the kitchen stove

Well, I may have fixed it. 'F5' is indeed the code for a bad electronic module, and there is indeed no replacement. And so, inspired by other posts here, I went a-hunting. There was a complementary pair of transistors on the board, 2n2222 and 2n3906, but an in-circuit ohmmeter test showed that those were probably okay. There was a gigantic microprocessor-sized chip beneath the fluorescent clock readout, an EEPROM, what looked like a processor peripheral made by Robertshaw, a Darlington amplifier array, and a discrete Darlington transistor pair.

Turning a necessity into virtue, I noted that since the module functioned properly, even turning on certain functions, for a couple of seconds. Then a self-check would fail, and shut the thing down. This made me think that the EEPROM was okay, and that the two processor-like chips probably were too. And if they weren't, I couldn't have replaced them anyway.

This left the Darlington arrays, which probably handled signals to and from the module. There's an oven temperature input, and probably something that tells us if the gas is lit in the broiler, and in the oven. And there'd be a switch input to tell if the door is open. That's four inputs. The outputs are to the broiler gas valve, the oven gas valve, the two ignitors for those units, and the motorized door latch that secures the door during the cleaning cycle. That's five outputs. Possibly something is multiplexed, or else I've added non-existent inputs or outputs, because there are only eight Darlington arrays, but okay.

Anyway, it seemed possible that these were ill, because a bad input would cause illogical test results. A bad output could screw things up too if the test procedure energized something and then measured its effects on the system, which is what they do in cars.

And so I've replaced the two Darlington devices. One cross-references to an NTE48, and the other to the NTE2013. They are the only devices that look like those on the board; replacement was a straightforward soldering job.

The stove seems to work fine now.

M Kinsler

I love it when a plan comes together. These are the kind of tales I love to read in here....

jak

This would not be an issue with our circa-1950 GE stove. :)

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I know, and while I was working on that module I was plotting means to de-electronicize the stove. Put in push-buttons to run the oven and broiler igniter coils. Switches to run the broiler gas valve. Maybe a switch to energize the oven-door latch and provide an override so the self-cleaning would work. And finally an old-fashioned oven thermostat to regulate the oven temperature. All told, it probably wouldn't have been all that hard once I got the wiring figured out.

Then I was going to take a picture of the whole affair, write a letter telling the story of why I had to do this, and send it to Amana's legal department to see if they'd faint.

As it is, I wrote a very short summary of the problem and my solution and sent it off to several of the commercial appliance repair part firms, e.g. repairclinic.com. They'll be puzzled, but if someone with any wits sees it they may realize that this is a viable alternative to simply scrapping one of these stoves.

For the last twenty years or so there's been little money to be made in the consumer electronics business, but it occurs to me that someone--and you'd have to be fairly sharp at building customized test equipment--might be able to make a living by re-building discontinued control modules such as this one.

M Kinsler

I think it would have been a lot easier to build a control board with a PIC or AVR microcontroller. Much of the original hardware could be salvaged assuming it was still good. I can't imagine the control is very complex from a software standpoint.