mini switchmode fire starter ?

[fabricator]

A computer accessory I bought today came with a tiny switchmode PSU in a mini plugpack (wall wart) casing. Its labelled as YD-001, 110v-240v 50/60hz, 5v 1000ma.

Having opened the thing up I'm concerned I even plugged this piece of junk in for the 5 minutes it took to test the device.

I consists of:
Low voltage cable soldered to the mains.
A tiny white crud coated circuit board.
A few 1/4w carbon film resistors, I love the one on the main input btw.
2 common signal diodes and a zener.
A sole power diode to rectify the mains to 400v dc.
A 2.2uf 400v cap, 'MQ' brand
A power transformer the size of the old 1k-8ohm audio transformers.
A sole to-92 device, no idea what it is.
suspiciously small 220uf 6.3v cap on the secondary.
A couple of small caps around the transistor (filter and timing ?)

Things missing:
3/4 of the bridge rectifier, removed to save costs.
any sort of fuse.
any sort of high voltage rated cable, resistors, mains filter components.
a proper diode to rectify the secondary voltage.

If this piece of junk can put out 1 amp without failing in short order I'll eat my hat.

Question though, would replacing the single diode on the hot side with the full 4 diodes effect the operation at all ?

I plan to fix the hot side with a new HV cap, full diodes, inline fuse, proper HV resistor etc. A new cap and diode for the output. Then use it to power some xmas decorations or something else that doesn't care much about voltage regulation.

To anyone else, just throw it in the bin, its not worth fixing unless your bored.

[ratdude747]

Re: mini switchmode fire starter ?

pics please...

[POM_MJ]

Re: mini switchmode fire starter ?

It look like just 5V/1A DC output (5W), it could be cut "2 transistors 5VSB circuit" from cheap PC. PSU.

[seanc]

Re: mini switchmode fire starter ?

This sounds like one I had. It was for an energy monitor. Hook the wireless receiver up round the mains cable by the breaker and it transmits to a little display (powered by the below)

Yes, it is a potential firestarter.
Mine failed - I cracked it open.

Replacement Motorola phone charger works fine

Results below:

[Agent24]

Re: mini switchmode fire starter ?

You got me worried about the tiny SMPS for my D-link switch now...

[i4004]

Re: mini switchmode fire starter ?

if anybody is surprised by this, it means he wasn't opening such devices before..hehe...

>Question though, would replacing the single diode on the hot side with the full 4 diodes effect the operation at all ?

peak voltage after the one or 4 diodes will remain the same, ie it will be the peak of AC sinus that's going in.
but it also depends on the rate that mains cap is discharging, ie if it's discharged fast, then 1 diode circuit may have lower voltage because full bridge will keep that cap fuller...

find datasheet about that to92 device(it's probably smps regulator) and then you'll see what it does, what voltages it accepts etc.

>Then use it to power some xmas decorations or something else that doesn't care much about voltage regulation.

problem of such supplies is not so much lack of regulation(they usually have secondary->primary feedback link) but lack of components and quality of components.
that's where they fail miserably.
it's just cheap chinese crap one should first fix, then use, just like you're attempting.

[japlytic]

Re: mini switchmode fire starter ?

Some serious corners have been cut. Having only one mains diode (not a bridge rectifier) can reduce efficiency, and reduce the life of the high voltage primary electrolytic capacitor through increased ripple current.

[Agent24]

Re: mini switchmode fire starter ?

Prime example of "Reduce component count and quality until it stops\explodes, then replace the last component removed and start mass production"

[ddscentral]

Re: mini switchmode fire starter ?

I have a couple of these 5v switching supplies (one 620ma, one 1A). Opened 1A one. Well it at least has 4 diode bridge. But it is probably one of these supplies which will catch fire if overloaded.