Bosch WTN83200GB tumble dryer (condenser, non-heatpump type): E90 code instantly - Page 1
Forum section: electronics / repair

author: tom66
author_rank: Super Contributor
timestamp: October 29, 2023, 09:48:06 am
content: So I have this Bosch tumble dryer, purchased second hand as we gave our older dryer to a family friend (a basic Indesit unit that was 10 years old and still working.) It is about four years old.After a few months now (no warranty) when starting a program the relays in the back of the machine click and few times on and off then I get E:90 on the display. No rotation, no heat, nothing. Bosch "helpfully" say this means a fault with the electronics, but they don't seem to have any public information about what type of fault this actually is. And there is no service manual I can find.I found a few videos about similar dryers with cold solder joints on the power control board, in particular around the relays, but upon removing it found no bad joints.However the relay clicking made me think, what if it indicates a bad contact in a relay. The machine isn't even turning the drum on, but it knows the door is closed. So, of the possible faults, I think it can only be a motor fault (bad start capacitor or bad motor) or a problem with the relays driving it. Since I have the board out I manage to get the relays to close using my power supply (being careful to not bias the power supply incorrectly - I traced the relay signals to the ULN2003 controlling them so I know which is the open collector and which is the supply rail.) Most relays tested fine at 0 ohms when closed but one - for the drum motor - tested as 8 ohms. When I cycled it a few more times, it tests at several kilohms. I think I found the problem.I took the relay off and tore it down out of curiosity and the contacts are very badly pitted. It is of no surprise the relay is no longer working.It seems Bosch cheaped out on this machine and used Hongfa relays with inferior contact plating. And annoyingly they used 9V DC relays which almost no one stocks. I even have some 5V and 12V relays and considered modifying the board to use a 5V relay with a series resistor but in the end just ordered some 9V relays from Rapid Electronics, Finder brand with more rugged contact plating than Bosch specified.Tangential rant: Right to Repair MUST include access to the service documents and tools professionals have access to, even if that means that consumers have to sign a disclaimer about their level of competence. It's unacceptable that Bosch dryers can have an error code and not document that error code anywhere for troubleshooting purposes, and the only option is to pay £100 callout fee plus the parts cost to fix the machine (!) (The dryer itself only cost me £100 second hand!!)(Pic shows PCB with relay already removed)

author: tooki
author_rank: Super Contributor
timestamp: October 29, 2023, 12:50:31 pm
content: Quote from: tom66 on October 29, 2023, 09:48:06 amThe issue is that the professionals don’t get much more info than this, either: they’ll see a code like that E90, and the service manual will say “replace the board”. If component-level troubleshooting and repair information exists at all, it’s strictly internal.I have wondered how it is for things like Apple motherboards, at least some of which are in fact reworked to become future service parts. (At least that’s how it was when I worked at the fruit stand 15 years ago; I can’t vouch for today.) I don’t know whether that rework was done at Apple’s original manufacturing partners, or if it was done by a third party. The OEMs clearly have to have at leastsomedegree of component-level information in order to do the manufacturing, and that likely includes component testing and replacement. Third-party component-level board repair companies would have to receive information from Apple. Schematics seem to leak out reliably, so those must be among the info shared most commonly with partner companies.Anyhow, the issue I see is where we draw the line. Saying “consumers have the right to the same information, documentation, tooling, and software as official service partners” isn’t suuuuuper helpful when those same partners get very little. :/ But at the same time, we certainly can’tforcecompanies to release the full design documents for their products.

author: tom66
author_rank: Super Contributor
timestamp: October 29, 2023, 01:34:00 pm
content: Quote from: tooki on October 29, 2023, 12:50:31 pmYeah, I agree. There is a balance but I think it's too far in favour of the companies right now.I did find some suggestion that I could buy a service manual for this dryer for £39 (from a company that hoards them from the professional side and then illegally resells them) but I was able to find the problem beforehand and without knowing what codes that are there did not convince me it was worth spending money on.I would like to see any appliances that are sold on the market in "significant volumes" could require at least:- A full breakdown of the components and orderable part numbers.- An overall "block diagram" of the system indicating what components controlled what, for instance, connector 7 on PCB 2 drives the drum motor. Schematics are a plus but, at least a major component block diagram for each board.- If the product has fault codes then the service guide should indicate the conditions for those fault codes being set and cleared.- Components for sale should be purchaseable at reasonable rates; a control PCB should not cost £300 for a dryer that cost £500 because it's clear that's ridiculous. Difficult to enforce but perhaps parts could be limited to 125% of the raw cost of production, which can be assessed by periodic audit.In general, it should be the case that appliances, televisions, and so on, are accompanied with enough information to service them just like cars are. Service documentation for cars is generally quite good, but in part that is essential because second hand cars support the leasing market. Car companies don't "care" about second hand cars, but they know if they make unreliable cars no one could afford to lease them and people wouldn't buy them because residuals would be crap.

author: tooki
author_rank: Super Contributor
timestamp: October 30, 2023, 07:52:08 am
content: I agree on a lot of that.The cost is a real sticking point, though: “production cost” isn’t the only thing that matters. The packaging and storage of spare parts adds a ton of cost. A part that forms, say, $5 of the BOM of the whole device might then need $5 of packaging, and if it has to be stored for 10 years, that storage costs money.A big part of the problem is that in many products, there’s only ever one production run. So when they order it, they have to not only calculate how many parts will be needed for the products intended for sale, but also have to predict how many spares they’ll need for warranty fulfillment AND to fulfill future spare parts orders. If they guess too low, then they’ll either have to replace entire units under warranty and run afoul of any laws requiring parts availability. If they guess too high, they’ll end up with a warehouse full of parts that cost money to make, money to store, and won’t ever be sold. “So just make more parts as needed”, one thinks. That might work for some parts, especially things like CNC parts that have very low setup costs. But if the injection molds for some plastic part have worn out, it may not make economic sense to spend $50K on new molds if you only need 1000 pieces. 3D printing may help with this in the future. Electronics is the worst, because the parts used in the board may not be available anymore. In that case, making another production run means engineering a new board that’s compatible with the existing product — a nightmare if it’s something like a digital sensor board where you’d have to then emulate the original part’s communication protocol.What we see in markets where long-term availability is contractually required (like military and aerospace) is that the cost of spares rises dramatically with time, as obsolete production processes have to be kept up just for this one niche application. That and/or huge lifetime purchases made, many of which ultimately end up getting scrapped or surpluses in the end, after being stored at great cost.I really don’t have an answer. Every solution sucks in one way or another.

author: tom66
author_rank: Super Contributor
timestamp: October 31, 2023, 08:16:13 pm
content: I'm happy to report that replacing the relay fixed the machine. I also replaced the identical Hongfa relay next to it. A dissection shows this to have been a good idea; it too had pitted contacts. This smaller relay is, I believe, for the low-temperature heating element. It would only be passing around 5A and it is a resistive load (I'm not sure why they use this instead of just slow-PWM on the high temperature element, but there's surely a good reason.) So I think Bosch just used junk relays on these machines. Shame.I didn't replace the two 16A relays. One is for the high-temperature heating element, around 9A, and the other appears to be some kind of overall interlock (not exactly sure, seems to switch live for all of the relays.) I hope they're OK, I guess we will see. At least the machine is not too hard to take apart to get to the power board and desoldering the relays was surprisingly easy for a 2-layer board.

author: floobydust
author_rank: Super Contributor
timestamp: October 31, 2023, 08:41:05 pm
content: I find appliance relays have a short life due to contact arcing - manufacturers are just too cheap to put in a RC snubber circuit to lessen arcing.For safety (against a stuck on relay causing a meltdown) they will have a master relay and then the individual heat control relays. So two would have to fail stuck on to overheat things.I also note the Bosch mix of cheap with higher quality relays on the board. It's sad they are worried about burning down someone's house but nothing about product longevity.Right to Repair is non-existant with German appliances, they want to maintain the monopoly on their service. As if DIY repairs make their products burn down houses or some other bullshit excuse.Miele, Blomberg, Bosch etc. - you won't find anything for wiring or service or schematics. Then they obsolete the appliance so the board is either unavailable or super expensive and just buy a new dryer, like you're made of money.I worked on appliance design where the safety standard has a 100,000 cycle endurance test to pass. You had to design for long life.