PME mount alarm

[Paul Haese]

Anyone who owns a PME would have heard that alarm at one stage or another. If the balance is not perfect or there is something dragging the mount stops and sounds a warning to let you know there is a problem.

This should also be borne in mind that the plungers in the plunger assembly need to be tensioned correctly. Software bisque have a PDF on this and anyone with a large scope on their PME needs to read te document.

Last night no matter what I did the mount kept stopping and sounding the alarm at intermittent times. Aside from the plunger adjustment, what other issues could be causing this? I need to check this out very thoroughly as I have the 12RC sitting on the mount now and I want to make sure I have covered all my bases. I checked all my cables externally and none were pulling.

I have checked inside the mount too to make sure no cables are pulling or getting caught. Nothing seemed at fault in there. Anyone have an image of the inside of the mount and where the cable ties are located which hold the through the mount cables of the mount itself?

Setting the plunger screw at 1/2 turn back from tight seems to have sorted the problem for now, but I am sure it will go off again in the future.

I have only had this scope on the mount once before and it worked ok, but I was not doing a pointing run or doing so many slews. Any tips from the PME owners? Have I missed something?

[gregbradley]

Seeing as you had trouble with your gearing it would seem most likely to be something to do with that adjustment. Its taken the heavier weight of the 12 inch to show it perhaps.

I haven't heard that alarm and the CDK17 is quite heavy.

I take it you are balanced and no guide scope on top?

I'd say you are on the right track. A post to PME support forum may be the go.

Greg.

[frolinmod]

Make sure the balance knobs are functioning smoothly and correctly as well. Easy to do while you're in there checking the spring plungers.

That's shocking that you have to run your spring plungers only 1/2 turn backed off. That's very tight! So tight that I'd think it would cause binding. I hope you did a good job greasing the gears with Lubriplate. I have a comparatively light load (an EdgeHD 14 and stuff) and can run mine at 2-1/2 turns backed off.

Don't forget to check for binding through the mount cabling.

Oh, I think you already know all this stuff, but gosh, what else could possibly go wrong?

[Peter Ward]

The spring takes up the tension, and the manual recommends backing off 1/10th of a turn to prevent binding (yes, RTFM :) )

.... it also says 1 and a half turns will totally disengage the worm...hence not sure where that 2 and a half turn suggestion came from ;)

I'd also be checking lubrication, and double checking balance.

Also simply turning the mount off for a hour...letting things cool...and re-homing can work wonders.

[Paul Haese]

The former issue was my thinking too. I figure the spring plungers were not set up properly when the mount had the new worm installed either.
Yes I am balanced and no guide scope either. Good point about the PME support forum.



Earnie the balance knobs are really smooth. I can back them off more but only went to 1/2 a turn back off from tight.

Yep lots of lubriplate, but it might be time for some more too.

Only place I did not check for binding in the mount was on the Dec shaft.

No problem about things going wrong. I have learnt from long experience that little problems help teach things that need to be learnt. :)



Thanks for chiming in Peter. Yeah I have RTFM a few times, but thought it was a knob tick or two.

I will check the balance again, but I am sure this is good. Mind you I went over that pretty late last night and could have missed just a fraction or two.

Maybe some more lube, though it did look alright when I had the inspection plate off last night. That said, double checking has everything to be gained.

Thanks guys for the suggestions. I'll get back to you when I find the culprit or I get stumped.

[frolinmod]

You're thinking of the balance knob, not the spring plunger. The spring plunger document says that the factory setting is 2-1/2 turns.

See the spring plunger adjustment document here:
http://www.bisque.com/sc/media/p/28021.aspx
Relevant section quoted in the attachment.

The balance knob typically needs to be backed off maybe half a turn by feel. When you have the covers over the worm blocks off in order to adjust the spring plungers, you can actually SEE rather than just feel how far to back off the balance knobs.

[Paul Haese]

Ernie this is as I remember reading. I see also the confusion that I might have caused too. I was talking about the balance knob when I said I had it backed off to 1/2 a turn. I should have used the correct wording. The spring plungers do not appear to be in very far at all and may in fact be in the correct position. I will check though. Thanks for the link and exert from the PDF.

I had also forgotten about the speed settings though. I will adjust that too.

[gregbradley]

I have read elsewhere that lowering the slew speed rates can also help prevent a stall. I read that when I was looking at weight capabilities of the PME and CDK forum advised against using a PME for the CDK20 as it would stall unless slew rates were set very low.

The PME as does the PMX, standardly slews very quickly compared to other mounts I have used. So there is plenty of room to slow it down and still be good.

Greg.

[frolinmod]

Oh yeah, right, speed settings. Good catch. For awhile I ran my mount at 100% speed and maximum acceleration. It sure runs like a bat outta hell with those settings. Didn't seem to affect accuracy any either. Sounds cool as all get out in operation as well, sort of like an assembly line robot. After awhile I returned to the factory default settings out of fear of possible long term consequences of which I may not be aware.

[Peter Ward]

Quite correct! :thanx:

[gregbradley]

Not quite on topic but I must say I am impressed with the PMX slewing.
It races to the target and stops and doesn't seem to need to correct its position and its bang on. Impressive engineering.

Greg.

[frolinmod]

I you want to be impressed, go into Telescope->Tools->Bisque TCS->Parameters and change:

Acceleration to 800.
Max Slew Speed to 100.

Watch the mount slew like an assembly line robot.

[gregbradley]

One thing you have to be really careful of with the PMX - the gears will slip with moderate pressure.

Today I was merely polishing the drawtube of my scope and with only moderate pressure it skipped on the gears a little bit.

So if you take the camera off the scope to unpack you MUST lock the axis otherwise it may flip out of control and possibly wreck something.

This seems to be the downside of this new clutchless design. The gears must have some spring mechanism to engage them and they may be a tad too easy. On the positive if your mount ever did heaven forbid track into the pier then the gears would slip and no damage would be done.

Greg.

[nickbtx]

Greg,
I've heard others post that their mounts have skipped teeth when a little pressure is applied. SB posted "Adjusting the Paramount MX Cam Stop," in the download section. http://www.bisque.com/sc/media/p/55408.aspx According to the paper, "When properly adjusted, it does not allow the worm to separate from the gear." If I'm reading that correctly, it sounds like an adjustment might be in order.
Nick

[gregbradley]

Thanks Nick. I'll read that and follow the instructions.

It makes sense that it needs adjustment. It nearly cost me $20,000 on the weekend! Luckily no damage occured.

Greg.

[Paul Haese]

Just a bit of an update.

I checked the spring plungers and these were ok, but one was a little further in. I have now shifted that out just a little to suit the other plunger which is correct.

The alarms still went off last night, but today I rechecked balance. I was only very slightly out of balance (I do mean slight too) and I have found that I need to be more than 1/10 turn from tight on the balance knob. It is about 1 full turn and a bit. Even then the alarm goes off. Maybe time to check electronics.

PA is now near excellent. 15 seconds on MA 25 seconds on ME, close enough for me.

Point is good too, but could do with more points. I had some trouble last night with pin point solving. Odd behaviour.

Working through this slowly, but would like some advice on the mount alarm stuff. Peter can you help please?

[gregbradley]

It seems like a very specific and possibly unusual fault.

Have you posted it on SB PME support forum? That way one of the Bisque brothers will answer.

An insect on your electronics board?? Or perhaps a sensor that has become faulty.

Greg.

[Paul Haese]

Not yet Greg, but I reckon I will get it posted tonight.

No insects in there. I had a good look this morning for problems. It could be that I need to adjust the worm either to the left or right. Remember I put it dead center but that might not be optimum. I asked on the Bisque about that particular thing and got no reply. That was months ago.:shrug:

[gregbradley]

Perhaps search the SB database. The Bisque brothers tend to put out pdf documents that highlight step by step fixes for known issues.

Greg.

[Paul Haese]

I have now had a bit of a look at the data base and forum and this issue seems to crop up from time to time in various forms. Mostly related to either over tightening of the balance knob, incorrect balance or the cold being an issue. None of which in my case are relevant. I changed the scopes over last night at 1am and even the TSA is doing the same thing. Although I got it behave for several hours afterwards.

I have checked the wiring, I have regreased the entire RA (RA is the light flashing on the communications board and on the board inside the mount), and made sure nothing was too tight or out of balance.

I have posted on the forum and waiting on a reply from the Bisque boys or someone in the know there. The problem is largely intermittent as the mount can run with both scopes for long periods of time an not have the alarm sound and halt the mount.

It could be the boards, motor (not likely as it is stone cold after hours of slewing), but I am confident it is not the weight or balance. Reason being is that it did it without the worm being engaged and without any weight on the mount at all at least once last night. I will check the electric today and have checked for insect and rodent invasions and that came up with nothing.

If anyone has any ideas it would be appreciated. Having clear skies and not being able to image is a little frustrating I must say. No doubt it is a minor thing and just needs to be found. :)

[marc4darkskies]

When you disengage (as if to balance) does the rig swing without resistance of any kind ... thinking of the bearings.

[Paul Haese]

thanks Marcus. That was all ok.

So what have I done. Well today I stripped the mount right down to get to the homing sensor. I had read on the SB forum that grease or oil on the homing sensor could cause this problem. Besides I would turn on the mount and it would read the Dec axis but fail on the RA, so I had to do something.

I have a video of what a PME looks like stripped down (LOL I can imagine the cringing going on :lol:) just to get to the homing sensor in the RA. Luckily it was not the Dec sensor as that is a lot harder to get into.

As it turned out there was some of grease/oil residue on the homing sensor and the internal gear wheel. I ran a paper towel over the internal wheel through the hole several times and ran the RA from horizon to horizon manually. That cleared out all the oil residue. I figure the oil is the 105 grease that has separated over the last 12 months and it has ran down the back of the gear and then run down the internal wheel (not the right term but whatever holds the gear in place as it is honey combed and aluminum). I also then took to giving the sensor a good cleaning. Only using paper towel and nothing else. Then it took me an hour to put the mount back together. That included adjusting the drive assembly, including tension of belts and centering of worm gear so that everything ran smoothly.

Once it was all back together I did a couple of tests before closing the hatches and it all homed correctly and started up fine. Then when I went to park the scope it once again stopped. Disgusted I simply turned the balance knob so it was looser and it has been fine ever since.

I did a 250 point Tpoint model (after several PA runs because I had to move the elevation to get into the mount) and it is pointing really well (but that could always be better). My target tonight is dead center of the sensor so that is near perfect for me. Nice to have this thing running again and without stopping every 5 minutes or so. I will do a few more nights with the TSA before going back to the RC.

I will post the video in the next day or so.

PS, pretty soon I will have worked on every part of this mount and done a crash course on how to service them. If I get it working really well I will put my shingle out. It might be cheaper than sending it back to the states for those that need their mounts serviced.

[marc4darkskies]

Yep, you're definitely going to be the PME go-to guy!! :lol:

[frolinmod]

Paul, where can we view your video?

Also, do you know how to get the covers off the main gears? I mean the ones that cover the huge RA and DEC gears, not the easy ones that cover just the worm blocks.

[Paul Haese]

Ernie I will post the video from my home address. I have limited broadband at present. I am sure you will find it amusing.

[Paul Haese]

All seems to be working well again. Not a peep out of the mount. No alarm sounding, guided really well last night and slews were equally as nice. All looks good, so I'll continued with a project and started another one. The RC imaging is next.

[rainwatcher]

PME, PEX, PHD - ? I guess if you dont have one there is no need to know. :)

[Paul Haese]

Ernie, I just read your question about the gear covers and yes I know where the fixings are located. The ones over the RA are located on the dec body. The rear cover of the RA is bolted in position via the mount body. I think the front cover would be the easiest to remove, but is a considerable strip down. As for the dec I have not seen those bolts yet. However, I would think these will be connected in a similar fashion to the RA set.

[Paul Haese]

I have uploaded the video I took of the stripped down mount. It is all pretty easy to pull apart and put back together. All seems to be working well now and no mount alarm sounding. I have done several sessions of imaging and not once has the alarm sounded. I think I can safely say that the problem is sorted.

Click here (http://www.youtube.com/watch?v=4syrxjIBrN8&feature=youtu.be)for Video of stripped down PME.