On Tue, 14 Jan 2014 09:48:15 -0800, Jeff Liebermann
wrote:

On Tue, 14 Jan 2014 08:44:28 +0000, T i m wrote:

Duz this sound familiar?
http://www.fixyourownprinter.com/forums/printer/72871

I'll try the 'impact reset' test and the good thing is you can
check the result there and then (with yer DMM).

I rarely see broken mechanical thermostats. More commonly, on HP
printers, I see accumulated toner residue piled up between the fuser
roller and the thermostat. Usually, there's some type of film between
the two, which prevents scratching the drum. I don't think I've ever
seen a blown thermostat on an HP which makes me wonder if replacing
the 170C thermostat with an identical Samsung part is a good idea.

Unfortunately without knowing the function / specification of both
parts I'm not sure I have a choice? By that I mean if I was doing such
for someone else, rather than what I might do for myself.

Yes, I've since spotted that. The problem is though, if they are both
thermal switches and of different temperatures (the second / higher to
be used more as a failsafe in case the first / normal switch sailed
unsafe) then we don't know which one on mine is still functional?

I don't have a schematic,

I have some block / logic diagrams but no schematic. ;-(

It does say this of the fuser though ... (in case it helps).

"....Fuser Ass’y
This unit consists of Heat Roller, a Thermostat and a Thermistor. It
melts and fuses the toner, transferred
by the transfer roller onto the paper, by applying pressure and high
temperature to complete printing job.
* Heat Lamp : Kunckle Type
* Fusing system : 3-Roll Fusing type
- Heat roller : Pipe type (Lamp inside)
- Pressure roller
- Pressure roller Shaft
* Thermistor - Temperature-Measuring Device
* Thermostat - Critical Temperature-Detecting Device
* The life span – 100k(black)/color(25k)

Thermostat
When a heat lamp is overheated, a Thermostat cuts off the main power
to prevent over-heating.
- Non-Contact type Thermostat"

but I'll guess(tm) that they are running
some serious heater current through the thermostat, causing the
contact to possibly arc. A few protective arcs under load, and the
contacts will build up a layer of oxidized copper which makes a fair
insulator.

Understood.

This is the power supply relay contacts of an HP LJII with
a similar problem:
http://www.learnbydestroying.com/jeffl/pics/drivel/slides/hp-relay.html
The little back dots make great insulators.

Ouch.

Adding a 2nd thermostat sounds like a retrofit to fix the problem.

Not the problem of going o/c I assume?

There should be a service note on how to do it, somewhere. My
guess(tm) is that two of the single thermostats will fit, if you can
find them.

Oh, I'm sure they / I could cover that, if I can find the right fit
and spec parts.

Incidentally, on the exploded view of the fuser, there's an
thermistor-NTC which is what probably controls the temperature.

Yes, I think I offered / suggested such elsewhere (but didn't know if
it was just to provide feedback to the controller board to say 'Warmed
up'?

I'm sure it goes to the laser engine controller or power supply.
That's the way it's usually done on printers that I'm more familiar
with, such as HP.

The thermistor goes back to the main controller board that is for
sure. I need to have a closer look at the PSU to see if there are any
other connectors from the other boards. Otherwise there is only mains
in and the outputs to the rest of the unit and the fuser. Would the
fuser normally be running at full temperature when the (a) printer was
at idle?

I've not experienced them till now (normally HPLJ here and still have
a trusty P2015dn on our LAN)

Retch. The P2015dn and similar printers are my worst nightmare.

Oh. ;-( Well, I bought it cheap s/h as I wanted a networked b/w
duplex laser and so far touching wood it's been ok.

What would you recommend then to cover a similar SOHO, networked
(wired) duplex mono role then Jeff?

There
are YouTube videos on how to replace the fuser that should give you a
clue as to how difficult and time consuming that series of printers
are to repair.

I'm guessing that like many things (including cars) these days they
are designed to be disposable. ;-(

I have three of that series printers that are on the
shelf awaiting repair of the formatter board, which suffers from lousy
soldering:
https://www.youtube.com/watch?v=x1acw-7kMws
https://www.youtube.com/watch?v=F1q2lmoLUzc

Luckily I have a mate with all the reflow gear. ;-)

Cheers and thanks again for all your help.

Good luck and I still don't like Samsung printers.

Thanks and ;-)

Oh, I contacted the supplier of the thermostat pair you kindly found
me and they have replied saying 5 off (minimum quantity) will cost me
80 USD delivered. Now, that's less than the cost of a new fuser but at
least with a new fuser I get a new fuser (as well). ;-)

I've set the printer to idle after 5 mins and will plug it into a
power monitor so I can check to see what sort of current /
background_current it draws then decide from there if I'd want to
leave it on 24/7 or not (as is).

I have 2 x HPLJ 4's that I'm not sure what to do with. They are big,
heavy, non-duplex and neither work properly (electronics faults). I
understand they are (were?) workhorses but they are just so big by
todays SOHO b/w laser standards (one has a JetDirect card fitted).

Cheers, T i m

p.s. I can't seem to get this Samsung to connect via WiFi. It 'sees'
al the local WiFi networks but doesn't want to connect to any (all
mine). The thing that worries me is that although I put the WPA
passphrase in in lower case it displays it in the status printout in
upper?