Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

10” LX200 Classic sparked and died

  • Please log in to reply
28 replies to this topic

#26 MikeBY

MikeBY

    Mariner 2

  • *****
  • Posts: 228
  • Joined: 28 Aug 2019
  • Loc: Huntington Beach, CA

Posted 24 September 2021 - 05:49 AM

I removed the C3 Tantalum Capacitor on the Power Panel and was getting ready to replace it when I noticed the C1 nearby was fried.  Can I use the same type (10µF 50V) electrolytic capacitor I'm replacing at C3 to replace the blown C1 or does the C1 need a different capacitor?  Strangely, my LX200 was working fine even with the C1 blown (see below).

Sir,

C1 is the ONLY capacitor that needs to be changed. There is no reason to change C3. C3 is across the 5v tightly controlled output of the voltage regulator right next to it and is well within it's 25v spec. C1 is across the +18vdc input and is the one at risk. On every board, there is 1 capacitor across the 18V input to the voltage regulator. That is the only capacitor that needs to be changed.

 

When C1 failed, it shorted out and then burned. When the short occured the scope would have stopped working  and the odor of the burning cap would have been noticed. Fortunately the cap did not continue to burn (the fuse should have failed). 
In large high power systems these capacitors can cause a full blown fire.

 

Please be sure you are changing the correct capacitors!

 

 

 



#27 NearVision

NearVision

    Ranger 4

  • -----
  • Posts: 381
  • Joined: 23 Sep 2017
  • Loc: SE Wisconsin

Posted 24 September 2021 - 07:27 AM

I've seen capacitors fail just because they want to even with the voltage much lower than they were rated for. It's VERY rare but can happen. Capacitors can fail simply from old age and the way these old tantalum caps fail is usually a spectacular fireball.

 

For the belt and suspenders types among us it doesn't do any harm to change all of the old tantalum caps while you are in there.

 

Again; it's very rare to just fail but it can happen. I've seen it 2 or 3 times in 50 years.



#28 Michael Covington

Michael Covington

    Author

  • *****
  • Posts: 6,953
  • Joined: 13 May 2014
  • Loc: Athens, Georgia, USA

Posted 24 September 2021 - 05:05 PM

Another thing worth remembering is that modern electrolytics are much better made than those of the early 2000s.  

I would use name-brand (Panasonic, Nichicaon, etc.) electrolytics rated for an extended temperature range, voltage equal to or higher than the original, capacitance preferably within about 10% of the original, higher if different (e.g., changing 3.0 to 3.3 is OK).  Even the highest-grade capacitors are quite inexpensive now.   

To avoid counterfeits, buy from a real distributor (Digi-Key, Mouser), not Amazon or eBay, and avoid Chinese off-brands.

Here's a lot more about electrolytic capacitor life.  I confine myself to (aluminum) electrolytics; tantalums are worse.
http://www.covington...ex.html#x191006
 


  • MikeBY likes this

#29 MikeBY

MikeBY

    Mariner 2

  • *****
  • Posts: 228
  • Joined: 28 Aug 2019
  • Loc: Huntington Beach, CA

Posted 24 September 2021 - 11:45 PM

I've seen capacitors fail just because they want to even with the voltage much lower than they were rated for. It's VERY rare but can happen. Capacitors can fail simply from old age and the way these old tantalum caps fail is usually a spectacular fireball.

 

For the belt and suspenders types among us it doesn't do any harm to change all of the old tantalum caps while you are in there.

 

Again; it's very rare to just fail but it can happen. I've seen it 2 or 3 times in 50 years.

For someone who does not have professional level soldering skills the risk damaging a trace, soldering pad or through hole on a 25 year old double sided or multilayer circuit board is far higher than the chance that a 25v tantalum cap used in tightly regulated

5 volt circuit will fail in a "short" mode and cause damage when only 5 watts of power are available. 

The OP is obviously confused. hanging He was changing C3 and 'noticing' C1.

Should have been changing C1 before even considering anything else. 

and he says he's going to wait on C8 on the main system board. 

I could understand reluctance to work on the two motor boards as they are particularly difficult to get to and have very delicate wiring to the encoder sensors.  

Those of us that have done this type of work professionally know that these boards are very easily damaged. 

Do only what must be done.

 

Replace the 18VDC AC powered supply with a well regulated supply. Those old supplies are poorly regulated and noisy. I've seen them put out 23VDC. 


Edited by MikeBY, 24 September 2021 - 11:46 PM.

  • Michael Covington likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics