm by Monkeh »
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #62 on: December 23, 2012, 03:29:42 pm »
you are wrong about reading  a schematic for a different device...
all 9384 are the same (board No F9384-3)... and the letter after it is the Memory size and the options
all 93X4 have common PCB.....the 9374 have some unpopulated comps
just

And you, apparently, are wrong about your floating ground idea, because the very images you just posted show pins 10, 11, and 12 as being +3.3V.

E: That also makes it clearer that I was probably seeing one of the 5.2V supplies on the label. Ahh, blurry images. The pinout doesn't seem to match the PSU label, though.

about float:
the Front-End is working @12V,5V...the HADs are working @ 5V....the MDXs are Working @ 5V,3V..and the SRAMs are working @3V

the pins:
pin1,2,3 are as they apear on video L-to-R ,T-to-B....sorry about that i mean as in schematic
 

Offline Monkeh

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #63 on: December 23, 2012, 03:36:01 pm »
you are wrong about reading  a schematic for a different device...
all 9384 are the same (board No F9384-3)... and the letter after it is the Memory size and the options
all 93X4 have common PCB.....the 9374 have some unpopulated comps
just

And you, apparently, are wrong about your floating ground idea, because the very images you just posted show pins 10, 11, and 12 as being +3.3V.

E: That also makes it clearer that I was probably seeing one of the 5.2V supplies on the label. Ahh, blurry images. The pinout doesn't seem to match the PSU label, though.

about float:
the Front-End is working @12V,5V...the HADs are working @ 5V....the MDXs are Working @ 5V,3V..and the SRAMs are working @3V

the pins:
pin1,2,3 are as they apear on video L-to-R ,T-to-B....sorry about that i mean as in schematic

Pin 1 is the top left pin when looking down at the connector body from the wire side, with the locking tab to the bottom. Making it the BOTTOM pin facing you from the perspective Dave was working from. Pins 10, 11, and 12 are thus the top pins, facing you, yellow wires. +3.3V. Nothing you've said and nothing in the pictures you've posted supports this floating ground idea. There's a short on the +3.3V rail.
« Last Edit: December 23, 2012, 03:38:43 pm by Monkeh »
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #64 on: December 23, 2012, 04:10:20 pm »
you are wrong about reading  a schematic for a different device...
all 9384 are the same (board No F9384-3)... and the letter after it is the Memory size and the options
all 93X4 have common PCB.....the 9374 have some unpopulated comps
just

And you, apparently, are wrong about your floating ground idea, because the very images you just posted show pins 10, 11, and 12 as being +3.3V.

E: That also makes it clearer that I was probably seeing one of the 5.2V supplies on the label. Ahh, blurry images. The pinout doesn't seem to match the PSU label, though.

about float:
the Front-End is working @12V,5V...the HADs are working @ 5V....the MDXs are Working @ 5V,3V..and the SRAMs are working @3V

the pins:
pin1,2,3 are as they apear on video L-to-R ,T-to-B....sorry about that i mean as in schematic

Pin 1 is the top left pin when looking down at the connector body from the wire side, with the locking tab to the bottom. Making it the BOTTOM pin facing you from the perspective Dave was working from. Pins 10, 11, and 12 are thus the top pins, facing you, yellow wires. +3.3V. Nothing you've said and nothing in the pictures you've posted supports this floating ground idea. There's a short on the +3.3V rail.

nope....

video ----- manual
pin1             pin12                     OK
pin2             pin11 <_____|     sorted
pin3             pin10 <_____|     sorted
 |O

<Edit>
maybe i am misunderstood
SAM's     pin11,pin10<------>GND  1 Ohm
SAM's     pin11<---->pin10      uknown
SAM's     pin12<---->pin11     uknown
SAM's     pin12<---->pin10      uknown

DAVE's     pin11,pin10<------>GND  0.1 Ohm
DAVE's     pin11<---->pin10      uknown
DAVE's     pin12<---->pin11      uknown
DAVE's     pin12<---->pin10      uknown
<Edit>
« Last Edit: December 23, 2012, 04:26:18 pm by pir »
 

Offline albertr

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #65 on: December 23, 2012, 04:29:31 pm »
...
all 93X4 have common PCB.....the 9374 have some unpopulated comps
...

Why do you think that 93X4 series have the same boards? I have a 9374L sitting here on the bench and at the first glance the main board looks quite different. Also the CPU board is different and so is power supply and its connector.

-albertr
« Last Edit: December 23, 2012, 04:35:54 pm by albertr »
 

Offline SeanB

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #66 on: December 23, 2012, 04:47:41 pm »
So officially is the LeCroy now LeCrisp?
 

Offline Monkeh

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #67 on: December 23, 2012, 05:02:44 pm »
nope....

video ----- manual
pin1             pin12                     OK
pin2             pin11 <_____|     sorted
pin3             pin10 <_____|     sorted
 |O

<Edit>
maybe i am misunderstood
SAM's     pin11,pin10<------>GND  1 Ohm
SAM's     pin11<---->pin10      uknown
SAM's     pin12<---->pin11     uknown
SAM's     pin12<---->pin10      uknown

DAVE's     pin11,pin10<------>GND  0.1 Ohm
DAVE's     pin11<---->pin10      uknown
DAVE's     pin12<---->pin11      uknown
DAVE's     pin12<---->pin10      uknown
<Edit>

Pin 10 and 11 go to the ASICs and have been shorted, probably in the ASICs. Pin 12 goes to the RAM and is not connected to the rest of the plane. All three are +3.3V from the PSU, no funny floating ground madness going on here.
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #68 on: December 23, 2012, 05:29:32 pm »
nope....

video ----- manual
pin1             pin12                     OK
pin2             pin11 <_____|     sorted
pin3             pin10 <_____|     sorted
 |O

<Edit>
maybe i am misunderstood
SAM's     pin11,pin10<------>GND  1 Ohm
SAM's     pin11<---->pin10      uknown
SAM's     pin12<---->pin11     uknown
SAM's     pin12<---->pin10      uknown

DAVE's     pin11,pin10<------>GND  0.1 Ohm
DAVE's     pin11<---->pin10      uknown
DAVE's     pin12<---->pin11      uknown
DAVE's     pin12<---->pin10      uknown
<Edit>

Pin 10 and 11 go to the ASICs and have been shorted, probably in the ASICs. Pin 12 goes to the RAM and is not connected to the rest of the plane. All three are +3.3V from the PSU, no funny floating ground madness going on here.

i don't say that there is no short @ all....
i just say that dave should not take off the MDX422a before take out all the other propabilities...
what makes you sure that there is not a floating ground related circuit at all?
and say into that 7layers pcb under the MDX422a ...is there any RF isolation plate?...maybe related to 3.3V and heating up ...putting extra heat to the MDXs?

love debating... keep it up   :-+
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #69 on: December 23, 2012, 05:34:56 pm »
...
all 93X4 have common PCB.....the 9374 have some unpopulated comps
...

Why do you think that 93X4 series have the same boards? I have a 9374L sitting here on the bench and at the first glance the main board looks quite different. Also the CPU board is different and so is power supply and its connector.

-albertr

i mean striped-out main-pcb
pic over the shorted area of a 9374L(from manual):
 

Offline Monkeh

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #70 on: December 23, 2012, 05:39:39 pm »
what makes you sure that there is not a floating ground related circuit at all?

I never said there isn't, I don't have a schematic. I am, however, sure that pins 10, 11, and 12 on the power connector are all +3.3V supply on one rail from the PSU, and 0.1 ohm between them and ground makes no sense at all unless something has failed.
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #71 on: December 23, 2012, 05:48:00 pm »
what makes you sure that there is not a floating ground related circuit at all?

I never said there isn't, I don't have a schematic. I am, however, sure that pins 10, 11, and 12 on the power connector are all +3.3V supply on one rail from the PSU, and 0.1 ohm between them and ground makes no sense at all unless something has failed.

agreed....i say maybe the funny L's floating ground passing under the ASICs
 

pir

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #72 on: December 23, 2012, 05:58:03 pm »
and to keep the thread up....look here:

 >:D

 

Offline Dread

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #73 on: December 24, 2012, 04:54:52 am »
Dave I just got around to watching the video so I came here and just wanted to say thank you for making the video in the first place.  I know at this point you must be having serious regrets at making this repair video because some people will interpret the lack of a fix as some sort of sign that your abilities are not on Par with the Gods of the repair world.

 I know that feeling very well, as a young student EE I had the great fortune of studying/working with a 20 year seasoned Tech during summers and Christmas breaks and that really helped me with my tuition fee's and skills but also made me feel like I was dancing around in the Dark as this brilliant guy would keep pointing out the obvious stuff I missed or taking something I had worked on for the better half of a day and fixing it in 30 minutes.

At one point after my third season in his shop I got stuck again and he pulled me aside and he said you know what your problem is you’re suffering from "TBL"!   A bit puzzled I asked what is TBL?  He said "Technician Brain Lock!" You see your first problem on a board and you get totally consumed with it to the point that you’re chasing it to the point of endless redundancy.

Dave Please don't be offended by my statements because I think you do one of the best shows on the internet and I hold you in very high regard but I honestly think you got a case of TBL going on with this LeCroy.  Five extra amps is a finger check, ok maybe you could stretch it to a temp probe, but Flir!   

In regards to fixing this unit it's purely up to you but in some ways this video has already taken on a life of its own and I feel a bit more examination without an assumptions that because one guy says his reads over 1 ohm and your reading .165Ohm makes it a clear indicator of a short may need to be revaluated, especially given the latching and current drop we see when the unit is partially running.  Instead step back and look at this from a new angle and my first and only suggestion is the one I gave you before in the first video post and has been repeated here several times by others.

Put the unit completely back together and supply that 3.3V externally and see what happens.   Worst case nothing, best case it works and power consumption drops to 6A and the third case is that the unit partially comes to life and can provide you with more data as to what is working and what is not.

Anyway I think I have said way too much on this.  I feel your pain my friend I guess the lesson from this one is don't publish a repair video until you have the unit working, that way the viewers feel like the movie had a proper ending. 

Best wishes for Christmas
Robert
« Last Edit: December 24, 2012, 09:04:02 pm by Dread »
The Optimist says the glass is half full, the Pessimist says its half empty, an engineer only see's a glass that’s twice as big as it needs to be!
 

Offline Nermash

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #74 on: December 24, 2012, 07:20:59 am »
EEVblog #500 - Dave designs and builds automated test bed for LeCroy board, with Internet connectivity!
Now everyone can probe, measure and power on the board with a simple click of mouse ;D :-DMM
« Last Edit: December 24, 2012, 07:23:00 am by Nermash »
 

Online notsob

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #75 on: December 24, 2012, 07:31:34 am »
Dave versus Lecroy 9384C

I smell a new T-Shirt coming on
 

Online jancumps

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #76 on: December 24, 2012, 09:32:44 am »
...  I know at this point you must be having serious regrets at making this repair video ...

it has been one of the biggest successes. Two follow up videos, two lively forum threads. Fun.
 

Offline amyk

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #77 on: December 24, 2012, 10:27:16 am »
ASICs not happy.

Low voltage high current devices like CPUs can look shorted (e.g. 1.2v core voltage, 20W in stopped state = ~ 16.7A or 72mohm resistance) but I don't think that's the case here.

Unless I'm missing something, from the posted schematic fragments it looks like they have neither power nor ground pins shown...

-5.2V and Vee means ECL logic.

The 9384M manual that was posted shows the MDX622 as an "2:8 ECL to TTL demultiplexer".

So officially is the LeCroy now LeCrisp?
I think it has LeCroaked.
 

Offline itdontgo

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #78 on: December 24, 2012, 12:42:46 pm »
Number 2 might just be hotter than the others because there is radiation heat transfer to it from 1 and 3.  Number 1 radiates into a cooler area and so should always be cooler than two.

Why not force it to run with your power supply connected and see what doesn't work on the scope?  If one channel is faulty presumably it's that channel's ASIC.

Offline itdontgo

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Re: EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2
« Reply #79 on: December 24, 2012, 12:44:43 pm »
Number 2 might just be hotter than the others because there is radiation heat transfer to it from 1 and 3.  Number 1 radiates into a cooler area and so should always be cooler than two.

Why not force it to run with your power supply connected and see what doesn't work on the scope?  If one channel is faulty presumably it's that channel's ASIC.

To isolate it you would need to put something like Al foil between the heatsinks to reflect the heat from the other two - but the you would also need that on one to reflect it's heat back at it like number is getting...


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