When it comes to the correct, first, hardware revision, there is no difference between 7520 and 7530. The 7520 is just 1&1 branded, comes in a black case and is limited in their proprietary firmware, the hardware itself is 100% identical (and the features under OpenWrt as well, so OpenWrt will unlock all hardware features, apart from DECT and FXS (phone-) ports, which will never work).
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That's only partially correct. You should make sure to not to buy a 7530 AX by accident. This model can't be used with OpenWrt.
On the other hand, the 1&1-branded black 7520 in the 'old' case with the fins are quite cheap to get here in Germany. At the moment there're some at kleinanzeigen for less than 40€.
I'm quite satisfied with mine, it handles my 100 MBit line without breaking in sweat. Which couldn't be said of my old BT HH5A, especially with the later versions of OpenWrt (22.03 and 23.05).
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Can’t go wrong with the 7520 IMO.
It’s around 40-60 euros on Kleinanzeigen, depending where you live.
(I got mine for 8 
)
The 7530 is around 80-100 euros.
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I found the 7530 for the same price i could get a 7520 and i like that it will definitely work since there's no "type B" of that model but i worry about the VDSL patch that might be needed for that model and i wonder if the hardware is identical then why do "some models of the 7530 require a patch to enable the VDSL modem" why don't some of the 7520 need that patch if the hardware is identical?
Also i worry if i buy a 7520 that it might be typ B, which would be incompatible.. isn't there some way to check if its typ B or not?
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UPDATE: I could buy a 7520 with fins for 25€ with shipping, it is 3 years old.. Is this old enough to likely be Typ A???
I guess just try and see if it works.
If not, you can always recover to the OEM firmware and sell it out again.
The wiki page seems to be referring to this patch:
https://forum.openwrt.org/t/adding-support-for-vrx518-and-maybe-vrx320/55160/389
The patch was not accepted, as far as I can see.
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Yes, as long as it looks like on the picture here, you are good.
https://boxmatrix.info/wiki/FRITZ!Box_7520
The version 2 seems to be quite rare, so I wouldn't worry too much about it.
Definitely.
I don't think they shipped any 7520 "B" in the old case with the fins.
oh really? interesting if thats true thats awesome
so i could even buy a brand new 7520 with fins (i saw one brand new for 30€ with shipping)
If in doubt, ask the seller for a picture of the botton label.
If there's a 'Typ B' like seen here, don't buy it.
Edit:
According to this, the Typ B got introduced around June '22. So any older models should be fine.
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OMG I THOUGH THERE WAS NO WAY TO CHECK BUT I GUESS THERE IT!
THANK YOU!@elder_tinkerer
OHH! ALSO VERY PRECIOUS INFO!! THANKS!
The relevant patch is the one in the following post, i.e.: Adding support for VRX518 (and maybe VRX320) - #391 by janh
This issue can affect both 7530 and 7520, and unfortunately, there is no known way to distinguish the affected devices. We also don't really know how common this issue is, but there have been multiple users with the issue here in the forum. But of course, the unaffected users don't ask for help here.
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Very important info, thank you.
DAMNN, THATS A QUITE IMPORTANT INFO! (device page only said it can affect the 7530)
How can the patch be installed?
Do you need to compile OpenWRT yourself to be able to install this patch?
(if yes thats very bad for me cuz i dont wanna compile every upgrade, or even just at all actually)
Yes, if you want to use the modem on an affected device, you need to compile OpenWrt yourself with the patch applied.
And every upgrade of OpenWRT also needs to be compiled?? man that sucks, how even is the process for compiling OpenWRT with this patch?
How can i check if my FritzBox 7520 needs the patch before installing OpenWRT?
And how can i compile OpenWRT with the patch included?
There is no known easy way to check this. However, when running OpenWrt, you can recognize affected devices by the message "dc_ep_clk_on failed" in the kernel log.
What you could do is to follow the steps for installation of OpenWrt, but stop after the initramfs image has booted (i.e. after step 5 in the instructions). Then you can check the kernel log before continuing. There won't be any permanent changes if you just reboot the device at this point.
You can follow the regular build instructions (check the quick start section in the README file, or the documentation in the wiki). The only difference is that you have to apply the changes to the source tree before you actually start the build.
To apply the patch, just download it (for example from patchwork), and then run patch -p1 < path/to/the/patch.diff.
Note that the patch hasn't been updated in a while, so while it probably still applies for OpenWrt 23.05, it doesn't work on the current main branch without changes.
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Install OpenWrt and check if DSL works.
If yes, you don’t need the patch.
There is no way knowing beforehand.
@janh
Thank you, that info was very helpful.
I succesfully installed OpenWRT on Fritz!Box 7520! Awesome! DSL also works!
I get over 100Mbs! Incredible!
Now i wonder why is the default or "supported" version for that model only 23.05.0??
Someone reported 23.05.2 works flawlessly, even when using DSL.. so can i upgrade to 23.05.2 ? or maybe even to the newest version 23.05.3 ?
Also; during installation i needed to install firmware to use DSL
wget -P firmware/09a9 https://gitlab.com/prpl-foundation/intel/vrx518_aca_fw/-/raw/ugw-8.5.2/platform/xrx500/aca_fw.bin
wget -P firmware https://gitlab.com/prpl-foundation/intel/vrx518_ppe_fw/-/raw/ugw_8.5.2.10/platform/xrx500/ppe_fw.bin
wget -P firmware https://gitlab.com/prpl-foundation/intel/dsl_vr11_firmware_xdsl/-/raw/ugw-8.5.2/xcpe_8D1507_8D0901.bin
How can i update/upgrade this firmware? Is the newest version of that firmware also on that gitlab ?
Or can i extract all 3 of them from https://download.avm.de/fritzbox/fritzbox-7520/deutschland/fritz.os/FRITZ.Box_7520-07.57.image just like @janh explained in the solution?
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