Difference between PPMT/IMPT and PMT

[GIS2013]

Hi,
I cannot understand the inconsistencies between PMT and PPMT+IPMT functions.
Say rate=8%, nper=12, and pv=994.
When I'm applying P/IPMT on this loan I get total return of 1429.3 (across all 12 periods). But when using PMT with the same parameters, the number is 1582.8, a big difference.
Why does it happen?
Unfortunately I cannot upload sample files due to admin restrictions.
Thanks

**It turned out I had a problem with the IPMT function. Solved now. Thanks.**