Hi @Laurence D. I was trying to answer this with the forum went up in smoke and sparks and water.
That method of testing will work on all the Eden WT, WTX, WTB, and Nemesis series amps that David designed. I presume it works on the WTP amps, which came from the Marshall designers, but I don't know for a fact that it does. If Armin (
@Bassmann1968) pops in here, he will probably know because he has one (has almost all the Eden amps actually) and was our electronics guru on the Eden Forum.
Basically if the gain set light comes on with the gain set high enough to trigger it, you know the signal is getting to the preamp. If hooking the effects-send up to the effects-return works, then you know the preamp is working. Usually that means there's a bad or corroded connection somewhere in the signal path. Cleaning the 1/4" jacks usually fixes it, but sometimes there's a further problem with it. Cleaning the jacks on an annual basis will avoid a lot of intermittent and hard to track down problems, so at the Eden forum we always recommended cleaning all the jacks before taking it to a tech.
Also be aware that some manufacturer's do not want you to put a spritz of contact cleaner into the jack because they have components behind the jack that might not respond well to that cleaning solution. So be sure to check the manufacturer's manual for direction in a non-Eden amp. If that's the case, you can still spray in on the plug and work the plug in and out of the jack 10 to 15 times on each jack, or take a long-handled Q-tip, spray it on the cotton end, and use that to clean the jack inside. Most electronics stores will have those specifically for cleaning contacts.