I am working on a Komatsu PC200-8 excavator. It recently developed an issue that when the boom is being raised and the swing is activated, the boom stops raising until the swing is deactivated. As soon as the swing is deactivated the boom lifts normally. All other functions work normally together. It just started out of the blue that the swing function overrides the boom raise function. One interesting note is that if the stick is extended completely and the joystick held in that position (stick out against relief pressure) then the boom and swing work together. Any ideas will be greatly appreciated.
If you follow the Komatsu troubleshooting for slow boom raise speed during swing operation it recommends to check the swing LS select spool for defects or damaged seals.
I see that in the manual...I will take a look at that spool.