KENWOOD TCX750 Toaster solenoid not powering

[assaf.aman]

Hi
I have verified that when the lever is down, both metal contacts close.
then when the contacts are closed, I checked for voltage on the solenoid and found out that both the solenoid contacts close 220VAC with the input phase.
I then checked the diode between them (D8 marked in the attached) and realized that it's short.
I guess this is the reason for the malfunction...

1. anybody knows the value of the diode I need for replacement?
2. any chance someone can share the board schematic? I searched everywhere, couldn't find it

Thanks

 

[Nigel Goodwin]

The diode is across the solenoid (to prevent the transistor been killed by back EMF), so you can't test it in circuit, as you're reading through the solenoid. It's almost certainly NOT faulty, those diodes never fail.

I wouldn't expect any schematics to be available?.

 

[assaf.aman]

Thanks. so what could be the reason that the solenoid is not powered? could it be that if one of the heating wires is broken, it would prevent the solenoid from powering?

 

[Nigel Goodwin]

Thanks. so what could be the reason that the solenoid is not powered? could it be that if one of the heating wires is broken, it would prevent the solenoid from powering?

Possibly, I'm presuming the solenoid is low voltage, and it's got to be dropped down from the mains in some way? - using the element(s) as a dropper would be a simple way. I repaired toaster a VERY, VERY long time ago, before they had any electronics inside - but they stopped been a viable repair decades ago.

 

[assaf.aman]

thanks

 

[Les Jones]

I agree with Nigel. I imagine there will be a timer circuit that drives the solenoid via a transistor or mosfet. You will have to trace out the schematic. The board looks fairly simple so it should not take too long.

Les.

 

[assaf.aman]

Hi guys,
thanks for the help so far. so I fixed the break in the heating wire and now the heating elements are heating, there is power to the timer circuit (led is ON) but still, the solenoid is OPEN.
So I moved forward to work on the timer circuit + potentiometer board.
potentiometer looks good. checked resistance between contacts as I turn the knobs...
moved on to the timer PCB..
first of all, I understand its some kind of generic PCB but following the coding on the back couldn't find anything
.went over all the resistors...all give good readings accept one which looks suspicious...R25 should give 220ohm but it looks like a short (I could assume my meter is bad but given that all other resistors gave values around to expected...)
as for the transistor or MOSFET, tried to read P/N but couldn't find any trace online...looks like RT2002H...or RT2602H....
I guess I could just try to replace R25 and see what happens...
but just in case someone has better knowledge of the chip pinout so I can test if its OK or FALSE
Thanks

 

[Nigel Goodwin]

R25 should give 220ohm but it looks like a short (I could assume my meter is bad but given that all other resistors gave values around to expected...)

As before with the diode, you can't just check components in circuit - the resistor is pretty well 100% NOT faulty - it's incredibly rare for resistors to go low in value. It reads 'short' because there's something else across it that your meter is reading through.

What is the actual fault with the toaster?, does it not stay down?.

 

[assaf.aman]

"does it not stay down? " YES! and I verified that the solenoid is not activated
I should mention that what started the fail is my son inserting a frozen Pitta bread....which upon setting the lever down, immediately shortcut the heating element (which I fixed)....

 

[Les Jones]

When Nigel mentioned the idea that the solenoid was powered by being in series with the elements (Via bridge rectifier) I assumed that the electronics were powered with the voltage developed across the solenoid. (I am also assuming that any indicator lights are only on when the lever would normally be held down by the solenoid. Is this assumption correct ?) I also thought that the timing was terminated by removing the drive to the gate of a triac that was in series with the elements (And solenoid circuit.). As the solenoid is not activated I don't understand what is holding down the voltage to the electronics to a sensible level. I have not seen any high power resistors that could do this in the pictures. Can you trace out the mains wiring path so we can work out how the solenoid is powered. As Nigel has pointed out you don't fault find by just randomly testing components. You trace backwards from the point where the fault is seen.
For that you first have to work out how it is designed to work.
Les.

 

[assaf.aman]

Hi

That's exactly what I was doing...started by acquiting the two metal contacts. I then moved on to the power relay. then I went over to the solenoid which led me to the timer circuit.

current update is that after testing again with the timer circuit connected to the main board, suddenly the solenoid started working and reacting to swiveling the timer knob.....so bottom line is the only fault was the break in the heating element....really dont know why it didnt work at the first time after I fixed the element.

thank you very much for your help

 

[Nigel Goodwin]

As I mentioned earlier, decades ago I repaired toasters - and pretty well all faults were element failures

Did find a dead mouse in the bottom of one toaster though

 

[Mickster]

Did find a dead mouse in the bottom of one toaster though

Well done?

 

[assaf.aman]

 

[Nigel Goodwin]

It wasn't my 'best' mouse - we took a washing machine to a 'place' in Hathersage, which was where parts of Jane Eyre were supposedly written, and is featured in the book, it's called North Lees Hall.

It's now a holiday rental - you don't want to know what it costs to stay there!.

Hathersage - Wikipedia

en.wikipedia.org

Anyway, we turned up with the washing machine, as arranged when no guests were there, and met the cleaners and manager - the cleaners were two lovely young ladies, and mentioned that there 'might' be a dead mouse behind the washing machine, and they were both terrified of mice, and could we remove it for them. Because of it's rural setting they tend to get field mice coming in, so put poison down for them.

Needless to say, we disposed of the corpse for them, they made us a lovely coffee, and we asked if we could have a look round the historic building, as we were their new 'best friends', they were happy to let us roam round - and it's a really interesting place. If you're REALLY, REALLY rich?, it could be worth a stay there.

 

[assaf.aman]

well that's life for you...you start with a broken toaster...and end with a dead mouse

 

[KeepItSimpleStupid]

friends had a consumer electronics store and found a sandwhich in the VCR and, of course, roaches in various electronics. I repaired amps for them and one piece was loaded with cat hair. The cat layed where it was warm.