28-02-2023, 07:33 PM
Firstly, thank you Jeffrey & Adrian for the suggestions and information detailed above. This has been very helpful.
What I found:
I can confirm that the mains switch has been hard-wired by someone. On close inspection, one of the shorts was slightly detached (bad soldering), hence no power to the transformer.
Removing the shorts confirmed that the switch is broken. (The switch is part of the tone control but is on a separate wafer.)
I was getting intermittent results from the transformer primary. I found that the voltage selector was a little loose, so I expanded the prongs to make a tighter fit. I am now getting the predicted reading of 38 ohms.
I haven’t traced out the exact transformer secondaries, but I’m getting readings of 1, 293 and 302 ohms from three of the terminals, so I think it’s good.
I will have to source some proper resistors for R18 before proceeding (I will probably look for 5-10W types to be sure). I don’t know how I’ll get around the mains switch problem as its probably not replaceable. I could detach the switch wafer and have a closer look, but I don’t think it’ll help. I will probably hard-wire it again and see how the lamp limiter test goes.
Many thanks again!
I’ll be back!
What I found:
I can confirm that the mains switch has been hard-wired by someone. On close inspection, one of the shorts was slightly detached (bad soldering), hence no power to the transformer.
Removing the shorts confirmed that the switch is broken. (The switch is part of the tone control but is on a separate wafer.)
I was getting intermittent results from the transformer primary. I found that the voltage selector was a little loose, so I expanded the prongs to make a tighter fit. I am now getting the predicted reading of 38 ohms.
I haven’t traced out the exact transformer secondaries, but I’m getting readings of 1, 293 and 302 ohms from three of the terminals, so I think it’s good.
I will have to source some proper resistors for R18 before proceeding (I will probably look for 5-10W types to be sure). I don’t know how I’ll get around the mains switch problem as its probably not replaceable. I could detach the switch wafer and have a closer look, but I don’t think it’ll help. I will probably hard-wire it again and see how the lamp limiter test goes.
Many thanks again!
I’ll be back!
