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[IMG2=JSON]{“data-align”:”none”,”data-size”:”full”,”height”:”83″,”width”:”800″,”src”:”http://invisibules.org/wp-content/uploads/2022/01/IMG_20220102_121105069-scaled.jpg”}[/IMG2]
Presumably one of those barcodes is the 12nc, and one is the serial?
Anyway, it doesn’t matter now, because even with the thermal cut-out bypassed the bad behaviour remains — so it’s not that. (You’ll be happy to know that the ginger biscuits turned out very well, even though I had to shake them several times to keep the oven on 🙂 When it’s cool I will open it up again and do some more searching.[I had another thought about the low temperature. I’ve realised that when the oven runs some air is constantly expelled through the door — so I think this would explain the low temperature? (And, not to mention sending my electricity bill soaring… and why it’s so hard to keep steam inside for baking.) I could replace the seal.]
Thanks again.
Thanks Dave. I’ve temporarily by-passed the temp limiter and will (carefully!) determine if the problem has gone away over the next couple of baking sessions.
The fact that slamming the door ‘wakes it up’ suggests bad connection, bad solder joint, or sticking relay to me.
I don’t think it’s a relay: Slamming the door can also turn it off (and, why would it have gone off in the first place?) But I will check later, thanks for the tip. When I fixed the relay before I just moved an identical but unused relay from elsewhere on the board. The rating is the same. Also, that relay controls only the element, not the lamp.
Bad wiring/soldering is more likely. I started investigating the wires, but whatever it is has to be common to the element and the lamp (and, I think the grill, but I haven’t checked) and nothing else. Which is why I focussed on the thermal limiter. But you are right, there could be other common paths.
The thermal limiter says “Type 261/PB” which seems to indicate the basic shape and function — normally closed and with a reset button?
Then 16/3 250~ which I think is the current/voltage rating? And then T175K which I suspect is the temperature of cut-out in … Farenheit — about 80 celcius?
What is the 12nc number?
cheersI’ve measured the sensor at about 1055ohms @ about 16 degrees room temperature. That seems pretty close to spec? The sensor doesn’t appear to be bent or touching the metal, so I don’t know if this is the cause of the under-heating.
As for the heater element+light going off at random I’m not much further on. When they are off the controller doesn’t seem to care, and all the front panel is alive, just that the temperature falls (as you’d expect.) Slamming the door in the right way usually fixes it, though it can go off again a short time later.
The shared connection between light and element is the neutral wire which passes through what I believe is the thermal cut-out (see image below) on the way back to the power block on the mains supply side. I’m trying to work out if the thermal cut-out is sensitive to vibration, but it doesn’t seem to be when cold at least. Could it be the problem when hot? I’ve temporarily by-passed it and will (carefully!) determine if the problem has gone away over the next couple of baking sessions.
[IMG2=JSON]{“data-align”:”none”,”data-size”:”full”,”height”:”185″,”width”:”200″,”src”:”http://invisibules.org/wp-content/uploads/2022/01/IMG_20220102_1119417071.jpg”}[/IMG2](I found this part online for about £40, which seems expensive given that other makes have them for under a tenner, eg: https://www.ebay.co.uk/itm/142870009152 — would it be reasonable to use one of these instead?)Happy new year!
ok, will do next week — I’ve been banned from interfering with the oven before christmas 🙂
Have a happy christmas yourself!Hi Dave — temperature reads about 25 degrees C low (using a dangling digital meat thermometer, and searching for the hottest spot), so it never gets near the “max” of 250. Though we didn’t measure it before the repair, we know that food takes significantly longer to cook than it did.
Success! We now have a working machine. Thank you so much for your help, Dave.
Summary: the tacho coil had gone open circuit. Thus the machine didn’t know that motor was turning or not, so refused to operate (presumably in case it was jammed.) Also, not knowing if the motor was turning it also refused to open the door for safety. I replaced the motor control unit, and it just works.
Thanks for sending the parts Dave (not arrived yet.)
To replace the magnet is it as simple as undoing this screw, or will that release the motor too?
https://www.dropbox.com/s/nkzqot3gdj…30685.jpg?dl=0
CheersDoh, I’m an idiot! I said:
> but is generating less than a millivolt when I spin the drum by hand
I’ve just realised that I measured it DC, but it must be AC… Too late now, it’s gone back.Ok, the plate is underneath. I did the mirror, torch and camera trick:
https://www.dropbox.com/s/ene8it9i1iknhg4/IMG_20210306_093240283.jpg?dl=0
Type Mrt 37 – 606/2 exactly as you said.
Should I return the alternative tacho, or am I going to need it?I’ve done some more investigation.
The only number I can find on the motor is 6201Z, here on the end of the shaft:
https://www.dropbox.com/s/nkzqot3gdj2flo8/IMG_20210305_161130685.jpg?dl=0
I managed to get the side off (and broke a few plastic clips in the process 🙁 ) but didn’t really find much else.
Here’s all I can see of the motor from the panel side:
https://www.dropbox.com/s/okzf6hh0982aaaz/IMG_20210305_154631241.jpg?dl=0
https://www.dropbox.com/s/us2upiz42xuz6sl/IMG_20210305_154640743.jpg?dl=0
Here’s the broken but correct tacho:
https://www.dropbox.com/s/qu4c6lnnbzo5mb0/IMG_20210305_155244704.jpg?dl=0
https://www.dropbox.com/s/2m8f7w9yp2b8p5x/IMG_20210305_155403328.jpg?dl=0
Here’s the wrong controller (left) and the correct but broken controller (right):
https://www.dropbox.com/s/il9gy281ydt8l5r/IMG_20210305_155503042.jpg?dl=0
The “wrong” tacho looks quite different, the coil apparently isn’t intended to go around the shaft, just sits at the end of it.
The “wrong” tacho is 500 ohms (seems correct), but is generating less than a millivolt when I spin the drum by hand — that’s way too low, I imagine. I don’t know what it ought to be, though.
Any thoughts? Thanks.I did find a manufacturer’s circuit diagram tucked away under the lid — is this standard practice? It shows the connections and component names, but almost no part numbers or component values. If it’s useful to anyone I could scan and post it?
It’ll be quite awkward to get to there (so far I’ve done everything from the front) – will take some time. What did you have in mind when I’ve found it?
Hi Dave — bad news.I got a replacement board from Ebay but it still doesn’t work.
The tacho coil on that board is about 500 ohms, great, however the board is a slightly different design to mine, and the coil is a different shape too (I don’t think it would fit in the old board, but I didn’t try.) The new board fits properly around the motor, but: there’s a 10 way connector. The 8 way which supplies juice fits nicely, but the 2 way next to it which connects to the tacho is not quite the same (the registration notch is displaced.) I jury rigged it by making up some crimp spade connectors to bridge to the connector. So it should work perfectly, even if I need to make it more robust later. But the machine does exactly the same as before, as if the tacho were open circuit. Motor turns for a few seconds and then the warning lights flash, just as before.
Not sure what to do next, but we’re running out of clean laundry!
Thanks again for all your assistance.Good call! The coil is at least 1 megohm… And maybe intermittent (hard to tell) that seems far too high?
(Funnily enough I fixed a coil on an electric piano last month. I spent hours unwinding and rewinding it.). Is this the kind of component one can buy?
thanksOk, experiments done. Even on wash cycle, as soon as the motor turns on, the errors appear. It makes sense that the problems are in the speed detection.
The magnet you mentioned is indeed on the motor, and looks ok:
https://www.dropbox.com/s/2rmf4l2aaqxu2c1/IMG_20210225_175032610.jpg?dl=0Ready to test with a multimeter – what should I test?
Many thanks
Thanks Dave — that makes a lot of sense.
I put the previous photo here, so there’s a lot more resolution. The outer ring of the tachometer is visible — and looks unbroken.
https://www.dropbox.com/s/fqm87icf39…ushes.jpg?dl=0
(The machine is currently reassembled because I wanted to try some more experiments. After experiments, I’ll take it apart again!)
