SC20H - no light in the red power switch

[nioclás]

Greetings

I forgot my beloved SC20H powered on yesterday. Apparently it had stayed on the whole night, I found out today that it was still on. The amp played just fine, but the red light of the power switch was off.

Now I notice that after the amp has been off for a while, when I switch the power on, the red light lights up, but after some time it gradually gets dimmed and eventually goes off.

I guess I did some damage by leaving it on the whole night... I was wondering how common is that? Are these switches really so fragile to die after a few extra hours on power? If it's broken, I guess I could buy a replacement, but I'm wondering should I be worried about something other than just the rocker switch?

 

[Jon Snell]

If it is a neon then the feed resistor may have failed. Not very common and should last a lifetime.
After checking the neutral wire hasn't fallen off, replace the switch and that will sort it out.

 

[PelliX]

Yup, those are neon lights inside the power switches, same (as in, I believe the exact same part no) as the modern DSL's. While they "can" go on for a lifetime, sometimes they die a little prematurely.

guess I did some damage by leaving it on the whole night... I was wondering how common is that?

Nah, a little wear on the valves, that's it. I wouldn't sweat it, you just got unlucky with the switch.

Are these switches really so fragile to die after a few extra hours on power? If it's broken, I guess I could buy a replacement, but I'm wondering should I be worried about something other than just the rocker switch?

Not really fragile but they can die, presuming the amp works fine otherwise there's nothing to worry about and the indicator is really only cosmetic. As for a replacement, they can actually be a little trickier than one might expect; I went through the same for my DSL. I ended up ordering the part through a distributor after contacting Marshall and they in turn referred me to a local music place. Obviously, they're just a generic switch, but the exact proportions, sharp corners, absence of markings and 'bow' made it hard for me to find a true 1:1 replacement. Generally, I wouldn't mind too much, but it's right next to the standby switch, so I wanted the two looking "right". Other option is to swap them both out, I guess, hehe.

After checking the neutral wire hasn't fallen off, replace the switch and that will sort it out.

If the neutral was missing, the amp wouldn't power on...

 

[Jon Snell]

The neutral wire goes to the neon and can break as can the resistor go high value inside the switch. Both are within the switch and are repairable/replaceable if you know how to disassemble the switch.

 

[PelliX]

This is effectively how those work.

I've had a bunch open over the years, not this one yet, though. It was on the blink (yes, literally ) for weeks. When I finally got the replacement part I flicked it on a last time out of habit... and it hasn't wavered since. I have the spare, but I'm not ripping the amp open for a cosmetic issue unless it re-appears, haha.

Also, OP: https://www.marshallforum.com/threads/dsl20cr-rocker-power-switch.128946/#post-2309701

That's basically the route I went down. If you're interested I have the replacement in its little baggy with some kind of a part no marking on it. Could dig it out if need be. I don't think the switches themselves have any kind of type indication.

 

[nioclás]

Thanks for the replies. Yeah, a spare switch is not easy to find, it appears. I managed to order one, but had to spend some time searching.

Interesting, though, that they would put a neon light instead of a LED, as seems to be more common nowadays.

 

[Jon Snell]

Rocker Switches, On Off Switch | RS

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Lots to choose from here.
I personally think a green switch looks different.

 

[nioclás]

Thanks for the link. Will bookmark it for future reference.
And there's an EU version too, yay (read: no exorbitant import fees & taxes)

 

[PelliX]

Interesting, though, that they would put a neon light instead of a LED, as seems to be more common nowadays.

LED's are low voltage DC components, whereas the neon light requires only a live wire. It's a lot cheaper and less error prone in such a critical spot to use the neon option. While one can install a LED - and there are switches that have this - it just doesn't make much sense for the use case.