Volvo Guard 1 Keyfobs

[James_EG_940]

Originally Posted by Forrest

Given all the basics are right the most common fault I’ve encountered is the legs on the Murata ceramic resonator breaking. See picture for help identifying this part. Either resolder or desolder and replace depending on the extent of the damage. The component is a few pounds on eBay.

Thanks Forrest, all good points worth mentioning.

Just to fill out - the white part in question is a 1Mhz ceramic resonator, and could theoretically be replaced with any other matching those specs providing it fits in the case. Currently the exact fit Murata ones are NOS on ebay for £1.80 for two plus £1.20 postage. They are otherwise no longer manufactured and most modern replacements operate at much higher frequencies and won't work.

Cheers,
James.

[James_EG_940]

Originally Posted by jpliddy

thanks JAMES for this post its very good . i programed a spare fob a few years back all was ok then i had a starting problem which is very rare in the 19 years ive had the car a knowlageable chap who knows a lot about this car/model told me to remove the fuse for the alarm which i did and the car was ok again .after a while i replaced the fuse and alarm all ok but ive not used the spare fob so only 1 original fob programmed in to car .
are you familiar with faulty tempreture gauge my car is a 940 diesel tdi
regards jim

Thanks Jim,

My only guess is that it was some fault with the immobiliser if the alarm fuse was responsible. The fobs just talk to the alarm unit which then tells the various other systems what to do (flash lights, unlock doors, etc) - fob shouldn't matter in that equation. I've had it get confused with me once before but this involved opening door with key after locking with fob and then car wouldn't start (immobiliser was still on).

There's a few things to try with the temp gauge but might be worth making a new thread. I'm not as familiar with the diesel lumps as I am with the petrol.

Cheers,
James.

[mike r owen]

Originally Posted by James_EG_940

Hi guys,

I have racked up a fair bit of experience with these fobs now so thought I would write an article and share it. This is a moderately long article with images, sorry to anyone on poor rural broadband!



These are the fobs used to set the alarm / remote central locking on cars with the flashing triangle on the driver's A pillar - not the later system with the blinking LED inset to the passenger side dash speaker grille.

There were some variants on this system, with some fobs having a second button to start the block heater. Other fobs worked on IR (like your TV remote) rather than radio - I have never seen one like this. To comply with different countries laws on radio emissions some work on different frequencies, this is indicated by the coloured band around the middle of the remote. As far as I know there were red, blue and black banded ones - blue is the correct colour for UK cars.

The VG1 system has issues with range, see how to fix that in another post of mine here: http://www.volvoforums.org.uk/showthread.php?t=200312 but this is largely not down to the key fob. The fob does however have its own slew of problems especially as they all are now 20 years old or older! The fobs are actually quite simple, once you remove the screw the case can easily be split apart with a finger nail - working from the short edge closest to the button around.


This allows access to the PCB for repairs, being very careful with the incredibly flimsy plastic colour ring!


Electronically there is a microcontroller which will repeatedly pulse a pre-programmed code when powered up, this is then broadcast on a 418.050MHz carrier. Due to the code being stored in the microcontroller it wouldn't be possible to reprogram with a new code without having the original computer code used to program the chip.

There seem to be a couple of circuit board variations, an older one and a newer one. I'm not sure how many years they were produced for but I have two "older" boards with a date code of 45th week 1994, another "older" one with 50th week 1995 and then a "newer" board with no date code. I think it's newer judging by the components used. They are functionally identical and both types can be simultaneously used with 1 car.


The main problems with fobs I have come across are: Battery leak corrosion, broken battery cover, failed switch, dead LED and dead batteries

Battery leak corrosion
These get left for decades with dead batteries in them which then leak and start to eat up the tracks of the PCB inside the fob. This can be cleaned up with alcohol and joints reflowed, if a track is completely gone it can usually be repaired with a jumper wire. Most problematic around the negative battery terminal which will already be electrolytically corroded.



Broken battery cover
A bit of terrible design here I'm afraid, the fobs take 4(!) cells, these are fitted into the fob in 2 pairs and arranged electrically as all 4 cells in series. to bridge the 2 pairs together a small spring strip is used which is a press fit onto a screw post on the back of the black plastic strip of the fob. The problem is that this tiny screw post becomes brittle, cracks apart from the tiny self tapper holding it in - this in turn means the battery essentially becomes disconnected! I have yet to get a good fix for this, araldite may be one fix, but there isn't much space to allow for the inevitable epoxy that squeezes out when you fit the parts together. Another option I have been considering is to make a highly accurate 3D model of the part and get a whole bunch of them 3D printed...



Failed switch
The tiny tack (tactile) switch on the fob wears out so that you have to press really hard for it to make contact which then breaks it further. Tactile switches do break quite easily and have a short service life - I've repaired a lot of DJ gear with faulty "attack" switches as we call them (attacked by DJs smashing at them). Repair is to simply replace the faulty switch. This can be one of the main reasons people say their fob doesn't work, it's the most common "I've changed the batteries but it still doesn't work" issue. I use these switches when replacing them: switch link


Dead LED
I have come across two fobs with dead LEDs so now I just replace them as standard. The ones on there are usually all faded and not exactly bright anyway. I couldn't source exact copies of the ones on the board so I use slightly longer ones and clip them down which works well. Would be very easy to change the LED colour too.



Dead Batteries
As I said earlier there is a little screw on the back, that releases the black plastic part on the front which retains the batteries. Polarity is important is not marked anywhere on the unit. The negative terminal is furthest from the switch, positive closest. Due to the two stacks though you will need to place them so that positive faces up out of the negative hole (ie negative side facing down to the PCB) and vice versa for the positive hole. Each fob uses 4x 1.5V watch batteries with the code: 391 or L1121 or any of the other synonyms for that type of cell. Use only genuine quality branded batteries to avoid leaks, I recommend Varta or Renata. Be very careful not to over tighten the screw when you replace it as once the little screw post splits (which it will!) it's game over. Amazon link for batteries



So that's about it. Apart from those things I mention above, they are fairly bullet-proof little units and should last a while. I'm all for trying to keep things stock and keeping some of the stock 90s electrics going is not always easy. Hopefully this is useful to the few of you that still have cars with this alarm system fitted. If it all seems like too much to repair your fob yourself then I would be more than happy to repair it for you, just PM me if you are interested - I will get an alert sent to my email address.

Hi Could you send me your email Mine is; a2mro@aol.co.uk. I have two of the grey fobs and would like to get the alarm working again, so any advice would be helpful. Kind regards. Mike Owen

[Clan]

The only problem i had with these whilst current and until about 2007 when they " died out" was a capacitor falling off and rattling around inside ... I soldered it back on and all was well again . Since then the overtightening of the screw can be a problem as I see above but nothing that can't be overcome .