LM2596t-5.0

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7 months 2 weeks ago #9639 by jonboy
LM2596t-5.0 was created by jonboy
Hi guys,
I brought my first nixie clock diy board from ian Sparkes classic version 5, last year, and have only just got around to building it. ( i know, why do long!)
I have two questions.
1) after building the basic circuit board components, things were looking good. When plugged in the red led came on to tell me everything was looking okay.
I then built up the extras for the front display case, the light sensor, rgb led, tick led, switch.
When I plugged it back in again to test it, the LM 2596 got really hot. So I unplugged it again, took off the external bits, waited for the chip to cool down, and plugged it in again.
This time the red led did not light up.
I used a 12v supply, and now I get 12v ish at all test points on the board, including the HV point. The led still lights if I connect it to a multimeter, but doesn’t when connected to the 12v supply.
So what have I fried?

My 2nd question.
When I brought my kit I brought a extra circuit board, so I could build another one Incase I messed up the first one. Looking around I am finding it hard to get a LM2596t-5.0 chip in Ireland. I usually order from Farnell element 14 as they do free postage in Ireland.
What though can I use instead of this?
Will a LM2596sx-5.0 be okay? Or even a LM2596s-5.0?
Any suggestions would be gratefully received.

I am looking forward to getting things back on track, so thanks for your help.

Jon

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7 months 2 weeks ago #9643 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic LM2596t-5.0
Replacing the LM2596 seems like a reasonable first step. It sounds like it isn't regulating anymore (12v readings all over the place) so it's definitely a prime suspect. Perhaps you created a short form Vcc to Gnd when you hooked up the external parts. LM2596 claims to have short circuit protection built in but I've yet to see a totally indestructible component!

It's hard to say what else might have been damaged. Seeing 12v at all the test points is a bit disturbing since there are several things on that board that would not like it. However, you said the power LED does not light now but is not damaged (still lights when tested with meter) so perhaps the 12v is getting thru at very minimal current(?). Also it's not clear from your post how much of the board you have completed, e.g. whether the microcontroller and other chips are installed yet.

Those alternate part numbers you listed for the LM2596 are functionally the same but the package is different. Looks like the "sx" and "s" are intended to be surface mounted but the pin spacing is the same as on the "t". It should be possible to make it fit without much trouble. Here's the data sheet, check out pages 36, 41 & 42.

www.ti.com/lit/ds/symlink/lm2596.pdf

Look into it later when the dust is clearing off the crater.

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7 months 2 weeks ago #9648 by jonboy
Replied by jonboy on topic LM2596t-5.0
I have ordered in a new LM2596t. I managed to get 2 sent over from USA via a site called arrow. I have never used them before but the offered free DHL postage to Ireland so I thought I would try them.

I had completed the whole board before this happened, all the chips and micro controller were on board, so hoping I haven’t done to much damage.
I suppose I have to start replacing things, so the LM 2596 seems as good a place as any to start. Hopefully it will desolder okay as the pins are very close together on this board. (Version 5b board)

Thanks for your help so far.
Jonathan

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7 months 2 weeks ago #9651 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic LM2596t-5.0
A good way to get the old regulator out is to cut off the pins close to the body of the part. This way you can deal with the pins one at a time instead of fiddling about trying to either get all 5 to melt at once or get 100% of the solder removed from every pin. Heat each pin from the bottom while pulling from the top side with needle nose pliers. Keep hot time to a minimum as it's pretty easy to cause a pad to lift from too much heat.

The micro and the decoder/driver may or may not have sustained damage. The optocouplers and the rest of the parts should be just fine.

I'm familiar with Arrow Electronics. Nothing bad to say about them - they're reliable in my experience. Free shipping to Ireland sounds like a really good deal.

Look into it later when the dust is clearing off the crater.

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7 months 2 weeks ago #9654 by Ian
Replied by Ian on topic LM2596t-5.0
Unfortunately, you'll have to take it a step at a time. Pull everything out of the board that is socketed, and we'll have to start over.

Ty's right, sacrifice the 2596. Personally, I'd cut the legs close to the body, and this gives you two possibilities: firstly you can solder the the new part directly on the stubs that are left over to see if there is more work that is needed. Secondly, it will let you pull the legs more easily. Don't try to do them all in one go, you'll just end up frying the board.

In general, if you need some new bits, I can supply them as part of the service. I don't usually charge for people needed extra pieces, the idea is to get the thing working. Please bear this in mind when we get to the next step. I suppose like Ty says, the controller has taken a hit.

I'm a bit confused why it should have failed. That's really unusual. The usual way is that a flying lead touched something it shouldn't have, or that there was something metallic laying around on the workbench which caused a short.

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7 months 2 weeks ago #9664 by jonboy
Replied by jonboy on topic LM2596t-5.0
That was very annoying, I had just typed up a great reply and I got logged out and think my reply has gone to the great internet in the sky!

Anyway, this is roughly what I just said....

I am glad I brought a extra board at the time I brought the kit, as rather than try and take everything off the board and reinstall it, I will just transfer it onto the new board.
I have resistors, capacitors, inductors, that are new so I won’t need to worry if it any of them that are blown. I just hope it’s not the atmega chip of the k155.

I think (know) most of what happened was my fault, I was trying to read and solder at the same time. It was the RGB LED that did it to me.

One section in the manuel where the picture of the RGB led is, it says the longest lead goes to the first pin on the SV6, but in the text says the red pin connects to pin 1 and the common anode connects to pin 4 of SV2
So while working that out, and now thinking that on the the SV6 the pins go from left to right red, green, blue, tick led and the common anode of both, go to SV2 pin 4, I think the stray wires may have come into contact with Vcc and ground and that’s what has lead to where I am now.

So, with two experts on hand, hopefully when my new 2596 arrrives I will be able to start again!!

Thanks for your help and I will let you know what happens soon.

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