Intermittent problem

[buddha]

Hi, I have a problem with a 625 receiver that has happened 3 times. I lose all satellite coverage completely. the first time was a month ago and I did all the basic checks, (powering down the receiver etc. the check switch gives a message that I have lost some satellite coverage. I set up a service call but the next day I canceled it as everything was working again. that lasted for about 3 weeks. Last week it happened again and after about 2 or 3 hours everything was normal once again. It has now happened again and the receiver is off now. The 508 receiver I have in another room is working fine. I have a Dish Pro Plus Twin LNB which has the integral switching. Is it possible to have half of the LNB working while the other half doesn't? The only other thing that I can think of would be either the receiver or the separator. I hesitate to have a serviceman come out when the problem has gone away. Has anyone had a similar problem?Thanks,I would appreciate any feed back.