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  • Joined: 11 Jul 2022
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Help needed to repair a SMS control pad
Post Posted: Tue Oct 04, 2022 12:29 pm
Hello

I have issue with a SMS control pad: Button 1 doesn't work and now even the UP on d-pad stopped working.

I tried to clean contacts with isopropyl alcohol but it doesn't worked, so I suspect the issue is more severe.

Do you have any tips?
UP and 1 button doesn't work, but the rest of button and directions work fine.

Thanks in advance.
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Post Posted: Tue Oct 04, 2022 12:59 pm
try it in the second port to ensure the problem lies in the pad and not in the console
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Post Posted: Tue Oct 04, 2022 1:07 pm
Maxim gave me a great tip on cleaning the pads which was to rub the conductive rubber disc on a piece of white paper which worked much better than a solvent cleaner for me.

Further to sverx's comment about checking the port, if it definitely is the controller you can also eliminate whether it's the conductive rubber or not by rotating the entire rubber assembly so that a different button actuates UP. If UP is still not working and if it's the same in both SMS ports then there must be a connectivity problem with the conductor from the switch contacts to the 9 pin connector. I think very unlikely there would be a problem with the switch contacts themselves as they are simply exposed tinned tracks on the PCB. If you have a multimeter and a short length of thin wire you can test for continuity between both sides of the switch contact pads and pin 1 (I think?) of the 9 pin connector.
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Post Posted: Tue Oct 04, 2022 3:01 pm
thank you for the tips!
I'll try both the "paper trick " and the second port work (but I don't think I have a 2 player game to test it at the moment).
Rotating the rubber is also a good idea.


Meanwhile I tried with a Mega Drive control pad (3 buttons) on port 1, and it seems to works fine, UP and 1 too.


willbritton I have a multimeter, but I'm a beginner, can you explain in depth how to test it with a thin wire?
Thanks
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Post Posted: Tue Oct 04, 2022 4:12 pm
Ah okay, so if the MD controller works it does suggest it's your SMS pad that's faulty.

Your multimeter almost certainly has a "continuity" mode, which is usually indicated by a kind of audible / speaker symbol somewhere. If you can't find it, send a photo of your meter if you like.

Continuity testing simply sounds an audible alert when the resistance between two points is close to zero. You can test this by putting the meter into continuity mode and touching the metal tips of both probes together. You should hear a beep. In the unlikely event that your meter doesn't have an audible continuity mode, you can set it to the lowest resistance setting (e.g. 200Ω) and again touch the probes together. They should read something close to "0" and will probably read something like "-" or "." when the probes are not touching.

Now that you know how to test for continuity, you can test your joypad something like this:

    1. Get a small piece of wire and poke it into pin 8 of the 9 pin connector. You can see the pin numbers here.
    2. Get another small piece of wire and poke it into e.g. pin 2 of the 9 pin connector. Pin 2 is the DOWN button, so we think that one should be working.
    3. Hold each probe of your meter to the ends of both pieces of wire and measure. You should first get no alert / high resistance.
    4. Now press the DOWN button (maybe with your nose ;) and you should hear the alert / see "0" resistance measured. This confirms that the DOWN button is working.
    5. Do the same test as above, but this time move the wire from pin 2 to pin 1 first. Pin 1 is the UP button. If the UP button is faulty, you will get no alert regardless of whether you press the UP button or not.


Assuming all this is okay so far, next steps:

    6. Take the joypad apart if you haven't already.
    7. Remove the conductive rubber from the D-pad.
    8. Measure the continuity between both sides of the circular UP button's tracks and the wire connected to pin 8. One or other side of the circle may be permanently connected to pin 8.
    9. Do the same thing with the other side of the circle and the wire connected to pin 1.


In a fully working joypad, one side of the UP button's circle should be permanently connected to pin 8 and the other should be permanently connected to pin 1. I assume that either or both connections aren't continuous in your joypad which is why you are seeing the fault. Again you can verify a working button's expected behaviour by doing the same tests on the DOWN button and pin 2 instead of pin 1.

If you confirm the above that either the connectivity to pin 8 or pin 1 is faulty (very likely it's the pin 1 connection rather than the pin 8 connection), you can then start trying to pin down exactly where the fault is.

Some possible culprits:

    - Severed connection between the cable and the PCB - this should be fairly obvious, you'll see a snapped wire close to the PCB. Easy to fix with a soldering iron and some wire strippers / a sharp knife.
    - Severed connection inside the moulded 9 pin connector - very hard to detect manually, and the only remedy would be to replace the moulded plug.
    - Severed connection inside the cable itself - hard to detect but very unlikely to occur.
    - Pin 1 of 9 pin connector blocked with dirt and / or chocolate pop-tarts. Common, a little hard to clean but at least nothing damaged!
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Post Posted: Wed Oct 05, 2022 7:30 am
If the cable is showing signs of being faulty its not always at the plug end. You can cut it about 5cm back from where it enters the controller and try continuity testing again. If that looks good you can reuse the cable.. its just slightly shorter.

Another option is to buy an aftermarket extension cable and cut the socket end off and use that as a replacement cable. Youll need to use continuity testing to confirm which colour wires go to which pin as they are normally different from the factory sega cables, so you cant just match the colours up.
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Post Posted: Wed Oct 05, 2022 9:26 pm
willbritton wrote
Ah okay, so if the MD controller works it does suggest it's your SMS pad that's faulty.

Your multimeter almost certainly has a "continuity" mode, which is usually indicated by a kind of audible / speaker symbol somewhere. If you can't find it, send a photo of your meter if you like.

Continuity testing simply sounds an audible alert when the resistance between two points is close to zero. You can test this by putting the meter into continuity mode and touching the metal tips of both probes together. You should hear a beep. In the unlikely event that your meter doesn't have an audible continuity mode, you can set it to the lowest resistance setting (e.g. 200Ω) and again touch the probes together. They should read something close to "0" and will probably read something like "-" or "." when the probes are not touching.

Now that you know how to test for continuity, you can test your joypad something like this:

    1. Get a small piece of wire and poke it into pin 8 of the 9 pin connector. You can see the pin numbers here.
    2. Get another small piece of wire and poke it into e.g. pin 2 of the 9 pin connector. Pin 2 is the DOWN button, so we think that one should be working.
    3. Hold each probe of your meter to the ends of both pieces of wire and measure. You should first get no alert / high resistance.
    4. Now press the DOWN button (maybe with your nose ;) and you should hear the alert / see "0" resistance measured. This confirms that the DOWN button is working.
    5. Do the same test as above, but this time move the wire from pin 2 to pin 1 first. Pin 1 is the UP button. If the UP button is faulty, you will get no alert regardless of whether you press the UP button or not.


Assuming all this is okay so far, next steps:

    6. Take the joypad apart if you haven't already.
    7. Remove the conductive rubber from the D-pad.
    8. Measure the continuity between both sides of the circular UP button's tracks and the wire connected to pin 8. One or other side of the circle may be permanently connected to pin 8.
    9. Do the same thing with the other side of the circle and the wire connected to pin 1.


In a fully working joypad, one side of the UP button's circle should be permanently connected to pin 8 and the other should be permanently connected to pin 1. I assume that either or both connections aren't continuous in your joypad which is why you are seeing the fault. Again you can verify a working button's expected behaviour by doing the same tests on the DOWN button and pin 2 instead of pin 1.

If you confirm the above that either the connectivity to pin 8 or pin 1 is faulty (very likely it's the pin 1 connection rather than the pin 8 connection), you can then start trying to pin down exactly where the fault is.

Some possible culprits:

    - Severed connection between the cable and the PCB - this should be fairly obvious, you'll see a snapped wire close to the PCB. Easy to fix with a soldering iron and some wire strippers / a sharp knife.
    - Severed connection inside the moulded 9 pin connector - very hard to detect manually, and the only remedy would be to replace the moulded plug.
    - Severed connection inside the cable itself - hard to detect but very unlikely to occur.
    - Pin 1 of 9 pin connector blocked with dirt and / or chocolate pop-tarts. Common, a little hard to clean but at least nothing damaged!



Thank you very much willbritton, a really great guide! :)

I tried to test continuity with pin 1,2 with the ground on 8, I have only a copper wire, I don't know if it fits correctly (sometime seems a little loose, not sure if it really make contact) but no alerts even with button presses.

I tested the wire only to make sure, and I get the alert from the multimeter.
I'll try again when I have more time.
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Post Posted: Thu Oct 06, 2022 1:27 am
Open the controller. Test continuity from PCB to plug.
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Post Posted: Thu Oct 06, 2022 6:32 am
You should at least be able to confirm that one of the working buttons (e.g. DOWN / pin 2) gives you continuity with pin 8 when pressed, which will confirm that your test procedure is sound. If you can't even get that then it's possible your piece of wire doesn't fit (more likely too thick than too thin I would say if you get no readings at all). Obviously the best connection would be the socket on the SMS but for that you'd need to open her up. Otherwise something like a small paperclip might be the right kind of thickness if you don't have any electronic components to hand. If you do, I would imagine the leg of a resistor would be about perfect!
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Post Posted: Thu Oct 06, 2022 2:56 pm
thank you guys
I had more time for testing today, and had more luck with the paper clip wire, very helpful tip.
this seems the results while pressing the buttons:

1 5
o o o o o
o o o o
6 9

1 Up - nothing happen, multimeter remain on "1"
2 Down - numbers shows on multimeter, no sound alert
3 Left - sound alert
4 Right - sound alert

6 TL (i guess it's Button 1, nothing happen, shows "1")

9 TR (Button 2? numbers moves but no sound)


In games, only UP and Button 1 doesn't works.

I think I should also mention that the multimeter is a cheap one and the probes aren't very sensitive in my opinion, maybe I should replace those.
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Post Posted: Thu Oct 06, 2022 3:57 pm
Good work!

Yes the fact that you see "1" for UP and TL is consistent with them not working. The "1" is the multimeter saying "resistance too high for the scale".

The lack of audible tone on DOWN and TR suggests that there is some non-negligible resistance on that path, but that the buttons still work means that it's not high enough to cause a problem. Likely the contacts are a little dirty or oxidised.

Next step is take the controller apart and measure continuity between your paperclip in pin 1 and both sides of the UP button's circular track layout. Let us know what you find there.
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Post Posted: Fri Oct 07, 2022 3:11 pm
willbritton wrote
Good work!

Yes the fact that you see "1" for UP and TL is consistent with them not working. The "1" is the multimeter saying "resistance too high for the scale".

The lack of audible tone on DOWN and TR suggests that there is some non-negligible resistance on that path, but that the buttons still work means that it's not high enough to cause a problem. Likely the contacts are a little dirty or oxidised.

Next step is take the controller apart and measure continuity between your paperclip in pin 1 and both sides of the UP button's circular track layout. Let us know what you find there.


Thank you :)

today's test on the pcb
I also made a photo in case, so you guys can see if something is wrong on the pcb or solders





while the wire for continuity test is on PIN 8, testing the UP direction, I get the sound alert on the contact that I marked with A1.
Nothing on A2

When I changed the wire on PIN 1, nothing from both A1 and A2.

Same results for Button 1 on the other pcb.
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Post Posted: Fri Oct 14, 2022 11:56 am
Last edited by willbritton on Fri Oct 14, 2022 12:40 pm; edited 2 times in total
The picture is useful.

Doesn't look like any loose connections, but the fact that you don't get continuity between the pad on A2 and your paperclip on pin 1 means there is a fault somewhere in the conductive path between those two points.

Just to make sure it's clear, although you probably already know this: there are two sides to each switch contact, each switch looks like a circle with the little fingers you can see, and one set of fingers is connected to the signal wires (pins 1, 2, etc.), the other set of fingers is connected to a common GND connection (pin 8). I've attached a colour coded picture to make this a bit clearer. So you see it's specifically the red coloured set of fingers for the UP switch that should connect to pin 1 of the 9 pin connector. The other side (the black coloured fingers) should connect to pin 8, as well as all the other black fingers, for the other switches.

Next steps: if you have a soldering iron I would just try reflowing the solder joint I've circled, for pin 1. It's possible that the joint has failed, although it looks pretty good and shiny to me. You might need to scrape away the yellow stuff on top first and get it nice and clean, and then just touch the soldering iron on the blob of silver solder to melt it, then remove the iron to let it solidify again. Hold onto the brown wire that's connected to it while you do this, so it doesn't fall out when the solder is liquid - don't hold it too close to the iron though as it will get quite hot. If you happen to have any flux to hand that you can use, more's the better, but most people don't have any flux and simply melting the solder should work just fine.

If you don't have a soldering iron, or if reflowing the joint doesn't work then you might want to try giving pin 1 of the 9 pin connector a really good clean. This is kind of tricky, but you could try wiggling your paperclip in so that any dirt is dislodged. If you have a can of compressed air, try squirting it into the hole for pin 1 many times to see if it blows out anything. A solvent like isopropyl alcohol might also work to clean the contacts, although you'll still need some kind of mechanical action to clear the debris.

If none of that works, then the problem is likely to be in the moulded plug. If so, you have two options - replace the plug, or replace the whole cable assembly. As @wasup suggests, buying some extension cable or similar could be a good option; you'll need to cut off the end you don't need and solder it to the PCB.
Untitled-1 (1).jpg (78.48 KB)
Untitled-1 (1).jpg

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Post Posted: Fri Oct 14, 2022 11:59 am
Hunter wrote

while the wire for continuity test is on PIN 8, testing the UP direction, I get the sound alert on the contact that I marked with A1.
Nothing on A2

When I changed the wire on PIN 1, nothing from both A1 and A2.


Sorry, just re-reading this, to be clear you should definitely be able to see continuity between pin 8 of the 9 pin connector and all four of the sets of fingers I've coloured in black. If not, then something very strange is happening. You may need to dig the test probe into the tracks a little bit, or scrape it on the surface to get a proper connection.
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Post Posted: Fri Oct 21, 2022 3:53 pm
willbritton wrote
Hunter wrote

while the wire for continuity test is on PIN 8, testing the UP direction, I get the sound alert on the contact that I marked with A1.
Nothing on A2

When I changed the wire on PIN 1, nothing from both A1 and A2.


Sorry, just re-reading this, to be clear you should definitely be able to see continuity between pin 8 of the 9 pin connector and all four of the sets of fingers I've coloured in black. If not, then something very strange is happening. You may need to dig the test probe into the tracks a little bit, or scrape it on the surface to get a proper connection.



thanks for the image and explanations
I tried to clean the pin 1 of the nine pin connectors, but still no continuity.


Yes, testing again I confirm that there is continuity between PIN 8 and all the fingers you colored in black (non only for D-pad, even for Button 1 and 2 ground seems fine).

I'll try to reflow the solders point for 1 (UP) and Button 1 and see if this solve the issues.
what's the best way to remove the flux?
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Post Posted: Fri Oct 21, 2022 5:22 pm
Not sure it is flux, it looks very thick and there's loads of it all around the connections, it could be some kind of protective resin or other protective compound, possibly.

If it's flux then it should come off very easily, I'd use a sharp craft knife and very gently scrape it away, but in any case if it's flux you might as well not remove it - it can only help the solder joint.

If it's hard resin then you might need to be more aggressive, and I'd say better to take it off as it might contaminate the joint.

If I were you I'd first try scraping a little away, then maybe try touching your soldering iron to a spot of the stuff on the PCB away from a solder joint. If it scrapes away easily, and burns off instantly with the iron and spits and smells like flux (!) then it is flux and you can carry on. If it doesn't seem to burn and / or if it is difficult to scrape off then it's something else and I'd clean it all away from the joint before reflowing.
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