Maytag dishwater control board... thermistor part number ?

Correcting typo in post title. I should drink my morning coffee before posting!

Cheers,

- Sylvain

years,

Why not try a resistor?

Arghhh, hope you're kidding Homer :)

Take care.

Ken

Not at all. Ask yourself what the thermistor does.

Hi Homer.

Ok, guess I'm old enough to be excused for talking to myself :) :)

Old enough that my memory isn't as sharp as it used to be. And my memory isn't as sharp as it used to be. :)

So, a thermistor when cold (ambient) is virtually a low value resistor. But as it conducts it very quickly heats up, and in doing so becomes a very high value resistor.

The failure of a plain old resistor not increasing dramatically in value could annoy what's on the other side of it.

Am I still right? (my memory isn't as sharp as it used to be :)

Take care.

Ken

I know what it does. It is a resistor that changes value, relative to the ambient heat. No manufacturer would use a thermistor where a much cheaper resistor would work.

Yes, but why? Is it for a slow start? Ambient compensation? Feedback compensation?

As a test, use a resistor. Figure out the value needed. That'll be a guide to the thermistor to use. At this point, is it a PTC or NTC?

Go ahead and try the resistor. Don't be surprised if you do a lot more damage to the machine. Personally, I would try to get my hands on a couple junk boards from a repairman or another source, and hope that its not the only part that fails. You have no idea what it does, or what damage you can cause. I watched a tech spend three weeks trying a resistor in a clothes dryer that was supposed to sense how dry the clothes were, before he gave up and bought a board. If I needed one, I would offer the local recycling place a few bucks to keep an eye out for the same type of dishwasher, and have them call me when it showed up, for another $10 bucks to the guy that found it. they strip the circuit boards out of appliances when they separate the metals, and sell them by the pound to places that legally burn the boards to recover the silver, gold, copper and solder. If I wasn't 100% disabled, I'd visit them a couple times a week and offer a little more per pound for boards in good shape. I sometimes find usable parts on old appliances at the local transfer station where I dump the used steel from computers, rather than drive 25 miles to the main recycling center. Things like 24 VAC transformers on old furnaces and central air units, small contactors and thermal safety switches.

All good suggestions. But sometimes you just have to cut and try.

Not on my toys. ;-)

Perhaps you missed this from the OP: -

"Incidentally, I have been fixing electronics professionally for many years, I do not need to be warned about safety, etc."

I took that as a statement of expertise.

Thanks to all for the input. Turns-out that this device is actually a surge protector !

I was able to find the wiring diagram of the dishwasher, and while there is no diagram for the control board itself, I was able to figure-out that the device is basically connected across the 120VAC power line mains once the door switches are closed.

Thus, the melted VR300 'thermistor' is actually a surge protector. Thankfully I had not tried the thermistor replacement trick yet.

I did further tests on that board, and discovered that a few diodes including at least one zener are either short or opened... Plus a 2N3904 transistor is short too. I guess the surge protector did not quite protect the rest of the circuit. I wonder if this occured during a storm (I was not at home when the dishwasher became defective).

Given that there are too many bad parts on the board, plus there may be more chips zapped too, and given my limited spare time (and my wife threatening to call a serviceman!), I will have to bite the bullet and buy the replacement board :( Darn, I thought it was going to be a simple single bad part...

Thanks again for all the input and interesting discussions,

Regards,

- Sylvain

Can you get a rebuilt to save some bucks?

Go to Repairclinic.com you will get all you want to know and by rhe part from them GREAT SITE

I take what I see in front of me as evidence. I have had hundreds of people assure me that they were VERY good electronics techs, yet they couldn't do anything right. Call me cynical, but after you've seen some really stupid stunts, you want to be damn sure of what is going on.

In this case, the bad part was across the AC line. What good would your random choice of a fixed resistor have done, other than cause more damage, or even start a fire?

A 1 meg resistor?

How many 1 meg thermistors have you seen?

It wasn't a thermistor.

You thought it was when you told him to replace it with a fixed resistor.