Is the problem solved?

NO .... i am yet to fly again but afraid that i will break my plane... any way trying to get heat sink for regulator so that heat dissipates.... what to do for the SMD 78L05 ?

If space provide, replace with regular large 7805 with heatsink i. e. TO220 package.
Costs is Rs. 5/- at Kolkata.

Thanks Kalyan & lastrites for all the support....
Cost of IC is not of much matter...... Point is investing time..... rather than flying i am stuck in this !!!!

Will do as suggested for a to220 package 7805.

But Still i wonder the heat .. I have used 7805, 09, 12 ICs at lot many applications but they were not so hot??

http://www.electro-tech-online.com/general-electronics-chat/18861-heat-sink-7805-a.html
http://www.dutchforce.com/~eforum/index.php?s=e10e05c80419782fedb0c7f8a9209ec1&showtopic=21384
http://www.electronicspoint.com/l7805cv-too-hot-t23923.html

Reduce the input voltage, you'll be a happy man! You need a heatsink badly if you're dissipating over 1.5w

Your 7805 might be oscillating crazy, what caps do you have connected?

lastRites, your point makes sense that if it wasn't there earlier, why now? rastsaurabh, did you ever check the heat before replacing these, they might have been overheating all the time.

In the end, there are only two choices, either generate lesser heat or get rid of the extra generated.

The excess heat in RF Amplifier transistor may be so hot so as to burn the transistor instantly if not antenna properly matched and reflected wave generated. But the regulator have no such issue except loading current and potertial difference between input and output voltage.

However, I am waiting for some study materials for clearing some issue simply. God knows how long I have to wait.

Kalyan Da, would not the circuitry get effected if he replaces 78L05 with regular one, in case there is some faulty bridging after the output.
The actual cause of heat generation has not been found yet.
I think this(any bridging) can also be a reason for excess heat generation.
the provided IC provides 500ma of current, while the regular is designed for many times more(2a i guess,dont know exactly).
So there are chances of frying the post circuitry i guess.

 

As this regulator feeds power to entire ckt, it should be hot. And it was earlier soldered with PCB foil as heatsink. Moreover, Now signal stable means, some leaky capacitor replacement improves some load behavior.
And,
troubeshooting needs step-by-step approach.

The TX is new and rarely used ...... why i suspected TX was that the model plane flew well initially but all of a sudden became uncontrolable and crashed. When i could not find any reason, I opened the TX and felt the 7805 to be hot so there is no pre post study. I used new alkaline batteries with were 12Volts but now are used up to 11Volts so i can expect some improvement when i fly.

@ girish - the cap i used are 47Mfd 25Volt Philips make. Replaced all 6 of them all were same value old ones are some unknown company.

Now insted of plane, use BEC and servos and test for at least 15 minutes at a long distance.
your tx should be stable now. All the txs are designed and optimized for NiMH and NiCD battery. So when new alkaline/dry cell is used (EMF=1.56volt), heat generation become so hot, it malfunctions. E-Sky are better in this case as they use 4 cell insted of 8 cell.

However, if final stage RF power is to be maximized, it's supply voltage should be as high as possible in addition of highly selective matched antenna using some network (PI or ladder). So a good regulator with high voltage battery (of-course within designed limit) can give higher range if not any other section malfunction. But if entire RF stage use 5 volt, then it is better to supply reduced voltage. in this case you can try to use a dummy cell (shorted one) and can get good result. If entire section works on 5 volt, you can save even 2 cell. But always test range while doing this experiment.

Good Luck.

If I want to use a normal lipo to power my tx(at full charge gives 12.6v) should we use an external step down regulator? What should be stepped down voltage, 10v?

LiFePO are better than LiPO.
In LiPO Use 2 nos 1N4007 in series to drop out voltage.

approximately causing a drop of 1.4 Volts ??