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Is this Losmandy 492 fixable?

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#1 MockTender

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Posted 24 January 2021 - 07:08 PM

Went outside to look at stars a couple of nights ago and everything worked fine, but the 492.  At first it would not sart up after plugging in to a AC to DC adaptor.  The indicator on the adaptor looked like the 492 was getting dc, but no lights came on the unit.  So I went to my truck to use the 12vdc outlet.  As soon as I turned on the 492, it started to smoke. I opened up the case and everything, but the small capacitor above the on/off switch looked fine.  That small capacitor was fried at each end.

 

So I have three questions:

 

1) I have read about problems with 492 switches- is this one of those problems? 

 

2) Could I relpace the capacitor or does this look and sound like a new motherboard?

 

3) What are the ways to safe guard against this happening again? 

 

 

Mark

 

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#2 D_talley

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Posted 24 January 2021 - 07:15 PM

I see you posted this twice.  I had that happen to my 492 and gave Scott a call.  He said that there was a batch of bad diodes that would let out the magic smoke.  I replace the diode and the system booted up fine.  Please check the board for a bad diode. I see one above SW7.  Clear evidence that it is the source of the smoke. 



#3 RichA

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Posted 24 January 2021 - 07:23 PM

I see you posted this twice.  I had that happen to my 492 and gave Scott a call.  He said that there was a batch of bad diodes that would let out the magic smoke.  I replace the diode and the system booted up fine.  Please check the board for a bad diode. I see one above SW7.  Clear evidence that it is the source of the smoke. 

Electronic manufacturers tend to use the bare minimum standard components they can get. When replacing diodes, caps, it's best to "uprate" them if possible, higher voltage for the caps.



#4 ngc7319_20

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Posted 24 January 2021 - 07:43 PM

Mine did the same thing.  The part is a diode.  On mine the +12V bus trace on the circuit board (underneath) touched one of the mounting studs / case, so +12V got shorted to ground through the diode.  Should be easy to fix.  You might pull the circuit board and check for un-insulated traces near the mounting studs.  Since it is a direct short of +12V supply line to ground, only the diode should be affected.


Edited by ngc7319_20, 24 January 2021 - 11:43 PM.


#5 ngc7319_20

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Posted 24 January 2021 - 11:26 PM

Found my notes...  Here are some pictures of the problem.  There is a sharp metal edge on the case that scribes into the +12V bus line on the board.  You  could check for same problem, then put some plastic tape where it is rubbing in the case.

 

1 opened case.JPG

 

2 PC board.JPG

 

3 closeup.JPG


Edited by ngc7319_20, 24 January 2021 - 11:51 PM.


#6 ngc7319_20

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Posted 24 January 2021 - 11:29 PM

Here's another board showing similar problem...

 

542019 xx.jpg


Edited by ngc7319_20, 24 January 2021 - 11:37 PM.

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#7 MockTender

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Posted 25 January 2021 - 04:34 PM

Thanks guys- great info!

 

Add mine to the list as well.  Contacted Losmandy.  The woman that answered the phone said that they no longer have any motherboards or parts for the 492 (they just weren't selling any).  She suggested I contact Brian in Tech Support and that he may know someone in the country that can supply the diodes and other parts.  Sent him an email- waiting.

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Edited by MockTender, 25 January 2021 - 04:36 PM.


#8 ngc7319_20

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Posted 25 January 2021 - 05:01 PM

This should work to replace the diode...  $0.35

 

https://www.jameco.c...Amp_879641.html

 

If you can pull any numbers off the old diode, we could try to get a more exact replacement.  But with 100 Volt, 4 Amp rating, this should work.  The diode needs to be installed the correct way around -- the silver band needs to be pointing to the right (like the old one).

 

The function of the diode is simply to block current if the input power polarity is accidentally reversed.  


Edited by ngc7319_20, 25 January 2021 - 06:16 PM.


#9 jp071848

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Posted 25 January 2021 - 05:06 PM

Thanks guys- great info!

 

Add mine to the list as well.  Contacted Losmandy.  The woman that answered the phone said that they no longer have any motherboards or parts for the 492 (they just weren't selling any).  She suggested I contact Brian in Tech Support and that he may know someone in the country that can supply the diodes and other parts.  Sent him an email- waiting.

Over on the Losmandy and Gemini Groups.io forums, there are three gentlemen (in California, the UK and in Oz) who do board level repairs on certain Losmandy control units. Sorry, not sure if the 492 is one of them. You may want to check over there and ask. Brian Valente, who Tanya suggested you contact, is active both here on CN as well as over on the Groups.io forums.
 




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