Understanding and repairing the STK500

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Hello AVRfreaks,

I found some threads about updating the STK500 with a new firmware and also some information about broken programmers, e.g. https://www.avrfreaks.net/index.p...
But I did not find too much information about the interaction between the two control devices, i.e. AT90S1200 and AT90S8535.

First I looked into the user guide for STK500 at
http://www.atmel.com/dyn/resourc...
But on page 59 in the diagram was only one block called "control MCU".

So I had a closer look at the schematic (included in the latest AVRStudio help) or e.g. found at
http://www.equinox-tech.com/down...

Why this all?

Yesterday I noticed that our STK500 does not work anymore.
The red LED (main power) was on, the green LED was off at first. The status LED was dark (no color change from red, yellow, to green).
When I removed the VTARGET jumper the green LED turned on. First I thought there was some short circuit between VTG and GND.
But I could not establish a connection to the STK. Also still no reaction on the status LED.

Because the VTG is controlled by an adjustable voltage regulator (LM317) in combination with a low pass and the PWM of the 8535 I assume that the 8535 is broken.
I also looked on the SCK, MOSI lines while flashing the firmware with AVRprog tool of the AVR4.13Build528 (firmware STK500.ebn). The signals looked OK.
The programming procedure first seemed allright, but the verifying failed on the first memory position (0000 was read).

Now I am wondering, if it is really the 8535, in other words, if it is worth to unsolder this part.

I found in another thread, that the main task of the 1200 is, to put the 8535 in programming mode, for firmware updates. - OK, I also saw, that the 1200 monitors the push buttons PROGRAM an RESET.

(Q1) What does the 1200 else do? - Does it wait on a certain pattern on the RS232 CTRL and then put the /RESET line low during the whole 8535 firmware update???

(Q2) Can I replace the old obsolete AT90S8535-8AC of the STK500 by a newer ATMEGA8535L-8AC found in the AVRISP?

(Q3) If the AT90S1200-12SC is also broken, can I replace it by the ATTINY2313V-10SU, which is also used in the AVRISP?

(Q4) When programming external devices (especially with own voltage supply), may both controllers (1200, 8535) get easily broken/damaged, though there is also a transistor circuit to the ISP6PIN/ISP10PIN connectors (PBM5=>MOSIT, PBM6<=MISOT, PBM7=>SCKT)?

First I was a little confused because there are other SPI lines ("SPI-SP"), called DSI, DSO, DCK, DCS in the schematic. These lines are also going from the 8535 to some transistor circuit for amplifying and then to the extension slots.
When I put a STK501 in, I also use the SPROG connectors for programming.

(Q5) For what is this additional SPI-SP which goes from the 8535 to the EXPAND1/J701 connector?

Thank you for an answer and your experience,
Michael

P.S: I also looked at the application note 68 (STK500 Communication Protocol) at
http://www.atmel.com/dyn/resourc...

In the beginning was the Word, and the Word was with God, and the Word was God.

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Have a look at Colin's guide to fixing the STK500

http://www.newae.com/old_site/do...

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A few years ago Colin O'Flynn wrote an article on fixing an STK500. You can find a copy here.

Dave

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Hello DK and Dave,

thank you very much. This is a good hint! A lot of information. Much more than in the Atmel documentation.

I will try it first with an ATmega8535.

Michael

In the beginning was the Word, and the Word was with God, and the Word was God.

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Hi skotti, thanks for posting this detailed info. I just bought an STK500 and have the exact same problem. It is: red power LED on, VTARGET green LED flashes once on power on if jumpered, stays on if jumper disconnected, no light from STATUS.

I've got 4.94V at all the MCUs on the board. Checked both sides of VTARGET jumper and no short to GND (~87K ohm). With VTG jumper removed, one side has 3.45V but drops to 0V once jumper is connected.

One strange thing is that my board has an ATTINY2313V-10SU instead of the 1200. It's in the same place, based on the schematic. My board rev is A9903.3.1000.D if that helps, 20061227 mfgr date.

I previously posted here: https://www.avrfreaks.net/index.p...
I will followup on your thread if I find anything.

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Finally sent back my STK500 and got another one. Everything works perfectly. Since the first was DOA and I didn't change anything, I'm guessing I didn't do anything wrong.

So if you power up and VTARGET LED won't stay green, you may have a bad board. I'm sorry I wasn't able to debug it further (no time).