BK Precision 1652 PSU Voltage Issues

[deezick]

Hello, I am having some issues with my bk precision 1652 0-24 volt triple output power supply. It seems that channel A only goes up to 20.5 volts and channel B goes up to 21.5 volts, when each should go up to 24 volts. I have double checked that the correct output is being displayed with my multimeter and it reads just about spot on. I think I narrowed the issue down to one location on the board that has some carbonization. It's four zener diodes and two 220 ohm resistors. I was wondering if this could be the voltage output issue for both channels or is it a red herring and I should look elsewhere? I would like to know and test as much as possible before I order the replacement parts from digikey as the shipping costs more than the components.

Here is what I have measured, zeners are from left to right.
Image of the area in question: https://imgur.com/gallery/ifIVWJF

Left resistor 218.5 ohms, right resistor 219 ohms. Both within spec.

Zener 1 (D21 )
   Anode to cathode resistance: 12.55 mega ohms
   Cathode to anode resistance: 12.89 mega ohms
Zener 2 (D22)
   Anode to cathode resistance: 12.66 mega ohms
   Cathode to anode resistance: 12.48  mega ohms
Zener 3 (D20)
   Anode to cathode resistance: 13.63 mega ohms
   Cathode to anode resistance: 12.03 mega ohms
Zener 4 (D22)
   Anode to cathode resistance: 11.91 mega ohms
   Cathode to anode resistance: 13.61 mega ohms

I can provide more information as necessary, the board is sitting right next to me.

[deezick]

bump - Ordered the diodes, let's hope that's the only issue. Once I replace them I'll go around checking regulators.