Solve ADSL is always down TPLink Wireles N ADSL2+ Modem Router

I still have Internet connection that use PSTN line with ADSL Modem.
within a few days backward, it had a problem, the connection was not stable, could be seen from the ADSL LED indicator, it would be down, initialize again, up and down again, of course the internet connection also would be down, wait, up  and down again.

Step what I did :
Check the telephone line, make a call. It was no problem.
Cleaning all sockets (using contact cleaner) from outdoor terminal until the socket at the modem. The result: connection was better, but ADSL LED indicator was still not stable.
I try to replace the splitter, the result : still not stable

I opened the cover of the modem, (it has 2 screw at the back).
Cleaning all dust using a brush. The result: connection was better, ADSL was still not stable.

When running, I found that circuit board and several components were hot, I took a fan and placed in front of the modem without the cover :
The result: until now the connection is stable, no problem again.

Before I decide to buy the new modem router,
If you have the same problem, you can try..