Bought cheap transistor tester from eBay and currently experimenting with firmware updates.
I was able to program it with this version of Markus transistor tester firmware:
To build, use a WinAVR programmers notepad, open Makefile and select Tools->Make all.
At first, was getting weir errors, but after adding msys-1.0.dll to \WinAVR-20100110\utils\bin everything built ok.
Before doing firmware experiments, I have made backup of original firmware, if somebody needs it, you can download it here:
I tried to reflash original firmware and it worked fine.
For programming I use my MiniPro programmer.