Announcement

Collapse
No announcement yet.

Rowenta TP 01 toaster repair

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Rowenta TP 01 toaster repair

    For today’s unusual (and perhaps pointless) repair, I have a toaster: Rowenta model TP 01.
    https://www.badcaps.net/forum/attach...1&d=1538425245
    https://www.badcaps.net/forum/attach...1&d=1538425245
    Normally, small appliances like this are too cheap nowadays to waste time troubleshooting. But whenever I have free time, I never miss an opportunity to analyze failed electronics/appliances, as it’s possible to always learn something in the process.

    In this case, the problem was that the toaster’s heating element was always stuck on – clearly a bad way for an appliance to fail (read: fire hazard!) Other than that, if you inserted bread in it and pushed down on the lever, the toast time/level worked correctly and would eject the bread when it was done.

    I was pretty sure this meant either stuck relay or contactor somewhere. So step one was to take it apart: remove the plastic knob on the toast lever, remove the toast time/level setting knob, and remove three secure Torx screws on the bottom. (Really? You think this can stop me? I didn’t even have a secure Torx driver with me, but a small crappy flat-heat screwdriver always works for everything ) And off came the top… 0.o naughty!!
    https://www.badcaps.net/forum/attach...1&d=1538425245
    https://www.badcaps.net/forum/attach...1&d=1538425245

    There’s not much to this toaster: a small PCB, a mechanical contactor, an open-ended coil/relay to hold down on the toast and the mechanical contactor while the heating element is turned on. Unfortunately, the contactor was disassembled before taking the following picture.
    https://www.badcaps.net/forum/attach...1&d=1538425245

    Here’s the PCB as well:
    https://www.badcaps.net/forum/attach...1&d=1538425245
    https://www.badcaps.net/forum/attach...1&d=1538425245
    Not much to talk about here - just three small BJT transistors, two electrolytic caps (KSC brand), some resistors and diodes, the Stop switch (metal plate on the PCB top), a thermistor (not sure if PTC or NTC), and the potentiometer for the toast time, of course. There is no microcontroller of any sort. Normally for simple circuits like these, I like to reverse-design them and draw the schematic. But I couldn’t get the PCB out easily, so I had to skip this one.

    Failure Analysis
    The mechanical contactor is made of two long copper strips held down on one end (with rivets) and with carbon contacts on the other. The strips basically became weak and had started to break off near where they were riveted to the plastic board (visible in above picture). As such, their retention had become too weak to break the electrical contacts once the toaster was supposed to turn off. And so the heating element would remain turned On all the time.

    My first idea was to just solder a piece of copper wire over the weak spots in the strips. But as I examined the switching mechanism more and more, I realized the copper strips broke because the plastic piece that pushes on them (to close the contacts) was doing it too close to the rivet points. So over time, the excessive bending made the copper strips weak. While this toaster has been in service for many years now, I still think it could have lasted a lot longer if those contact strips were riveted maybe a little bit higher or shaped differently.

    The Fix
    After some thinking, I came up with my own design. Using a piece of copper sheet, I made two “J”-shaped pieces. Then I broke off the original copper strips completely from their riveted counterparts and attached them to the J-shaped pieces (because these old strips had carbon contacts stamped onto them). For better electrical and mechanical connection, I also soldered them together. This is how the finished J-shaped contacts looked:
    https://www.badcaps.net/forum/attach...1&d=1538425245
    https://www.badcaps.net/forum/attach...1&d=1538425245

    I should note here that I didn’t make these different on purpose. The shorter piece was just the first one I made. Then while making the second piece, I realized I didn’t actually have to cut its length (could use the entire width of the copper sheet I had, thus saving me a little work on cutting). In addition to that, a longer piece flexes less per Δlength, so in theory it should last longer.

    Here’s how it ended up all looking:
    https://www.badcaps.net/forum/attach...1&d=1538425403
    https://www.badcaps.net/forum/attach...1&d=1538425403
    https://www.badcaps.net/forum/attach...1&d=1538425403

    To hold everything together onto that mechanical contactor, I used two small bolts.
    https://www.badcaps.net/forum/attach...1&d=1538425403
    After this (not visible in above picture) I coated both the bolt heads and the nuts with glue, to prevent the J-strips from going loose, as I didn’t install lock-washers (didn’t have any of that size).

    And that’s it. I tested the toaster afterwards, and it worked great. The new J-pieces made very good electrical contact and didn’t heat up (important for high-current applications!) They also broke the electrical connection reliably every time. Although there was a bit of electrical arcing/sparking from the carbon contacts when disconnecting, I would say it wasn’t anything abnormal, as quickly disconnecting a high current load always does that to some extent (in this case, due to the quick motion of the spring-loaded ejecting mechanism.) Overall, I think my repair will hold longer than the original part. Of course, only time will tell.
    Attached Files
    Last edited by momaka; 10-01-2018, 02:28 PM.

    #2
    Re: Rowenta TP 01 toaster repair

    a pcb full of shit when all it needed was a bi-metal strip!!

    Comment


      #3
      Re: Rowenta TP 01 toaster repair

      Wow, when I pulled apart a toaster, all I got was that bimetallic strip, no PCB at all (except for a bit of FR4 like material for things that could get hot...)

      Granted slice to slice reproduceability was fairly awful in this toaster along with cycle time... must be the main reason for building a toaster with a PCB - just for cycle time?

      (And how are you using 220V devices in the USA? Must have a beefy step up transformer?)
      Last edited by eccerr0r; 10-01-2018, 05:53 PM.

      Comment


        #4
        Re: Rowenta TP 01 toaster repair

        fixed a toaster in Indonesia more than 10 years ago . i needed my toast in the morning .. removed the cockroaches and twisted the broken elements back together . tested it and fine .. manager of the place complained the chef was getting electric shocks of it ... i never got my morning toast .. i did say do not touch the ,metal bits . bloody things not worth messing with .. just use gas

        Comment


          #5
          Re: Rowenta TP 01 toaster repair

          Now how did you test it with that europlug?
          Things I've fixed: anything from semis to crappy Chinese $2 radios, and now an IoT Dildo....

          "Dude, this is Wyoming, i hopped on and sent 'er. No fucking around." -- Me

          Excuse me while i do something dangerous


          You must have a sad, sad boring life if you hate on people harmlessly enjoying life with an animal costume.

          Sometimes you need to break shit to fix it.... Thats why my lawnmower doesn't have a deadman switch or engine brake anymore

          Follow the white rabbit.

          Comment


            #6
            Re: Rowenta TP 01 toaster repair

            You need the Talkie Toaster from Red Dwarf. https://www.youtube.com/watch?v=lhnN4eUiei4

            Comment


              #7
              Re: Rowenta TP 01 toaster repair

              We can send spacecraft out past Pluto, study sub-atomic particles, peer at anything inside the human body with MRI - yet I've never come across a device that will automatically and repeatably toast bread.

              Timer based toasters give different results depending on whether operated from cold or loaded with the fourth batch. Bimetallic sensing compensates up to a point but over-compensation is a problem when attempting to get a light toast in my experience.

              Having noticed how my smoke detector knows exactly how "brown" my toast is, one project I've been contemplating is to duct air to a hacked detector and sense the actual carbon content tripping the toaster at the required point.

              Comment


                #8
                Re: Rowenta TP 01 toaster repair

                Originally posted by eccerr0r View Post
                (And how are you using 220V devices in the USA? Must have a beefy step up transformer?)
                Nah, I wish.
                This was over at Europe while visiting extended family.
                So if you see me repair something with a Schuko plug, it was probably done over there.

                Originally posted by stj View Post
                a pcb full of shit when all it needed was a bi-metal strip!!
                Originally posted by eccerr0r View Post
                Wow, when I pulled apart a toaster, all I got was that bimetallic strip, no PCB at all (except for a bit of FR4 like material for things that could get hot...)

                Granted slice to slice reproduceability was fairly awful in this toaster along with cycle time... must be the main reason for building a toaster with a PCB - just for cycle time?
                Bi-metallic strip is good for keeping or reaching a set temperature, not timed applications. Moreover, the toaster heating element is not tightly enclosed, so keeping a set temperature is going to be hard (especially with varying room temperatures).

                I think AdriamM put it pretty well:
                Originally posted by AdrianM View Post
                Timer based toasters give different results depending on whether operated from cold or loaded with the fourth batch. Bimetallic sensing compensates up to a point but over-compensation is a problem when attempting to get a light toast in my experience.
                Indeed, toast is more time-dependent than temperature dependent (though variations can certainly appear if for example taking bread from the fridge vs. bread at room temperature and also the slice thickness). And most of the toasting appears to be done by the IR radiation of the element rather than the hot temperature surround the element that gets conducted to the bread.

                I was actually repairing a mini toaster oven about 10 years ago and was wondering the same thing: why did it have two different controls, one with a PCB and another with a bi-metal strip? Took me some time to figure that the bi-metal strip was just for baking/broiling something at a set temperature (but no automatic turn off), whereas the PCB was for the "Toast" function, which basically ran the same set of heating elements as the bake function, but only it was timed and not temperature dependent. I couldn't figure it at the time, so I just disabled the PCB and left the mini toaster oven work only as a... well, mini oven.

                But on that one, the PCB was much more complicated with some kind of a chip. At the time, I didn't really have enough electronics knowledge to figure it out, nor the tools to fix the PCB. The PCB was actually damaged due to poor soldering - relay output solder point was no soldered well, so it melted a hole through the PCB (that's what 10 Amps does with a loose solder joint ).

                Originally posted by R_J View Post
                You need the Talkie Toaster from Red Dwarf. https://www.youtube.com/watch?v=lhnN4eUiei4
                Ha!

                Or the 10-second toaster from PhotonicInduction
                https://www.youtube.com/watch?v=UUPSGvWr6xE
                Last edited by momaka; 10-03-2018, 06:00 AM.

                Comment


                  #9
                  Re: Rowenta TP 01 toaster repair

                  Hey, is there anyone here by any chance who can help me with identifying the potentiometer in there? I'm a complete ignoramus in electronics sadly, so the marking '2KA' on it kind of tells me nothing, but I do need to fix this somehow very much. Thanks in advance for your help.

                  Comment


                    #10
                    Re: Rowenta TP 01 toaster repair

                    2k is the resistance of the track, and it will be Linear.
                    the other stuff you need to match is just physical dimensions so it will fit.
                    but electrically your describing a 2k Linear pot.

                    Comment


                      #11
                      Re: Rowenta TP 01 toaster repair

                      "3399" looks like the American date format, LOL wut? (for week 33 in 1999)

                      International date format would be "9933", IIRC.
                      Last edited by RJARRRPCGP; 07-03-2019, 02:28 AM.
                      ASRock B550 PG Velocita

                      Ryzen 9 "Vermeer" 5900X

                      16 GB AData XPG Spectrix D41

                      Sapphire Nitro+ Radeon RX 6750 XT

                      eVGA Supernova G3 750W

                      Western Digital Black SN850 1TB NVMe SSD

                      Alienware AW3423DWF OLED




                      "¡Me encanta "Me Encanta o Enlistarlo con Hilary Farr!" -Mí mismo

                      "There's nothing more unattractive than a chick smoking a cigarette" -Topcat

                      "Today's lesson in pissivity comes in the form of a ziplock baggie full of GPU extension brackets & hardware that for the last ~3 years have been on my bench, always in my way, getting moved around constantly....and yesterday I found myself in need of them....and the bastards are now nowhere to be found! Motherfracker!!" -Topcat

                      "did I see a chair fly? I think I did! Time for popcorn!" -ratdude747

                      Comment

                      Working...
                      X