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open source GPIB adapter

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dazz1:

--- Quote from: caiser01 on November 26, 2023, 02:25:57 am ---
Maybe, but the fact that your LED never blinks whenever the bootloader is in flash makes me suspect at least part of your problem lies elsewhere. I'm suspicious you have a short or a bad solder connection on at least one of the AVR pins. In particular, I'm wondering if you could have a short or intermittent connection to ground from pin 10 of the AVR since the bootloader is invoked by grounding that pin.

For QFN parts, I've had good luck clearing solder issues by heating the chip until the solder reflows, then giving the chip a few gentle but firm taps right in the center with handle of my tweezers.

--- End quote ---

I found a solder bridge on the MCU pins 36/37.  I cleared that and now the LED flashes/stays on when it should.  That is a step forward.
The USB is not enumerating so possibly a bad solder joint there.  I have already re-checked my design and it seems to be OK. 

dazz1:
I soldered two wire-wrap wires to the USB D- and D+ lines on the connector side of the 22R series resistors.  I wanted to see what data was reaching the connector.
Many techs start fault finding from one end of the signal path.  It is a lot faster to start in the middle of the signal path and just repeat the halving process until the fault is found.  If (say) there are 16 test points in a signal path, and one is faulty, halving the signal path will find the fault in no more than 4 tests.

In all cases, with the adapter plugged into an operating GPIB bus, the LED would flash once, then remain on, indicating a valid connection to a live GPIB bus.  If the GPIB bus was made inactive, (turning off the test equipment), the LED started flashing.  No evidence of any issue with the GPIB bus, MCU or software.

I did see usb renumeration, but only if the USB-C cable was plugged in one way.  If the plug was rotated 180 degrees, there was no USB traffic. 
I swapped cables.  Same symptoms.
Static testing of the USB-C connector showed no solder bridges.
Checked all the resistors in-circuit with the USB connector. 
I (re)checked the connector data sheet and compared against the circuit diagram and foot print.  All good.  No problem found.
Close inspection indicated some of the solder joints might be suspect.  I resoldered the connector joints and tried again.

I have gone from renumeration one-way back to renumeration no-way.  I see no data on the USB lines.
The only thing I have touched is the USB connector, so I suspect the connector is faulty.  Swapping that out is going to be a challenge. 

Images show initial USB signal followed by streaming data and an overview of the setup.   
The computer is an old Asus eeePC running Linux.  I just wanted to see a valid USB connection (command:  lsusb )

tautech:
Isn't USB C polarised ?

coromonadalix:
not supposed to  if the design is verified,   that's the advantage of usb-c,   no up / down nightmares

but have to deal with more pins on the connector

dazz1:

--- Quote from: tautech on December 03, 2023, 10:31:33 am ---Isn't USB C polarised ?

--- End quote ---

Not long ago, I would have said I don't know the answer.   ???
Now I know just enough to be certain I suffer from the Dunning-Kruger effect.  Therefore I can say with some confidence that the usb-C is polarised in a way that you can tell if the plug is in one way, or the other.  CC1 and CC2.

The attached image compares the connector datasheet pinout with my PCB layout.  The pin-out is asymmetric.  I was checking to see if I had made a mistake with the pcb layout. I hadn't.  :phew:

All of the diagnostics I have done point to a faulty connector.  I don't remember why I chose this connector, but I sourced it from Aliexpress, and that was probably a mistake.   :palm: Things like that happen under the effect of Dunning-Kruger. 

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