You have deployed a large scale network. I guess your topology is as below, right?
D-link router(DHCP enable)——3 TL-WA5210Gs(AP mode)))))))(((((((10 TL-WA701NDs(Repeater/Bridge with AP/Client mode)

It seems the issue is not caused by the DHCP, but too many of clients.
1. What mode do the TL-WA701NDs in? How many devices connect to them? You should realize that all the clients connected to TL-WA701ND will ultimately shift their flow to the main router. So have a check if the client number is beyond the ability of D-link 2740.
2.You have a better choice to add more TL-WA5210G/TL-WA7210N to build P2P link and wired connect TL-WA701ND to them, look at the topology as below:
D-link main router(DHCP enable)——3 TL-WA5210G(AP mode))))))))))))))((((((((((((10 TL-WA5210G(Client mode)——10 TL-WA701ND(AP mode)
3. TL-WA5210G is a 11g product. Use it as main AP will force the whole network to work under 802.11g standard with a maximum speed 54Mbps. It's so slow. Replace the TL-WA5210G with a TL-WA7210N or CPE210.

how can I know the maximum users the router can hold in total?
I have about 70 users connected to these repeaters. (I saw them in DHCP clients)
All 701 work in bridge mode with the 5210

and before two months there were about 90 users but I didn't find any problem like this.
the main problem is that 701 couldn't obtain ip address from the main router
so when I unplug 5210 lan cable and plug it on again then the 701 got ip and works fine

I guess the problem is that the area is in severe interference. When you unplug TL-WA5210G and plug it again it shift to another cleaner channel so it works fine. You can have a test: record the channel of 5210G and when the problem occurs, shift to another channel to see if this helps.

ashreedeh wrote

10 Ap 701 connected to 5210
The AP is connected wirelessly to 5210

really crazy deploy, cant see that working at all, and if it does, first Clients connected drain the network, there is no QOS on it, but if that works for you go ahead.
Im not posting this as a solution, it might help, its not about your model but both are APs, here http://forum.tp-link.com/showthread.php?74783-TL-WA901ND-AP-Stops-Working-Needs-Rebooting&p=164013&viewfull=1#post164013

stupidbird wrote

I guess the problem is that the area is in severe interference. When you unplug TL-WA5210G and plug it again it shift to another cleaner channel so it works fine. You can have a test: record the channel of 5210G and when the problem occurs, shift to another channel to see if this helps.

actually it works on a fixed channel
and it is channel 11

ashreedeh wrote

I tried to change outdoor channel , but it doesn't work....

On #1 you posted, but it doesn't work.... even changing channel

actually it works on a fixed channel and it is channel 11

then on #11 you post it works on ch. #11
Now i have questions for you, if it worked, (as you post) why you opened a thread for.
what do you call works, 24/7 or couple hours.
701 has a reputation of a bad device, and you are using it as repeater (you never posted, but thats what i read from your thread) and thats the worst mode 701 works.

Indeed repeater mode is not recommended in this P2MP scenario as danymarc said. Apart from external collision, topology in your case is with severe interference. What's more, TL-WA5210G is an old 802.11g product, the scale of network may be beyond its ability so I've advise you in #2 to replace the device with TL-WA7210N/CPE210 and change the operating mode of 701 in AP mode.
The problem is likely not caused by DHCP issue, look at my experience below:
I configure TL-WA5210G in AP mode:
1. When I go far away with weak signal strength of AP, my mobile phone is able to connect to it but couldn't get IP from TL-WA5210G.
2. I stand in front of TL-WA5210G, my phone still couldn't obtain IP when there are 7 devices connected to AP and running high flow application.

MR .Danymark

I meant by it worked ( every AP got ip address from the 5210 )
it seems that solution (changing channel radio) good but aftersome time (5 days to 10 days) the problem appears again.


I repeat it again 5210 is working on a fixed channel but sometimes is not giving all clients ip addresses but it gives them only if I reset it or change 5210 channel and that is only for about 5 days or 10


another thing Sir , Both the 701 and 5210 most work on the same channel .... so whenever I try to change it in 5210 I must change it on all other 701 connected to the main 5210

I was thinking the problem is caused as Router can't give ip to all users so I was thinking if I stopped router DHCP and enabled it on 5210 that would help me
That's why I posted another thread .
Regards and sorry for any inconvienence

stupidbird wrote

Indeed repeater mode is not recommended in this P2MP scenario as danymarc said. Apart from external collision, topology in your case is with severe interference. What's more, TL-WA5210G is an old 802.11g product, the scale of network may be beyond its ability so I've advise you in #2 to replace the device with TL-WA7210N/CPE210 and change the operating mode of 701 in AP mode.
The problem is likely not caused by DHCP issue, look at my experience below:
I configure TL-WA5210G in AP mode:
1. When I go far away with weak signal strength of AP, my mobile phone is able to connect to it but couldn't get IP from TL-WA5210G.
2. I stand in front of TL-WA5210G, my phone still couldn't obtain IP when there are 7 devices connected to AP and running high flow application.

Sir how can I get this device in Syria?
I searched alot , but there is only 5210 available in our country
and concerning 701
it actually works in bridge mode with 5210 and I have very good connection and internet
I am not facing any issue with that
the only problem is that (mostly at night) all 701 wich are connected to one of my 5210 can't obtain ip addresses
while all the other 701 which are connected to the other outdoor are working fine
even if I reset all devices it works only for sometime and then the same devices seem to be offline

I noticed also that this problem occur at night when most users are online!
so if you think the problem is caused by huge clients. then I f I enable IP QoS rules will this help or what?

Regards

I can't see QoS option in the TL-WA5210G. Maybe you can enable it in the main router? Theoretically IP QoS helps in this situation, but it's not a long-term policy.
In one point, the user will get bad experience. Besides, with the development of internet, more and more flow will needed in each application. And this expose the bottleneck of TL-WA5210G. The best way is to replace it.
If you can't get 7210/CPE210, UBNT Bullet M2HP/Rocket M2 can do the job as well.