12V on the 5V rail

[A Former User]

@Haggan90 said in 12V on the 5V rail:

I can't find the 74HCT02 chip.

and yeah, u2 is done for

[Haggan90]

@bearer Yeah, that's what I tought.. Could it be fixed if I just replaced U2?
What does U2 do?

[A Former User]

@Haggan90 said in 12V on the 5V rail:

Could it be fixed if I just replaced U2?

Theoretically. It provides 3.3v to the system. U11 / 74HCT02 drives the heater mosfets. But there could be more damage as well. I'd remove U2 and apply an external, preferably current limited supply to test.

[Haggan90]

@bearer Ok!
I've removed U2, where can I connect 3.3V and what should I set the current limit to?
Btw, I tried the SD card and it seems to work fine.

[dc42]

A current limit of 200mA should be enough if nothing else is damaged, until you turn the WiFi module on. With WiFi on you may need 600mA.

[A Former User]

@Haggan90 said in 12V on the 5V rail:

where can I connect 3.3V and what should I set the current limit to?

i've found that making a cable to connect to CONN_SD gives me convenient access to gnd, 3v3 and 5v connections. You can use single du-pont style wires as well. In general you can use any 3.3v pin shown on the wiring diagram. as dc42 said, 200mA is a good starting point; if it goes into current limiting mode try 300mA but if it takes more than a second or two to charge up capacitors and start up then start looking for what gets warm.

[zapta]

@Haggan90, you can find the duet wifi schematics in the link below. It may help you understand what's is going on.

https://github.com/T3P3/Duet/tree/master/Duet2/Duet2v1.04

[dc42]

You can feed the 3.3V into any endstop connector.

[Haggan90]

@dc42 I connected 3.3V and nothing got hot.
When I connected USB I got 4.4V in the 3.3V rail...

[A Former User]

@Haggan90 said in 12V on the 5V rail:

When I connected USB I got 4.4V in the 3.3V rail...

after removing the 3.3v volt regulator? strange, please post a picture of the board?

[Haggan90]

@bearer I connected 3.3V to where the regulater output was.

[dc42]

@Haggan90 said in 12V on the 5V rail:

@dc42 I connected 3.3V and nothing got hot.
When I connected USB I got 4.4V in the 3.3V rail...

Remove the other blown chip too.

[Haggan90]

@dc42 You mean the U11 / 74HCT02?

[dc42]

@Haggan90 said in 12V on the 5V rail:

@dc42 You mean the U11 / 74HCT02?

Yes.

[Haggan90]

@dc42 aha ok! I have to do that at work where we have a hot air solder gun

[Haggan90]

@dc42 Hi!

Sorry for taking such long time for this, but now I have manage to replace the U2 and U11.
When I connect the Duet to USB I get a warning of high current cunsumtion on the USB port, and U2 get's really hot.

Do you have any slightest idea of what else could be broken?

[dc42]

What else is getting hot? Start by checking the processor, SD card (if it is in the socket), and WiFi module.

Are you certain that you used the correct chip to replace U2? Different hardware versions of the Duet WiFi use different chips in that position.

[Haggan90]

@dc42 hi!
As far as I can nothing else get's hit then the U2. Here are the new components.

[dc42]

What part number did you use for the 3.3V regulator, and what hardware revision Duet board is it? I think you may have used the wrong regulator.

[Haggan90]

@dc42 Hi,

As voltage regulator I used a: AP7361C-33E-13
And as the U11 mosfet driver I used a : SN74HCT02PWR