I think what you are seeing, is voltage drop of capacitors discharging b/c you are testing in circuit. I'm not sure what type of test you run. "OL" is open loop and it means no conductivity. No conductivity of collector/emitter is not an indication on it's own for transistor's health and a PNP transistor behaves differently than an NPN one. "Fried" transistors conduct on a path where they shouldn't, like C-B and E-B on an NPN transistor or the opposite way, B-C and B-E on PNP. If you get conductivity where you shouldn't, or get OL where conductivity is expected, the transistor is shot. At this stage, voltage drop or HFE (gain) is of no interest. All we need to figure out right now is the extent of the damage, if any, on your PCB. Test transistors out of circuit to be sure. You can make use of the following info: TR01...TR04 (diff pair) are NPN TR05/TR06 are PNP TR07/TR08 are NPN TR11/TR12 (power trans.) are NPN TR13/TR14 (power trans.) are PNP TR15/TR16 are NPN TR17/TR18 are PNP Follow the schematics and also test any low value resistor (under 1KOhm) that you see on that board. If you're not getting the specified value within the specified tolerance, de-solder out one lead of the resistor and measure resistance out of circuit. The same for diodes, except use the diode test mode on the meter. The standard 1N4148 diodes on that board, like any regular diode, only conducts when the red probe is on the anode (+) and black probe on the cathode (-). You should be seeing about 0.6V - 0.65V forward voltage when you a test a 1N4148 diode in diode test mode on the meter. The Zeners should show about 0.74V. You can easily check the trimmers (VR01...VR04) variable resistance between wiper and one of the leads to see if they function right. Replace them only if they are faulty, which I doubt. Please use the correct measuring units and it would really help if you specify what your meter scale is set to, when you report results. Whatever it is you're seeing, it's not 300 volts.