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The D.I.Y safety thread

Always unplug from the mains the item you are working on after making any tests or adjustments. Better to have to repeatedly plug it in and out than forget you left it plugged in when you finished working the night before.
 
Possibly a silly one, but works for me - on several things I've built or modified for my own amusement, somewhere inside / at the psu on each rail or at each regulator is a simple cheap red LED, independent of anything in the casework/front panel. It's well worth the few mA draw simply because with the lid off, when you are fiddling with it during 'development' (or revision or repair): you can see the bloody thing is live locally. [ETA:] and while- no maybe 5v wont do you any harm - it does remind to take care probing voltages in case the probe slips and does collateral damage at an IC or similar, e.g. the risk of shorting two pins and similar non-safety-critical, but avoidable events.


(NB The LED is usually used for some other purpose too, like biasing a current source or sim. Which is where I started thinking - that was useful...)
 
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One of the early tips that stuck with me was heatsinks can be hot, not as in heat wise, but electrically. One you never forget ;-)
 
Thread update:

I've just taken delivery of one of these

It seems well enough made, with a nice beefy transformer inside.

Please note that there are two sets of outputs. The screw terminals are not connected to earth and provide a truly isolated output but the UK socket is earthed as normal. I have disconnected to the earth on mine.
 
S-Man said:
For commissioning bits of kit:
1) Check all 0Vs are connected together using a mutimeter - e.g input socket to output socket to power star to signal star to transformer centre tap etc.
2) Check all PS wires are the right polarity in the right place. Recheck that the bridge rectifier terminal match where the smoothing caps connect e.g. follow the + lead and make sure it goes to the + terminal on the cap etc
3) Check (lack of continuity) between power rails and OV. A DVM will usually count up or down in this situation.
4) Power up via a variac and wind up very slowly from zero. If the variac starts to hum - power down immediately. At very low volts check that supply rails are the right polarity.

Follow the usual power up procedure from then.
Click to expand...

Great advice...

I would add check continuity between an IC's metal case and the heatsink it's mounted on. There shouldn't be any, unless the heatsink is isolated from the case - I kinda think that is bad practice and I always try to isolate the heatsink from the IC.
 
It always astonished me that very old TVs had a live chassis. It was literally a metal framed chassis to support the boards, the Lopt (25000v potentially) and everything else in it and it was live.
The fact that guys used to work in these in confined spaces and reach in to test components in peoples homes is beyond belief!
I once visited a guy who looked somewhat flustered, on asking him how he was doing he told me some b.....d had shorted the mains switch of the tv he had just opened up, It was buried at the front of a set and he’d got a belt that threw him across the room. He was not a happy camper!

From what I’ve seen in pics these days most if not all modern hifi units have the live mains connections and switches pretty well shrouded which I’m guessing is now a safety requirement.
Isolation transformers, dim bulbs and Variacs are well worth investing in if they can make diagnostics both safer and easier:)
 
I used to repair tv's, and some sets you would attach the meters ground clip to the chassis and the speaker would crackle then you knew the plug was wired backwards.

Pete
 
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