EEVblog #401 - Lecroy 9384C Oscilloscope Repair - Part 2

[vaualbus]

I've a idea the Why the short can't be  under the metallic cover?
 You've never checked under there.

[ftransform]

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.

[lewis]

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:

[lewis]

Sorry, I'm getting off-topic and will shut up now...

[pir]

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>

[Monkeh]

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.

[EEVblog]

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.

[Monkeh]

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.

[Electr0nicus]

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.

[Monkeh]

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.

Who's Sam? I don't know who Sam is. I am not psychic.

[pir]

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

[Monkeh]

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.

[pir]

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

[Monkeh]

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.

[pir]

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
 

<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>

[albertr]

...
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

[SeanB]

So officially is the LeCroy now LeCrisp?

[Monkeh]

nope....

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

<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]

nope....

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

<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]

...
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):

[Monkeh]

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]

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]

and to keep the thread up....look here:

 

[Dread]

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

[Nermash]

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