Losmandy Titan motor lag/stalls

[Lester]

Hi all, I had not used my mount for a few months and decided to try it tonight. Got the message RA motor lag. I checked the mount balance which was good, then disconnected the motor from its attachment to the mount and turned it back on. Still got the message motor lag. I disconnected the Dec motor from its housing and tried again with the same message.

So I have discounted the mount causing the problem and now think it must be the computer box. Any tips would be appreciated, thanks.

[Peteren]

Have you checked your power supply? Anything less than a clean 12VDC will give RA stalls

[h0ughy]

yeah i run mine at 15 volts through a lab transformer - specifically to stop this

[Lester]

Thanks Peter and David, I will check the power out put of my power supply in the morning. It has worked okay in the past, but will still check it.

[Lester]

The power supply was putting out 12.8 volts so I changed it for a new 13.8 volt 10 amp supply I had for a spare and still get the same RA motor lag/not tracking message. This is with both motors disconnected from their gear boxes, so no binding of gears etc.

Is there anything else I can try? Thanks.

[pmrid]

Hello Lester, My Titan does that occasionally - and the culprit has always been my worm setting. Although I tend to "set and forget" the worms, they do occasionally get a bit clagged up - changes of season (heating/cooling metal parts changing the gaps a bit is a possible culprit. Also, not using the mount for a while may have seen the grease get a bit clagged up - perhaps a bit of sea air would aid that process.

Anyway, I have generally found that a worm rest did the trick. If you're doing that, you could take the opportunity to judge the state of the grease as well.


Peter

[Lester]

Thanks for your input Peter. As I have disconnected the motors from the Titan mount they are not trying to drive the mount, so no binding of gears is an issue now. The motors just don't power up at all.

After much reading on the net, I am wondering if there is a internal battery in the Gemini that has to be removed/replaced to stop this lag message from coming up? I did read that the Cmos (what ever that is) has to be reset by removing an internal battery. So I will have a look internally and see if I can find anything that looks like a battery.

[Lester]

I found a battery inside the unit and removed it and put it back in, without any change to the motor lag message. The battery is marked 3 volts and it is 2.8, don't know if that should make much difference as I presume it is just a memory powering battery.

[asimov]

I'd be contacting Losmandy.

[pmrid]

Change the battery anyway.
Swap the motors around. Assuming the dec motor was not a problem, you would expect the Lag message to crop up on the dec axis. But if it shows up on RA still, that would suggest the problem was in the control box and not the motor.

I run my Titan t 18 VDC and it loves it. Might be worth pumping up the voltage - even to 15.
Peter

[Lester]

Thanks John and Peter. Yes I have changed the motors around, plus cords and still get the RA motor lag message and then stops tracking. I doesn't even sound like it fires up the motors at all.

Just pulled out the circuit board incase there was a spider or something behind it shorting out some where; but all clean. Off to get some contact cleaner to spray into the sockets and plugs and a new 3 volt battery now.

If this doesn't change anything I will have to try and contact Losmandy.

[mithrandir]

Lester, if the battery is below 3V replace it.

As for 18V, I found a thread from 2010 about an 12->18V inverter from Snaptec http://www.iceinspace.com.au/forum/showthread.php?t=66854

I emailed them last night to see if they would make it a standard item, probably made to order.

If not, they have a 12->15V version that is known to work.

[asimov]

IMO if it's been working all this time with 12V, to suddenly feed it more voltage is not the answer.

[asimov]

Similar to what happened to my CGE mount Lester. Spent weeks following advice, buying new power supplies etc etc only to eventually find out it was a burnt chip on a board worth 50c.

[mithrandir]

... in which case Brendan has lots of experience replacing chips in Gemini-1 and Melbourne is a lot closer than Hollywood.

[wasyoungonce]

Lester is this a Gemini 1? The battery has nothing to do with "motor lag" prompts or issues.

Motor lag is that the encoder is not counting enough ticks of rotation when given a command to move. Do the motors drive at all?

You said you took them (the motors) out and still this gave "motor lag" so try this:
1st Do the removed motors rotate freely without power?

2nd. Do the removed motors rotate with power applied...aka does the RA rotate in sidereal. Put the DEC motor on the sidereal cable and try that motor as well! Try commanding them at faster rates..do they speed up?

3rd. Do the removed motors have resistance on the spindle if you try to rotate this by fingers? Or do they give some sort of jerky movement?

Usually motor lag is imbalance or such like and this problem can just be a motor issue but unlikely if both motors have issues.

Each motor is driven by a "H" bridge then the encoder is counted via motor encoder IC's (U16/17 numbers under ICs) and these IC's are what goes bad, usually. They have inbuilt firmware and need to be sourced from Losmandy.

These motor encoder IC's are usually damaged by putting the motor cables on incorrectly (although there are other things that can cause this damage), passing +12V motor H bridge drive to the +5V encoders...the result is smoke or something like this (peel back the sticker).

[Lester]

Thanks again everyone for your feed back; am getting to my end of ideas, so all appreciated. Hi Brendan 1. yes the motor rotate freely without any power to them.
2. I can get the Dec motor to rev at a high speed, but only for a short time, about 1 second. I change the motors over and always get the same out of the Dec outlet, so to me it isn't motor or lead related. The RA motor will not speed up, goes slow for a short period then the device beeps and says motor stalled or motor lag.
3. When there is power to the motors the Dec motor locks (I cannot turn it by fingers) and the RA motor is easy to turn. I have changed the motors over and still the same; always the Dec outlet to motor locks and the outlet from the RA to motor is easy to turn.

On opening the controller there is no sign of heat being anywhere. As my mount is in a observatory I have not moved the cables at all until last night to see if it was motor related or the console. I am sure it is the console.

[Lester]

Sorry missed your first question Brendan. It is a Gemini level 4, 2006

[Lester]

Brendan, after looking closely inside my unit the IC is 3750022 -01 REV 2, so a different number. It has the 10 outlets on each side and a R15 and R16 along side of it. No sign of heat damage.

[wasyoungonce]

Lester

The RA drive is not working it should have resistance with power on and indeed should rotate at sidereal rate, the DEC pinion with power on should be nice and hard almost impossible to move. So, you definitely have an RA PCB issue.

Just check the controller is in sidereal mode and terrestrial mode? Have you also tried a cold boot?

The motor encoders outputs for RA/DEC (and motors) are controlled by U11/12 PIC micro-controllers & CPU. These are interchangeable. My best bet is that you have a bad RA motor encoder IC or maybe one of the PIC micros, not so sure about DEC might be ok.

I have seen funny movements from DEC & RA motors before and this was the PIC micros U11/12...amongst other ICs that were damaged. These IC's rarely go bad but I have replaced qty 2on same board.

Rene said he has never seen a "H" bridge (LMD18210T) fail so I'd discount this for a start though you never know.

The only other possibility is a bad EPROM (U7) or CPU. Of course you need a suite of IC's on hand to check all this.

I'm doing 2 Gemini's ATM.....one is ok just about to send off, the other had a few faults, nearly all fixed now, just waiting for U16 motor encoder IC from Losmandy.

Oh the sticker on the motor encoder IC is just a firmware revision tag and so far as I know these are interchangeable from one PCB revision to another...but that said you would never remove them and replace them as they would be damaged on removal de-soldering. You replace them on spec...that is if replacing CPU EPROM and PIC micros didn't fix issue and voltages measure ok.

[Lester]

Hi Brendan, I have done a cold start and it is in sidereal rate. As all this is now getting way over my head, can I post my unit with motors, leads and hand controller to you?

[wasyoungonce]

I'll PM you.

[wasyoungonce]

Lesters Gemini all fixed sent back to Lester this morning. I absolutely love his Maxon motors.

My std servo motors go thru harmonic shudders & vibrations when ramping up & down high speed slew changes. His are perfect!.......mmmm maxon...where's the "drool" emoticon when you need it!

[Lester]

Must say I am very pleased with the indepth communication from Brendan, informing me of what he was doing etc. Eventhough some of it did go over my head as I am not overly versed in such electronics. It did give me peace of mind that my unit was in good hands. I was extremely pleased to not have to send my Gemini unit back to USA. Thanks a heap Brendan, you are doing a great service for the astro community in Australia. All the best.

[wasyoungonce]

Many thanks Lester...for interested folks the fault was a motor "H" bridge IC. Quite rare for these to go bad and an odd fault to indeed.

I investigated if fully as to why it went faulty ......but came up "I don't know"!:shrug:

[Lester]

I hooked up the motors and Gemini to the Titan mount this morning, and delighted to say everything works as it is supposed to again. Thanks to Brendan. I cannot recommend this chap highly enough, a great asset to the astronomy community. All the best.

[wasyoungonce]

Many Thanks for your kinds words Lester and thanks for letting me have the pleasure of tending to your baby!:thumbsup:

I must say I do like working on Gemini 1 units, they are a very cleaver design made top be repaired to component level. You don't see that often in designs these days.

[allan gould]

Well done, Brendan. If anything goes belly up with my Gemini unit I know who I will be contacting first.

[wasyoungonce]

Thanks Allan...I now pretty much have almost a full compliment spares parts for the G1: IC's; transistors; diodes; resistors and capacitors. I went thru and identified them all and stocked up, appart from EPROMs. I'd hate to be given one to repair and have to wait for parts to arrive.

Those with Gemini 1's ...please be careful with your DIN motor leads and how you put them in. Many a one is damaged by this when done incorrectly.

Rene did a nice job designing the Gemini 1, it was made to be fixed. I suspect the G2 is as well, but this time with better ground loop protection and I do know it has much better motor encoder protection!

So those with G2's...major problems of the G1 should never occur.