Fist thing I think of is that this may happen if you use a 2 amp power supply, 3 to 5 amps may give a better results.

If you already use a 3 A power supply, try using another to rule out that it is caused by this.

When you are sure that your dish cable and settings are fine and you have tested it with several tuners, then it could be other things as the tuner slot pins, or some outdated solder on the print side, with bad connection it may give this issue.
Or, if the box is old, and used for a long time, than it may be bad solder balls to/from the cpu to the motherboard.
Often to see when you add some weight to the cpu, and noticed that the signal strength gets better.

These are some things of what it could be, however there are a lot of more things which could give this issue.