Pix and Cyclops, thanks for your response.
Here are the actions I did:
1. Abis capture: Subscriber are taking traffic near the cell, good RxQual, good RxLev. Note that HSN is activated. So I suspect hardware issue.
2.Change dTRU: no change on stats.
3.Check VSWR: no problem on feeders.
4.Swap 2 SD on 1800: No change on stats.
5.Change dTRU position (Slot): The TCH assign get low, so need to revert back.
6.Drive test: I don’t have good knowledge on TEMS but I got 2 blocked calls over 40 calls attemps and many others call are switched on 1800 during call setup (As I have 2 SD on 1800). But on stats I still have 20% of SD setup success.
7. Revert back all the SD on 900 and change the combiner.
Now I’m waiting combiner to be changed and see the stats.
We also have some issues on the transmission (Abis freezing) but it is very rare.
I didn’t check access parameter as the problem appeared without any change made on the cells or its neighbours.