Help - Vixen GP not tracking accurately in DEC

[dweller25]

Hello,

I have a problem with my Vixen GP, it is driven with Vixen motors in both axis and is not GOTO.

For the past few weeks whilst observing I have been having to correct for upwards DEC drift of the planets by pressing the down DEC button on my control box.

Last night I decided to adjust the altitude the mount was set to (52’) to compensate for the upwards drift, I ended up at 35’ before the upward drift reduced and even then it was still there, so put the altitude setting back to 52’.

Then I unplugged the DEC lead to see if the Dec motor was getting some kind of false instruction from the control box but I still saw the same upwards DEC drift.

I have also changed - out of desperation - the Vixen tripod for a Berlebach - that did not work.

So, I have run out of ideas - if anyone has had this problem and/or knows of a fix please let me know.

Thank you.

[mikeDnight]

Hi Dave,

Does the same thing happen if you try tracking stars?

[CraigT82]

Sounds like the PA is way off? 

[AstroKeith]

Sounds like you arent using the polar align scope? Any reason?

You can also get a dec drift if the mount isn't north aligned, not just latitude aligned. This will be most pronounced away from the meridian.

[dweller25]

Thanks for all the replies,

I just checked the pressure adjustment plate on the DEC worm and it was slightly loose. Combined with a slightly back heavy scope I suspect the DEC may have been slipping ?

I will check it tonight…..

@mikeDnight - will try that tonight.

@CraigT82 @AstroKeith - its the GP-E so it does not have a polar alignment scope BUT to my eternal shame I have NEVER polar aligned since starting out in 1985 😱, but this is way more drift than I normally get.

[Franklin]

Could be a tripod leg slipping or even a tripod leg spike sinking into wet ground?

[Franklin]

Another thought, the axis lock has a small circular pad at the end of the bolt which presses down to create friction, maybe you could try adjusting this. I've seen some GP mounts where the lock lever must be turned through 90deg to lock, mine lock and unlock with only about 10deg of movement. If it's not fully locked and you're using a heavy scope that's not perfectly balanced, the weight of the scope could cause the Dec axis to drag.

[dweller25]

16 minutes ago, Franklin said:

Another thought, the axis lock has a small circular pad at the end of the bolt which presses down to create friction, maybe you could try adjusting this. I've seen some GP mounts where the lock lever must be turned through 90deg to lock, mine lock and unlock with only about 10deg of movement. If it's not fully locked and you're using a heavy scope that's not perfectly balanced, the weight of the scope could cause the Dec axis to drag.

Yes, good point - mine starting getting to 180 degrees before locking so I changed it to 90 degrees last year.

See my above post as I think I found the problem which I will confirm tonight.

Thanks

Edited January 21, 2023 by dweller25

[Cosmic Geoff]

If the polar alignment is perfect, you should not need to touch the DEC axis at all when tracking.

[Franklin]

Just now, Cosmic Geoff said:

If the polar alignment is perfect, you should not need to touch the DEC axis at all when tracking.

Correct but I can't see it being the tracking at all as this is all locked, axis gear to worm to gear to motor. The only place where slippage can occur, if the scope is out of balance, is a) the axis lock is not fully engaged or grease has got in the wrong place and b) if using a clutch, then grease may have got behind the clutch lock which is causing it to slip.

[dweller25]

3 minutes ago, Franklin said:

Correct but I can't see it being the tracking at all as this is all locked, axis gear to worm to gear to motor. The only place where slippage can occur, if the scope is out of balance, is a) the axis lock is not fully engaged or grease has got in the wrong place and b) if using a clutch, then grease may have got behind the clutch lock which is causing it to slip.

Yes, I will check the plastic pressure pad behind the DEC axis lock nut tomorrow if all does not well tonight - thanks

[dweller25]

41 minutes ago, Franklin said:

Correct but I can't see it being the tracking at all as this is all locked, axis gear to worm to gear to motor. The only place where slippage can occur, if the scope is out of balance, is a) the axis lock is not fully engaged or grease has got in the wrong place and b) if using a clutch, then grease may have got behind the clutch lock which is causing it to slip.

I just removed the external brass bolt to reveal the DEC plastic/teflon pressure pad.

The bolt and pad are covered in grease, it looks like the DEC unit needs taking apart for cleaning off excess lubricant.

Thanks for the heads up 👍

Edited January 21, 2023 by dweller25

[Franklin]

18 minutes ago, dweller25 said:

The bolt and pad are covered in grease, it looks like the DEC unit needs taking apart for cleaning off excess lubricant

This is most likely the root of the problem, should be fine once cleaned up and adjusted.

[Peter Drew]

52 degrees seems a little low to me for Bury, we are nearer 54 and we are only just "up the road" from you.      🙂

[dweller25]

Thanks @Peter Drew I just changed it 👍although it acted the same way when I set it to 60’ or 35’

Edited January 21, 2023 by dweller25

[dweller25]

Well, hallelujah, its back to normal again, Jupiter has stayed dead central for the last 15 minutes - the GRS is visible btw.

I think it as a combination of grease on the DEC pressure pad and imbalance of the OTA.

i will leave it for now as its working but its probably only a matter of time before it happens again, so I ordered a lens spanner so I can take the DEC bearing out and degrease it when the time comes.

Thanks to everyone for their input 👍🙂

Edited January 21, 2023 by dweller25

[Franklin]

There's a lot of info online regards fine-tuning the Synta EQ5, a clone of the Vixen GP, but I have to say that some of the material I've seen is a bit iffy imo. I've had dozens of Vixen mounts over the years and the only ones I've ever had to fettle were the Made in China ones, like the Porta range. Japan made SP mounts over 35 years old yet still buttery smooth like the day they were made, Vixen quality!