Question about GE JVM1490 Convection/Microwave Oven

12 Answers

Unit Does Not Power Up

Out of the blue, the unit will not power up. I've got 120 VAC at the receptacle. I've checked the internal 20A fuse and it's good. The unit was purchased new in 2003 and is S/N SF900722K.

Thanks!

Posted by on

  • 19 more comments 
  • JD5652 Nov 01, 2008

    This is a troubleshooting follow-up to the above post. I have confirmed that the Primary Interlock Switch (top), Interlock Monitor Switch (middle) and Door Sensing Switch (bottom) are all functioning properly. However, the Secondary Interlock Relay (RY2) is not picking up. I jumpered across the relay/relay contacts (W/W to W) to satisfy the interlock, however, the unit still did not power up. I have 120 VAC on the W/W side of Relay RY2. It appears that I have the correct voltage every where except on the PCB side of the circuit.



    Does this mean that the fault lies in the PCB somewhere?



    Thanks!

  • JD5652 Nov 01, 2008

    Thanks Ginko, however I do have power to the control circuit. The power cord is acceptable as well as the fuse and the interlock switches. I am pretty proficient with a multimeter. See the troubleshooting follow-up I posted.

    Thanks!

  • JD5652 Nov 01, 2008

    Ginko-

    If it were simply a bad RY2 relay, then the PCB circuit should have powered up when I jumpered the relay/relay contacts....correct?

    It appears there may be other problems with the PCB.

    My goal at this time is to determine whether the fault lies on the PCB or other area (e.g. HV transformer, HV capacitor, etc.).

    Thanks!

  • JD5652 Nov 01, 2008

    Further troubleshooting notes.... I disconnected and removed the PCB. THe circuit is configured as follows: Primary Interlock Switch (top) closed, Door Sensing Switch (Bottom) closed and Interlock Monitor Switch (Middle) closed. This configuration satifies all requirements for the unit to power up.... mind you not operate, but power up.

    When the unit is plugged in I'm getting some serious transformer hum. I am getting 120 VAC on the primary side of the LVT. Does anyone know what the voltage is suppose to be on the secondary side of the LVT.

    Any troubleshooting recommendations for the HV transformer?

    Thanks in advance!

  • JD5652 Nov 01, 2008

    Solution #1 -

    I will consider your service if I need to have the display repaired.

    Thanks!

  • JD5652 Nov 01, 2008

    Irish Druid-

    Thanks for the detailed troubleshooting steps. Here's what I found:

    - Magnetron resistance across terminals = 0.4 ohms
    - Magnetron resistance to ground is infinite
    - HV rectifier (diode mounted on magnetron?) conducts in both directions therefore lloks like it's bad
    - LV Transformer primary reisistance readings
    BLK-W = 0.6 ohms
    BLK-Rd = 22.3 ohms
    Wht-Rd = 22.6 ohms

    Is this correct?

    - The PCB seems questionable since the RY2 relay will not energize with 120 VAC applied to W/W.

    Any further recommendations?

    Thanks again!

  • JD5652 Nov 01, 2008

    Electech-



    When you say secondary side are you talking about the LV transformer or the HV transformer?



    The HV capacitor is almost impossible to get a set of leads on as it;s buried in the chassis. It "looks" OK...no bulges, leaks, etc.

  • JD5652 Nov 01, 2008

    electech-

    Are you referring to the LV or HV transforder secondary voltage of 40 V?

  • JD5652 Nov 01, 2008

    OK...I was confused on what was the LVT... The LVT is mounted on the PCB (P/N 6170W1G001A)...correct?

    I also have a small transformer mounted in front the high voltage transformer (P/N 6170W1D049A). This small transformer is P/N 6010W2L003D.

    DO I have this right?

  • JD5652 Nov 01, 2008

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12 Answers

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  • Master
  • 535 Answers

Chak the power cable its working or bed if its ok then chak the power supply stage from the ckt bord or chak on off switch if its ok then chak the tansformer if its ok then chk the power tansistor 

Posted on Nov 02, 2008

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  • Contributor
  • 728 Answers

You migght have a short that is causing it to go into auto shutdown which will not let it heat up so that it will not catch fire. It is a safety feature if it detects a short. Get it checked up at a shop to confirm the suspicion and to get it fixed.

Posted on Nov 01, 2008

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  • 449 Answers

Hi!!!

yup replaced it you have spend
to alot when you repair it

Posted on Nov 01, 2008

  • ronald suboc
    ronald suboc Nov 01, 2008

    hi!!!

    try replaced you have to spend
    alot when you repair it??


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  • Expert
  • 94 Answers

Scrap it and buy new for less than 70 dollars lol. whats your hourly rate ?

Posted on Nov 01, 2008

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  • Master
  • 958 Answers

Please test the secondary of the low voltage transformer. you should get at least 14 volts ac there then it would be rectified to produce 12 volts dc to control the digital of the unit.

if there is no voltage across the secondary and there is voltage in the primary, then you have an open winding in the primary of the low voltage transformer.

all you have to do is replace the low voltage transformer.


thanks 4 using fixya,

drcool

Posted on Nov 01, 2008

  • francis rivero Nov 02, 2008

    hi JD5652,

    i've seen that you did not accept my solution but there was no comment if you checked the primary resistance of the low voltage transformer. the one in the pcb.

    please let me know cause base on your input, that is the only problem that could have happen. the primary wire is so thin that it could just snapped from a glitch in the power supply.

    or on the other hand, look closely in the pc borad, you might find circuit lines cracking up and opening the circuit.

    please do address us experts just like what you did to the earlier posters.

    tnx again 4 using fixya,

    drcool




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  • Master
  • 6,966 Answers

Hi,

If I may offer an alternate possibility, it could be that the power supply of the circuit board is the issue. This power supply is separate from the HV PSU and provides the low voltage needed by the logic circuitry of the PCB/controller. Often the voltage required is +5VDC but there are models that uses another +12VDC for powering the relays.

Depending on the design, country of manufacture or intended market, the low B+ power supply could be a simple stepdown transformer with diodes, capacitor and regulator to produce the +5 (and +12). In some models, the low B+ power supply is an SMPS (switch mode power supply) wherein the mains is directly converted to about 200VDC, converted to high frequency downverted to high current +5 (and +12).

Hope this be of initial help/idea. Pls post back how things turned up or should you need additional information.

Good luck and kind regards. Thank you for using FixYa.

Posted on Nov 01, 2008

  • Louie  Role
    Louie Role Nov 08, 2008

    Hi again,

    Any development(s) so far?


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  • Master
  • 624 Answers

If you have the right voltage on the primary of the LVT and nothing on the secondary, it is bad. You can also check it with a multimeter. Make sure power if unplugged and put meter in ohms, if it is open, it is bad. The low voltage transformer should be used for the voltage supply to the control board. If you have no voltage going to the control board, that is your problem, or at least one of your problems. You should have a standby voltage of at least 5 volts going to the control board to power the microprocessor. I think that your problem is in the LVT or the standby circuit coming from the secondary of the LVT.

Posted on Nov 01, 2008

  • Dave DeGain
    Dave DeGain Nov 01, 2008

    If you have more than one smaller transformer, then you will need to determain which one is used for supplying the control board voltage. It would be best to check them both. I do not have the part numbers and schematic for this model, so I can not verify the details you are asking about. From all you have posted, I really think that you have either a bad transformer (not the main power transformer) or the supply circuit that the transformers feed have a bad component. First thing to check is the transformers. If you have an A/C voltage on the primary and no A/C voltage on the secondary, there is a good chance that the transformer is bad. Transformers are nothing more than wire wrapped around a core, the primary is isolated from the secondary, they have different wires. Check each pair (primary and secondary separately), they should measure on an ohm meter like a wire, nearly a short. If the primary or the secondary on either transformer is open they are bad. I have seen some standby transformers (the smaller ones used for turn on voltages) that have a secondary winding that will measure much higher than a short, but will not be like an open, and they are good secondaries. I hope this helps, let me know if you would like more help from me.

    Thanks and good luck,

    Dave

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  • Master
  • 899 Answers

What is the voltage on the secondary side?
have you check for any shorted capacitors?
bulging , leaking?
checked solder connections?
diodes?
resistors?
rectifier IC?
does the secondary output read 40v? or less?
it sounds like the transformer is probably going but let me know the voltage output on it

electech

Posted on Nov 01, 2008

  • 4 more comments 
  • jason Nov 01, 2008

    yes the lv side

  • jason Nov 01, 2008

    sorry I thought they were helping , but I'm back

    what is the volts?

    and is there any display? dim or bright?

    if there is absolutely no power going thru there is got to be a pico fuse or possibly a transistor fuse on the secondary side

    where does the power stop?

  • jason Nov 01, 2008

    this is the best of tests , but ut is to long to post here and working on a microwave is no joke so please be very careful!!!

    here is the link http://repairfaq.ece.drexel.edu/sam/micf...



    electech

  • jason Nov 01, 2008

    that diode is good! but to for sure tell you will need to apply 12v on it but i am sure thats not your problem it has got to be power stopped somewhere

  • jason Nov 01, 2008

    .here

  • jason Nov 01, 2008

    whats the voltages on the LV transformer output?

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  • Master
  • 2,712 Answers

On the GE microwaves using the "smartboard," it is sometimes possible to locate a bad soldering connection on the board that can be repaired, restoring function to the board. Otherwise the entire board must be replaced. It looks like you will have to replace the entire PCB, if you are unable to diagnose a specific fault or component failure, or broken solder. That would be the easier way..
Check these as well:

  • Magnetron is fried. Resistance between the magnetron terminals should be less than 3 ohms. Resistance from the magnetron terminal to ground should be infinite.
  • Fried HV capacitor. Use your ohm meter to test it.
  • Fried control board. If power is going to the board but not going off to the other components, the board is bad and needs to either be replaced or track down the bad connection (GE/Hotpoints).
  • HV Rectifier is shorted or open. Test forward and reverse bias with a megohmmeter. If continuity in both directions, rectifier is shorted, replace. If no continuity in either direction, rectifier is open, replace.
Anyways, here is a simple guide for component testing..hope that helps.

Posted on Nov 01, 2008

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  • 1,011 Answers

Sir,

click this link for more information....

http://www.microwavedisplay.com/

thanks
goodluck

Posted on Nov 01, 2008

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  • GE Master
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Try first a different power outlet.

If the fuse it is good good that is probably a lose wiring.

If you have a multimeter test the wirings.

Posted on Nov 01, 2008

  • 3 more comments 
  • Ginko
    Ginko Nov 01, 2008

    After trying a different outlet, If you have a multimeter test the wirings. A bad power cord can be cause for the problem.

    If the power cord is fused, like in UK check the fuse in the power plug.

    If that is ok then it is either a faulty oven control, or the fuse inside the oven, placed on the oven control.

    You need to access to the oven control assembly to get the fuse. This involve taking apart the oven, and should be done by a technician.

    If you want tto do it yourself, you find parts and diagram here.



  • Ginko
    Ginko Nov 01, 2008

    If you have have 120 VAC on the W/W side of Relay RY2, then power cord is OK, that sounds more as a faulty relay.

  • Ginko
    Ginko Nov 01, 2008

    Yep, if you jump the relay contacts, the controls should be powered up, providing thet you jumped relay right contacts, and close the circuit activating the switch.

    To test the control assembly, you need to energize the contacts to the power supply wirings on the control assembly PCB.

    First you test with a multimeter if there is power coming to the assembly, otherwise it is either a faulty relay/circuit breacker (double check) or one of the wirings to control pcb has shorted inside the oven.
    If a wiring has shorted, you wont have continuity in the wirings from relay to timer/control pcb.


  • Ginko
    Ginko Nov 01, 2008

    The magnetron is fine, if there is no continuity when you ground it, and reads resistance between terminals is fine.

    See here how to test a magnetron:


    How To Test The Magnetron Used In Microwave Ovens



    Microwave Oven Repair Guide - Test microwave magnetron



    Sci.Electronics.Repair FAQ: Notes on the Troubleshooting and ...



    Click here to read all comments to your question


  • Ginko
    Ginko Nov 01, 2008

    Evidently you cannot read my comments, again here is the threa:
    Click here to read all comments to your question

    Sorry about this.


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  • 505 Answers

Try a different wall outlet and check if its turning on.

Also keep the unit off for some time and then check. As you have said that you already checked the internal fuse so there may be problem with the internal circuitory. Get the unit service by a technician.

Thanks

Posted on Nov 01, 2008

  • Indrajit Roy
    Indrajit Roy Nov 01, 2008

    Yes its placed correctly.



    Thanks

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