Samsung ML-2250 fuser melted

Samsung ML-2250/2251N because of faulty power supply the fuser is melted.
The heat and pressure roller are melted so the whole fuser and supply bord
must be replaced. Does anyone know what parts on power suppy bord are faulty
so they can be replaced not the whole board.

THX

--

On 8-May-2007, "fantom_slobode" <ekskaliburNOSPAM@net.hr> wrote:

> Samsung ML-2250/2251N because of faulty power supply the fuser is melted.
> The heat and pressure roller are melted so the whole fuser and supply bord
> must be replaced. Does anyone know what parts on power suppy bord are faulty
> so they can be replaced not the whole board.

Can't speak for that model, but a common design comprises a
thermistor bridge to measure the temp, with interlocks to
cover a paper jam, cover open, sometimes a startup timer,
all feeding an opto-coupler, to provide electrical isolation, to
drive a triac, in series with the mains and fuser heater.

Usual failure is the triac, occasionally the opto-coupler,
sometimes both as one failing takes out the other.

Triacs being power components usually have thick pins and
an attached heatsink. Opto-couplers are commonly in a
6-legged pack, with only 4 active legs, one at each corner.

For early printers triac and opto-couplers are easily sourced.
I had to replace mine about 4 years ago.
I added an extra heatsink to beef up the triac cooling, there
being clearance for it, added a socket for the opto-coupler
(in case it ever goes again) and added a LED in series with
the opto-coupler LED so if it is on, the triac and heater
should be on.
Now I can watch the fuser power duty cycle and am
better placed if it fails again.
Triacs and opto-couplers are simple to test with a
meter, 9V PP3 battery, one or two resistors, and a
red LED.
It might be a little more difficult with later models
due to flow soldered flat IC's, and tiny resistors/capacitors
with no markings of any use.

http://www.eserviceinfo.com lists the service manuals but unlike
most of their manuals these don't seem to be free.
If things are accessible, and if it's dead, and not under warranty
you have nothing to lose by having it to bits.
There are sources for parts for most printers.