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Trying to fix a Garmin sat nav. Can't identify the reed switch. Pic attached

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gazzarose

New Member
Hi guys, to make a long story short, I bought a cheap sat nav off ebay that was adevertised as not working, and it turns out that its the sensor (which I've heard is some kind of reed switch) that senses when the aerial on the back of the unit is flipped up (which has a magnet in it), so it turns on the GPS receiver.

I've taken it apart but I can't tell which one is the reed switch as I've never had anything to do with surface mounted components before. Im guessing the reed switch is stuck on, so always thinking the aerial is down. So I need to disconnect the reed switch.

Heres a pic of the area of circuit board directly behind the flip up aerial so the reed switch should be here somewhere.

8939-l_b4791916978f41ecbebb480a2fbe5314.jpg


Thanks in advance.

Gareth
 

Sceadwian

Banned
Try taking a picture of the area near the aerial itself not the opposite side of the board. The reed switch is going to be ganged to the antenna is some way, either physically or magnetically. Also, use a white sheet of paper in front of your light source for taking pics, it'll eliminate that glare.
 
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gazzarose

New Member
Thanks for the reply. Thats the closest side of the cicuit board. Its seperated from the aerial by the satnav housing. The push switch you can see is the reset button which is under the aerial. I've looked on the aerial board and its just a shielded casing for the aerial with no external components so Im pretty sure (if there is a reed switch) it should be in the area I've photographed. Is there another way that the aerial could switch itself on or off? Theres no physical switch between the aerial and the casing so it has to be some kind of proximity switch.

Can any one identify any of the components in the picture so I can start ruling them out?

Thanks again

Gareth

Also sorry for the glare, its the flash from my phone, I tried taking the pic from 18" away then zooming in, and it helped a bit, but thats the best I could get. I could try with a desk lamp if I can find one.
 
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kinarfi

Well-Known Member
Could have a hall effect device instead of a reed switch if you think it's magnetically coupled.
also, have you held a needle or similar near the antenna to see if it has a magnet or are you thinking some proximity switch is involved?
And (after rereading your post) you may need to close the switch instead of opening it and you might want to 'sweep' the board with a magnet and see if that trips it on.
 
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Sceadwian

Banned
Nothing on that side looks like a mechanical switch, they all standard low lead count SMD components, probably transistors regulators and probably a few diodes. The only thing I'm not quiet sure of is the black circular component towards the center right of the picture, but I think that's just an inductor, it's definitely not a reed switch, they're generally small rectangular jobbies and relatively large. I just re-read your post and you said it does have a magnet on it, which means that it's likely a hall effect sensor not a reed switch which means it could be any one of those three terminal chips. Typically hall effect sensors don't go bad though. Why have you amused that it's a reed switch and why are you sure that it's the switch that's bad and not something else like a bad filter cap or regulator on the power side?
 
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gazzarose

New Member
Im tried putting magnets near the board and nothing happens.

The only reason I thought it was a reed switch was from google searches where my problem kept coming up, and it was mentioned by someone that they had fixed it my doing something with the reed switch, but they didn't go into any more detail. So im not positive that it is a magnet and reed switch.

Its a Garmin Nuvi 660. It just says "GPS is Off" on the top of the screen, which is the same as my other Garmin sat nav says when you close the aerial down.

Thanks

Gareth
 

cobra1

New Member
im going to assume you already have it apart, before you did this did you do a full system reset, or just pressed the reset on the back???

if you only reset it by pressing the reset on the back then put it back together and try a full reset. i will tell you how when its back together.

the problem is not the sensor that tells you the aerial is up, its inside the antenna.

you can use an external antenna to solve your problem also.
 

gazzarose

New Member
Oh right, I've got a external aerial in my car, but Im not sure it works, cos when I plugged it into my other sat nav, the accuracy went up instead of down. Cos when I tried it with this broken 1 it didn't do anything, so I could try and get hold of another Aerial to try. I've taken it apart but rconnected everything so I could test it as I went along, so I could try the reset now, I only tried the one on the back.

Thanks

Gareth
 

cobra1

New Member
ok, prees the top left hand corner of the screen, and at the same time switch it on, keep you finger on the screen,

you should eventually get a box pop up, there will be an option to clear user data, or something like that. select that option and it should reboot, upon startup it will ask for your location and stuff, complete that section and see what happens.

doing this reset will get rid of any corrupt gps data, if this doesnt work it is most likely the antenna at fault as there is a compnent inside that is prone to failure.

hope this helps you
 

gazzarose

New Member
Just tried that but it still doesn't work. It still says "GPS is Off" at the top of the map screen. I think my mate might have a spare GPS aerial somewhere so may try that. So the "GPS is Off" bit just means that the internal one i of does it? So just out of curiosity then, how does it know when the aerial is up or down? Is it witch craft?

Thanks

Gareth
 

cobra1

New Member
without having the board in front of me i couldnt tell you, if you think its a magnet then get a piece of steel and find out the EXACT location of the magnet, then put it near the pcb where it should sit and look for wahtever is under the magnet, that will be your sensor,
if there isnt a magnet then i would need to see it to determin how it works
 

gazzarose

New Member
The pic that I posted is the area directly by the aerial when its folded down, so if there is a sensor it should be there.

So If I tried another external aerial it should work? I'll try and get hold of one.

Thanks again

Gareth
 

Sceadwian

Banned
Better full size pictures of the entire unit might help. If there is a sensor and it's there, it's hall effect. If you can do what cobra said and determine the exact location of the magnet and where it comes very close to the PCB, it should land virtually on top of one of those there legged IC's, hall effect sensors tend to be transistor output. Once you determine which one it is you can test the leads. One will be VCC, one will be ground, and the other will be the signal out. Depending on the output type of the hall sensor shorting the output to gnd or VCC will cause the unit to turn on, if indeed that's what it is, it should have a current limiting resistor somewhere on the output line, if you're worried you could try using a 1k resistor as a jumper just for testing, but you'll really want to test this while the unit is powered on so you can find out what is what.
 
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cobra1

New Member
The pic that I posted is the area directly by the aerial when its folded down, so if there is a sensor it should be there.

So If I tried another external aerial it should work? I'll try and get hold of one.

Thanks again

Gareth

that pic is no good, the magnet wont cover the whole thing, just one tiny area, in order to determine which component is a sensor you first need to know where the mgnet sits, instead of just guessing it helps to find the magnet first.

can you open up the antenna and take a pic of the inside and post it up here
 

Sceadwian

Banned
That looks suspiciously close to that button there.. Check the button with a meter on continuity setting to see if it still works.
 

gazzarose

New Member
the button does work, but it just resets the whole unit, when its in its case the button is protected from accidental pushing and the aerial doesn't touch it, when I took it apart I was expecting to see some kind of micro switch or something but theres nothing there, so it must be a proximity sensor of some kind.
 

cobra1

New Member
im going to stick my neck out here and say that the 3 legged ic to the upper right of the white push button is going to be your hall sensor.

can you get something metal (steel) not stainless though and move it around the black shroud covering the ribbon cable. just to see if there is a maget in there


is there anything written on that ic i mentioned??
 
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gazzarose

New Member
I can't seem to find a magnet anywhere, I took the black shroud off the aerial board and its just covering the connector for the ribbon cable.

I think it says A5XGC on the IC, but I can't be certain. I havn't got a magnitfying glass so I can't get close enough.
 
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