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GDS810 Scope locked/disabled vertical offset


Good day Guy's

My GDS801 Gm_Instek Oscilloscope (same as IDS810 from ISO-Tech) is refusing to vary/change the vertical position (DC-Offset) on Ch1&Ch2. It is as if the position-controls are locked or disabled.
Auto-Set changes the values to a more applicable level, but again I can't change it, even after that. Power-down doesn't solve the problem. Apart from that, the scope is working fine.

Any ideas .. please help !


- both front panel rotary encoder are mechanical broken (unlikely, but possible)
- the rotary encoder "logic" on front panel PCB is broken (there will be combination of diodes, resistors, mux)
- the common voltage source for DC offset is bad (unlikely, but possible)
- the S&H opamp for DC offset is broken

I would say take it apart, check first what happes on rotary encoders (changes when turning the knob), then
check if the changes are also on front panel mux and mainbord (to ensure some cables are not broken).
If this works you will have to locate the S&H on the mainboard and of course opamp which supply the DC offset
voltage to front stage.

If you don't know how/where to locate S&H make some pictures of the board, maybe someone here will have an idea.

Tinhead, thx for the reply.

I have a feeling it's the software over-riding my commands. If I turn the position knobs, the offset voltage does change (up/down) by a few mV, but then jumps back to were it came from. The scope is only about 3 years old, and not abused.
It feels like something (software?) is locking my effort. But nowhere is this type of function mentioned in the user manual.

You're comments ?


i don't know that scope, but i don't think that there is a lock function for dc offset only (if there is a lock then for all settings).

You can try your luck with GW Instek services@goodwill.com.tw They let us down horrible, but maybe they are good to you.


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