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Unread 02-19-2018, 10:21 PM
teletype-guy's Avatar
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PDP has no CAN and no lights

Hey folks:

We have no lights on our PDP other than a brief blip of each (approximately together) at power-up. The PDP does not show up in the web dashboard, though the CAN interface and PCM are in the dashboard. I can upload firmware to the PCM, change its id number, and such.

- the roborio image and java dev environment etc -- all up-to-date.

- installed phoenix lifeboat today and updated the RR with its stuff.

- running from IE with SL I see the RR web server just fine (usb connected though I can't imagine ethernet would be different).

- cabling all looks good; termination in the RR of course, then to the PCM, then to the PDP with term jumper on.

- have not put a scope on the bus yet, but presume it is fine as the RR and PCM talk just fime. Seems like the PDP's CAN circuitry is hosed. All the power distribution stuff is just fine.

- tried disconnecting CAN from the PDP and still see no lights except brief power-up blips.

- tried connecting only from the RR to PDP, but still no joy.

- tried drinking heavily and that did not help either.

Can't just swap it out as we are using our only PDP on our competition bot. As we are flat broke I advised that they not spend $200 on a backup PDP, but now, well, sheesh. Our proto bot uses an old blue panel.

We used this same PDP last year and only use the PCM for piston control. Never gave a second thought to the PDP as anything other than an end-of-line resistor. This year we wanted to measure some currents and found the issue.

Anyone have any insight? Seems like the PDP CAN is damaged or just needs to be flashed, but I can't get to it the normal web way. I see no recessed button for factory reset or anything. It has some sort of bootloader -- is that an option? I have various jtag prog pods as well.

Stumped and bummed, Gil Smith
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Unread 02-20-2018, 08:37 AM
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Re: PDP has no CAN and no lights

Hmmmm. If you disconnect all breakers and CAN wires, do the two status LED's at least start blinking?

Basically, if just applying 12V to the input terminals (with nothing else hooked up) doesn't cause an expected sequence of lights, you can safely say something internally is fried. Per R72, you'll have to be careful about what repairs you attempt. I'm not privy to the details of re-flashing bootloaders for it, but personally I'd be a bit concerned about running afoul of R72 (just me though).

Assuming replacement is the path to go down: Even without budget, a few possible options: Borrow one from another local team, email CTRE about possibly RMA'ing it.
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Unread 02-20-2018, 10:58 AM
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Re: PDP has no CAN and no lights

I did try a power-up with can disconnected from the pdp and had no lights.

Did not pull all the breakers -- that is a quick one to try after I get into the school later.

We can live without the current measurements, and it does not seem to affect bus communications.

My biggest concern now is whether the inspectors will have a problem with the lights off.

thx
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Unread 02-20-2018, 11:04 AM
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Re: PDP has no CAN and no lights

I've seen this before as the result of a PDP connected in reverse polarity.

IIRC you'll need the PDP connected to CAN and visible from the dashboard if you want to pass inspection. Emailing CTRE sounds like a good bet as they might be able to repair it for cheaper than a brand new one.
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Unread 02-20-2018, 12:39 PM
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Re: PDP has no CAN and no lights

Please remove all the breakers and check that the polarity of the power input to the PDP is correct. Then power up the PDP with just the CAN buss connected. Don't believe the color code on the wire, use a meter.
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Unread 02-20-2018, 12:42 PM
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Re: PDP has no CAN and no lights

Quote:
Originally Posted by Al Skierkiewicz View Post
Please remove all the breakers and check that the polarity of the power input to the PDP is correct. Then power up the PDP with just the CAN buss connected. Don't believe the color code on the wire, use a meter.
Good advice. What should the meter read if the polarity is correct?
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Unread 02-20-2018, 01:06 PM
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Re: PDP has no CAN and no lights

Disclaimer: While maybe helpful, my advice below seems like it may void your warranty. Proceed at your own risk if you care about that sort of thing.

I'd suggest opening the PDP (if you can) at this point. A cursory inspection to see if any stray swarf or conductive material has made it's way in the device (and subsequently removing it) could be helpful. Additionally, I believe the Weidmuller connectors, status LEDs, and some ICs are located on a daugherboard inside the PDP. Checking for damage and making sure that's seated properly seems like a reasonable idea.

Let us know what you find, and I hope this helps.
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Unread 02-20-2018, 02:06 PM
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Re: PDP has no CAN and no lights

Probably not what you want to hear, but I've encountered this before.

Here's the email I sent to CTRE:
Quote:
Hey,

We have an out-of-warranty PDB board that failed on the bench. No wiring changes were done between it working and not working.

The microcontroller either no longer has any code on it or the vreg for the microcontroller has stopped working between a power cycle. The PDB no longer shows up on the CAN bus and the LEDs remain off.

The rest of the PDB still works, supplying power to all the devices. Upon opening the PDB, I did not see any apparent issues.

Any chance there is a way to force the PDB into boot-loader mode? I doubt it since there aren't any buttons or anything other than a CAN connection to the PDB, electronic wise.

Thanks

Ryan Nazaretian
Garnet Squadron
FRC 4901
Here was their response after sending it in for RMA:
Quote:
Ryan,

Depending on which Hardware rev of PDP you have < 1.5 VS 1.5 & >, The problem is most likely a failure of one or more of the current sense amplifiers. In this failure mode the amplifiers sink excessive amounts of current causing the linear regulator to over heat and enter thermal shutdown. To prove this you can connect the PDP to a linear power supply, set the voltage to just above dropout say around 6 volts. If the unit stays powered under this condition but not at say 12 volts Vin, the amplifiers are the culprit.

This problem was due to a batch of silicon that was manufactured out of spec. We have implimented a work around to address this issue so if future Silicon is "out of spec" we will notnhave this issue. Hardware rev 1.5 and higher have this change.

I hope this helps.
Mike Copioli
If you have a way to control output voltage, say with a bench power supply, try to input at 6V and see if the LEDs light up, then turn it up to 12V and see if the LEDs turn off. Also, this PDP was originally from the 2015 season, so an original board, and it failed in 2016, when they were aware of the issue and seem to implement a workaround on/after 2016.
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Last edited by RyanN : 02-20-2018 at 02:35 PM.
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Unread 02-21-2018, 09:10 AM
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Re: PDP has no CAN and no lights

I found out that we did have a mis-wired battery so it did indeed have a reverse-polarity incident. This was probably what did it in.

We have ordered a new PDP and will install it in the pit at Denver, and send to original for repair post-season. I'll probably peek inside first.

It was a looooong day yesterday. Glad it is in the bag now

Thanks all for the suggestions.
gil
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