What Zener Diodes on a Linear Power Supply

[caspian]

Dear members,

I have a linear variable power supply with unknown brand name that I used for voltage injection.
Then it failed. I discovered that its transistors (Q1 and Q2) are shorted.
In addition, I discovered that its zener diodes are defective.
I can replace the burned transistors.
But I do not know the model of the zener diodes. the model number is not marked on the zener diodes.
Therefore, I cannot replace the zener diodes.
I do not want to test the zener diodes in a test circuit to discover their model or value.
no schematics are available for this power supply.

Does this power supply worth repairing when I do not know the model/value of the zener diodes?
Does the power supply fail soon if I replace the transistors but do not replace the zener diodes?
If I must replace the zener diodes, what model/value of zener diode do you recommend for replacing all the zener diodes on the board?
Can they all be replaced by just one model/value of zener diode?

Thanks

[eccerr0r]

for most zener diodes, dmms' voltage source is too low to cause zener breakdown so it'll look like a normal diode. kind of hard to know what voltage is needed without the schematic...

[eccerr0r]

How do you know they also failed? Usually board blackening happens if zeners fail else they don't typically fail.

You may be okay to replace transistors without the zeners, but depends on how it's connected (schematic? or at least foil side of board?) Also what ICs are being used, LM723's?

[caspian]

there is no visible sign of damage or burning on the zener diodes and the board.
I tested the Zener diodes on board using the diode mode of multimeter. however, I do not know why my multimeter struggles to apply voltage on some of the zener diodes. On one direction, it shows infinite resistance. but on the other direction, sometime it shows 0.6v and sometimes it shows infinite resistance.
I used to use this power supply for voltage injection on laptop mainboards. I do now know why Q1 and Q2 got shorted.

[eccerr0r]

for most zener diodes, dmms' voltage source is too low to cause zener breakdown so it'll look like a normal diode. kind of hard to know what voltage is needed without the schematic...

[caspian]

ok, so the zener diodes are fine.
Thanks @eccerr0r