Indonesian officials said the devices were not with the recovered section.
The plane's black boxes will likely be found in "a few days," the crash's chief investigator said, after searchers were able to hear more pings, even if they haven't yet pinpointed where they came from.
The investigator, Mardjono Siswosuwarno, told CNN that smaller boats picked up several pings emanating near where the commercial jet's tail was found.
"I think we will be able to find the black boxes in a few days, because the location where pings were detected is not very far from the tail," Siswosuwarno said.
On Sunday, one of the search ships detected two ping signals 1.5 miles away from where the tail was found, according to an Indonesian technical assessment agency.
Siswosuwano told CNN that several pings were detected emitting a frequency of 37.5 MHZ, leading search team to believe they are getting closer to finding at least one of the black boxes.
"The interval and frequency are right. The sound is very clear, the typical sound of black box ping."
The flight data recorder and cockpit voice recorder were housed in the Airbus A320-200's tail.
The data recorder provides a wide range of information about what the plane was doing, from its air speed to the position of the landing gear, said Greg Waldron, the managing editor of Flightglobal, an aviation industry website
. The cockpit voice recorder captures communications between the pilots.
Batteries that send out the pings last 30 days -- it has been 15 days since the jet fell into the Java Sea.
The aircraft went down on December 28 with 162 people on board while heading to Singapore from Surabaya, Indonesia. The plane's pilot had asked to change course and climb to a higher altitude minutes before contact was lost, Indonesian officials said.
Divers, helicopters and vessels are checking the area where the pings suspected to be from the flight recorders have been detected. Sonar equipments also detected objects that could be the front part of the plane, according to an AirAsia update.
Tony Fernandes, the airline's CEO, tweeted that he had heard promising news that the black box may be found soon, but also expressed wanting to find the fuselage.
The fuselage is where many of the bodies of those onboard could be found.
Officials also said search ships detected a large object underwater, about 30 feet long, close to the possible pings -- raising hopes that major wreckage could soon be found. But there is also caution as there are all kinds of debris in the sea.
A total of 48 bodies have been recovered so far, according to Indonesia's search and rescue agency.
The vast majority of the people on AirAsia QZ8501 were Indonesian. There were also citizens of Britain, France, Malaysia, Singapore and South Korea.