Microwave timer/clock 4 digit 7-segmnt display is out. Timer works fine.

[Angelo Campanella]

My ancient Amana Microwave oven numerical display is out. Has been acting up
for years, but I now use it daily. (Batching it. Dear Wifey now in heaven.)

I can punch in the time I want, and the oven will run and turn off
accordingly. But I can't see the countdown any more because the display
digits are out.

Well they really are not out... just that the lower left segment on all four
are lit continuously, not other segments ever avtivate. Once and a while #1
"4" and occasionally #2 "2" light on cue during the countdown. I've opened
it up and measured power supply voltages and they are correct and normal at
the power supply.

I suspect it to be a power supply problem somewhere in the + busses, or
possibly a common ground not making ground. But I have no clue as to where
to start probing. Each digit is red gas discharge unit, unpluggable from
their socket... really ancient... 1976 vintage.

Any suggestions?

Ange

 

[N_Cook]

My ancient Amana Microwave oven numerical display is out. Has been acting up
for years, but I now use it daily. (Batching it. Dear Wifey now in heaven.)

I can punch in the time I want, and the oven will run and turn off
accordingly. But I can't see the countdown any more because the display
digits are out.

Well they really are not out... just that the lower left segment on all four
are lit continuously, not other segments ever avtivate. Once and a while #1
"4" and occasionally #2 "2" light on cue during the countdown. I've opened
it up and measured power supply voltages and they are correct and normal at
the power supply.

I suspect it to be a power supply problem somewhere in the + busses, or
possibly a common ground not making ground. But I have no clue as to where
to start probing. Each digit is red gas discharge unit, unpluggable from
their socket... really ancient... 1976 vintage.

Any suggestions?

Ange

I assume it has a dedicated LED driver, that sort of age probably internal
metalisation drift inside the chip or die carrier. Will it go to a museum?,
I would not have said uwave ovens were around in 1976

 

[William Sommerwerck]

Nixie tubes were relatively expensive. I don't think any microwave oven used
them. Certainly not in 1976, when LEDs were common and cheap.

If all the lower-left segments are on continuously, I'd suspect a problem in
the logic driving them.

 

[Angelo Campanella]

I checked to output by measureing the time to boil an 8oz cup of water.
The tag say 700 watss of cooking power, and my timing result was
approximately that... close enough to sy the magnetron was still OK.

What color is the display?

Red. LED seems pausible.

VFD were common in early microwaves.

I can see blinking when I san my gaze across it, so it's swithced likey
at 60 Hz or 120 Hz.

If it's not a power supply bus, then it's a bus driven by logic. I just
don't have a schematic for that generic sort of diplay logic.

I know you guys recommend that I replace it, but I don't see anything I
like. The chamber is nice and big... I've been eating meals prepared in it
for over two years now. Soups and pastas, coffee every day... It's my
mechanical mama.

Ange

 

[Angelo Campanella]

I assume it has a dedicated LED driver, that sort of age probably internal
metalisation drift inside the chip or die carrier.

True... but which component? "Driver" comes to mind.
But I have no schematic to identfy components. The model numer is

Model: RR6W, P72110-4M
S/N: H56559799
1600 Watts

(I recently measured it as 1,480 watts when running empty.)

Mfg Date May, 1976.

The cook space chamber is over a cubic foot in volume (14"x14"+x9"+).

Will it go to a museum?,

It could... for a price.

I would not have said uwave ovens were around in 1976

They came out that year or the year before. This unit is:
Ange

 

[Angelo Campanella]

Sounds more like a Nixie tube. Red would mean LED. 1976 vintage
would probably be red LED. How about making life easier and disclose
the Amana (Radar Range) model number?

Model: RR6W, P72110-4M
S/N: H56559799
1600 Watts

(I recently measured it as 1,480 watts when running empty.)

Mfg Date May, 1976.

The bad news is that if all the digits are equally bad and they're
individually unpluggable, then it's probably something in the
electronics. Stuck digits and working timer sounds like a display
multiplexer/driver circuit.

I need a schematic, or a generic schematic to hunt down the bad driver.

It would probably cost less to replace
the oven than repair it, but such an old Amana is a collectors item
and is probably worth restoring. I'm rather surprised that the
magnetron is still functional.

I checked it via boiling time for a cup of cold watrer... it's close to the
rated 7oo watts.

ange

 

[Angelo Campanella]

Nixie tubes were relatively expensive. I don't think any microwave oven
used
them. Certainly not in 1976, when LEDs were common and cheap.

If all the lower-left segments are on continuously, I'd suspect a problem
in
the logic driving them.

True... soemthing common to all 4 digits.

Ange

 

[Angelo Campanella]

Red is LED. Orange could be vacuum fluorescent or LED. I'll be on
LED.

OK, it's gotta be LED.

Could I trouble you for the Amana model number so we don't have to
continue guessing.

Set recently but again, but here again:

Model: RR6W, P72110-4M
S/N: H56559799
1600 Watts
(I recently measured it as 1,480 watts when running empty.)
Mfg Date May, 1976.

Please re-read the previous comments. Nobody suggested you replace
it. This isn't a newsgroup dedicated to appliance salesmen. If it
cooks well, it should be possible to fix it.
What's the problem? Too many features? Short lifetimes? Bizarre
warranties? Lousy construction? All of these?

1- War stories of new microwaves, mostly of Pacific Rim manufacture,
failing after a few years of service.

My son bought me a new one a Christmas go, but it turned out to be
smaller and of Pacific Rim manufacture, so I gave it back to him to give to
somebody else. This Amana is still the war horse.

2- I like this size (over a cubic foot). I think I'd like another Amana... I
think Raytheon bought them out some years ago. The name is still around. I
looked up their web age, and several models are available . A cubic foot+
unit cost about $150 last year... It's in he back of my mind.

I think you might find it useful to learn how to cook.

I'm looking for a human replacement, but so far no luck.

To keep my weight down, I eat a lot of salads; they require no cooking.
I cook soups from scratch and spaghetti & pastas with the u-wave. I eat very
little meat, mainly chicken, since red meats are heavy and affect my blood
pressure. I eat most anything on special occasions only.

Think of it as
chemistry and not an art form. Microwave cooking is ok for many
things, but there's plenty of dishes that are best cooked over a
flame, on a grill, or in a real oven. Then there's barbecue.

Cooking, especially frying, sends all kinds of odors into the house
(3-bedroom ranch, closed tight in the winter) that odiferate for hours
later... I eat meats mainly when eating out with friends.

The other son gave me a Forman burger grille. I only used it once. It
really smelled up the house . The range hood was not really of much help.
The Forman grille is best used outdoors.

Back to my Amana RR6W, my only hope to get display functioning back is
to identify the failed component (driver chip?), or replace the entire panel
module... both of which seem highly unlikely. This news group is about the
place I can find to even have an intelligent discussion on the matter. What
is needed is an old-timer that remembers the 7 digit LED display technology
of the '70's and also know the Amana microwave oven use of them.

Getting that circuit board out in the clear to work on it seems to be
nigh impossible. It is in place behind and parallel to the numbers panel.
But its back side is shielded over 2/3 its area with the power supply and
its heat sink. Numbers are on the top end. The bottom end is not in a
connector slot, but rather it's stationary with power supply bus wires and
switching relay control wires soldered in place.

Ange

 

[N_Cook]

I checked to output by measureing the time to boil an 8oz cup of water.
The tag say 700 watss of cooking power, and my timing result was
approximately that... close enough to sy the magnetron was still OK.


Red. LED seems pausible.


I can see blinking when I san my gaze across it, so it's swithced likey
at 60 Hz or 120 Hz.

If it's not a power supply bus, then it's a bus driven by logic. I just
don't have a schematic for that generic sort of diplay logic.

I know you guys recommend that I replace it, but I don't see anything I
like. The chamber is nice and big... I've been eating meals prepared in it
for over two years now. Soups and pastas, coffee every day... It's my
mechanical mama.

Ange

So what are some of the numbers on the chips inside and any numbers seen on
the sides of the display/s ?

 

[William Sommerwerck]

The chamber is nice and big... I've been eating meals

I think you might find it useful to learn how to cook. Think
of it as chemistry and not an art form. Microwave cooking
is ok for many things, but there's plenty of dishes that are
best cooked over a flame, on a grill, or in a real oven. Then
there's barbecue.

A microwave oven doesn't actually "cook" anything -- it just heats it. That
works great with soup, pasta, bacon, and a few other things.

Have you seen Betty Crocker "Warm Delights"? It's actually a repurposing of
her awful microwave brownies (which were actually more trouble to make than
regular brownies).

 

[Angelo Campanella]

So what are some of the numbers on the chips inside and any numbers seen
on
the sides of the display/s ?

I managed to pry out 7-segment chip digit #2 chip for review.

It's a 19mm x 10mm 14 pin (3 pins not present) HP5082-7730 609 C.

The face is a transparent matte plastic surface that seem to have red solid
state material for each of the 7 segments over the interior material.

The back side, between pin rows, is pink transparent potting that covers a
PC board holding the 14 (really net 11) pins.

Ange

 

[Angelo Campanella]

So what are some of the numbers on the chips inside and any numbers seen
on
the sides of the display/s ?

I managed to pry out 7-segment digit #2 chip for inspection.

It's an HP 5082-7730 609-C, 19mm x 10 mm, 14-pin (3 missing) pluggable chip.

It has a matte face, transparent at the 7 segments to interior solid state
material.

The bottom side is filled with clear pink potting where a PC board holding
the pins is visible.

Ange

 

[Spehro Pefhany]

I managed to pry out 7-segment digit #2 chip for inspection.

It's an HP 5082-7730 609-C, 19mm x 10 mm, 14-pin (3 missing) pluggable chip.

It has a matte face, transparent at the 7 segments to interior solid state
material.

The bottom side is filled with clear pink potting where a PC board holding
the pins is visible.

Ange

That's just a regular old 0.3" seven-segment common-anode LED display,
like the old Monsanto MANxxx displays.

http://www.datasheetcatalog.org/datasheets2/31/319472_1.pdf

Extremely low efficiency by modern standards, but good quality for the
day.

We've got an antique Amana Radarrange with similar red LED displays.

Here's a more modern equivalent that is pin-compatible:
http://www.kingbrightusa.com/images/catalog/SPEC/SA03-11EWA.pdf
(but more than 10x as bright at the same current)


But it's not likely the displays that are causing the problem-
probably the drivers or some connections or circuitry further back.





Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

That's just a regular old 0.3" seven-segment common-anode LED display,
like the old Monsanto MANxxx displays.

http://www.datasheetcatalog.org/datasheets2/31/319472_1.pdf

Extremely low efficiency by modern standards, but good quality for the
day.

We've got an antique Amana Radarrange with similar red LED displays.

Here's a more modern equivalent that is pin-compatible:
http://www.kingbrightusa.com/images/catalog/SPEC/SA03-11EWA.pdf
(but more than 10x as bright at the same current)

(well, pin compatible on the segments, but it has a right-hand decimal
point rather than the rare left-hand on the microwave oven, so not
really 100% compatible...)


Best regards,
Spehro Pefhany

 

[William Sommerwerck]

I recently measured it as 1480 watts when running empty.

Akkk! If you keep running it empty, you might damage the magnetron.

I'm reminded of the opening of "The Outer Tsimmes"...

"There is nothing wrong with your television. But if we keep f***ing with it
like this every week, pretty soon there will be."

 

[Geo]

All well and good. But I need a typical driver circuit diagram to probe voltages. It could be something as simple as a dropping resistor that's opened up, or a local filter capacitor that is shorted... I need a pin voltage map to find which voltage is missing.

If you look at this page:-
http://www.decodesystems.com/old-displays.html
There are two gifs from an HP appnote.
They shows suitable multiplexing circuits.
It is possible that your circuit has stopped multiplexing so only single
segments permanently on.
May be missing a clock signal.

 

[N_Cook]

I managed to pry out 7-segment chip digit #2 chip for review.

It's a 19mm x 10mm 14 pin (3 pins not present) HP5082-7730 609 C.

The face is a transparent matte plastic surface that seem to have red solid
state material for each of the 7 segments over the interior material.

The back side, between pin rows, is pink transparent potting that covers a
PC board holding the 14 (really net 11) pins.

Ange

Can you view the board enough to count the pins on each of the non-display
electronic chips?

 

[Angelo Campanella]

Can you view the board enough to count the pins on each of the non-display
electronic chips?

Have to unscrew the bezel allen screws again. in a few days..

Ange

 

[Angelo Campanella]

If you look at this page:-
http://www.decodesystems.com/old-displays.html

Seems to be near what I have.

There are two gifs from an HP appnote.
They shows suitable multiplexing circuits.
It is possible that your circuit has stopped multiplexing so only single
segments permanently on.
May be missing a clock signal.

I'm an old discrete component and vacuum tube guy.

I presume that "strobe" means hat there is only one driver, the SN7447
which is the only segment feeder, that the digit switched on at the moment
by the strobe signal will take segment current and light up.

The current comes from the 7447, whatever of the 7 lines is to run to
make the number of the instant.

In my uwave, only E segment is lit and the E of all 4 digits are on all
the time. No other segments of all 4 digits ever light. Well, actually the
4 of digit 4 is lighting every time its turn comes in the countdown. Perhaps
that digit is more sensitive.

One thing for me to look at is the health of the seven 47 ohm resistors.

Another is to check the + voltage supply. Do I expect 5 volts or some
higher value? The two raw dc supplies are 10 or 20 volts (the filter
capacitors gave away their location.)

Ange