Rigol DS1052E trigger not working

[kagurazakahope]

I've bought this nth hand DS1052E with rather cheap price. Everything else works fine but the trigger seems not working at all.
Firstly I noticed I can't get the waveform stable, then I realized it was AUTO triggering so I changed to NORMAL, and it keep showing WAIT at the top left and won't trigger at all.
I've tried CH1, CH2, and even EXT connected to the compensator, none of them worked.
I've tried to adjust the trigger settings with different modes, slopes, values and that didn't work.
If I push the FORCE button it can trigger.
Once or twice when just booted I got few triggers in NORMAL mode, but those were not stable at all, it triggered at random positions.
I disassembled it and cleaned the circuit boards but it didn't help. Haven't found any noticeable broken though.

I tried to search for the circuit diagram online but haven't found anything useful.

Could anyone help to provide some advices?
I've tried everything with all the trigger settings.
Level didn't work, it won't trigger no matter what level I set, including %50 when I pushed the button. Although it could correct detect the 50% level.
Edge didn't work, Pulse Width didn't work, Slope didn't work. I mean I've tried every type of "When" with reasonable values on all those trigger modes, and none of them was working.

I was measuring the internal compensator signal, which is a 1KHz square wave with 3Vpp. I could see the square waveform if I use AUTO sweep mode, but it kept jumping around and didn't get stabilized. That's what AUTO does as mentioned in the manual, it triggers anyway even without a valid trigger detected.

Also I've upgraded the firmware from originally 2.2 SP1 to 2.2 SP2 which is a rather stable version and the problem is still there.
I'm wondering if there is any circuit diagram, at least for the trigger part. I highly suspect there is some failed component along the path.

[Doctorandus_P]

How much experience do you have with oscilloscopes?

Have you turned the  trigger level knob? (I assume you did, but you did not mention it in your post)
And pushed the 50%  knob?

How much of the manual have you read and understood?
The trigger menu of the DS1052E has about 10 settings, most with several options, and some options can severely limit the amount of trigger events.

For example, I've never been able to trigger at all on a specific pulse width, any pulse seemed to be either too narrow or too wide.

[kagurazakahope]

Thanks for the reply.
I've tried everything with all the trigger settings.
Level didn't work, it won't trigger no matter what level I set, including %50 when I pushed the button. Although it could correct detect the 50% level.
Edge didn't work, Pulse Width didn't work, Slope didn't work. I mean I've tried every type of "When" with reasonable values on all those trigger modes, and none of them was working.

I was measuring the internal compensator signal, which is a 1KHz square wave with 3Vpp. I could see the square waveform if I use AUTO sweep mode, but it kept jumping around and didn't get stabilized. That's what AUTO does as mentioned in the manual, it triggers anyway even without a valid trigger detected.

[MikeK]

Have you tried the AUTO button in the top-right corner of the controls?  I don't mean the Auto triggering setting in the menu.

[kagurazakahope]

Yes I have. It was the same issue, the waveform was just moving around.