uC working but JTAG not communicating after short on JTAG pins

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Short story:

 

While measuring a signal I incidently made a short on the back of the JTAG connector.

The uC is still working, I can see this as the LED that I have in my application is still blinking, but unfortunately JTAG communication does not work anymore.

I already checked the ATMEL ICE programmer with  another controller and it works without problems, so programmer is excluded.

I already measured all components that are between the JTAG connector and the uC JTAG pins and everything seems ok, so I am out of ideas.

Now I am checking on the scope the JTAG lines an a good microcontroller while doing some simple operation like reading the Signature Bytes or reading the Fuses, to have an idea how the JTAG signal should look like.

 

And the final question, is it possible that the uC works, but the JTAG from the microcontroller doesn't work anymore???

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Any short can burn out a port pin and leave the rest working, time to replace the chip and be more careful next time!

 

Jim

 

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bbogdanmircea wrote:
I already checked the ATMEL ICE programmer with  another controller and it works without problems, so programmer is excluded.
An Atmel-ICE has effective ESD suppression and some EOS protection (likely 12V, maybe 24V, not 120V)

An AVR has minimal ESD suppression (CDM) that's not specified in a datasheet (maybe ESD data is in AVR reliability data)

The EMP from an air discharge within a few meters of a JTAG connected AVR may damage the AVR though some of the energy will be dissipated in the Atmel-ICE.

External ESD suppression will direct the excessive current away from the AVR; a low magnitude resistor between the ESD suppressor and an AVR will current divide between the two (100 ohms, some are 10 ohms)

Simple R-C-R may suppress ESD enough though one of the R is 2K ohms approx which will limit JTAG speed.

JTAG signals are uni-directional; current divider or a series terminator, ESD-rated voltage translation buffer, AVR.

 

Architecture Description | Atmel-ICE

What’s The Difference Between HBM, CDM, And MM Test? (ESD)

AN2519 AVR Microcontroller Hardware Design Considerations

[page 11]

Figure 4-5. JTAG Interface Connections – Correct and Incorrect Ways

(add an R to AVR)

 

edit :

A '244 is an order of magnitude less expensive than an AT90CAN128.

USB AVR JTAG Debugger & Programmer from KEE Electronics

[picture, right-most IC]

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Thu. Oct 17, 2019 - 07:03 PM
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Ok thanks, that's so sad as now I have a working board that I can't flash anymore :D.

Only 2 remaining and then I am out of boards, and soldering a new uC IC seems quite impossible even with an infrared lamp.

Any measures that can be taken to protect the pins in case of a shortcircuit?

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I am still debugging with the oscilloscope in parallel the TMS TCK TDI TDO pins for a good and the bad board while doing a voltage read, signature read and fuse read from Atmel Studio.

What I am seeing for the bad board is:

-TMS and TDO seem to be equal and are not getting to 5V, they seem to oscillate betwenn 0 and 2 V when the binary values are sent.

-TCK seems to be okish, the first clock steps are between 0 and 5V, then the following burst are between 0 and 3V.

Would this point to an internal short between TMS and TDO pins as the signals are quite equal? I measured and there is no continuity between them.

I am still hoping that some passive component is dead and I can revive my JTAG ...

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ki0bk wrote:
time to replace the chip and be more careful next time!
+1

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Any tips for soldering a 14 mm TQFP64 with an infrared station or a soldering iron? is it doable?

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bbogdanmircea wrote:
a soldering iron? is it doable?

With a fine tip, fine solder, a steady hand, and good eyesight - yes.

 

Or google "SMT hand soldering" or suchlike - there are many videos, etc, on how to do it.

A common trick is to just put a load of solder on, and then use de-solder wick to get the excess off ...

 

If it's a commercial project, find someone who does re-work - most (prototyping) board houses should be able to do it ...

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
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Soldering a new TQFP is fairly easy with a fine tip iron.

 

De-soldering the old TQFP is almost impossible with a soldering iron.

 

Follow Andy's advice.   Ask someone to remove it for you.

 

David.

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bbogdanmircea wrote:
... and soldering a new uC IC seems quite impossible even with an infrared lamp.
Had similar thought about BGA; a technician opened my eyes.

bbogdanmircea wrote:
Any measures that can be taken to protect the pins in case of a shortcircuit?
Current limit (resistance)

R-C-R increases ESD tolerance though at 2K ohms approximate total the JTAG speed will be reduced.

R-TVS-R is more ESD effective though will likely source current into the VCC or VDD regulator's output; a shunt regulator will limit the voltage (most voltage regulators aren't two quadrant)

Series termination or current division into an ESD-tolerant '244 then to the JTAG separates the MCU from ESD and EOS; a damaged '244 can be replaced.

 

 

"Dare to be naïve." - Buckminster Fuller

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A hot air SMD rework station makes the task easy to do.

 

Jim

 

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bbogdanmircea wrote:
Would this point to an internal short between TMS and TDO pins as the signals are quite equal?
or the power for those signals' pins is damaged.

 

"Dare to be naïve." - Buckminster Fuller

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De-solder :

Chip Quik® and the infrared

Hot air - QFP tip and Chip Quik.

Home improvement store heat gun and Chip Quik.

 

Solder :

Drag solder with a hoof tip on the soldering iron (clean, flux, solder)

bbogdanmircea wrote:
is it doable?
Yes though there are a few or several methods.

 

"Dare to be naïve." - Buckminster Fuller

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gchapman wrote:
Home improvement store heat gun

Sure, that'll get it off.

 

Keeping everything else in place will be the fun part!

 

surprise

 

An important question to ask is: is it worth it?

 

Or, to put it another way: would simply getting a new board be easier / cheaper / quicker / more effective / more likely to give a usable & reliable result ... ?

 

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
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awneil wrote:
... and then use de-solder wick to get the excess off ...
Solder wick can cause certain forms of damage (minor with practice)

Solder will move towards heat (clean and hot soldering iron tip, forward : push solder towards a pin's tip, reverse : pull solder from a pin's tip)

awneil wrote:
... most (prototyping) board houses should be able to do it ...
Metro areas will likely have a technician for hire (how I became QFP aware via the telephone book, today am uncertain how to locate one who's a technician other than by synchronicity)

 

"Dare to be naïve." - Buckminster Fuller

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gchapman wrote:

Metro areas will likely have a technician for hire (how I became QFP aware via the telephone book, today am uncertain how to locate one who's a technician other than by synchronicity)

Perhaps LinkedIn ???

 

 

Click Link: Get Free Stock: Retire early! PM for strategy

share.robinhood.com/jamesc3274
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Aluminum foil cheeky

Plumbers, HVAC technicians, and others source their heat guns from the local industrial supply stores; these will have nozzles and stands.

awneil wrote:
An important question to ask is: is it worth it?
Yes as rework is a handy skill (essential?)

A SMB/SME might not have enough accounts payable and receivable to hire a technician; the engineer does it all (universities are short on skills training)

 


STEINEL Electric Heat Gun Kit 120VAC, Fixed Temp. Settings, 750°F - 30TU15|HG 350 ESD - Grainger (ESD safe)

 

"Dare to be naïve." - Buckminster Fuller

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"Dare to be naïve." - Buckminster Fuller

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https://www.youtube.com/watch?v=TXBGtkd1mcw&t=445 for 1m45s in Engineer It - How to prevent electrical overstress of analog integrated circuits - YouTube (9m29s)

Size the resistors and TVS or zener diodes given the short's maximum current and maximum ambient temperature.

Shorts to off-line power - add a telecommunications PPTC :

TSM250 PolySwitch® Resettable PPTCs - Littelfuse | Mouser

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Fri. Oct 18, 2019 - 05:49 PM
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bbogdanmircea wrote:
a soldering iron? is it doable?

 

Yes, you can solder a TQFP chip to a board using a soldering iron.

See this video - starting at 2:00.

 

To remove the 'bad' chip, first cut the leads off the chip using a

small diagonal cutter or a dremel tool with a cutting disk.

 

Now, with the chip removed and the leads still soldered to the PCB,

unsolder the leads one at a time.

 

 

 

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A very experienced HW colleague managed to swap out the tiny uC with a new one for 2 boards with an infrared station.

It was impossible to do with an iron, as the chip is so small, you can barely see the leads with a magnifying glass.

One uC worked ok, I could program it, the other not, so even with a soldering station it is pretty non reliable if it will be successful or not.