Broken regulated PSU?

[edeca]

I bought one of these: **broken link removed** for general DIY usage. However, it doesn't seem to work. I am unsure if this is my own stupidity or if it was DOA.

I set the voltage to 9v and plug it into my little 7805 board, no juice. Tried it with an LM317 board, no luck either.

A multimeter across the jack shows 0v, even though the LED on the wall-wart is lit. I have tried multiple voltages and am definitely not drawing more than 500mA in any case (it claims to have auto-shutoff, probably via thermal fuse?).

Is the regulated PSU DOA, or am I wrong for some reason? I expect I should be able to test the voltage with the meter in this way.

 

[MikeMl]

I'd check the wire/connections between the supply and the connector where the adapter plugs in? Do you have a DMM?

 

[ericgibbs]

hi ed,
I have had problem with the crappy slider volts out select switch not indenting correctly ie: o/c

NOTE: disconnect the circular 2.5mm connector from the project PCB BEFORE you play with the switch.

 

[edeca]

Thanks to you both. Yes, I have a DMM and that's what I'm using. I could open the thing up and dig around, but I'd rather return it if it is faulty.

I was merely wondering two things:

1) I assume, as it has always worked for me before, that it is fine to use a regulated wall-wart to feed a regulator (e.g. 7805 or LM317). Of course the output voltage from the wall-wart needs to be high enough to power it, so I usually select 9v.

2) I also assume that measuring output voltage with a DMM is sensible. I seem to remember that DMMs have a small internal load resistor specifically for this reason.

Good thought about the switch, I will play. I am surprised that it is broken as it is a rather big beast!

 

[cr0sh]

For 1 and 2 - yes.

If you bought this new, I would return it, personally - not worth the time and effort for a defective wall-wart.

 

[edeca]

It appears to be fine now. Eric's suggestion of playing with the switch seems to have worked!

 

[Gayan Soyza]

Edeca I hate those slider type power supplies.They gave lots of troubles.I have never seen a regulated supply on those type models

 

[ericgibbs]

It appears to be fine now. Eric's suggestion of playing with the switch seems to have worked!

hi ed,
You can get inside those psu's 4 screws at the plug side, its possible to modify the resistor to the 4.5V select switch and change the useless 4.5V to 5V.
If you try this, two coiled springs will drop out, these are used to pick up the back of the mains plug power pins.
Dis-assemble holding the power pins upwards.

 

[Boncuk]

You might of course rework the PCB using a good quality dual slide switch with audible detents,

one like this:

Boncuk

 

[edeca]

hi ed,
You can get inside those psu's 4 screws at the plug side, its possible to modify the resistor to the 4.5V select switch and change the useless 4.5V to 5V.
If you try this, two coiled springs will drop out, these are used to pick up the back of the mains plug power pins.
Dis-assemble holding the power pins upwards.

That's really useful, thanks! I had noticed that there are 4 security screws, now I know it wasn't DOA I don't mind opening it up (I've got a set of the right screwdrivers). I might swap that resistor out too, I did wonder where 4.5v came from.

It would be an interesting "simple" project to generate a circuit from the components given that it apparently has the extra features (short circuit protection etc).