Some troubles with fonts for embedded system

Question

When I run my application on Set Top Box the font quality degrades. The degradation manifests itself as follows: 1. The letters in a word is not the same brightness, the pixels of one letter also differ in brightness; 2. Vertical Alignment moves down, in the worst case the bottom line bump on the top. 3. There is a feeling that used font is not I wanted (although the log indicates that the font that's what I need).

Most interestingly, it's fine in the desktop version of the same code, the same fonts. Below are additional information about used enviroment and experiments that I done.

1. Fonts - TrueType, is loaded into the system using QFontDatabase :: addApplicationFont;

   For PC: QT 5.2.1

   For STB: QT 4.7.2

   I use for fonts QFont :: PreferAntialias, setStretch (100)

2. I have replaced setPixelSize calls on setPointSize - did not help;

3. Suspecting QT version - made application for PC using qt 4.8 - for this version all are well;
4. I have played with different weights and sizes of font - used for this font information, which pulled via QFontDatabase. Did not help;
5. I have tested on different plasmas with different diagonal - one result.

The last thing I have learned - DPI. Here are DPI for my PC and STB:

            Physical          Logical
      STB    72x72             72x72

      PC    90x116             96x96

Well, perhaps all. If you help I will be very grateful.