Last 142 I'd worked on was actually fairly recently.
Sold it a few weeks ago, just after fixing it and recapping it.
It also had a problem with no AM modulation at first.
Turned out to be a bridged solder joint on the AM regulator - that time.
So I fixed the horrible solder job and replaced the C1419 with an upgrade TIP part.
But there are soooo many different things that can cause that AM no modulation fault. Anything from the mic element all of the way down to where the AM signal reaches the mixer chip - including the mixer chip. SO to ask what the problem may in this instance is to ask which part out of some 20-30 different parts is fault. In fact, it could even be more than one part - too.
When something breaks, it doesn't always break the way you'd hope it would. It is always the weakest link(s) in the chain, either thru abuse or end of service life for a component ('caps'). Some people just love to shove all the modulation they can down that pipe and seldom care about what happens - until it breaks - of course.
Having said that, this is why I pointed out that the schematic is really your best friend. If you can learn to trace thru the path of AM audio on the schemo, all you have to do is start at the very beginning of that circuit ant test everything thru to that end. Often enough, most likely that you seldom have to go the whole distance. But you will always be assured of finding the fault(s) if you do the grunt work.
And it is grunt work.
But once you get that discipline to lean the schematic and test components; then there is no stopping you. You will be fixing everything that comes your way. Broken radios find their way to you and you fix them and turn them around.
