Prev: MAKE UPTO $5000 MONTHLY! $2000 INYOUR FIRST 30 DAYS!
Next: Weird telephone problem
From: mike on 18 Jul 2010 19:34
Mr. Land wrote:
> OK, I see there is a long history of microwave over repair questions.
> But I don't seem to see a thread that has my question:
>
> So I have an older GE JVM1190 over-the-stove microwave unit.
>
> Symptom is no heat.
>
> When powered up and programmed to cook, the unit makes the expected
> humming noise (the same it's always made) but a cup of water in the
> chamber will not heat up.
>
> I've studied the microwave FAQ repeatedly and I believe I understand
> the dangers.
>
> I constructed a long wooden-stick-based discharger for the HV cap,
> discharged it (didn't get any spark at all), then ensured there was no
> residual voltage on either of its terminals. Then I shorted the
> terminals.
>
> First I "tested" the magnetron: infinite resistance from either
> cathode connection pin to ground, very low resistance between the two
> pins themselves. Seems OK.
>
> Then I tested the HV diode by placing it series with a 390 ohm
> resistor and applying 15 VDC, and meauring the voltage drop across the
> device. -15V negative biased, about 10 VDC forward biased...this
> seemed to be within range.
>
> Finally I tested the HV cap. It reads infinite resistance to the
> chassis from either terminal. Between the terminals my capacitance
> meters reads around 0.86 uF... which seems to be correct.
>
> I've heard mention of a possibly bad HV fuse. AFAICT, this unit
> doesn't have one of those.
>
> So...the HV cap seems good, the mag seems good, the diode seems good,
> the unit seems to draw appropriate current when in cook mode,yet the
> over won't heat food.
>
> What am I missing???
>
> Could the magnetron still be "bad" despite the fact that it doesn't
> read shorted/open?
>
> Thanks.
I just fixed mine.
The push-on wire connection to the interlock switch had developed
some resistance, melted the wire and trashed the connector.
Had the same problem at the wire from the power cord to the main switch.
It hadn't failed...yet...
From: Mr. Land on 19 Jul 2010 01:54
I have new info.

Firstly, though THANK YOU ALL for taking the time to try to help. I
appreciate it.

So....I have replaced the magnetron in this before. AND, I read that
there seems to be a rash of
problems with these magnetrons.

But, the new info: my wife told me she'd heard the uWave emit this
"loud arcing noise" just before it
stopped heating food.

I couldn't find any evidence of arcing within the HV section itself,
however, when I removed the magnetron and
inspected the "antenna" (?) it looked as though it had been arcing:
there is a brass-colored conical tip that's flattened at the top
with a hole in it. That extends down towards the body about 1/2", then
there is a violet-colored band of some
material I can't identify...it appears to be some sort of insulating
material. Then under that is the RF braided gasket.

Well, where the purple insulating bushing and the copper tip
meet..there is a slight blackening and pitting...as
though arcing had occurred part of the way around that seam.

Does it make sense that the magnetron would arc there?

Ordering a new one tomorrow...

Thanks!
From: Mr. Land on 19 Jul 2010 02:38
On Jul 16, 7:04 pm, Cydrome Leader <prese...(a)MUNGEpanix.com> wrote:
> Mr. Land <grafton...(a)yahoo.com> wrote:
> > OK, I see there is a long history of microwave over repair questions.
> > But I don't seem to see a thread that has my question:
>
> > So I have an older GE JVM1190 over-the-stove microwave unit.
>
> > Symptom is no heat.
>
> > When powered up and programmed to cook, the unit makes the expected
> > humming noise (the same it's always made) but a cup of water in the
> > chamber will not heat up.
>
> > I've studied the microwave FAQ repeatedly and I believe I understand
> > the dangers.
>
> > I constructed a long wooden-stick-based discharger for the HV cap,
> > discharged it (didn't get any spark at all), then ensured there was no
> > residual voltage on either of its terminals.  Then I shorted the
> > terminals.
>
> > First I "tested" the magnetron: infinite resistance from either
> > cathode connection pin to ground, very low resistance between the two
> > pins themselves.  Seems OK.
>
> > Then I tested the HV diode by placing it series with a 390 ohm
> > resistor and applying 15 VDC, and meauring the voltage drop across the
> > device.  -15V negative biased, about 10 VDC forward biased...this
> > seemed to be within range.
>
> > Finally I tested the HV cap.  It reads infinite resistance to the
> > chassis from either terminal.  Between the terminals my capacitance
> > meters reads around 0.86 uF... which seems to be correct.
>
> > I've heard mention of a possibly bad HV fuse.  AFAICT, this unit
> > doesn't have one of those.
>
> > So...the HV cap seems good, the mag seems good, the diode seems good,
> > the unit seems to draw appropriate current when in cook mode,yet the
> > over won't heat food.
>
> > What am I missing???
>
> > Could the magnetron still be "bad" despite the fact that it doesn't
> > read shorted/open?
>
> > Thanks.
>
> Is the transformer secondary good? check its resistance from the HV
> terminal to the chassis. Open = bad.
>

Yep, all resistances among transformer wires correspond to those shown
in the
block diagram enclosed in the unit.

> Is that microwave old enough to use a reed relay for defrost mode?
>

I don't believe so.

> Do you have a way to measure the HV from a microwave oven safely?- Hide quoted text -
>

I have a TV HV probe, but that's not safe...to use it with neg voltage
I'd have to reverse it, but then
the working end wouldn't have anywhere near enough HV insulation/
standoff...it'd be just an alligator
clip...no thanks! %^)

> - Show quoted text -

From: LSMFT on 19 Jul 2010 08:32
Mr. Land wrote:
> OK, I see there is a long history of microwave over repair questions.
> But I don't seem to see a thread that has my question:
>
> So I have an older GE JVM1190 over-the-stove microwave unit.
>
> Symptom is no heat.
>
> When powered up and programmed to cook, the unit makes the expected
> humming noise (the same it's always made) but a cup of water in the
> chamber will not heat up.
>
> I've studied the microwave FAQ repeatedly and I believe I understand
> the dangers.
>
> I constructed a long wooden-stick-based discharger for the HV cap,
> discharged it (didn't get any spark at all), then ensured there was no
> residual voltage on either of its terminals. Then I shorted the
> terminals.
>
> First I "tested" the magnetron: infinite resistance from either
> cathode connection pin to ground, very low resistance between the two
> pins themselves. Seems OK.
>
> Then I tested the HV diode by placing it series with a 390 ohm
> resistor and applying 15 VDC, and meauring the voltage drop across the
> device. -15V negative biased, about 10 VDC forward biased...this
> seemed to be within range.
>
> Finally I tested the HV cap. It reads infinite resistance to the
> chassis from either terminal. Between the terminals my capacitance
> meters reads around 0.86 uF... which seems to be correct.
>
> I've heard mention of a possibly bad HV fuse. AFAICT, this unit
> doesn't have one of those.
>
> So...the HV cap seems good, the mag seems good, the diode seems good,
> the unit seems to draw appropriate current when in cook mode,yet the
> over won't heat food.
>
> What am I missing???
>
> Could the magnetron still be "bad" despite the fact that it doesn't
> read shorted/open?
>
> Thanks.

Find the fuse,it's in line.

--
LSMFT

I haven't spoken to my wife in 18 months.
I don't like to interrupt her.
From: Michael A. Terrell on 19 Jul 2010 21:20

"Mr. Land" wrote:
>
> On Jul 16, 7:04 pm, Cydrome Leader <prese...(a)MUNGEpanix.com> wrote:
> > Mr. Land <grafton...(a)yahoo.com> wrote:
> > > OK, I see there is a long history of microwave over repair questions.
> > > But I don't seem to see a thread that has my question:
> >
> > > So I have an older GE JVM1190 over-the-stove microwave unit.
> >
> > > Symptom is no heat.
> >
> > > When powered up and programmed to cook, the unit makes the expected
> > > humming noise (the same it's always made) but a cup of water in the
> > > chamber will not heat up.
> >
> > > I've studied the microwave FAQ repeatedly and I believe I understand
> > > the dangers.
> >
> > > I constructed a long wooden-stick-based discharger for the HV cap,
> > > discharged it (didn't get any spark at all), then ensured there was no
> > > residual voltage on either of its terminals. Then I shorted the
> > > terminals.
> >
> > > First I "tested" the magnetron: infinite resistance from either
> > > cathode connection pin to ground, very low resistance between the two
> > > pins themselves. Seems OK.
> >
> > > Then I tested the HV diode by placing it series with a 390 ohm
> > > resistor and applying 15 VDC, and meauring the voltage drop across the
> > > device. -15V negative biased, about 10 VDC forward biased...this
> > > seemed to be within range.
> >
> > > Finally I tested the HV cap. It reads infinite resistance to the
> > > chassis from either terminal. Between the terminals my capacitance
> > > meters reads around 0.86 uF... which seems to be correct.
> >
> > > I've heard mention of a possibly bad HV fuse. AFAICT, this unit
> > > doesn't have one of those.
> >
> > > So...the HV cap seems good, the mag seems good, the diode seems good,
> > > the unit seems to draw appropriate current when in cook mode,yet the
> > > over won't heat food.
> >
> > > What am I missing???
> >
> > > Could the magnetron still be "bad" despite the fact that it doesn't
> > > read shorted/open?
> >
> > > Thanks.
> >
> > Is the transformer secondary good? check its resistance from the HV
> > terminal to the chassis. Open = bad.
> >
>
> Yep, all resistances among transformer wires correspond to those shown
> in the
> block diagram enclosed in the unit.
>
> > Is that microwave old enough to use a reed relay for defrost mode?
> >
>
> I don't believe so.
>
> > Do you have a way to measure the HV from a microwave oven safely?- Hide quoted text -
> >
>
> I have a TV HV probe, but that's not safe...to use it with neg voltage
> I'd have to reverse it, but then
> the working end wouldn't have anywhere near enough HV insulation/
> standoff...it'd be just an alligator
> clip...no thanks! %^)


Some HV probes have a polarity switch, but you could add a small full
wave bridge for the meter movement so that it doesn't matter.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
First  |  Prev  |  Next  |  Last
Pages: 1 2 3
Prev: MAKE UPTO $5000 MONTHLY! $2000 INYOUR FIRST 30 DAYS!
Next: Weird telephone problem