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Classic culprits in this department has got to be the WM and WMA series. Dodgy interlock caused by constant door slamming, arcing and sparking within the heater coil and contacts, next thing…..BANG!…it takes out the PCB with it!
So, my question (to those electronic whiz kids that may know the answer? i.e Tony EMW etc) is, why do they take out the board and the connector block terminals with it? Why do they not have in-line fuses so that when an interlock does short out within it doesn’t interfere with other components? Why do these modern flimsy interlocks blow anyway, they never used to? Historically interlocks just simply failed to work, went dead, just sat there!
Modern Zanussi interlocks (as far as I know?) don’t cause this type of circuit blowing phenomenon, they just don’t work! Bosch interlocks are also in the same category, never a problem overall. 😕
Rule of thumb to anyone with an ounce of sense and understanding here in the trade must surely know to always replace an Interlock if they spot blackened and charred PCB’s?
Why do these Interlocks give so much grief? What can be done to prevent it from happening? Has anyone in R & D not given this some thought I wonder?
Re: Interlocks blow PCB’s – why?
The old bimetallics just used to seize up and stop. The PTC devices tend to go out with a bang………
Chris.
Re: Interlocks blow PCB’s – why?
Modern Zanussi interlocks (as far as I know?) don’t cause this type of circuit blowing phenomenon, they just don’t work! /quote]
Zanussi machines that have an interlock with the built in opening solenoid have a tendency to short and blow tracks out on the PCB so not exclusive to hotpoint!
Re: Interlocks blow PCB’s – why?
On the hotpoint wm machines it usually just the neutral connection to door lock blows ive repaird a few pcb on this with solder
Re: Interlocks blow PCB’s – why?
Hotpoint interlocks (WM and WMA series) have a tiny heater inside them to heat up the bi-metallic strip that effectively bends across and starts up the machine. More importantly, the strip slowly cools at the end of the wash, giving the delay before a door will open. Problem is, these heaters need a live and neutral supply to work and eventually the heating element melts or simply burns out and live meets neutral inside the interlock. This then blows tracks on the timer where the interlock is fed. I guess manufacturers could fit fuses but it’s hardly in their interest to do so. After all, another 50p spent on something like that cannot be justified in their eyes these days. Another problem is that sometimes the ‘blow’ takes out or scrambles part of the program on the microcontroller that times the whole sequence. Blowing interlocks have kept many engineers busy in the last 10 years or so and perhaps we should he glad we’ve got them ! Other makes keep us busy with shorting pumps (Zanussi & Hoover), mains-carrying tracks 2mm apart that ‘jump’ the gap (Indesit, Ariston, late Hotpoint) and cheap short-life components (Servis).
Re: Interlocks blow PCB’s – why?
bobokines wrote:Same question with dispenser solenoids!
Bob
As i found to my cost recently on Bosch dishwasher after replacing PCB.
BANGS. 😥
Re: Interlocks blow PCB’s – why?
Tony_EMW wrote:Problem is, these heaters need a live and neutral supply to work and eventually the heating element melts or simply burns out and live meets neutral inside the interlock. This then blows tracks on the timer where the interlock is fed.
Indeed so, and we all profit from their frailty and for that we must all give thanks. :worthy:
But it does surprise me that door interlocks over the years have not changed, they still rely on the 240v heater coil and two lumps of dissimilar metal to lock the door???? 🙄
Technology has advanced to such great heights and washing machines programme cycles, sensing circuitry and infinate variant programme options all packed into a tiny controlling module. Yet the module goes BANG simply because it relys on a 30 year old designed door locking device to make it work…..? 😯
There must be an easier way and an opportunity for some egghead to invent a modern solution and reap the patent rights in so doing I suppose? Meanwhile it surely is not beyond the realms of possiblity for manufacturers to insert an inline fuse based on similar lines used in so many DC circuits by protecting against cross polarisation?
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