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When working on a circuit of two or more directly coupled transistors, there is one point you have to remember.
The circuit has the capability of producing enormous gain and even though any gain over unity is capable of producing self-oscillation, you will find two directly coupled transistors need a lot of special attention to prevent self-oscillation. A transistor has the potential of providing a gain of about 50. Two transistors have the potential of providing a gain of 2500. This means a  1mV signal (such as noise) will be amplified to more than 2.5v!
There are three main causes for self-oscillation:
1. Input lines being left open.
2. Noise on power rails.
3. Very high-gain stages
4. Connecting the circuit to a power supply,  CRO or other mains operated device. 

When every you see two or more directly coupled transistors you have to tackle the circuit in two parts.
Firstly you have to take DC voltage measurements.
You will need the circuit diagram as the voltage measurements are very critical.
If both transistors are designed to be turned at the same time, you need to check the biasing components.
If one transistor is keeping the other off,

10-03-04