JUMA PA1000 was designed before the popular FT8 have been invented. At that time the design goal was a very light weight amplifier for SSB and CW. Because of the light weight the cooling does not allow full power key down operations. Here are few advice to adapt JUMA PA1000 for FT8.

1. Low PA Voltage reduction to 45V or lower
JUMA PA1000 has been supporting high (56V) and low (50V) PA voltage. High PA voltage is recommended for full power SSB to allow headroom for linear operation. The low PA voltage is recommended for all reduced power modes and all carrier type modes eg digi-modes. Although the 50V low PA voltage improves the efficiency it may not be enough for FT8. That's why the low PA voltage should be lowered down to 45V or even lower with the following simple modification in the serial numbers older than S/N 2024200.

Resistor R102 about in the middle of the main board defines the low PA voltage reduction. It is a 1206 size SMD resistor with a typical value of 390k. By reducing the resistor value to half or more will provide abt 45V low PA voltage. Instead of replacing the resistor it is easier to solder a 270k to 330k resistor in parallel. It is not critical, 43V-45V is fine. You will find a suitable resistor value by following the voltage indication in the LCD.
2. Adjust FAN MAX RPM

3. Over Temperature Limit change (optional)
JUMA PA1000 is measuring the final LDMOS transistor case temperature instead of the heatsink temperature. Thus it is indicating quite high readings. Nominal over temperature protection limit has been 100ºC. You may consider to raise the limit to 110ºC by replacing the resistor R66 from 15k to 12k.