Using 3.3v Arduino instead of 5v

I have a little issue as I got defective board.
But I have a few 8Mhz 3.3v boards, the question is can I just use it insted of 16Mhz 5v one.
It's connected to tm1639 display and rtc module 3231.
Of coirse I recompile my sketch for 8Mhz chip.

I'm not experienced enough to flash fuses, otherwise I would make what I need.

The tricky thing is that you will be using ~3.3 V logic levels instead of ~5 V. You need to make sure that the other components in the circuit will read the ~3.3 V logic output from the microcontroller and also won't subject the microcontroller to more than 3.3 V logic input.

I had a look at the datasheet for the TM1639, which says this (after I ran it through Google Translate:

Logic supply voltage VDD 5 V

High level input voltage VIH 0.7 VDD - VDD V

So if you were to power the TM1639 at the expected 5 V, the minimum high logic level would be 0.7 * 5 V = 3.5 V, higher than the logic level supplied by your microcontroller running at 3.3 V.

Logic level converter modules are widely available for a very low cost. Using one of these between the microcontroller and the TM1639 will ensure that your logic levels are within the specifications of the part. You might get away without the level converter, since the ~3.3 V is close to the spec, but operating out of spec is not a recipe for reliability.

The RTC should be able to run at 3.3 V, so you only need to make sure to power it at 3.3 V, not 5 V, and there's no problem there.

For what it is worth, I have run TM1637 units at 3.3V and not had a problem. Since it is technically out of spec your mileage may vary.

Thank you for replays, the best way was to use 3.3v and it works fine.