[el.patron]

LM2596S based voltage converter

Hi there,
I replaced the voltage regulator with a LM2596S-based regulator you find tons of at ebay. These regulators have some advantages:
- very low margin needed, so the regulator works down to 6,xx Volts and Tech2 survives engine start on my car.
- the LM2596 has an On/Off-pin, to get the same behavior as the original tech2 to power on and off with the power button. Unfortunately the high/low-logic is inverse, so that I had to add a transistor (BC547) and two resistors (4.7k and 1 kOhm) to integrate it correctly. The pin 5 of the regulator had to be lifted from the board to solder a wire to it.

Enclosed find some pictures. The regulator is sticked to the board with some very adhesive double sided adhesive tape... and trimmed to 5V before
Works very fine.

 

[el.patron]

trim 5V

I struggled also a bit with that. I had to turn the brass screw on the trim poti maybe 10-20 times counterclockwise to bring the poti to a working range. At start just screwing half turn left or right changed nothing.
Good luck!

 

[el.patron]

Yes, I used an external power supply, and checked the output voltage with a multimeter. But you could also use the power supply provided with the Tech2.

 

[el.patron]

So you're saying a bonafide Tech2 won't reboot during start up (ie: will stay on running whatever mode you started with) while attached to the obdII port?

The rebooting issue with a clone Tech2 is because of NQR (not quite right) parts in the VCI?

Otherwise my clone works fine--seems a bit risky to mess with it--especially while I'm still under warranty...

An original Tech2 under normal battery conditions does not reboot during engine start. This is related to the voltage regulator on board and the margin it needs to maintain 5V output to the Tech2 board. The original voltage regulator can keep this voltage with a dropped battery voltage down to 7V or even lower.
This is not related to the VCI hardware.

 

[el.patron]

I thought I had a stack of 4.7 OHM resistors to get this mod done this weekend, only to find out I didn't. 47, 4.7K, but no 4.7.

Good that you replied. I meant 4.7 kOhm and 1 kOhm, but I am quite sure that both 1kOhm will also work.

 

[el.patron]

Worked on a Cadillac today and probably started the car a dozen times with the scanner attached and not a single reboot. I am very pleased with this mod. ;ol;

Thanks for update and good to hear that it also works for you.

 

[el.patron]

1. I am planning to test your modification instead, is seems this is the regulator you used? http://www.ebay.com/itm/LM2596S-Step-Down-Power-Supply-Module-DC-To-DC-Voltage-Regulator-Buck-Converter-/381435199537?hash=item58cf4f4031:g:dCYAAOSwsB9WClvd
2. Also, I’m not very good at electronics, so I’d like to double check that I interpreted your pictures correctly: Picture 2:The yellow wire and the 1kOhm resistor on the red wire is attached to the BC547 collector, the 4,7kOhm resistor on the blue connects to the base and the black wire connects to the emitter?
3. Picture 1:Is pin five on the regulator attached only to the yellow wire (not to the added PCB)?
4. The two black wires goes to the (-)IN and the two red ones to the (+) IN on the added PCB?

It's allways good to be careful

ad 1: yes, I used one of these...
ad 2: yes
ad 3: yes, lifted from the PCB without contact to it, and only connected to the yellow wire
ad 4: yes.

Good luck!

 

[el.patron]

Thanks for a superfast reply!
I have BC547B/547C and BC548/548B/548C at home. From this link:
http://bme.yeditepe.edu.tr/Labs/datasheets/BC547.pdf
It seems the difference between 547/B/C is min and max "DC current gain"
Could I use any of those I have instead of BC547?

I'm quite confident, that any of them will work!

 

[el.patron]

Hello again! I have now installed the modification and can confirm it works perfectly, no more restarts when starting the engine! It was a bit tricky to remove the Morsun regulator since it is attached at 5 pins and the solder fills the hole in the PCB. I used a de-soldering braid rolled tightly around the pins and heated using a lager soldering iron repeatedly. The suction pump did not work at all. Thanks again for sharing the solution!

I also can confirm that it is very tricky to remove the regulator. Finally I worked with a friend and two soldering guns to heat all the pins simultaneously and lift the regulator bit by bit...

Thanks for confirmation.

 

[el.patron]

Sorry to revive an oldish thread but I`ve just replaced the voltage regulator on my Chinese Tech2 as per el.patrons instructions.

I`ve very pleased with the results, it works perfectly now!

Thanks for update and good to hear that it works for you!

 

[el.patron]

Thanks a lot for the perfect solution and very cheap solution for the problem ,
you are a real genius and i like your work very much specially the transistor point to give the terminal inverted signal ,

really many many thanks for you

Thanks for your encouraging feedback

Interesting to know, that there are also Saab in Qatar

 

[el.patron]

Jimmy

i am facing the same problem ( GND FET Failed )
So, did you found any solution for this problem.

I did not face this issue, but I would first check on the GND-connections of the TECH2 board to the voltage regulator. There are different ones for the input and the output side. Maybe the solution is there...

 

[el.patron]

I can check at the weekend...

 

[el.patron]

yep, I also get the GND FET error. Haven't noticed before, but I will further use the Tech2...
If anybody finds an isolated converter which works down to 7V, please report here!

 

[el.patron]

i did not notice any problem caused by this error , and every thing working very good , so i think this error is not a big issue , and it has no effect on our scanner .

I think this might be relevant avoiding ground loops when using the scanner on the car, but powered from the net from the building around. I assume this to be no issue when the scanner is only connected to the car.