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the kitchen stove

Discussion in 'Electronic Repair' started by m kinsler, Jun 14, 2007.

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  1. m kinsler

    m kinsler Guest

    Well, hi once again. It's been about eight years since my last post
    to this group. The old mail browser I'd been using got overloaded,
    and I got wound up with real life, sort of. But it was only
    temporary, and now I have a problem of my own.

    We took a lightning hit to somewhere along our power line tonight. I
    have a whole-house lightning protector, but there was a nice crackle
    from the power supply of the computer I was working on. That wasn't
    the problem, though. In the kitchen, the stove--Amana model AGS761W,
    a gas stove probably made in 1994, was beeping, showing 'F5' on its
    display. Unplugged it, tried all sorts of resetting techniques,
    nothing: it runs for thirty seconds and then beeps and displays F5.

    The part in question is called an ERC, electronic range control, part
    number probably is 343461 but at this point I'm not sure, and all the
    parts houses tell me that it's no longer being made and unavailable.
    I have inquiries into Amana and repairclinic.com. eBay doesn't seem
    to have that control, though there are a couple of electronic control
    modules for other stoves, so I know I was doing a thorough search.

    My guess is that 'F5' means 'bad module' or something helpful like
    that. Without the oven, I have an exceptionally unhappy Natalie, and
    she'd like me to get it figured out already. I cannot fathom being
    able to come up with a workaround for this unit: it incorporates the
    oven thermostat, the oven timer, and the self-cleaning oven stuff.

    My strategy is to start at the power supply, which would have taken
    the initial hit from a power-line overvoltage, and then test each
    component in turn. Trouble is, the power supply is fine, because the
    various clock functions work, right up until the unit fails some sort
    of a self-test procedure about twenty seconds after you plug it in.
    Then we see 'F5.'

    If anyone has any experience in this sort of thing, please let me
    know.

    Mark Kinsler http://www.mkinsler.com, if it still works.
     
  2. m kinsler

    m kinsler Guest

    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
     
  3. jakdedert

    jakdedert Guest

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

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

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
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  5. m kinsler

    m kinsler Guest

    And so I've replaced the two Darlington devices. One cross-references
    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
     
  6. James Sweet

    James Sweet Guest

    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.
     
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