Bosch tumble dryer: delay after switching on

[bill.shitner]

It's a condenser model, about 10 years old. The fault is that when the rotating switch is turned from the off position to any of the programs ("very dry", "cupboard dry" etc.), which normally causes an LED to light up and the machine to be ready for action (pressing the "start" button should set things in motion), there is a significant delay.

If the machine has been recently in operation, then there is no delay in lighting the LED when a program is selected. However, if the machine has been turned off for a few hours or more, then the delay is around 45-60 seconds. To be clear, it isn't an LED fault; the machine will not begin operating until the LED lights up and there is an audible click (a relay, I assume) when it does.

My first thoughts are a knackered built-in battery or a dead capacitor. Does that sound about right? If the machine still works (with a delay) in its current state, then I'm not sure what function the battery/capacitor is supposed to have. Maybe power for a memory function in the event of a mains disruption, to allow the machine to pick up where it left off?

Advice welcome.

Thanks.

Ant.

[John Kenyon]

A few years back, my parents had an issue with a washing machine where it would fail to power on every time when turned off (i.e. not left in "end of program" standby) Randomly turn the power off then on again a few times, and you could persuade the thing to power up correctly until the next time it got turned off again.

Extracting and opening the control module revealed a bulging electrolytic capacitor. Replacing the capacitor fixed the issue. Note that this was a "normal" capacitor, not a "supercap" used to hold settings etc.

I would do a physical inspection of any control board looking for bulged caps. (a google image search for "bulging capacitors" will show you what you are looking for).

[Brian Gaff]

Door delay sensor faulty and affected by temperature? IE I can't do anything just yet I think my door is still open, but its not of course. Brian

[newshound]

My non-condensing machine switches off when it decides it is dry, but often re-starts a few times before it finally stops.

So this could perhaps be a sensor holding it "off" until it is happy that it is damp enough to be required to be running. Given that all tumble driers collect fluff to some extent (even if not around the heating elements, like Whirlpools) I think I might also be looking for fluff in the air passageways, particularly around sensors.

[bill.shitner]

Thanks for the replies.

It's not a wet sensor or door sensor. There is no electronic door lock to prevent opening and the wet sensor merely stops the machine when clothes are dry, but the machine continues to light the "on" red LED.

Regards.

Ant.

[Lee]

then as the other post suggests could well be capacitor failure. Another possibility is the startup resistor going high in value, if the design uses one.

*The SMPSU failed on our Bosch TD (due to capacitor failure) but becuase it was still under an extended warranty they changed the entire panel, with the LCD display and everything.

[Lee]

Hmm, managed to screw up the formatting...

Our Bosch TD has a SMPSU, it suffered capacitor failure and the whole panel was replaced. If yours is similar then suggest SMPSU trouble shooting steps...