Toolboard reports 2000C hot end

[jens55]

The subject says it all .... 2000C no matter if the thermistor is connected or not. On another tool board, disconnecting the thermistor gets me -273 or so degrees.
There is a possibility that I short circuited the heater but I do not see how that would affect temperature measurement. I had a look at the toolboard and saw nothing obviously toasted.
Blue and red lights are on, activity light flashes as in being in sync (like the other tool boards).
Currently thermistor and heater are disconnected and temperature still shows 2000C.
Changed config.g to use second temperature port (temp1 instead of temp0) with no change, still reading 2000C.
This happened when I was cleaning some crap off the hot end with the printer on. First thing I tried was a reboot but no change. I also changed another tool board to read from temp1 instead of temp0 just to make sure it was behaving as it should and yes, it showed -273 with nothing connected to temp1, switched it back to temp0 and am reading proper temperature on the working tool board.

Thoughts on what could be happening ?

[dc42]

@jens55 I suspect that the reference resistor on that thermistor input has failed. This can happen if there is electrostatic discharge to the thermistor pin, or if the heater is shorted to the thermistor input for more than a few seconds. We've beefed up that resistor on later tool board revisions to make it more resistant to ESD.

Have you tried using the second thermistor input on the tool board?

It's possible to replace the resistor, although a little tricky because it is small.

[jens55]

@dc42, I have tried going to the secondary (temp1) input and there is no change, the system still reports 2000C

[dc42]

@jens55 if you have a multimeter, with the thermistor disconnected and power applied to the tool board, can you measure any voltage between the two pins of the TEMP0 connector? Similarly for TEMP1. Also check the voltage between the 3.3V and ground pins of the IO1 connector.

[jens55]

@dc42, no voltage between either the two pins on temp0 or temp1, 3.3V on io1 between 3.3 and ground ... as far as I can tell ...

[dc42]

@jens55 if you send M308 S# where # is the sensor number, what is the result? If it's "VSSA fault" then the PTC fuse has failed. Likewise if you measure 3.3V between VSSA on the TEMP connector and GND on one of the IO connectors.

[jens55]

@dc42 M308 S2 gives me a 'bad vssa' in the reported string. I also get 3.3V between VSSA and GND

Just to confirm, on a 1LC board ver 1.1, it is F1 which is green with the markings bF? is the ptc fuse 0ZCJ0020FF2E that is listed on https://docs.duet3d.com/en/User_manual/Troubleshooting/Parts the correct replacement? Can I just solder it on top of the dead littlefuse ?

Looks like my thermistor has one line tied directly to the stainless case and I likely connected one of the heater leads to the hot block which then zapped the fuse. But why was it killed and not just reset?
What did I do to make the re-settable fuse permanently dead (besides the short) so I don't do this again?

Since I can't turn the heater on to test if I killed the FET as well, what is a good way of testing the FET?

[jens55]

I just noticed the 0ZCJ0020FF2E resettable fuse is about twice or so the size of the currently installed fuse. It is also a fraction of the price of the original Littlefuse which appears to be non-resettable (based on what Digikey tells me). I guess I will have to be a bit more creative to install the larger fuse .... I rather have a resettable type in there than a non-resettable.

[dc42]

@jens55 tool board 1.1 has a 10 ohm resistor R47 in series with the VSSA fuse. It's very likely that is the failed component, not the PTC fuse.

[T3P3Tony]

@jens55 the fuse fitted to the toolboard should be a 0ZCJ0020FF2E,care you sure it's twice the size?

[jens55]

@dc42, thanks for the heads-up. The resistor was removed in the newer version of the board, is it ok to just bypass the resistor? The question on how to best test the heater output FET(s) is still out there. It would be awfully annoying if I bring in one part when a different part also failed. Part cost is negligible but it takes time and additional freight to get a tiny part in. Maybe I should just bring in fuses, resistors and FET's and hopefully be done with that issue ....
What is the part number for the output FET's for Q1A and Q1B? Is there a document mentioning replacement parts for the 1LC ?

[jens55]

@T3P3Tony said in Toolboard reports 2000C hot end:

The 0ZCJ0020FF2E is 0.128" L x 0.065" W (3.25mm x 1.65mm)
The 0438.250WR is 0.061" L x 0.033" W x 0.020" H (1.54mm x 0.85mm x 0.50mm)

The document I referenced above that lists spare parts does not refer to the 1LC specifically so I don't really know what is there right now.

[dc42]

@jens55 you can test the heater output FETs by using M950 to configure OUT0 as a GPOUT port and then using M42 to control it.

You may get away with bypassing the resistor, however in later tool board revisions we reduced the value of R32 from 2K2 to 1K0 in order to increase the voltage drop across the fuse.

[jens55]

@dc42, thanks for your help! I will do some test in the morning. Hopefully the output FET's are ok.

[T3P3Tony]

@jens55 the toolboard uses the 0ZCJ0020FF2E
That link is for a fuse on the Duet 2.

We do need to expand the spare parts documentation with more Duet 3 information.

[jens55]

@dc42, with your suggestion of switching the output to a general i/o, I was able to determine that the FET was ok. I now realize that the FET is non-replaceable by mere mortals, having the connections underneath the chip. Measuring R47 in circuit seemed to suggest that it was open circuit as you thought. I set out to bridge it with a 1/8W (?) thru hole resistor but I buggered it up something fierce. I then proceeded to jumper the resistor from the VSSA pin on temp0 to the fuse and although not pretty, it seemed to be ok. Alas, powering up the printer showed that the temperature is no longer 2000C but shows as 'N/A' with both no thermistor connected as well as with the thermistor in the circuit. I am assuming that I buggered things up with the 'fine' solder tip that, under a magnifying glass (cause my eyes couldn't see the thing), compared to the flea poop sized resistor looked like a giant sledge hammer.
Looks like a new tool board from Filastruder is my next step.
Again, thanks for your help!

[jens55]

In case it sheds a light on the 'n/a' reading for temperature, here is my diagnostic output:
m122 b22
Diagnostics for board 22:
Duet TOOL1LC rev 1.1 or later firmware version 3.4.4 (2022-10-14 11:46:33)
Bootloader ID: SAMC21 bootloader version 2.3 (2021-01-26b1)
All averaging filters OK
Never used RAM 2512, free system stack 88 words
Tasks: Move(notifyWait,0.0%,153) HEAT(notifyWait,0.2%,111) CanAsync(notifyWait,0.0%,65) CanRecv(notifyWait,0.1%,76) CanClock(notifyWait,0.0%,65) ACCEL(notifyWait,0.0%,61) TMC(notifyWait,3.0%,57) MAIN(running,91.9%,351) IDLE(ready,0.0%,26) AIN(delaying,4.9%,142), total 100.0%
Last reset 00:01:47 ago, cause: software
Last software reset time unknown, reason: AssertionFailed, available RAM 3392, slot 1
Software reset code 0x0120 ICSR 0x00000000 SP 0x2000415c Task Freestk 129 bad marker
Stack: 00000544 00022ffc 00019b65 20003134 00016cff 20003134 000163d1 20000ed0 00000000 00000001 00008275 200071c8 200071c8 200071e0 00000000 20000f50 00011647 000223b8 00022474 00021ac8 00019b05 200071c8 200071c8 20000f50 000083ed 200071d8 000009c7
Driver 0: pos 0, 830.0 steps/mm,standstill, SG min 0, read errors 0, write errors 1, ifcnt 29, reads 53648, writes 14, timeouts 0, DMA errors 0, CC errors 0, steps req 0 done 0
Moves scheduled 0, completed 0, in progress 0, hiccups 0, step errors 0, maxPrep 0, maxOverdue 0, maxInc 0, mcErrs 0, gcmErrs 0
Peak sync jitter 0/4, peak Rx sync delay 196, resyncs 0/0, no step interrupt scheduled
VIN voltage: min 24.4, current 24.5, max 24.5
MCU temperature: min 22.7C, current 27.4C, max 27.4C
Last sensors broadcast 0x00000004 found 1 114 ticks ago, 0 ordering errs, loop time 0
CAN messages queued 2196, send timeouts 0, received 2217, lost 0, free buffers 37, min 36, error reg 0
dup 0, oos 0/0/0/0, bm 0, wbm 0, rxMotionDelay 0
Accelerometer: LIS3DH, status: 00
I2C bus errors 0, naks 3, other errors 0
=== Filament sensors ===
Interrupt 5726621 to 0us, poll 4 to 620us
Driver 0: ok

The firmware version is the same as my other (working) tool boards

[jens55]

Final post on this matter ... I did an M308 S2 and got a correct reading but DWC still showed n/a for the temperature. I double and triple checked config.g and was certain that things were set up correctly. By chance, I opened up a new browser window and sure enough, temperature was reporting correctly. I think this is relating to the bug (?) I reported in a different thread that sometimes DWC slows down after a while and the only way of fixing the problem is to close the DWC browser window and re-open it.
In any case, the operation seemed to have been a success and, for future screw ups, I have two tool boards coming from Filastruder .....

[dc42]

@jens55 so it sounds to me that your tool board is working!

I almost suggested that you try putting a solder bridge across R47, but I didn't in case that didn't work because the value of R32 was still the original 2K2 value (whether that works will depend on the cold resistance of the PTC fuse, which has quite a wide tolerance). The ideal fix would be to either replace R47 (it can be removed using a soldering iron bit large enough to cover both pads, just put some fresh solder on the bit and the resistor will stick to it) or to solder a new 10R 0402 resistor on top of it, which can be done if your soldering iron has a sufficiently fine tip.

My diagnosis is that you had a short between VIN (perhaps from a heater output) and the VSSA side of the TEMP input. We have seen before that this can cause R47 to fail, which is why we removed R47 in versions 1.2a and 1.3 of the tool board.

[jens55]

@dc42 , yes it is working - really surprised me after the botch up job I did. I was not able to see the pads any more (covered with blackened flux which I was unable to shift with an alcohol soaked Q tip) which is why I ran the resistor from the fuse to the VSSA pin on the temp0 connector.
What actually happened was that there was a short between one side of the temperature probe and it's stainless case. I had inadvertently shorted the heater power to it's case or the hot end block which then completed the path through the case of the thermistor back to the tool board frying the resistor.
Your diagnosis was spot on!
I surprise myself how I constantly find new ways to screw up my printers