Need help replacing surface mount chip

Electronics
#1

So I have a Celestron telescope w/alt-az mount where the altitude won’t work (azimuth works fine). I keep getting an error. With the help of an astronomy forum (Cloudy Nights), we’ve narrowed it down to the L293DD chip on the board. I can pick one of those up from Mouser next Friday (unless someone happens to have an extra one!).

Is there anyone that can help me desolder the old chip and then solder the new L293DD chip onto the board? I have experience soldering circuit boards, but have never done it with a surface mount chip. I want to make sure to not burn or damage the board. I’d probably be looking for help next weekend if someone with experience is available.

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#2

Normally I’d say “electronics office hours” but I can’t do another one before the 23rd.

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#3

I can come Into the workshop next Sunday afternoon and give you a hand if that works for you. I usually get there around 1 or 2.

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#4

I will not be in again until the 23rd

#5

Did you guys get it done?

#6

No I by next Sunday I mean the 12th of May

#7

I have done some professional soldering so. Could be an alternative. Do we have quick chip? Or low melt/ silver solder?

#8

Sorry for the late response. I’m at a conference which is why I can’t do it any earlier than next weekend. It looks like I can go to Mouser to pick one chip up or get it off Amazon with 1 day shipping. Worst case, if I have to wait until the next weekend (17/18/19), I can do that too. I’ve been told that 98% of the time, that is the chip that goes bad, so to change that out.

#9

So I just got home from the conference and got a pack of 5 of the chips delivered today from Amazon. I can come on Sunday, but want to make sure you don’t have anything planned for Mother’s Day before we make plans to meet.

Here’s exactly what the person told me…

I’m pretty sure (98%) that it’s the usual issue with Celestron mounts: the L293DD chip has died on at least one of its four outputs. Replace that chip, and it very likely will be all good again. Maybe the ALT “PIC” chip could be bad. That’s a lot more rare than the L293DD though, and much more difficult to deal with. Replace the L293DD first, and odds are that’ll take care of things. If not, then the ALT PIC is the culprit.

#10

Yeah I will be available Monday afternoon I don’t have anything planned until later that evening. It should only take a few minutes to get the new chip installed and anytime between 1 and 4 should work for me

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#11

I hope you meant Sunday and not Monday. LOL I will plan to be there Sunday between 1-4pm…probably closer to the 1-2pm timeframe.

#12

sorry yeah I mean sunday (today)

#13

I’m heading out. I’m going to grab some lunch and then I’ll be there. It should be by 2:30pm. I wanted to bring my telescope so I could test it there, but not with the rain. I’m bringing the board and chips though. Hopefully, at least 1 chip is good! :joy:

#14

I wanted to thank @RiBarrjr for helping me replace the chip today. Unfortunately, it didn’t work. :sob: So either it’s the PIC chip or the L293DD chip we replaced it with is bad. I couldn’t bring the actual telescope to test things there because it was pouring rain all day. I’m going to call the manufacturer to find out the cost to replace the board, but I might need to wait until the 23rd to have someone help show me how the board can be tested to narrow down the issue better. If it’s the PIC chip, then I just need a new board. :cry:

#15

I’ve already done the EXACT same thing to my alt-az Celestron mount.

Do yourself a favor that I didn’t do:

Do not try to de-solder the chip. Snip its leads and pull the chip off. Then individually pull the remaining legs off with a soldering iron and tweezers.

I have a desoldering station with hot tweezers at my office and would be happy to help you. When I did mine I didn’t do this and ended up lifting some traces so I had to solder in bodge wires to repair. I know how to avoid this now.

Hit me up. We can meet at my office and bang this out.

Edit to add: Didn’t read the thread and didn’t realize you’d already replaced the chip. First, I’d have ordered from Mouser not Amazon. Second, you may find that the board is not available from Celestron. Mine wasn’t.

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#16

Just like @mdredmond mentioned, I was told the board would be hard to find. They suggested doing this to see if it’s something other than the PIC chip since I was able to have it connect to the Celestron update software once. When I was doing that, the software wouldn’t see it for the numerous times I tried. Then I got it to recognize it one time and quickly did the update. Then it wouldn’t recognize it again. It was like it had a blip of a moment where it connected correctly.

Concentrate on the signal path from the ALT MC PIC back to the hand-controller, checking for bad connections along that path. Also check the onboard power supply – regulated 5.0V. Maybe look at it on a scope to verify that it is clean – check the capacitors.

Is this something that can be done at the Makerspace if I bring in the telescope? This would actually be really educational for me if we can do it there. I was telling @RiBarrjr how I wish there were classes because I would love to learn how to use the tools we have. I couldn’t bring it in yesterday because it was pouring rain.