It is always recommended to test your repair before applying any adhesives or putting it fully back together. I am going to assume you did this so you have easy access to the internals for testing purposes?
I have seen similar problems when the battery was not connected properly. First recommendation would be to try disconnecting and reconnecting the battery again.
If that ends in the same results, I would question the screen you bought. Here on iFixit, parts are often listed properly with exactly what models they are compatible with. For example, the screen for this model is only compatible with SM-A515F, SM-A515FM, SM-A515FN, SM-A515GN, SM-A515W, and SM-A515YN. This is notably not all the versions of this phone released in all regions throughout the world. If you bought your part here and your model of A51 is not one of these versions, the screen is incompatible and can lead to unknown errors such as you described. If you bought your screen on ebay/Amazon/etc., many vendors are not as open and/or honest with what exact models their parts are compatible with, and may sell you a part that simply does not work on your device. If you bought a screen in a frame, you have more considerations because things like antennas that may be embedded in the frame are calibrated to the frequencies in different countries and will not work and cause errors if installed onto an incorrect motherboard.
As Jerry recommended, giving us exact details on the part you bought as well as your device will help to identify this issue and possibly find an exact solution to this error.
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Hi Michalis,
Which screen replacement did you do; the one with the frame or the one without? There's a significant difference between those two replacement procedures so we'll need to know which one you did so we can figure out what might have gone wrong. The iFixit guide describes the procedure for the screen without a frame.
crwdns2934271:0crwdnd2934271:0 Jerry Wheeler crwdne2934271:0
I have Samsung A02s and went for my screen to be fixed by vendors since then the current seems not going through what is the main issue if my phone charging properly before the screen replacement
crwdns2934271:0crwdnd2934271:0 Farasisko samwel crwdne2934271:0
@farasiskosamwel
How long ago was it fixed by the vendors?
If only a short time e.g. 2-3 weeks, take it back to them and show them the problem.
They should have checked it was working properly before handing it back to you after the repair was done
crwdns2934271:0crwdnd2934271:0 jayeff crwdne2934271:0