Products > Test Equipment
Tektronix MDO3014 failure, MDO3000 series
GridWork:
--- Quote from: kcbrown on February 08, 2021, 05:19:03 pm ---
--- Quote from: GridWork on February 08, 2021, 04:16:05 pm ---New update:
I spent most of the weekend trying to trouble shoot what's going on. So far here is what I know:
* The main application processor is being reset due to a global reset from the supervisor circuit.
* The supervisor is causing a reset because main voltage is dropping out.
* The voltage dropout is due to the power controllers on the mezzanine board shutting down.
* I am trying to route out where the shut down is coming from. The 1.8V controller "RUN" comes from the power good on the 5.0VD controller.
* It appears that something on the main board tells the AUX DC/DC controllers to start up, not sure where that is yet.
I will try and get some pictures posted of the board and attach to this message.
--- End quote ---
This is actually good news if I'm reading it right. You might not need to re-flash the front panel controller after all, if it's being reset in the way you suggest. Smells like a hardware fault.
The very first thing I'd look at is the actual voltages going into and out of the various voltage controllers, see how they vary over time.
--- End quote ---
I've been looking at the voltages on all of the DC/DC outputs (and the 12V power supply output), there doesn't appear to be any increased current draw prior to shutdown. There are two dual channel Linear controller chips responsible for the 5.0VD, 3.3V and 1.8V, they are being commanded off from a discrete FET pair (on the backside of the board), but I'm not sure what from. The front panel micro appears to be dead, i.e. no code. It was working prior to the re-flash even when the intermittent reset started.
This scope has been sitting on my desk for the last 5 years, and actually un-plugged during a good chunk due to lack of use.
One of the really frustrating things is the small components, traces and vias. For as much space as appears on the boards, there is no reason to use the grain of sand parts that they have. 0603's would make for something much more repairable.
kcbrown:
--- Quote from: GridWork on February 08, 2021, 05:58:50 pm ---I've been looking at the voltages on all of the DC/DC outputs (and the 12V power supply output), there doesn't appear to be any increased current draw prior to shutdown. There are two dual channel Linear controller chips responsible for the 5.0VD, 3.3V and 1.8V, they are being commanded off from a discrete FET pair (on the backside of the board), but I'm not sure what from. The front panel micro appears to be dead, i.e. no code. It was working prior to the re-flash even when the intermittent reset started.
This scope has been sitting on my desk for the last 5 years, and actually un-plugged during a good chunk due to lack of use.
One of the really frustrating things is the small components, traces and vias. For as much space as appears on the boards, there is no reason to use the grain of sand parts that they have. 0603's would make for something much more repairable.
--- End quote ---
It's probably a bill of materials thing. The front-end likely needs the grain-of-sand parts because (I would expect) they have less in the way of parasitic characteristics, and since they're already specifying those parts, they may as well use the same types for the rest of the scope. That would also simplify the pick and place requirements since fewer strips of parts would be needed to feed the pick and place machines.
You looked at the DC/DC outputs. What of their inputs? If you can identify which one (if any) is getting a failed input, that might lead you down the right path. If you've got a cracked trace or something, you might be up against a thermally-generated failure and the only way you'd be able to see that is by looking at the inputs right at the voltage controller. But if the voltage regulators are also controlled by a FET pair, and you've already identified the signal from the FET pair as causing the voltage controllers to shut off, then there's nowhere to go except back to the source that feeds the FETs.
If you've got a microscope, you should use it to look for cracked solder joints and other types of damage that could be responsible.
Sounds like tracing these things out is a real pain. :(
Do you have close-up photos of the area around the FETs (both the side where the FETs are located and the other side)? It might be helpful for us to see what you're up against here ...
GridWork:
--- Quote from: kcbrown on February 08, 2021, 11:14:01 pm ---
--- Quote from: GridWork on February 08, 2021, 05:58:50 pm ---I've been looking at the voltages on all of the DC/DC outputs (and the 12V power supply output), there doesn't appear to be any increased current draw prior to shutdown. There are two dual channel Linear controller chips responsible for the 5.0VD, 3.3V and 1.8V, they are being commanded off from a discrete FET pair (on the backside of the board), but I'm not sure what from. The front panel micro appears to be dead, i.e. no code. It was working prior to the re-flash even when the intermittent reset started.
This scope has been sitting on my desk for the last 5 years, and actually un-plugged during a good chunk due to lack of use.
One of the really frustrating things is the small components, traces and vias. For as much space as appears on the boards, there is no reason to use the grain of sand parts that they have. 0603's would make for something much more repairable.
--- End quote ---
It's probably a bill of materials thing. The front-end likely needs the grain-of-sand parts because (I would expect) they have less in the way of parasitic characteristics, and since they're already specifying those parts, they may as well use the same types for the rest of the scope. That would also simplify the pick and place requirements since fewer strips of parts would be needed to feed the pick and place machines.
You looked at the DC/DC outputs. What of their inputs? If you can identify which one (if any) is getting a failed input, that might lead you down the right path. If you've got a cracked trace or something, you might be up against a thermally-generated failure and the only way you'd be able to see that is by looking at the inputs right at the voltage controller. But if the voltage regulators are also controlled by a FET pair, and you've already identified the signal from the FET pair as causing the voltage controllers to shut off, then there's nowhere to go except back to the source that feeds the FETs.
If you've got a microscope, you should use it to look for cracked solder joints and other types of damage that could be responsible.
Sounds like tracing these things out is a real pain. :(
Do you have close-up photos of the area around the FETs (both the side where the FETs are located and the other side)? It might be helpful for us to see what you're up against here ...
--- End quote ---
Pictures inbound:
MDO3000 Mezzanine board
TOP
BOTTOM
LTC3850
So what I have found is that the LTC3850 on the Left supplys the 1.8V and 5.0V Digital. The LTC3850 on the right supplies the 5.0V Analog. The LTC3850 on the right PGOOD output feeds the RUN for the one on the left. The 5.0VA (right) is the controller that shuts down first. The RUN1 on it gets commanded off from Q305 (back side, bottom right). Now I've got to figure out what drives it.
kcbrown:
--- Quote from: GridWork on February 09, 2021, 04:06:53 am ---So what I have found is that the LTC3850 on the Left supplys the 1.8V and 5.0V Digital. The LTC3850 on the right supplies the 5.0V Analog. The LTC3850 on the right PGOOD output feeds the RUN for the one on the left. The 5.0VA (right) is the controller that shuts down first. The RUN1 on it gets commanded off from Q305 (back side, bottom right). Now I've got to figure out what drives it.
--- End quote ---
If I'm reading it right, the code on those transistors is I09, which makes them an SST109, an N-channel JFET (see https://www.sphere.bc.ca/download/smd-codebook.pdf). The gate is on pin 3, the single pin on the left side in the photo. That connects to R321, which connects to the via just next to the lower left corner of Q305. That via dives through to the other side, but the other side is unpopulated. In fact, the way the other side is unpopulated, and the way these components seem to connect to the unpopulated side, makes me wonder if this is the right place to be looking. This is really weird.
Do you have a macro lens or something that you can use to get close-in shots of these two areas?
Back side:
Front side:
I've also attached a horizontally flipped version of the front side. I've tried to match the boundaries and resolution as much as possible so that you can overlay one on top of the other to make it easy to see where any given via goes through and connects to:
The problem is that the original images aren't quite high enough in resolution for me to be able to clearly make out the traces and where they go. Additional side lighting from the bottom right might help with that.
GridWork:
--- Quote from: kcbrown on February 09, 2021, 05:28:30 am ---
--- Quote from: GridWork on February 09, 2021, 04:06:53 am ---So what I have found is that the LTC3850 on the Left supplys the 1.8V and 5.0V Digital. The LTC3850 on the right supplies the 5.0V Analog. The LTC3850 on the right PGOOD output feeds the RUN for the one on the left. The 5.0VA (right) is the controller that shuts down first. The RUN1 on it gets commanded off from Q305 (back side, bottom right). Now I've got to figure out what drives it.
--- End quote ---
If I'm reading it right, the code on those transistors is I09, which makes them an SST109, an N-channel JFET (see https://www.sphere.bc.ca/download/smd-codebook.pdf). The gate is on pin 3, the single pin on the left side in the photo. That connects to R321, which connects to the via just next to the lower left corner of Q305. That via dives through to the other side, but the other side is unpopulated. In fact, the way the other side is unpopulated, and the way these components seem to connect to the unpopulated side, makes me wonder if this is the right place to be looking. This is really weird.
Do you have a macro lens or something that you can use to get close-in shots of these two areas?
Back side:
Front side:
I've also attached a horizontally flipped version of the front side. I've tried to match the boundaries and resolution as much as possible so that you can overlay one on top of the other to make it easy to see where any given via goes through and connects to:
The problem is that the original images aren't quite high enough in resolution for me to be able to clearly make out the traces and where they go. Additional side lighting from the bottom right might help with that.
--- End quote ---
I do have a macro and have gotten some more detailed pictures, just ran out of time getting some update here. I think I may have mistyped the transistor, I think that some how Q304 is the one initiating the shut down. It's the only active device I have found connected to the "RUN" pin on the 5.0V DCDC. All of the other components attached to the "RUN" are anodes from various diodes on the board.
There may be another development here on the scope. The tech support individual I've been e-mailing mentioned a service note "CS-SUP-0110" about scopes randomly powering down. I have to see if the RMA department changes this from a customer funded repair to something different.
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