diff --git a/Won't-boot.md b/Won't-boot.md
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@@ -105,3 +105,7 @@ Firmware starting at version 1.5.4 and onward contain the <a href="https://githu
 
 ### Additional notes : 
 I used to have many frequent “black LCD boot brick” when exchanging binaries compiled with different gcc-arm… version , from 9.4 to 10.3 or 12 . But thanks to @u–foka‘s PR fix pmem -> make backup_ram_t data members volatile [#1135](https://github.com/portapack-mayhem/mayhem-firmware/pull/1135), all those problems are gone , and now I do not have any persistent memory boot problems , so I do not need to go back to any old version 1.4.3 anymore. 
+
+
+## H4 users
+If you got any addon plugged in, try to remove it, and power off, wait a bit, and power on your device. If the addon board / module has problems, it can extremely slow down the boot, and the working. (usually happens when the I2C line goes wrong, and each operation have to wait for the timeout)
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