Whirlpool L1373 repair attempt

[Maxwell]

The MMUN2132 was replaced today, as it was clearly shorted.

Putting the PCB back into the machine I am now confronted with another fault code, F06, motor tacho failure... which seems reasonable as the motor is not being powered. I cannot hear the relays engage on the board when trying to power the motor, hence more must be out of whack with the PCB.

I can confirm that the machine now does control most of the components properly, water valves are opening, drain pump is running, door lock engages, etc.

One step closer, I guess?

Next up is doing more testing of the PCB, not sure what to look at next, something is keeping those relays from tripping, need to figure out what. Maybe the other MMUN2132 that switch the motor relays on are shot two? That seems unlikely... I have also not checked the motor triac yet, but I doubt that is the problem here, as it is not even engaging the relays, thus triac isn't even being powered just yet.

Will post back when i know more.

 

[Maxwell]

Tumtidum,

Replaced another shorted MMUN2132 today. The MMUN powering K2 relay coil was also fried, I also replaced the K3 one because it gave off weird reading in circuit, seemed fine once isolated but seeing as it was off anyway i did replace it also.

The motor spins up now, but halas it spins up full blast right away, and does not seem to want to agitate. I'm not sure where to look next. It produces the same fault as before, F6 motor tacho fault. Maybe i'll have a look around where the tacho data comes in and see if anything is out of whack, I'm also not sure how the machine handles motor agitation, i need to do more checking.

 

[debe]

In front loader machines Motor Tacho feed back is critical to the operation of the machine.

 

[Maxwell]

In front loader machines Motor Tacho feed back is critical to the operation of the machine.

Yes, critical to speed control.

However, the machine goes full blast as soon as the motor is energized, the tacho measures this and reports an error to the machine. So i'm thinking the tacho control circuit is doing what it's supposed to do, but the PWM control that feeds the TRIAC is not, and is instead sending a flat voltage to the TRIAC, making it open up full blast right off the bat. I'll do some tests soon as i'm able, so far i've found a suspicious resistor in the TRIAC gate circuit that is supposed to be 1Kohm but is only measuring 80 ohm, which may be a false reading, but i wont know until i remove it and test it out of circuit.

 

[73's de Edd]

Sir Maxwell . . . . . . .

Here it is . . . .motor control . . . .complete from head to tail.
Can we assume that your last mentioned resistor quandry was
being R833 ?
Check when having one lead swung out of circuit.

CIRCUIT SYNOPSIS:


73's de Edd

 

[Maxwell]

Sir Maxwell . . . . . . .

Here it is . . . .motor control . . . .complete from head to tail.
Can we assume that your last mentioned resistor quandry was
being R833 ?
Check when having one lead swung out of circuit.

73's de Edd

Thanks for the schematic!

R033 was indeed the suspected resistor, but it checked out fine when out of circuit so that was a bust, as was the entire TRIAC gate circuit. I check every component between the TRIAC's gate and the main IC and everything was within spec. Unless the actual TRIAC is fault, i guess that leaves just the tacho feedback circuit.

Which i had a jolly good time trying to find, as the board is only marked on one side, and my reading made no sense at all.

I finally tracked it down the area market in the board view.

I'm getting 6.7ohm measurement from tacho pin 1 (J002 pin 1) to ground. I'm also getting open circuit from pin 2 (J002 pin 2) to R043 and R040. According to the schematic i should be getting a short here as one side of those resistors is directly connected to the tacho output.

Strangely i'm also getting a short from pin 2 to the area circled in blue on the image, this hook sup directly to the SOT23 diode (BAV99) that is there.

So yeah, i'm confused. I'll have another look at the schematic when i get more time and see where that BAV99 is supposed to hook up to because right now it seems like the pin configuration on the schematic is different from the PCB. I'll also have a look at the machine itself and try to figure out exactyl where the tacho pins do hook up to.

 

[Maxwell]

Ok so i found out why i couldn't find anything wrong with the tacho sensor circuit, nor the TRIAC control circuit...

Because there IS nothing wrong with it. So essentially after i replaced those relay switching transistors, the fix was complete as far as electronics are concerned. I guess i'll have to check the motor tacho coil next.

I'll continue to update the thread with my findings/fixes for completeness sake, but from now on this will have little to do with electronics

 

[Maxwell]

Ok so i found out why i couldn't find anything wrong with the tacho sensor circuit, nor the TRIAC control circuit...

Because there IS nothing wrong with it. So essentially after i replaced those relay switching transistors, the fix was complete as far as electronics are concerned. I guess i'll have to check the motor tacho coil next.

I'll continue to update the thread with my findings/fixes for completeness sake, but from now on this will have little to do with electronics

Had another look at the machine yesterday and it seems that somehow the magnet had come loose from the motor, I glued it in place with resin and it seems fine now. Dirty fix but apparently there is no way to replace that magnet as the manufacturer does not sell it separately.