<div dir="ltr"><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, 19 Mar 2022 at 19:34, Chris Ellis via Wolves <<a href="mailto:wolves@mailman.lug.org.uk">wolves@mailman.lug.org.uk</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi James<br>
<br>
On Sat, Mar 19, 2022 at 2:52 PM James Dutton via Wolves<br>
<<a href="mailto:wolves@mailman.lug.org.uk" target="_blank">wolves@mailman.lug.org.uk</a>> wrote:<br>
><br>
> Hi,<br>
><br>
> I know this is not Linux, but I know some people on this list play with electronics.<br>
> I have a component I wish to replace on a PCB.<br>
> NCP1250<br>
> It is a TSOP−6 package about 1.5 x 3 mm. It is a chip with 6 pins.<br>
><br>
> I have not done surface mount stuff before.<br>
><br>
> As it is so small, what do people suggest as options for going about doing it?<br>
<br>
That should be pretty manageable with just a standard soldering iron.<br>
<br>
The general trick with SMT hand iron work is rather counter-intuitive,<br>
basically be messy and then clean up. Desoldering braid and some flux<br>
paste is very essential.<br>
<br>
Essentially, tack one lead into place to align it. Then drag a solder<br>
ball over the pins, don't worry about bridges. Then clean up with the<br>
desoldering braid. Volia a clean looking SMT joint.<br>
<br>
The other option is to buy a hot air SMD rework station, you should be<br>
able to get one on Ebay/Amazon for ~£30ish (tend to go by the name<br>
858D). You can use this to reflow just the specific parts. Easy to<br>
remove the part.<br>
Then add solder to each pad with an iron, cover in flux and use the<br>
hot air to reflow.<br>
</blockquote><br><div>Hi Chris,</div><div><br></div><div>Thank you very much for the advice and tips.<br></div><div>I have not needed or used a desoldering braid before.</div><div>I have a heat gun (blower) but I think it is more suitable for plumbing than PCBs, It has wide nozzles that would heat the whole PCB!!! <br></div><div>I was wondering how to do just one chip at a time so thank you for pointing me towards the 858D.</div><div><br></div><div>I am going to purchase some braid and the 858D before I continue.</div><div><br></div><div>I had already replaced the triac, because it was an obvious short, but it did not fix the PSU.</div><div>I have then removed some components to test them, and the rest I have tested in place.</div><div>As it turns out, all the components that have lost their labels are faulty, so it is turning out to be quite easy to fault find, if I was starting again from new, I would just check the ones with damaged labels!!!</div><div>It seems that SMT resistors are failing to become open circuit, and all the transistors/triacs fail to become shorts.</div><div>Is that a general rule for SMT resistors, or are they specific to this PCB ?</div><div><br></div><div>It has been fun finding out about SMT. For example, in my testing I found a few components that appeared to be shorts, but on further investigation I found out what a label of "0" means, :-)</div><div>In a through hole, one just uses a bit of wire, but for SMT, one uses actual components that look like resistors.</div><div><br></div><div>In case it helps others. With mains voltage and SMPS (PSU) , the voltage can be 340 Volts. But as the front end of the circuit is a rectifier, one can do all the testing with a 12V DC or 48V DC supply and the PSU should still function fine, and one can test with non-dangerous voltages. It does not necessarily provide the full amps at the output when you have it working, but it is much safer to work with and diagnose.<br></div><div><br></div><div>Kind Regards</div><div><br></div><div>James</div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div><div>Kind Regards</div><div><br></div><div>James</div><div><br></div><div><br></div><div><br></div><div><br></div><div><br></div></div></div>