[Paul[_13_]]

On 8/2/2019 10:49 AM, Scott Dorsey wrote:
In article , Paul wrote:
I found the PWM chip. It's a 1271A, PTAC. So it's this one,
if I am not wrong:

pdf.datasheetcatalog.com/datasheet/on_semiconductor2/NCP1271-D.PDF

I have confirmed that I am getting AC and DC off the first main
rectifier, and there appears to be nothing on the secondary of the main
transformer.

I was NOT able to see a 65kHz driving signal on the driver pin 5,
but I assume this is because the oscillator is still off.

Right. For the oscillator to turn on, you have to have good voltages at HV
and Vcc to run the oscillator. The ground has to be good.

AND... on a cursory reading of the datasheet:
pin 3 (CS) has to have less than 1V on it. If it has more, it will
shut down for overcurrent.
pin 2 (FB) has to be less than 3V.
pin 1 (skip/latch) has to be lower than 8V.


Pins 1 and 3 had 0 Volts.

Pin 2 had 1.3 Volts.

Pin 6 has about 2 Volts.

Pin 8 has about 320 Volts on it, coming off the first rectifier.
Is that normal?


If all of these things are true, and the pwm chip is good, it should oscillate.
If it's not oscillating, check voltages and if voltages are out of range look
for bad electrolytics before you look for bad resistors.

And yes, the chips fail.
--scott