Just need to find somewhere to get the replacements. Out of interest can you advise how I measure the R, G and B signals? I dont have an oscilloscope, only a multimeter.
You'd need an oscilloscope to measure the RGB signals. Your multimeter will have a diode test function which you can also use to quickly test the transistors. All bipolar transistors will measure as though they're two diodes. For the 2N3904, which is a NPN transistor, leave the red probe on the base terminal (use Google if you don't know which one that is, package type is SOT-23), then with the black probe on either the collector or emitter terminals, the meter should show approx. 0.65 - 0.7V across either of the two junctions. In this case you can measure the transistors in circuit without removing them.
Most electronics parts suppliers will carry 2N3904 (also known as MMBT3904), they're one of the most common small signal transistors on the planet. Or you should be able to substitute with most equivalents such as BC847, 2N2222, etc.
If you're feeling lazy, and in the very high probability you're not using a modem that relies on the ring indicator signal, just remove Q571 near the serial port and use that as the replacement transistor. You'll need to find out which is the defective transistor as mentioned above to know which one to replace.
