Is my JTAG ICE mkII DOA?

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Freaks,

I have been working on as small project for a couple of days. I am using a home grown board with a standard LM78 series regulator.

I was powering the board with a standard 12VDC wall wort type supply (I assume this was isolated). No problems. The finished project requires a 24VDC supply. I connected one of the 24VDC supplies we are using for several other products (Brick type) and flame on! It almost immediately fried the voltage regulator.

Seeing the error of my ways, I repaired the card, removed the offending supply and went back to the wall wort.

My card works fine with the 12VDC supply or the 24VDC unit but when I connect the JTAG pod the regulator starts to cook. I have inspected the JTAG card and cannot see any damage. The JTAG connects to the computer without issue. All of the leds appear to behave normally.

Can anyone direct me to a schematic of the JTAG unit?
Has anyone dealt with this failure before?
Any suggestions on how to proceed?

Thanks for the assistance.

A.

AVR Studio 4 Ver. 4.18 684
avr-gcc Ver. 4.3.0
ISIS 7
ELECTRA

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Freaks,

I removed the SP720 protection ic. I have a little experience with these. When they "protect" your circuit they can create a short between the vcc and gnd.

I have put together a new development board. I have only installed the power connector, voltage regulator and ISP connector. The ICE still creates a direct short from vcc to ground on the connected board.

I know the voltage from the board under development is measured by the ICE but does anyone have an idea of where it goes from there or what else it is used for?

Thank you,

A.

AVR Studio 4 Ver. 4.18 684
avr-gcc Ver. 4.3.0
ISIS 7
ELECTRA

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I managed to repair mine by just replacing the protection IC there are however a couple of voltage translator chips which follow that may have been damaged.

Have you checked which pin is shorting to ground? Any chance of a solder bridge when you replaced the chip? Or worse still the chip put in reversed... (I know silly question :) )

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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John,

I left the SP720 chip off the board. I do not have any of the SPI lines connected. The only thing connected was vcc from my board under test. I confirmed the 5vdc before connecting anything. Everything is fine until I power up the ICE.

I will have a replacement SP720 by Tuesday but I am sure that is not going to correct anything.

Does the ICE need to see the vcc from the device being programmed? I would guess it does. How else would it know what programing voltage to use.

I will do as you suggest and try to determine which chips are connected to the target board's vcc.

Thanks,

A.

AVR Studio 4 Ver. 4.18 684
avr-gcc Ver. 4.3.0
ISIS 7
ELECTRA

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Quote:
Everything is fine until I power up the ICE.
If there is a dead chip then the short would be present even with the ICE off???

Are you using the 6 pin ISP interface and just connecting pins 2 (VCC) and 6 (GND) to your board? Do you have the correct orientation and pin numbers? I know more stupid questions..

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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John,

The short only occurs when the ICE has power. I have been programming this way for several days so I am confident that my ISP connection is okay.

If a short would be present with power on or off, it means that the ICE is somehow applying power to the board being programmed. Does the ICE match the external board's voltage for some reason?

A.

AVR Studio 4 Ver. 4.18 684
avr-gcc Ver. 4.3.0
ISIS 7
ELECTRA

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Quote:
Does the ICE match the external board's voltage for some reason?
Yes, it adjusts the above mentioned buffers according to the target's VCC.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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John,

I would bet that this is the problem. I have noticed that the ICE has an LM317 on board. Do you think this provides the variable voltage? I guess at some pint the ICE measures the target's voltage and then varies the output.

If this is the case, I guess I am out of luck. It could be either the A/D or the D/A that is FUBAR.

A.

AVR Studio 4 Ver. 4.18 684
avr-gcc Ver. 4.3.0
ISIS 7
ELECTRA

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Don't really know much more unfortunately. I was fortunate enough to be able to repair my unit by replacing the transorb IC, everything else is just guess work.

I'm guessing that the target's VCC feeds power to the level translator chips only.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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John,

If I manage to breath life back into it, I will let you how.

Thanks,

A.

AVR Studio 4 Ver. 4.18 684
avr-gcc Ver. 4.3.0
ISIS 7
ELECTRA