Hello,
Sorry for the length of this text, but I think I have to explain my problem, as it drive me crazy, and also need your help.
I bought ZWO ASI290mini for guiding purpose to increase sensibility, in replacement of an old SBIG external remote head (a ST-237).
I would like to precise that with my old external remote guider (ST-237) for my old ST-2000XM (SBIG) guiding is OK, smoth and perfect (nice calibration and nice guiding, no drift). Connection to my mount with ST-4 but just difficult to find guide star due to the lack of sensibility, the reason why I want to use a 290.

Here is my configuration:

Losmandy Titan/gemini 1 mount connected to PC via RS-232 / USB
The CCD for images: ST-2000XM-> USB + maximDL V6
The guiding camera: ZWO 290mini: ST4 cable to gemini 1 to the mount and USB cable to the Computer (I use bin x2)
The old guide camera: ST-237(ST4), not sensible but it work.
Software side: maximDL, ascom 6.5, gemini 1.0.56 (later do not work with gemini1), last ascom driver/soft for ZWO
Day 1 and day 2: with ASI290mini as guiding: I launch poses of 20mn on IC59 => 35 perfect photos, I dismantle and put everything away because of future rain.
Day 10: I get everything out, reinstall everything, as usual ... and impossible to obtain a guide which holds the road! multiple reboot, disconnection, reconnection ... all was wrong! Impossible to calibrate, DEC axis refuse to move but all axis includinding DEC move with the virtual interface of the gemini on the computer, and mount move with CCDware Pempro with “moving mount with auto guide port”…
I tried different ST4 cable…the same sthing…
Day 11:
No mechanical neither cable change since the day before, I do a guide test.... perfect that guides for 10 minutes ....
launch the guiding by maxpilote => like the day before that move only on a single axis (RA)
I stop everything, look for mechanical, cabling, balance… I reboot the pc, restart the camera and mount several times, nothing, nada, damn it!
I redo a balancing, nothing changed,
I redo a pointing position, nothing changed
I restart a guide test with maximDL v6 => Calibration still ok on RA but never move on DEC. I tried differend MaximDL configuration… the same.
I redo a guidance calibration at another place in the sky (towards M101) => calibration it works!!!, I redo others calibration with different exposure times => it works
I'm relaunching a guide .... doesn’t work: guiding is perfect on RA, and drift on DEC (I explain later), I redo calibration on M101…doesn’t work!!!
I checked again the mount, the balancing, the connections .... I do not see anything abnormal.

What I mean by guiding problem:

Guiding in RA: PEC or not PEC ... => perfect!
In DEC, a large drift which is not correcting, the guide star is gradually drift out, going to 0.5, 2, 5... 10/12 pixel off and there is a sudden move to come back not to 0 but to 1 or 2 pixel... then it drifts again, stabilizing more or less out of 5 pixels... then it move suddenly .... and it continues and so on.... there is no repeat frequency, no repeat schema and random speed of the drift.
A priori the drift is always done in the same direction, I tried maximDL v5 and V6, multi guide star, blocked in maximDL the correction in +axis to leave only the –axis (opposite of the drif) on the DEC axis, nothing helps, always the same!!!

Day 12:
I use another computer with a new fresh installation...:

the same problem.
I remove the ASI290mini, do not change mechanicals stuff, neither the sky position, install my old ST-237 guider, take again the first computer: everything work fine, without sudden move, I have regular correction (so that is clearly not a mechanical problem on the mount) ... I done a guide test for 1 hour without problem!!!

So, I contact the seller to change the ASI290mini. I received the new one…
With the new one, it is the same problem!, exchange with the old ST-237 guiding cam, all is working fine and smoothly…

What I am suspected:

Driver problem? I use last one.
Parameter problem in MaximDL? (I tried PHD2…the same problem)
A cable problem (if PIN are correct, I have done another cable, test it and the problem is the same)
An issue with Gemini 1? Will it work with a Gemini 2?
I suspect that the first 2 working days the problem was the same but the drift was small for an unknow reason, as I could create last night a small drift of 2/3 pixel with sudden move

I need ST4 guiding. I tried to use ascom guiding but I do not succeed to figure out.
Some of you already had same issue? How do you trick it/solve it? Is it a known issue? Do I something wrong?
Please help!