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.
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
(for week 33 in 1999)
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