asterisk users - Apr 2004 - FAX 25% of the first page and only via Zap

HI!
I have problem with fax via Zap channel.
could see only 25% or less of the first page while sending via Zap
channel, however when I send a fax from the same fax machine but via SIP
channel everything is pretty fine.

Please give advice in which direction to dig.
Thank U in advance.
-- 
Best regards
Vlad