Laser fuser thermal switches?

Hi all,

I fault found (what I believe is) an open cct thermal switch in the fuser of a 'faulty' Samsung CLX 3175 laser printer I was recently given.

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One is marked 170/0 100209 and the other is unmarked.

Because it looks like there are two in series, as a test I shorted one out and the printer fired up and seemed to work ok. ;-)

So, am I right in thinking there are two in series as a failsafe and they are used as an overtemp and that the actual temperature might be managed by a thermister and finer / electronic (PWM?) controls?

I believe I could buy a new fuser at a reasonable price and that would obviously come with a pair of new thermal switches but as the fuser is otherwise working it would be nice if I could simply replace this faulty device (and if so from where please)?

Cheers, T i m

Reply to
T i m
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I think the fuser temperature is pretty much determined by its current draw (resistance) and any control is simply on or off. Looks like those are just to kep it from burning the house down.

Why there are two is a mystery to me. Maybe it consists of two elements in series and if one shorts it would trigger ? Something like that ?

Reply to
jurb6006

This is probably true.

Could be an overtemp, could be a normal operating control. Sometimes there will be an "operating" thermostat at X degrees C in series with a "limit" thermostat at (say) X+20 degrees C. In this configuration, sometimes the operating thermostat is designed to turn on and off indefinitely, but the limit thermostat is more of a thermal fuse - it opens the circuit once and stays open forever after that.

Maybe. It could be that the electronic control has also failed for some reason, such that the printer appears to work in a short test, but if you leave it on for a long time or run a long print job, it might overheat again. If you do replace the switch, it's probably a good idea to run the first several print jobs while you/someone is nearby, to shut off the printer in case of excitement.

That looks like the Korean interpretation of a Klixon 7BT2 thermostat. They are available in a variety of mounting options and terminal types, but all with pretty much the same size body.

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The White-Rodgers 3L11 series is similar, but the ones I can find quickly all have a mounting foot, which you may not need in your application. These are distributed in small quantities by Mouser (US):

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(or search 3L11-325 at mouser.com)

Cantherm R53 series also appears to be similar. These are distributed in small quantities by Digi-Key (US):

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The ones Digi-Key sells come with a mounting flange, but it looks like it would be easy to remove this with pliers.

Hopefully the "170" in the part number on yours means 170 C, but it would be good to find out for sure.

It looks like your two thermostats have been joined by spot-welding the terminals; you may have to replace both thermostats and come up with a way to join the terminals on your own - a really short jumper wire, perhaps.

In the US, these are all over the place inside home refrigerators, clothes dryers, etc. An appliance repair shop will probably have some, but they will probably only know them by the manufacturer part number and not just the fact that it's for 170 C or whatever.

Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.

Matt Roberds

Reply to
mroberds

Ok.

;-)

Don't think so in this case as these thermal switches are connected in series and with no other connections etc, and I can only see the ends for one heater / lamp?

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I think the two in series is as you say and a safety thing ... and as only one is marked they are possibly both the same temperature rating.

I have seen n/c thermal switches and assuming 170 marking is the temperature in Centigrade, I could potentially get a similar replacement but they are set in holes and facing the fuser roller so the dimensions could be reasonably critical.

I guess I could just run the printer, turning it on and off as required and if it seems reliable / useful, treat it to a new fuser in any case?

Cheers, T i m

Reply to
T i m

Ah, that makes sense and was another option I considered (and the code on the pair could have been a Samsung part number for the two devices combined as a 'solution' (they are cold welded together with a bridging plate).

The paper certainly comes out pretty warm but then I think this is the case when they have upped the page rate? The paper isn't curled etc, if that says anything?

Hehe. I have probably put 60 pages though it whilst testing today and it seems to have survived that ok. However and as I mentioned just, the paper did feel pretty warm (I can put the IR thermometer on it and see what sort of temps are going on).

Thanks for that, plenty of choice there. I did have a quick look for a Service Manual as there may well be some calibration / temperature measurements in there but as yet, only have the parts section (with exploded diagrams).

Again, that was something I also considered.

I guess I could test the remaining working one with a DMM, heat gun and IR thermometer?

Understood.

Also understood. I have changed such (and thermal fuses) on a few things now.

Understood. ;-)

As the fuser comes as an assembly and therefore no sub-part information is available, I might just run the printer as-is for a while (switching on and of as required) and if it proves reliable, then maybe treating it to a new fuser in any case. At least that way I might be able to see if there are any more useful markings on the new one and if so, see if they are indeed just in duplicate (switch + switch) or as you say, something more final, like switch + thermal fuse (and have the old fuser for other spares). ;-)

Cheers and thanks for all the links etc.

T i m.

Reply to
T i m

The main reason I figured the temperature is self regulating is that the fu ser is one of those parts that are different on a 120 volt unit or a 240 vo lt unit. It probably just kicks on with a relay.

I could be wrong, but I doubt they could get precise enough temperature con trol out of one of those little bimetal jobs to assure consistent print qu ality.

Of ocurs eI could be wrong, but there is still usually a different part for 24 volt operation, whereas most modern power supplies switch automatically . Some don't even need to switch, they just have good enough regulation to run fine anywhere from 50 - 250 VAC.

Reply to
jurb6006

What is "faulty" about the Samsung CLX 3175 printer? Are you getting an error message on the front panel? Is it perhaps a "Deve Home Sensor Error" message?

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

Nothing now. ;-)

I was.

No, it was something about cycling the power (that made no difference) but a Goggle search from that suggested a fuser fault (as one of the main causes).

The fuser was indeed cold and (as it turned out) because of what looks like a thermal switch (or fuse) that had gone o/c. Shorting said device with some copper wire removed the error message and allowed the printer to return to a working condition. ;-)

That said, because I don't know of the type / function of the o/c device, I now may not have either:

1) The extra safety functionality (thermal fuse) 2) The right running temperature (two different temperature threshold devices in series and the lower temp unit has failed).

As what is probably and aside I'm also seeing a horizontal band across the page. It could be off the OPC drum. I'll have to measure the circumference but it looks about right.

Cheers, T i m

Reply to
T i m

Understood.

I think I read somewhere that someone had changed a thyristor (triac?) on the SMPS but it could be used in the same on/off way of course.

This is the PSU:

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The input (240V in this case (UK)) is in the bottom left and the output to the fuser on the bottom right.

That was what I was thinking and why I wondered if the thermistor (that also sits over the fuser roller and beside the thermal switches / fuse) may control it more finely. Mind you, even the temperature range you might see with something with the hysteresis of a bi-metal switch may not be sufficient to affect the ability to fuse toner (I don't know if that is the case etc).

There is indeed (assuming you meant 240V there). I have seen them both in the parts list and the voltage would (of course) affect both the rating of the heater / lamp and the thermal switch (working voltages, although they would probably be 240 in either case).

Clever aren't they. ;-)

Cheers, T i m

Reply to
T i m

Duz this sound familiar? See 2nd to last comment near bottom of page. That's my favorite fix of mechanical thermostats.

Finding the exact replacement has been a bit of a challenge. This is the best I can do for now: which isn't going to be easy to obtain. The CLX-3175FN manual shows the part as a 4712-001027 but that's a single thermostat, not a double. Incidentally, on the exploded view of the fuser, there's an thermistor-NTC which is what probably controls the temperature.

If the fuser wasn't getting hot, but the mechanism was still moving, then you could have a nice pile of toner piled up in or under the fuser. Remove and clean.

Note: I don't fix or like Samsung printers.

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

Hehe! Sfunny, it sounding like there was something 'loose' in one or both of them but now I know how easy it is to get the fuser out (easy but fiddly / slightly tedious with all the plugs you need to disconnect to free the fuser wires (although that might be easier now )). I'll try the 'impact reset' test and the good thing is you can check the result there and then (with yer DMM).

That's the badger!

I wonder if they would send me a sample? ;-)

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?

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'?

Whilst I didn't check that (in my euphoria re finding the 'fault' and the potential of checking it again), I'm not sure the print error is of the right interval for the circumference of the fuser rollers. I see a horizontal line / mark at about 2" down a sheet of A4 and again at about the same from the bottom. It may be fading with use.

I've not experienced them till now (normally HPLJ here and still have a trusty P2015dn on our LAN) and so this is the first one I've looked at. Hundreds of years ago I worked for Kodak on their microfiche/film cheque processing machines so I have some experience with this sort of thing. In comparison though, there was much more 'metal' in the Kodak stuff. ;-)

Cheers and thanks again for all your help.

T i m

Reply to
T i m

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.

I don't have a schematic, 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. This is the power supply relay contacts of an HP LJII with a similar problem: The little back dots make great insulators.

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

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.

Retch. The P2015dn and similar printers are my worst nightmare. 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 have three of that series printers that are on the shelf awaiting repair of the formatter board, which suffers from lousy soldering:

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

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

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.

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

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

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

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

- Non-Contact type Thermostat"

Understood.

Ouch.

Not the problem of going o/c I assume?

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

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?

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

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

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

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

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?

Reply to
T i m

See if the fuser heater current goes through the thermostat. I suspect that it does, which means the thermostat has to disconnect under load. Nice way to create a small arc.

A what?

Main power as in the AC line power? I doubt that. Probably just the fuser heater power.

My wild guess(tm) is that the 170C was too low in temperature to stay closed while the printer was being used as a printing press. The manufacturer usually recommends a duty cycle, such as 20 mins print,

10 minutes rest, etc which of course, nobody follows. The thermostat would probably open a few times during such heavy duty printing. The thermostats are not meant to survive too many such cycles. Rather than welding the contacts shut, which would be a safety problem, like a common household circuit breaker, they're made to open at ever decreasing temperatures, eventually resulting in a permanent open circuit. Note: this is a guess, this is only a guess.

No. Most laser printers have 3 or 4 levels of power savings. Then printing, the fuser heater power is full blast. Between print jobs, usually for about 10 minutes, the power is at about 30% of full blast. If the printer goes into standby, the fuser power is at about 5-10% which is just enough to get the first page printed reasonably fast and avoid major inrush current. In shutdown, the fuser power is totally off. I have no idea what Samsung does in this printer.

I like the HP 2300DTN printer. I own 3 of them, and have resold or arm twisted customers into buying approximately 15 of them. The first page comes out in about 3 seconds. Duplex printing is handy to save paper, but is admittedly slow. However, like all HP printers, these have a lifetime shortening feature which I believe HP has ignored because it causes obscure late term failures that sell many replacement printers. Here's the fix: I've also found the same sticky solenoid problem in all HP printers of the same vintage (2200, 2230, 4100, 4150, 4200, 4250, 4300, etc). Also, you might have problems with magnetized solenoids: You'll need an antique 1/4" magnetic tape bulk eraser to fix that. Otherwise, the 2300dtn have been a great printer.

Todays design methodology is actually fairly simple and somewhat economical. The manufacturer sets a target lifetime for the product. He then cost reduces components and assembly techniques until literally everything fails at the same time, somewhat after the target lifetime. Anything that lasts longer than the target lifetime is considered a waste of money and is further cost reduced. I can critique HP's latest laser printer offerings on this basis, but I'm late for a paying appointment.

I have a hot air SMT desoldering station. It doesn't work. The main problem is that when the solder is hot enough to reflow, the blowing air pushes the parts out of position. An IR reflow station is what you want. However, I pizza oven or electric toaster oven is good enough.

I think I can find a replacement single thermostat in the US for much less. Later tonite...

eWaste.

Temporarily clear the WPA encryption key from the wireless router and see if it will connect with no pass phrase. If that works, try entering a simple WPA2-AES pass phrase and see if that works. The usual problem is that some devices enforce the 8 character minimum pass phrase length, while others ignore it. The other common problem are Apple Airport base stations that need a firmware update in order to coexist with other devices. Yet another are web forms that don't like spaces in the pass phrase. The encryption key can have spaces but the web form transfers the spaces as garbage. Isn't compatibility great fun?

Gone...

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

It does, both, they are in series with the heater / lamp.

;-) Pass!

Yup.

Hehe.

Ok ...

Well, I've set it to 'sleep' after 5 mins and after 30 mins you can still feel warmth coming out of the paper exit port (I assume that to also be a thermal vent for the fuser).

It looks fairly 'chunky'?

Oh?

Nice.

Got one of those. ;-)

Ok.

Yeah, that's the sort of thing my mate has built / modded / bought etc.

Oh, cool, thanks (but aren't we still unsure what role both devices covered? Stat+backup stat. Stat+Overtemp Stat? Stat+Thermal fuse?

Hmmm, shame.

We have 8+ on all of them. I can do as you suggest but with a spare router.

Isn't it just (not). ;-)

Whoah, where did Jeff go ...?

Cheers, T i m

Reply to
T i m

Before electronic filing, my tax preparer customers would run their laser printers almost full time during late tax season. Five inch thick returns were common. A floor fan blowing on the printer was also common. All of them went through the same exercise. They would buy a cheap laser printer, run it like a printing press, destroy it, and then buy something more suitable.

HP is unique in that it has a built in safety feature to prevent overheating and over use. It's the sticky solenoid and foam rubber pad I mentioned in a previous rant. When the machine is cold, the solenoids work normally. However, as the solenoid becomes hot from use, the glue and foam rubber pad melts, causing the solenoid armature to stick to the frame. The timing error usually produces a paper jam which offers the user a chance to slow down while practicing profanity.

There has been some suggestion the sticky foam safety feature is not intentional, but I suspect otherwise. HP has used exactly the same design for their sticky solenoid safety feature since the HP LJII which suggests that it's a successful method of controlling the printing duty cycle.

I use a Kill-a-watt AC power meter to measure power consumption in various states. Occasionally, my measurements agree with the data sheet. You might want to measure the standby and power save power consumption, which offer clues as to the fuser power consumption.

It's bigger than your P2025 but not as big as a production printer such as a 4150, 4250, or 4300. Certainly smaller than an 8000 series printer. Two of mine show about 80,000 pages. The other is at about

10,000 because I replaced the formatter board. I replace most of the rubber parts when I rebuild a printer. I get about 5000 pages per toner cart. If you want better, you'll have to live with bigger.

Yep. If my guess is correct about thermostat cycling due to excessive use, putting in the wrong thermostat will make it worse if set to a lower temperature, or melt the fuser if set to a higher temperature. At this point, I would so some measuring with an IR thermometer or thermocouple. My guess(tm) is that the operating temperature is too close to the thermostat temperature.

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

Wow.

The guy opposite has done similar with a few small Brother and Samsung mono lasers. I think he has since been given something bigger. ;-)

Hehe.

;-)

Approximate values. Warm-up power mostly 900W for about 30 seconds.

12 or 900W on a 7:1 duty cycle after that. After 5 mins it sleeps to a constant 10W.

Printing 3 colour pages from standby: Going from 45 (motor running) to 900+W (fuser on + motor running + paper handling) for the duration of the print process then back to 12

- 900 (7:1 duty cycle) till standby.

!

My (new to me) Samsung: Total Page Count : 3260 / 1976 Page(s) (Color/Mono) Toner Page Count : ( Yellow / Magenta / Cyan / Black ) ( 998 / 995 / 994 /

731 ) Page(s) Fuser Life : 14995 Page(s) Transfer Roller Life : 5223 Page(s) Tray Roller Life : 5236 Page(s) Total Image Count : 15040 Image(s) Imaging Unit Life : 15040 Image(s) Transfer Belt Life : 15040 Image(s) ADF Scan Page Count : 176 Page(s) Platen Scan Page Count : 187 Page(s)

... an I think it's done that over a few years.

Quite.

So, you feel the temperature is being controlled via the thermistor controller PSU rather than the stats? That they are just there for over temp?

I guess if I pop the side off (now I know how) I can (carefully, 240V) monitor the feed to the fuser heater and see if it's 'switched' at that point. If it isn't yet the machine current is still fluctuating then it must be the stat that is managing the temperature (rightly or wrongly etc)?

Cheers, T i m

p.s. The guy who can supply the stats can also supply the complete new fuser and I'm currently awaiting his reply on that.

Reply to
T i m

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