Re: Roberts RT7 - problem
Incorrect polarity, after prolonged connection (a minute or two) will theoretically cause significant damage, but in reality it'd likely blow out an electrolytic cap before anything else.
Strange, but not unusual, to find bare-ended power leads. This suggests someone has removed the PP10 connector, tried the radio by touching bare wires onto some battery or other, then abandoned it for some reason. Possibly the fault pre-existed your ownership.
Transistors must be checked following removal, but the OC series don't give much trouble other than at the output stage through a fault or abuse. Capacitors and resistors can be checked in situ providing nothing else is connected in parallel with them.
T2 is the output transformer ie that which drives the loudspeaker. If that and the battery are warm, excessive current draw is indicated. I'd check this with a meter and suspect either or of the output transistors, which I think are OC81's on this model.
You're on the right track regarding Steve's suggestion of injecting a signal. Use the headphone socket of whatever. Imagine a 3.5mm jack with bare-ended wires leading therefrom. Just connect two of the wires to the RT7 as Steve's described. Remember that the jack output from a CD player or whatever will likely be stereo.
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