siliconchip.com.au Australia’s electronics magazine April 2019 57
RS components. I also found that C6
(10μF 50 V) was shorted out on both
Air Fryer power boards. Replacing
the regulators, 30W resistors and 10μF
capacitors got the units back up and
running. Note that the power board
will not produce any output unless
it is connected to the control/display
board.
While I had the units open, I also
added a metal oxide varistor (MOV;
blue disc) across the 30W protection
resistors at the IC’s high voltage in-
puts. It should reduce voltage spikes
getting to the Viper16 IC. I am hoping
that this will prevent similar failures
in the future.
There is a similar problem with
some Toshiba TV power supply
boards. These use a similar high volt-
age 8-pin DIP IC (ICE3B0365) for the
5V standby power supply. These are
also made by ST Microelectronics. I
have three boards where the same IC
has failed.to fix them but this raises the possibil-
ity that these designs are not rugged
enough for our electrical grid...
This problem may be of interest to
your readers as it appears to be a com-
mon fault with Philips HR2940 Air
Fryers. I have two units which were
both dead, having no display.
The first problem was removing the
top cover to get to the power board.
You need a long T20 screwdriver as
the screws are deeply recessed. My
photo shows the unit after the cover
is removed, with the power supply
board visible.
The power supply board uses the
ST Microelectronics Viper16 8-pin DIP
flyback switching regulator IC. This
has an internal high voltage (700V)
FET which failed and destroyed the
two 30W resistors feeding it. The fuse
survived(!) It seems that these ICs are
not able to handle the high voltages
they can be exposed to.
Replacement ICs are available fromWith the narrow pin spacing of mod-
ern ICs, the worst thing you could or-
ganise is dumping a conductive mat-
ting over and between the tracks and
the pins of the ICs and surface mount
parts.
Many bits of gear are thrown out
just because they have been used in
this environment for several years and
then simply quit working. They usu-
ally wind up in the council cleanup.
The simple cure is the get out the
methylated spirits, some old tooth-
brushes, small art painting brushes,
clean rags, old newspapers, magnify-
ing glasses, a fine bladed scalpel, and
ensure no ignition sources exist.
Pour a small amount of metho into
a lid or other container, and use the
tools to wash/scrub down the PCB
with all the sluiced-off waste going
onto the newspaper.
Use the scalpel and toothbrushes to
very carefully clear between the fine
pins of the ICs. Mop up any leftover
metho with a tissue or a rag; you can
even use a hair dryer to dry it off, en-
suring that no metho hides under the
ICs or other components.
Re-assemble the equipment, and
that’s it. While cleaning up this PC us-
ing the above method, I discovered a
bloated 3300μF capacitor, so I replaced
that too. Then pow, up it came first go,
and I’m typing this tale on it.
So before you throw any gear out,
give it the big clean; you may be sur-
prised just how well it works, and just
how easy it is!
Philips air fryer repair
R. S., of Fig Tree Pocket, Qld has
multiple failed power supply boards
exhibiting the same fault. He was able
SCClose-up of the power supply board used in the Philips HR2940 air fryer.
The only IC (a Viper16) in the unit had failed due to high voltages.Before and after cleaning the PC motherboard; note a few of the ICs had not been re-seated yet.