Toaster PCB Repair

[nmercier]

I have an expensive toaster that will not stay down and after testing found the voltage to the electromagnet does not change.
This has led me to believe the pcb component(s) are faulty.

I have done a fair bit of electronics work but this is my first-time attempting PCB repair. My first and foremost question is if I replaced all the components would it be guaranteed to work or is there more to it than that? Second most, I am not sure which are the power pins to the electromagnet, so I just recorded all measurements and found that both DC and AC voltages are read from my multimeter. How/why?

Here is the data I have collected thus far. The following are the voltages for the electromagnet initially and after 5 minutes on the lowest toast setting. I would anticipate the electromagnet to be 12vdc so I am unsure if I am recording what should be the off voltage or on voltage.

Pins 1 and 2: 31.4v AC/0.271v DC -> 31.4v AC/0.276v DC

Pins 2 and 3: 1.92v AC/8.71v DC -> 1.90v AC/8.78v DC

Pins 1 and 3: 29.9v AC/8.80v DC -> 29.9v AC/8.97v DC

The zener diode in the top left of the first image (ZD1) has a 0.512v forward bias and 0.729v reverse bias with my multimeter. Furthermore, the resistor R5 (top right of first image) is reading 0.5 ohms which should be in the megaohms if I read it correctly. This is a 4 slot toaster which has one of these circuits for each two slots. The issue occurs for both with the same faults found. I have not tested the capacitors as I do not have a capacitance test on my multimeter. Likewise, I do not know how to test or read the thermistor; it has 404 written on it and is reading 0.384 megaohms at room temperature.

 

[D.A.(Tony)Stewart]

The solenoid should latch the down position only with AC power on . If the solenoid never gets current, trace why not.

The thermistor 404 could be 400k @ 25 'C and senses when to release the solenoid at some temperature or timer preset.

 

[barry]

1) Without knowing what those pins connect to, those measurements are useless
2) "The zener diode in the top left of the first image (ZD1) has a 0.512v forward bias and 0.729v reverse bias with my multimeter." What does that mean? How are you applying a bias with a meter?
3) We really don't have enough information. I assume your toaster uses and electromagnet to hold the bread down (as opposed to a bi-metallic strip and latching mechanism). There needs to be a switch that tells your circuit to engage the magnet. Is that switch ok? Is the magnet ok?

 

[D.A.(Tony)Stewart]

The Solenoid is shown in your photo but not connected.

 

[betwixt]

toasters like these can work in two ways: either by actually measuring temperature and comparing it to a predetermined trip point or by using a timer that is partially set by a control (how toasted you want the bread) and partially by a sensor.

If you tell us what the markings on the IC are it will help us determine which type it is.

Brian.

 

[Gaber Mohamed Boraey]

Hello
Please tell or send photo of the model, so we may find service manual or something help us understand the circuit

Or for now test with out any voltages , the zener, resistor and transistor, and if any shirt circuit in this IC?, test this little pcb components

If everything ok, then it’s not the pcb

 

[D.A.(Tony)Stewart]

There must be DC current flowing thru the coil to latch down, somehow a transistor switch must close that loop and a flyback diode must catch the current when released. That will be the switching point.

Yet I do not see any connections between the Black, White wires from the solenoid and the RWB wires on the control board.