21 replies to this topic

[TONGKW]

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Last night while setting up my 8” LX90 in the dark, I found the telescope was not operational.
I discovered I had accidentally connected the electrical supply cable ends to the wrong terminals of the 12-volt battery. After I reconnected the supply cable ends to the correct terminals, the Audiostar hand controller had “died” and is not working anymore.
It would appear there is no reverse polarity protection in the system.
May I know the extent of damage that this wrong connection had caused.
Is this damage repairable by a person with little knowledge in electronics or the whole telescope has to go back to Meade for the repair.

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[Christopher Erickson]

It should be repairable by someone with reasonable electronics knowledge.

 

There will be parts that need replacing and probably melted traces that will need jumpering.

 

You might need a new hand controller too.

[TONGKW]

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I have managed to open up the fork arm's end cover and removed the power circuit board to have a look.
As can be seen in the picture, there is a burnt trace from pin 1 on JP3 to pin 4 in JP1.
There appears to be no other burnt mark elsewhere.
As a test, with the Audiostar hand controller in place and the 12-volt supply switched on, when I touch a copper wire between pin 1 and pin 4, the telescope comes back to life.
It would appear the damage is just the burnt trace.
I like to effect a permanent repair, is it easy to get hold of a replacement power circuit board?
Failing that, is it possible to install a jumper wire between pin 1 and 4?
Also may I ask is there anything else that I need to check.

 

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[nitegeezer]

This trace can be repaired, but be very careful.  This time the trace worked like a fuse and probably saved the board.  If you replace the trace with any significant sized wire, it will not be the weak link in the chain and next time the failure could be more catastrophic!

[Peterson Engineering]

This is a universal Meade weakness.  For the lack of a 50 cent diode.  You may want to use a diode or a fuse as your jumper.

 

Pete

[Starkid2u]

No, what you WANT to do is contact jaymcgil19 here at CN. He repairs the LX series of Meade telescopes. Lay everything out for him and he will tell you what's next. You can send him just the electronics or the whole scope, depending on how bad the damage is. It sounds like it localized but let him tell you what's what. He took care of my LX 200 Classic and I couldn't be happier! Good luck!

 

STARKID2U

[Geo.]

This is a common problem. I've repaired the same scope twice. The second time was to replace the fuse I added=8)

 

Here's your problem: 

 

 

 

You ran reversed polarity to the EXT. GND. and PWR +. 

 

This shorted the trace, but the motor control boards and HBX are protected by their L7805 voltage regulators.

 

Putting a jumper between JP3 pin 1 and JP1 pin 4 should get you up and running, but adding a diode and fuse are a good idea as any jumper will carry more current than the trace and the damage will occur somewhere else.

 

 

[TONGKW]

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Thank you all for the information and advice.
As can be seen the obvious damage and there may be some other partial damage to the power panel, I would like to carry out a permanent repair by replacing the power panel rather than solder on a jumper wire.
From now on I shall use an external battery with a fixed plug-in end connection to prevent such stupid mistake from happening again.

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[Christopher Erickson]

Here is a version of the schematic that I created.

 

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[TONGKW]

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CN fellow member Geo is so kind to provide me with a spare power panel to replace the damaged one.
I have thus managed to effect a proper repair to my LX 90 by replacing the power panel instead of soldering up the burnt trace on the damaged power panel.
I am told the LX 90 shares the same power panel with the ETX90, ETX105 and ETX 125.
My LX 90 fork is an old one having the power panel with eight pin out whereas all the newer panels have 10 pin out.
The two extra pins are for LNT/AUX and not needed in my case.
I exercised care to make the connections.
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My LX 90 is now alive and well.
To prevent the same mistake of connecting the wrong battery terminal from happening again in the dark, from now on I use a 12-volt battery with a fixed outlet terminal wire and a fixed end plug, like the one shown here.

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[TONGKW]

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My LX 90 is a “Frankenscope” and consists of an old LX 90 fork and a Meade 8” SCT OTA from the LXD 75 series and mounted on an old Gitzo 1505 aluminum tripod.
My LX 90 setup is still transportable by one person.
The weight of LX 90 fork and OTA is 33 lb and the Gitzo 1505 tripod 10 lb.
I put the LX 90 into a luggage case with wheels, hand carry the tripod and with accessories in a backpack.

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[LU1AR]

After read this tread, I add a protection diode inside the old ETX125 I'm restoring. I will use an external -fused- battery, with a fixed plug-in end connection. I have managed to open the bottom cover and located the power circuit board.
The diode1N4001 replace the short trace, from center pin on S1 to pin 3 in JP1. This avoid damage your telescope, and accesories. I hope this will be usefull. Edgardo

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[Piet Le Roux]

Good day Edgardo,

The diode in series will definitely give you reverse polarity protection but you will also be getting a 0.6 volt drop so your 12 Volts will drop to 11.4 volt. I prefer to install a fuse via a fuse holder and after the 1-2 amp fuse I place a diode with its cathode to positive and anode to negative : this way there is no voltage drop and during reverse polarity the fuse would blow immediately. One could even use a high current zener diode of about 16 volt : then you got reverse protection and over voltage protection.        

Edited by Piet Le Roux, 09 March 2020 - 02:31 PM.

[Piet Le Roux]

I finally had the time to install a better aux 12 Volt input socket and fuse holder on my LX90. I basically  connected it in parallel with the internal batteries, that I don't use, but all the positives are fused before #2 of the switch and has diode protection, between #2 of the switch and negative, for reverse protection. I don't like the aux input on the panel because its not robust enough for frequent use and has a internal switch that disconnects the negative of the internal batteries and aux input, this is prone to cause a bad connection.

 

[Andrekp]

Good day Edgardo,

The diode in series will definitely give you reverse polarity protection but you will also be getting a 0.6 volt drop so your 12 Volts will drop to 11.4 volt. I prefer to install a fuse via a fuse holder and after the 1-2 amp fuse I place a diode with its cathode to positive and anode to negative : this way there is no voltage drop and during reverse polarity the fuse would blow immediately. One could even use a high current zener diode of about 16 volt : then you got reverse protection and over voltage protection.        

I was going to note this voltage drop as well.  I build guitar pedals.  I put in reverse polarity protection normally.  Instead of using the 400x diodes, I tend to use Schottky diodes, which have a much smaller drop.  .2-.3 volts if you pick through.  It is also quite possible that the voltage drop doesn’t matter, since anything inside that cares about voltage, may well be using a voltage regulator circuit to feed it that is lower voltage than the 12v in.

 

Andre

[Watto1963]

Afternoon all. Looking for some thoughts please.

My LX90 has been stored in the garage for several years. Just got it out, popped in a new set of batteries, flicked the power switch and nothing. Autostar did not come on nor did the power light. I then plugged in a 2.5mm 12V 6A power adaptor into the scope by the power switch, still nothing. So I have extracted the Power PCB. Now I really have no idea what to look for but I have a photo here in case there is something obvious to one of you?

Also, my question would be, if the power light does not come on, does that mean the issue will be limited to the Power PCB? I'm hoping that will be the case as I could then send it off for testing..

 

 

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[michael8554]

First you need to test for the presence of 12V on the rear of the power socket, and at the connection to the Power PCB

 

Then look for damage on the component side of the PCB.

[Watto1963]

Thanks Michael8554

So I have tested the output from each battery pack, one gives out 6v, the other 0.3v!!! I'm not out of the woods yet because -

Why is my power adaptor not working, tested that and it's fine. Potentially the port in the scope is no good (never tried it before). ??

So looking at the picture I suspect the copper cable is corroded and not letting the current through. So to fix this first I think. My question is, anyone know what on earth the corroded connector is called? I cannot find one that looks like it, so knowing it's name will help.

[michael8554]

Well you may need to repair the corrosion at some point.

 

But if the mount isn't powering up with the power adapter, then you should concentrate on tracing 12v through the power socket and onwards.

[Watto1963]

Update - After just connecting the power two pin connector to the power PCB, I have 12 volts and a power light coming on!! So after removing power, I reconnected the DEC and RA 4 pin connectors to the Power PCB. Turned on, no power light.

So I still have to start checking the PCB will my multimeter (this will be a learning curve!!) but any thoughts whether the above scenario suggests a Power PCB problem still?

[Watto1963]

Update - After just connecting the power two pin connector to the power PCB, I have 12 volts and a power light coming on!! So after removing power, I reconnected the DEC and RA 4 pin connectors to the Power PCB. Turned on, no power light.

So I still have to start checking the PCB will my multimeter (this will be a learning curve!!) but any thoughts whether the above scenario suggests a Power PCB problem still?

So I failed to get the cover off the panel without fear of completely busting it. 

So after a 2 month wait, Meade USA sent me a new Power Panel PCB. It has a 10 pins rather than 8 pins . I just attached my 8 PIN connector from JP3 end as per original setup. 
Power on, successful! Connected the controller and bother motors can be activated, so the "spare 2 pins" don't seem to be an issue.
Just need to re-assemble the cogs on the mount arm etc.

Any thoughts on the type for grease/lubricant worth using for the gear?

[Skywatchr]

So I failed to get the cover off the panel without fear of completely busting it. 

So after a 2 month wait, Meade USA sent me a new Power Panel PCB. It has a 10 pins rather than 8 pins . I just attached my 8 PIN connector from JP3 end as per original setup. 
Power on, successful! Connected the controller and bother motors can be activated, so the "spare 2 pins" don't seem to be an issue.
Just need to re-assemble the cogs on the mount arm etc.

Any thoughts on the type for grease/lubricant worth using for the gear?

Use a good synthetic that has good low temp characteristics (doesn't get thick/stays consistent), and one that resists the base oils from separating over time. There are lots to choose from these days.  I've used SuperLube with PTFE (Teflon) for many years but I am sure there is something better by now.