Second show-stopper problem

I was getting the TVR ready for its MOT, and it died. Using VEMSTune I found the ECU had dropped into bootloader mode while the car was idling. Nothing untoward happened beforehand - it just stopped.

The ECU is now firmly stuck in boot loader and nothing seems able to recover it. Sending "S" over a terminal results in "AVREFI" being returned, but nothing much else seems to happen.

Would appreciate suggestions!

(Thanks to Emil for his guidance on checks already)

-- Please contact me (emil at vems dot se) or irc


Issue efficiently resolved by the VEMS team. All back together now.

First show-stopper problem

For no good reason, battery calibration has gone wrong. Two days ago, cal value of 187 read correctly. Now, the same cal value gives 18.6v. The only change has been to fit some bigger injectors. (Same sort of HighZ? injectors, so should be no different)

All the wiring has been checked, and it's OK. So what's caused the change?

The wideband lambda has also given up. Megatune says it is turned off, but the LCD shows changes to EGO correction, but never displays a lambda reading. This problem appeared at the same time as the battery cal. I suspect a connection between the 2 - most likely A to D related.

Going to try a firmware update tonight to make sure it's not a memory corruption issue.

* Not memory corruption - I reflashed the firmware and there's no change.

The ECU is 6 months old. Number 326. I did the required AREF mods a month ago and there have been no issues with it until now.

Check the mod again, measure voltage on AVR pin62 and pin64

* Component values all look OK, but voltage is nothing like the expected 4.9ish (much lower).

o this suggests something around AREF is bad

* Total current consumption is 300mA

* voltages at pin 62 and pin 64 are both 3.1v.

* Voltage at the regulator is 3.19.

* When removed from the board (ie reg is run unloaded), the regulator produces 4.8v

* Supply voltage to the MAP sensor is 3.19v.

* I've removed the MAP and the AREF mod to see what happened - it made no difference. They've both been replaced now and did not change the problem.

* MCP3208 - check the grounds of it

* maybe some BAV99 protection diodes

Obviously, something pulls down the analog supply (to 3.19V) that should be appr 4.8 .. 5.1V

* GNDs seem to be fine, but will check again before swapping the regulator

* The voltage regulator gets extremely hot now. (It used to only get mildly warm)

* Nothing else on the board gets hot in the same way.

* I think this is a clue...

After checking the grounds (AGND and GND) at a few places, including AVR, MAP sensor and MCP3208: take a higher current (0.5A .. 1A) 5V source (even the onboard MC33269-DT5 main regulator is fine) and power AVCC that is currently only 3.19V.

* Check voltage

* check what's hot

* with DVM, 200mV range (0.1mV or better resolution) find where the current flows. The voltage drops (with the schematic and layout will help you)

Latest - 11/06/06

I have replaced the small 5v regulator with a larger one.

Te ECU now draws 600mA (total), however the voltage reading on the LCD now reads 11.7v (this is the correct voltage)

The new regulator very quickly gets too hot to touch, so there must be something still failed low resistance on the board. This should prove that the AREF mod is working now...

I've found the problem! The MCP3208 chip near the EC18 connector seems to have failed - it gets very hot. What does this chip actually do? And where can I obtain a replacement?

- This is for the extra analog inputs (2xEGT, 6 inputs for any use. fuel pressure for example. WebShop will send you MCP3208 for no chaege.

Thanks Marcell! I've removed the chip now, and all things have returned to normal. The ECU consumes the correct amount of current, voltage is reported correctly and the small regulator shows 4.8v at the output again.

Thanks Emil. I presume it's not a problem to remove the chip for the moment? It will be replaced as and when I get a replacement and have need of the extra inputs...

At the moment I'm not actually using EGT or extra analog inputs over and above the standard ones (TPS, WBO2, IAT, CLT...)

Problem solved. Thanks to everyone who helped.