Measured everything again. inputs/outputs of the toshiba T6A39's en T6A40. Can't find anything wrong. Again, disassembled the display and put it together again. Soldered a new LM234. For now it is working again, but still very sensitive to temperature changes on the 4,7 uF caps.
I ordered the LM324, didnt look any furhter on the details of this chip. But I checked the original one that I took of the first time. And it is a LM324M. Not sure if this would make a big difference, I checked some data sheets. And at least from the few doc's that I looked in, I can see that the LM324 actually can manage a bigger output current than the lm324M.So that would be a plus or the lm324. But I read from the LM324M specs that it has an internal temperature adjusting circuit, can't find that on the lm324 specs. Anyway I ordered the LM324M and will test it, also ordered new Panasonic 4,7 uF caps. Maybe the panasonic's are better then the "Würth Elektronik" ones I have now.
Anyone can confirm differences in behaviour from the lm234 and lm324M?