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Repairing Sony car radio MEX-BT3800U

starLED

Member
Hi guys!

I have a Sony car radio MEX-BT3800U that I need to fix.
Problem is that some buttons are stuck and others won't work.
I need help to determine how to test them with multimeter continuity.
This is the radio:
IMG_20210123_191141.jpg

There are two types of SMD buttons:
1) button without LED, it has 2 leads on each side.

IMG_20210123_191155.jpg

2) button with LED, it has 3 leads on each side.
IMG_20210123_191208.jpg


Which leads I need to test to determine if button is stuck?


Also, are these buttons available in electronics store, if I need to replace them?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I've never seen those exact buttons - however, as some of them work OK, check on one of the good ones to see which contacts join together, then check the faulty ones using the same pins.

Historically some of the old Sony TV switches used rubber 'springs' inside, and these used to break - so there was no spring action to keep the contacts apart - a careful physical comparison of all the switches often allowed you to spot the faulty ones.

You can download the service manual for it from:


But as it's a modern unit they don't give you a schematic - but it looks like the buttons just switch different value resistors across a couple of I/O pins.
 

starLED

Member
I have determine this:
1) button without LED, with 4 pins, cross leads are joined together
2) button with LED, with 6 pins, bottom leads are joined together.

I think I found which one's are faulty.
It's LSW908 and LSW910 buttons with LED, they are giving buzz on multimeter, so probably those are closed switches.
It's a Shuffle button that I used frequently, well to shuffle songs :), and Album+ button.

There is an advice on YT to put alcohol on buttons and then to use blow dryer, so to clean contacts.

I will try that first, before removing faulty button.
 
Last edited:

starLED

Member
I had to remove/desolder LSW910 button.
When I removed button there was a metal circle under (it's left of the button on the image bellow).
Is that circle part of a button or part of a PCB?
IMG_20210124_105629.jpg
 

rjenkinsgb

Well-Known Member
Most Helpful Member
That appears to be part of the button.
The bit you removed likely has a slightly domed "click" disc in it, that bridges the outer and inner electrical contacts when its pressed.
 

starLED

Member
That appears to be part of the button.
The bit you removed likely has a slightly domed "click" disc in it, that bridges the outer and inner electrical contacts when its pressed.
I actually removed, pulled off just a plastic casing of button.
I thought I desoldered it, but I didn't actually.
My 30w iron couldn't melt solder, it's probably not a lead, but silver joint.
I was afraid to use 60w iron.
Can it stay this way, or should I remove that part also?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I had to remove/desolder LSW910 button.
When I removed button there was a metal circle under (it's left of the button on the image bellow).
Is that circle part of a button or part of a PCB?
It's part of the button - you haven't actually removed the button, you've just broken part of it off.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
It is probably lead-free solder, which needs a bit more heat than tin-lead.

The easiest way is sometimes to add a small amount of flux cored tin-lead solder, which makes the overall joint flow better.

Then use "solder wick" to remove all the solder from each joint.
(And then carefully lift off the switch base).
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I actually removed, pulled off just a plastic casing of button.
I thought I desoldered it, but I didn't actually.
My 30w iron couldn't melt solder, it's probably not a lead, but silver joint.
No, it will just be unleaded solder - as anything remotely modern is.

I was afraid to use 60w iron.
Can it stay this way, or should I remove that part also?
If you want it repairing?, and you can source new buttons?, then it needs to come off.
 
Last edited:

starLED

Member
If you want it repairing?, and you can source new buttons?, then it needs to come off.
I will not place a new button right now, so it can stay like this.

I can't find original button, the closest that I found in electronics store is this:
 

starLED

Member
The missing resistors might be for buttons that have internal LED's?.
Not sure, you can see on the left side there are also a lot of missing resistors.
Probably there are variations of this model which include maybe more/less LED's, or other features.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Not sure, you can see on the left side there are also a lot of missing resistors.
Probably there are variations of this model which include maybe more/less LED's, or other features.
There are four different models listed on the service manual, probably they have different numbers of buttons, and in different places.
 

starLED

Member
There are four different models listed on the service manual, probably they have different numbers of buttons, and in different places.
I looked up, they look all the same, model numbers are just for different countries.
PCB is probably shared between different similar models.
This was top of the line model and other models lacked some features, but they looked similar.
 

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