That DMM is based on ICL7106/7 which means that its not the problem in "black blob chip" since that would mean that meter wouldn't be able to measure anything. Problem is most likely in voltage divider array or the diode.

 

I have new information.
Before i was going to dismantle the DMM again and check the components that you suggested to examine,
i test the ohm meter function again and i found out that it works fine(even was accurate when i checked a resistor),it did problem several seconds(after i checked battery voltage and return to ohm meter function)and work fine again(after turn off and turning back to ohm meter),so it seems like it is intermittent problem.even though at the last time checking,turning off the DMM didn't cured the problem.
So i can't rely on this action.

I am not sure,but i think that when i measure a DC voltage(checking battery...)and then select the ohm meter to check some resistor resistance this problem occurs,but i am not sure.
Before i will make any action,does this addition information change anything in your diagnostic?

 

From your pics it looks as though the circular/arcuate copper tracks of the rotary switch have muck/tarnish on them. Might be worth cleaning those tracks in case a track for the resistance function is making intermittent connection with the switch wiper.

 

Thanks alot for your help