how can i check series of a diodes

i want to check a series of diodes mounted on a pcb how can i do it

Use a meter. If it has a PN junction check function, use that. Shorted and open diodes will be easy to spot. Forward conduction drops should be very similar for the same type of diode.

See here for some basics. Note you can usually check the diodes in-circuit unless there are low impedance paths in parallel with them.

i m not asking abt to check a single diode i want to knw the technique for checking diodes connected in series

Pass a voltage-limited controlled current through the diodes wired in series, around 20mA.

Each diode will drop a certain voltage across itself, depending upon the diodes used and the current.

If the sum of the voltage drops is in the expected range, then it's likely that the diodes are all good.

If the voltage is at the limit, one or more diodes are open.

If the voltage is less than expected, one or more diodes are shorted.