Spot the mistake?!

[AC/HL]

With the items mentioned above it is to get approvals. No mains switch means less internal mains wiring. Cheaper too, and one less item to fail. It's been the norm for many years now.

[threeseven]

Have to say that I don't work on much modern equipment, consequently I haven't noticed this trend. IMHO it is potentially hazardous if users aren't aware of the issue and leave such equipment permanently connected to the mains.

[Nickthedentist]

This trend has certainly been going on since the 1970s, probably longer, so it's hardly just "modern" gear.

Think of all those 1970s mains/battery radios and radio/cassettes whose transformers are energised so long as the sets are connected to a mains supply.

A neon or LED to remind users that the device is still connected to the mains is always a nice idea.

Nick.

[dseymo1]

If the decision is made not to switch the primary, wouldn't it make more sense to have the switch isolating the output terminals? That way, at least switching is clean, without a gradual sag from the discharging cap.

[G6Tanuki]

Loads of mains/battery stuff ['integrated' tape/CD/radio ghetto-blaster-style audio systems, 'midi' hi-fi and clock/alarm/radios] for the last 3 or 4 decades has used 'secondary-side' switching: much of this stuff powers the audio-amp side non-stop when on mains-power, which leads to neighbour-RFI-annoyance to those of us who like to operate on 3.5MHz double-sideband-and-full-fat-carrier AM in the early-hours.

At least when you switch to SSB the reproduced audio from these 'always-on' broadband-detectors-and-amplifiers is unintelligible.

[threeseven]

I remain surprised! I used to work in the service trade for Philips in the 70's and can't recall any examples of secondary switched equipment, and that included alot of portable stuff. Obviously I'm familiar with lots of switchless stuff, like wall warts etc, but at least you are aware it will be powered until switched off at the socket or removed. So yes, you learn something every day!

[antenna441]

In the good old 1980s I bought a Ferguson 14" colour TV It had a video i/p and I used it as a monitor for my BBC model B. It was only recently when I threw the set away, that I discovered that the mains was hard wired to the transformer, and the switch was on the secondary.
Slightly more scarey is an uplighter that I was asked to look at recently. It has two lamps, one on a flexible, and two separate rotary dimmers with on/off switches. Imagine my surprise, when I opened the control box, to discover that the on/off switches were not in the mains feed, but just disconnected the gate of the thyristors, so the whole thing was live all the time. I told the owner that he would be advised to throw it away and not get it mended. I have never come across this arrangement before, and I hope not to again.

[kalee20]

Originally Posted by dseymo1

If the decision is made not to switch the primary, wouldn't it make more sense to have the switch isolating the output terminals? That way, at least switching is clean, without a gradual sag from the discharging cap.

You'd get,a gradual sag whether the switch was in the primary OR the secondary. A gently sagging (or rising) output shouldn't do any harm, as long as it doesn't fo anything silly, like reverse in polarity or overshoot, or be out of sequence relative to other outputs. And extra switching actually on the output would degrade regulation, owing to the extra resistance introduced.

[McMurdo]

Originally Posted by threeseven

I used to work in the service trade for Philips

My Philips CD player is switched on the secondary as is my Pioneer RDS tuner.

I also have another hifi separate somewhere which even leaves the VFD heater on when the mains switch is off...you can see faint glowing red lines in the dark.

[dseymo1]

So much for advocates of energy saving by switching devices off when not in use, rather than leaving them on standby...
(Either way, there's little benefit in most cases IMHO)

[Nickthedentist]

Originally Posted by antenna441

In the good old 1980s I bought a Ferguson 14" colour TV It had a video i/p and I used it as a monitor for my BBC model B

Their B&W 12" and 14" sets from that era also had the mains transformer permanently connected to the mains with the switch on the DC line.

The reason, I suppose, was so that the switch still operated when the set was run from a 12V DC supply in a caravan or what have you.

In contrast, I can remember a mid-1970s Hitachi 12" B&W set which had a very nice belt-and-braces arrangement. There was a 2-position rotary, mains on/off switch on the front panel with an LED which lit when the mains was switched on. Additionally, there was the usual on/off switch combined with the volume control which controlled the DC side of things as in the aforementioned Fergusons. Notably, It was the first use of an LED in consumer electronics that I'd ever seen.

Nick.

[threeseven]

Originally Posted by McMurdo

My Philips CD player is switched on the secondary as is my Pioneer RDS tuner.

After my time My 80's Denon CD player and 90's Cassette deck both have conventional primary mains switches, so it seems the configuration of power switching has no pattern.

[Apfelmus]

Originally Posted by threeseven

I spotted a quite serious constructional error made by the original builder.

Is the chassis properly grounded?

cheers
Martin

[threeseven]

Yes, it was, and is now.

[russell_w_b]

If it were me I'd've fitted Hellerman sleeves to the mains-side transformer terminals and a boot to the back of that fuse-holder.

[Kala_12]

I had (still have) a pair of computer loudspeakers that turned out to have the on/off switch in the low voltage side. I found this out when they failed and I looked inside to find that the rectifier diodes had burnt out. Yes, the switch was after the smoothing cap. I replaced said rectifier and they are still going strong - mind you, I now unplug them when not in use.
Stuart.

[Techman]

I've only had a quick look through this thread, so someone may have already mentioned it. I can't quite tell from the picture as the wiring is too close together to follow, but - is that fuse holder connected the wrong way round?

As regards to the 'small' switch - the output may be several amps at DC, so that switch may struggle to 'break' that sort of current at DC if it were placed in the output as mentioned. It may survive better on the AC side of the rectifier. Probably better to be 'safely' fitted in the mains side of the unit.