Rebrands of Hung Chang 5804 oscilloscope

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Hi all!

I have been looking for HC-5804 manual/diagrams, to repair a unit I received recently.
It has many defects, like no sweep, even with external source, and the dot is faint sometimes.
For those problems, I can use the 5504 manual, for which the horizontal and z-axis circuits are the same.
However, the 5804 has a CPU board, to control horizontal/vertical/sweep/storage modes via press buttons/leds in the front panel.
But the circuit is in some locked mode, and I can't change any of those settings. I can't enable, for instance, ch2.
The cursors are controlled by same board, and are working fine.
To diagnose that circuit I'll need its circuit diagram.

I couldn't find any portion of such manual/diagram.
I suppose there may be some other rebrands of the HC-5804 with easier/possible to find manual.
I could find some Beckman and Protek, but rebranding the 5602 instead, and others, not the 5804.
Any help is appreciated!

Thanks!