Failed reverb in Yamaha organ

[winelight]

Hi there

I have an old Yamaha organ and the reverb (spring reverb) doesn't work.

However, if I turn reverb on and twang the string manually, it makes a sound. So the pickup end is working.

So what I'm asking really is using your skill and knowledge, what's more likely to have failed? The transducer itself (it looks OK and I can't imagine what could go wrong with it) or the driver transistor (2SD142)?

OK I know the answer is test to see if there's any output from the driver stage, but I don't have any test equipment beyond a multimeter. I suppose what I'm hoping is that someone has enough knowledge of 40-year-old spring reverb units to know whether the transducers are likely, or most unlikely, to fail.

Or is there a failure mode of the 2SD142 that would make it easy to test if I remove it from the board and test it with the meter? My hazy recollection of blown power transistors is that the internals vaporize and they go open-circuit.

(The faulty tremolo was easy to diagnose - the drive belt had entirely perished!)

[SamRodgers]

A multimeter with transistor test range can be bought for very little money.
An oscilloscope (ideal for this type of fault-finding) for about £120.