Philips AZ787 Boombox Inverter Issues: Voltage Drop Under Load & Troubleshooting Steps Taken

Hello, I would like to ask for help.
Converter from Philips AZ787 boombox. Without load, it takes a very long time to rise to the output voltage of 9.87 V.
When the load (boombox) is connected, the voltage drops to 2 volts, so the boombox does not start.
After loading the bulb with 6.3 V, the output voltage drops to zero - the bulb does not light.
After loading with a red diode with a 50 Ohm resistor, the voltage drops to 6 V - the diode is on. However, if the diode is connected to the output before connecting 230 V - the voltage at the output does not appear - the diode is off.
What I did:
I checked the bridge, all diodes, transistor - everything is OK. I replaced the output capacitors, nothing has changed. I am wondering about the transformers: between the pins 1-3, the resistance is 9 Ohm, between 2-4 only 0.1 Ohm. Did I miss something.

You have also measured the SMD elements - at least in the system.

Are the electrolytic capacitors on the primary side checked / operational?

Schematic diagram of the converter


You have the complete service manual here.

I do not have to replace the capacitors on the primary side, they look ok. I shorted one by accident after disconnecting the power supply and it discharged with a bang, so I think they are ok.
The SMD diodes are working, I measured the resistors and they also seem ok.

Here you have the application chip of the inverter controller. Meter in hand and go. Something is telling me that he may be "set".

The application shows that there is a 1uF capacitor on the primary side, has it been checked / replaced?

No, I did not replace this capacitor. I'll try to do it tomorrow.

A new day, a new hope and ... failure.
Capacitor 1uF C906 replaced and no change. I checked all the resistors and diodes again. Everything looks good. Now I saw there is one more 1uF C908. I do not know if there is any point in replacing it.
Probably the controller has fallen, unfortunately I am not able to replace it. You will probably need to convert the radio to a traditional power supply.

On the Alliexpres auction site $ 2.20, in Poland you probably won't get it.

I give up repair. Thanks to everyone for your help. I close the topic.