Hello, I have one problem using HEF4750V and HEF4751V

HEF4750V is Frequency synthesizer form Philips
http://www.semiconductors.philips.com/acrobat/datasheets/HEF4750V_CNV_3.pdf

HEF4751V is Universal divider form Philips
http://www.semiconductors.philips.com/acrobat/datasheets/HEF4751V_CNV_3.pdf

First at all I want to say that I have working synthesizer with above
schemes. I make it working on radio bands 1.8Mhz 3.5Mhz 7Mhz ... 28.5Mhz
The channels are to 1Khz and I using DAC to make sub channels to 10Hz
It works fine but has some errors.

I control the universal divider HEF4751V and DAC with PIC16F84.

In this PLL synthesizer the value of N, by which the output frequency is
divided in order to compare it with the reference frequency(1Khz) is construct
by this formula

N = A - B or
N = A - B + 10^6 (if A - B < 0)

A and B is numbers which can be programmed in HEF4751V

In my synthesizer I use only A number.
I put for A number this 35.600Mhz + 3.5Mhz = 39.100Mhz for my VCO.
in this situation N = 39.100 - (B=0)

THE PROBLEM:
I read in some other design of such synthesizer that I can program
B number in such way that I can just put in A direct frequency as 3.5Mhz and
N will be 39.100!

By my calculation B must be this

B = A - N + 10^6 = 3 500 - 39 100 + 10^6 = 964 400

Problem is that when I put this B = 964 400 in HEF4751V my PLL is locket
but the channels do not change :(
for example on 1.8 3.5 and 7Mhz it locks near on 40.500Mhz
I change A but it stay on one frequency

Has some one do such synthesizer and can help to me with above problem?