STK500 bugged down

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Hello guys.

Im from the Philippines and got my STK500 late 2003 from a local distributor. I used it until late 2004, when suddenly my adaptor (locally purchased) went to a 20V output, thus feeding my STK500 with 20V! Now, it cant be detected by the AVR studio the last time i tried it. I think the microcontroller that programs the target MCU was destroyed after that spike in input voltage.

Is there a way it can be repaired in the Philippines? If not, i figured ill buy a new development board, say the AVR Dragon. Any suggestions?

Thanks...

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Digikey currently have a deal (though it may not be available to you in the Philippines?) of STK500 and a Dragon both for $49 - may be worth a look

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> Im from the Philippines and got my STK500 late 2003 from a local
> distributor. I used it until late 2004, when suddenly my adaptor
> (locally purchased) went to a 20V output, thus feeding my STK500
> with 20V!

The power-supply input circuitry of the STK500 consists of one 7805
(for the internal 5 V supply) and two LM317 (for the adjustable
Vtarget and Varef supplies) in parallel. Both should accept input
voltages of at least 35 V, according to their datasheets (the LM317
even more). So supplying 20 V for a short period of time should not
be an issue.

However, the circuitry draws quite a bit of current (~ 120 mA without
a processor mounted), so the current consumption of the internal
circuitry is approximately 100 mA. When feeding 20 V, the 7805 has to
convert (20 - 5) V * 0.1 A = 1.5 W to heat. The cooling area for this
regulator is only a few cm², so it will quickly become hot. Normally,
the 7805 should shut down itself when getting too hot, but I guess
this IC is the first suspect to watch for.

So use a multimeter, and start verifying that all voltage regulators
are working correctly. If one of them burned, replacing should not be
too difficult though you need something stronger than a finest-pitch
soldering iron due to the heat-sink copper area below these ICs.

If the supply voltages are within range the next candidate would
indeed be the main processor. As you've got an older STK, this is
probably still an AT90S8535 which is no longer available. It can be
replaced by an ATmega8535 but then you also have to modify the
bootloader in the AT90S1200. Colin O'Flynn has described this here.

Alternatively, I could get you a modified AVR910 loader that could be
used with an ATtiny2313 as a bootloader, but that would require you to
also replace the AT90S1200 by an ATtiny2313 (which could be required
anyway though, as it might be burned as well).

> Is there a way it can be repaired in the Philippines?

A good tool to repair high-pincount SMDs is a standard hot-air gun
which you can usually get in classic hardware (i. e. nails, screws
etc., not computer hardware) shops. Preferrably use one with
temperature control. Heat up the PCB *carefully*, and after maybe 30
s, you can remove the faulty ICs with a pair of tweezers. To clean up
the solder pads, as well as to solder in the replacement ICs, use much
flux (which you could clean out afterwards), as this will keep the
solder on the pads and pins, rather than forming bridges between the
pins.

The schematics PDF for the STK500 can be downloaded from the products
area here on avrfreaks.net.

Jörg Wunsch

Please don't send me PMs, use email if you want to approach me personally.

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[OT]Jörg - welcome back![/OT]

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Yeah, returned from vacation. Perhaps, some might have heard me
as S5/DL8DTL. :)

Jörg Wunsch

Please don't send me PMs, use email if you want to approach me personally.

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Alright. Thanks guys.

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Hi,
The first casuality of high supply voltage insertion is the transorb (SM6T18CA) placed between the DC socket and bridge rectifier on the STK500 board. Check if it is shorted. You can desolder the transorb and use a regulated 12V supply and check the board. If it is working replace the transorb with the same or equivalent rating. This transorb is added to protect board from this kind of faults.

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ok. thanks, simma. ill check my board this weekend.