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Working, then not, now 7805 is hot ;(

Posted by mustache 
Working, then not, now 7805 is hot ;(
January 24, 2016 05:57AM
Hi guys

I bought a kit from alibaba (geetech aluminum i3 prusa) and it was working fine (could do manual control over repetier host, homing, bed/extruder heating). The only thing that was missing was the extruder fan. This was not plugged in yet because i was missing a cable.

Now i get the cable, plug it in, and try to run the printer again. Now nothing works. The LCD barely lights up for a few secs then turns off again. I cant connect to the printer over usb either. And the 7805 is getting VEEEERRY hot. As in hot enough to burn myself.


Im assuming the 7805 is burned through, and this has to do with some USB 5V/7805 disturbances.

Would you recommend simply soldering out the 7805? Could this solve my problems?

Cheers



EDIT: Soldered out the 7805, still no connection to the printer....Considering just going for a RAMPS board.

Edited 1 time(s). Last edit at 01/24/2016 10:20AM by mustache.
Re: Working, then not, now 7805 is hot ;(
January 24, 2016 12:49PM
Have you verified the voltage on the 5V pin?

How exactly did you connect the extruder fan? Any chance that you caused some short between 5V and 12V or 5V and GND?

For solving the USB 5V/7805 issues, see here.
Re: Working, then not, now 7805 is hot ;(
January 24, 2016 11:46PM
Hey

I just plugged the cable into one of the two pin connectors between the stepper drivers, surely this is ok? I dont know how i would have produced a short

No I dont have my voltmeter on me at the moment. Ill try to check that

Edited 1 time(s). Last edit at 01/24/2016 11:47PM by mustache.
Re: Working, then not, now 7805 is hot ;(
January 25, 2016 12:28AM
Quote

I just plugged the cable into one of the two pin connectors between the stepper drivers, surely this is ok?

Surely this is ok. I was more afraid that you were using the auxiliary 14pin connector - there, the 5V and 12V are side by side and can easily be shorted...
Re: Working, then not, now 7805 is hot ;(
January 25, 2016 01:31AM
I ordered a new 7805 and will try to get that back in, then report back.

Is there a way i cant tell whether or not the microcontroller is functioning properly?
Also is it possible the ftdi chip was fried along with the 7805?

Cheers
Re: Working, then not, now 7805 is hot ;(
January 25, 2016 02:12AM
Quote

Is there a way i cant tell whether or not the microcontroller is functioning properly?
If you have an ISP programmer or another Arduino (Uno, Nano, Mega ... using ArduinoISP sketch) you can try to upload a program via the ISP header. This should work even if the FTDI chip is dead.

Quote

Also is it possible the ftdi chip was fried along with the 7805?
Check if your PC detects a USB port when you plug in the Sanguinololu. If yes, chances are that the FTDI is still ok, if no ... sad smiley
Re: Working, then not, now 7805 is hot ;(
January 25, 2016 03:50AM
I do ideed have another arduino, ill check that out. My pc detects soething is plugged in but cant recognize what it is. It doesnt recognize it as a COM despite drivers installed

I think i may end up with a replaced 7805 and just say screw the usb interface. I should be able to do everything via lcd and sdcard
Re: Working, then not, now 7805 is hot ;(
January 25, 2016 04:26AM
You could also try to connect a cheap USB-to-TTL converter directly to the TTL pins (RX0/TX0/DTR) that are underneath the USB plug. But first you should try to see if you can program the ATmega644/1284 directly via ISP, using your other Ardiuno as an ISP programmer (see here).
Re: Working, then not, now 7805 is hot ;(
March 12, 2016 06:43AM
UPDATE:

So I havent gotten around to trying to upload anything via a second arduino.

I have tried the following:

Removing the LM7805:
Didnt help at all. No connection from PC possible. nothing.

Replacing the LM7805:
With 12V , Without USB from PC plugged in-> LCD screen flashes on then fades to black. Nothing is displayed
With 12, With USB from PC->LCD screen stays on, PC recognizes COM port and repetier host can connect. Havent been able to actually control the printer this way though
Without 12, With USB-> status LED is bright, i have 5 V on the 5V lines, but the PC doesnt recognize the COM port anymore...

Replaced LM7805 is still getting really hot..even with no peripherals attached..


How can it be that only when both the 5V from the 12V supply and the 5V from the USB supply are attached that my PC recognizes the COM port? What could be the reason that the LM7805 is getting so hot?
Re: Working, then not, now 7805 is hot ;(
March 12, 2016 08:26AM
Another Update:

I've just removed the stepper drivers from the board... the lcd now stays bright and the lm7805 no longer gets too hot. looks like they are fried..

the lcd still is not displaying anything though.

when trying to reupload firmware im getting the following message:


avrdude: stk500_getsync(): not in sync: resp=0x00

i have the autoreset jumper in
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