soldering to pcb rs232 pins

Forums › Gadgets, robotics, home automation, electronics (including wearables) › soldering to pcb rs232 pins

rmt38

320 posts

Ultimate Geek
+1 received by user: 56
Inactive user

Topic # 151482 27-Aug-2014 10:32

I've not done this before, so hoping to get some advice or pointers before proceeding.

I've bricked a device, and it does not have an rs232 port, so want to try adding one. I do not have any electronic equipment, or for that matter experience using them, and am looking at buying some. After doing some research the following sounds suitable for pcb modifications that do not involve removal of existing bits and pieces from the pcb.

25W soldering iron.
solder wick
flux
usb ttl uart doodad of some sort.

So, is this sufficient for tools? Is there a good place to get them? If it's not sufficient, then why not and what do I need? Is there a good cheap beginners kit which anyone would recommend?

The device is my LG BP125 dvd/bluray player. The bricking won't be the last time, as I am trying to get the firmware format right.

I've narrowed down the uart pins. On the top of the PCB, there are TP701 and TP702. These go nowhere and pretty much go in directly to the MediaTek 8551 chip pins of T3/FEGIO10 and U1/FEGIO11, whose primary purpose according to the service manual for another model with the same chip is PC RS232 RX/TX respectively.

My understanding is that it should suffice to solder these two pins to the usb ttl uart doodad, as well as a ground pin, and the power pin of the doodad can be ignored. Then it's a matter of getting the terminal configuration correct on my computer with the doodad connected. This sound like I'm on the right track?

Any advice is appreciated. Cheers.

Here's the top of the pcb:

Top of PCB

Bottom of PCB:

pcb bottom

linw

1894 posts

Uber Geek
+1 received by user: 369

Subscriber

Reply # 1116327 27-Aug-2014 11:09

Strange you don't have solder on your list. Add 60/40 resin cored solder and delete the flux. The solder has resin flux in it.

Also, get a bigger wattage iron, say, 40W. This would handle things with more metal e.g. bigger wire. Just don't hold the iron on for any longer than necessary or you could damage parts or lift tracks off the board.

Google soldering and you will be deluged with good info.

Good luck.

floydbloke

1669 posts

Uber Geek
+1 received by user: 788

Reply # 1116343 27-Aug-2014 11:19

Jaycar is probably the best place to get a cheap iron and some solder (cat no.TS1465 and NS3092 should do you, < $20). Ebay is probably the best place for a USB-TTL cable/adapter, < $5 but it will come form somewhere in Asia so could take a couple of weeks to land. Drivers for it shouldn't be too hard to track down(most of them seem to be PL2303 based, this driver should work: http://www.prolific.com.tw/US/ShowProduct.aspx?p_id=225&pcid=41.
That should give you a virtual serial port on your PC, so note the COM port that has been assigned use something like TinyTerm as a terminal emulator to connect.

If you don't have soldering experience this will probably be the trickiest part. I suggest you practice first by pulling to bits a redundant piece of electronics (like a walkman or an alarm clock) and solder some wire to some rand point on the PCB _ DON'T PLUG IT IN.

Most of the trouble in the world is caused by people wanting to be important. (T.S. Eliot)

rmt38

320 posts

Ultimate Geek
+1 received by user: 56
Inactive user

Reply # 1116567 27-Aug-2014 15:09

floydbloke: Jaycar is probably the best place to get a cheap iron and some solder (cat no.TS1465 and NS3092 should do you, < $20). Ebay is probably the best place for a USB-TTL cable/adapter, < $5 but it will come form somewhere in Asia so could take a couple of weeks to land.

Here's a decent looking one on trademe:

http://www.trademe.co.nz/electronics-photography/other-electronics/electronic-components/other/auction-770910999.htm

What's the best way of connecting up to the trace points on the pcb?

Just to confirm, I need to connect the ground and tx and rx, but do not need to connect the 5v?

rmt38

320 posts

Ultimate Geek
+1 received by user: 56
Inactive user

Reply # 1116570 27-Aug-2014 15:12

linw: Strange you don't have solder on your list. Add 60/40 resin cored solder and delete the flux. The solder has resin flux in it.

Also, get a bigger wattage iron, say, 40W. This would handle things with more metal e.g. bigger wire. Just don't hold the iron on for any longer than necessary or you could damage parts or lift tracks off the board.

Google soldering and you will be deluged with good info.

Oh, I've done tonnes of googling and watched various videos. The problem is that the information isn't specific enough for me to be sure, and sometimes it conflicts. So it's best to double check.

Thanks for the advicew :-)

floydbloke

1669 posts

Uber Geek
+1 received by user: 788

Reply # 1116639 27-Aug-2014 16:09

...

Here's a decent looking one on trademe:

http://www.trademe.co.nz/electronics-photography/other-electronics/electronic-components/other/auction-770910999.htm

...

That should work.

...

What's the best way of connecting up to the trace points on the pcb?

...

Get some solid core (not stranded, it'll fray everywhere) hook-up wire. Do you have an old piece of ethernet cable (not flylead - you need the stuff that goes in the wall), you can strip that back. Strip a bit of plastic of the end and melt some solder on to the copper. Touch the iron on the solder pad on the PCB until it melts (a second or two) . Touch the pre-tinned wire on to it and watch it fuse together (another half second or so). Remove the iron and let the 'weld' cool for a second or so to set it. You can now let go of the wire. Rinse and repeat for the second one.

As I mentioned earlier, have a practice first on some old redundant kit.

For the other end, again strip it and the end should just about fit in the connector of the USB converter. If it's a bit loose you can again tin it with some solder find an old header pin and solder that on the end.

Remember the TX pin from the USB converter(white) connects to RX on the PCB.

Ground will definitely need to be connected, the converter should be able to get its V++ from the USB port

Does the docco have the comms settings? I'd expect something like 9600 baud, no parity, 8 , 1.

Most of the trouble in the world is caused by people wanting to be important. (T.S. Eliot)

Niel

3267 posts

Uber Geek
+1 received by user: 77

Trusted

Reply # 1116661 27-Aug-2014 16:20

Don't need flux, it is not tarnished. You do need solder. Assuming the assembly is lead-free then you should get lead-free solder, because lead and lead-free does not mix (incorrect term, but not enough space for details) and will form a weak joint. That said, I have mixed it a number of times and will still last a number of years as long as it is not subject to vibration.

You can never have enough Volvos!

Niel

3267 posts

Uber Geek
+1 received by user: 77

Trusted

Reply # 1116666 27-Aug-2014 16:32

Do not connect the 5V, it just comes from the USB port. Question is, should it be 5V levels or 3.3V levels? The converter probably output 3.3V, the player could be either (you can check by measuring between ground and either RX or TX). You might want to connect a 100 Ohm resistor (any power rating, suggest 1/4W and solder it to the PCB) in series with the RX and the TX lines (i.e. 1 resistor for each).

You can never have enough Volvos!

rmt38

320 posts

Ultimate Geek
+1 received by user: 56
Inactive user

Reply # 1116759 27-Aug-2014 18:22

Niel: Do not connect the 5V, it just comes from the USB port. Question is, should it be 5V levels or 3.3V levels? The converter probably output 3.3V, the player could be either (you can check by measuring between ground and either RX or TX). You might want to connect a 100 Ohm resistor (any power rating, suggest 1/4W and solder it to the PCB) in series with the RX and the TX lines (i.e. 1 resistor for each).

I don't have a multimeter, and after doing a bit of research on it, it should like more research is needed to get a decent one that is useful for pcb-related work.

Here's the chip pin details. It sounds to my inexperienced eye, that no testing should be needed. 3.3V is what it should be, but 5V is safe. Is this correct?

gzt

10033 posts

Uber Geek
+1 received by user: 1516

Reply # 1116765 27-Aug-2014 18:38

You might get lucky with the soldering but this might not be a good project to start on. It takes a while to get the technique and avoid overheating, overuse of solder, correct temperature. If you get it wrong with this board you may not get a second chance. Compulsory warning over ; ). Anti-static protection would be a sensible addition to your kit.

floydbloke

1669 posts

Uber Geek
+1 received by user: 788

Reply # 1116803 27-Aug-2014 19:51

floydbloke:... something like TinyTerm as a terminal emulator to connect.
...

I got that wrong sorry, use Tera Term. (TinyTerm would probably work, but it's not free, Tera Term is free.)

Most of the trouble in the world is caused by people wanting to be important. (T.S. Eliot)

Niel

3267 posts

Uber Geek
+1 received by user: 77

Trusted

Reply # 1117346 28-Aug-2014 16:27

rmt38: Here's the chip pin details. It sounds to my inexperienced eye, that no testing should be needed. 3.3V is what it should be, but 5V is safe. Is this correct?

Correct, based on the information presented.

You can never have enough Volvos!

richms

21292 posts

Uber Geek
+1 received by user: 4296

Trusted

Subscriber

Reply # 1118461 30-Aug-2014 11:41

Get a roll of "wire wrap" wire - its ideal for this sort of thing, nice and thin. I went thru miles of the stuff back in the day on playstations and then xboxes.

Strip off the insulation, put it and some solder against the soldering iron to tin it with a layer of solder, then put the wire over the terminal and push down with the soldering iron till it all flows together. Remove iron and hold the wire still till it solidifies.

If its going to be permanant then use some hot glue a couple of cm down the wire to hold it to the board so it doenst move and break off over time.

Richard rich.ms

Niel

3267 posts

Uber Geek
+1 received by user: 77

Trusted

Reply # 1118463 30-Aug-2014 11:44

Good reminder about the wire wrap wire. Just keep in mind usually it is mildly poisonous so don't put it in your mouth when you run out of hands ;-).

You can never have enough Volvos!

SepticSceptic

1735 posts

Uber Geek
+1 received by user: 348

Trusted

Reply # 1121218 3-Sep-2014 16:03

You can get solder-thru wire wrap, where you don't need to strip off the insulation - just needs a second more of extra soldering time, and the insulation chars off, allowing the wire and the joint to be soldered.
Wirewrap can be tricky to remove the insulation from, as the wire is easily nicked by the stripper, and once nicked, is a weak point, and will fail with more than a couple of flexings.

My thoughts are no longer my own and is probably representative of our media-controlled government