Vu Duo Tuners

Hi Everybody.
For sometime now I have a Vu duo sat receiver added to my older DM800. With this new set I have some problems with the tuners.
I noticed that only a few channels could be received with the new Vu Duo receiver. Investigating the matter further I noticed that if I was manually
scanning a transponder, I could receive the channels only if I was off setting the freq. by 3 upwards. To make you understand what I mean,
On trying to manual scan transponder 11038V 22000 5/6 on 19.2E, setting 11038V , nothing was received. Off setting the frequency by one, nothing was received, offsetting by two again nothing, off setting by three, thus 11041V then the channels of the transponder were received.
Trying further upwards, I could receive the channels up to 11052V, if going another one up, nothing was received. So my conclussion was that
to be in the middle of the freq range I had to increase it by five or six units upwards. That was true for all freq. of sat at 19.2E. Trying the same on the other tuner, I had the same results. To rule out LNB problem, I change with the LNB I use for my DM800. The results came to be the same.
The DM800 frequ. were OK with the other LNB, whilst the freq of the VU Duo needed Off setting to be received. As I am in the electronics business, I wonder what the two tuners have in common to behave like that. Do they have a common stabilized power supply, which now is in fault? Does anybody has any circuit diaqram of the unit. I beleive is a hardware problem. By the way I am using BH 1.6.3 image. As I bought the unit from England, via internet, is any place in England that these sets can be serviced? The place I bought it, is not responding. An advice welcomed.
Ledra