P80 8638452 What causes a window master switch to fail?

Post by **scot850** » 28 Jun 2018, 16:21

I decided to take apart a 'failed' master-switch from a 98 V70 to see if I could figure out why it failed. It is an overly complex design but other than possibly the mechanical wear on the sliders that move the positions of the 'contact fingers' there is no obvious reason they should fail.

I can clearly see wear on the center section of the sliders where the button pin sits but again there should not be wear as the button pin should be locked into the hole in the slider.

The driver's door window slider is of a different design and color to the other 3 windows, I am reasoning that is due to the one touch function of the driver's window.

I will attach some pictures of the disassembled switch mechanism for those who may be interested.

Does the driver's window switch fail mostly due to more use or is it something else? I am curious of what the function of the circuit board and relay? is on the under side of the assembly. Is that part of the door lock control or does that work in some way with the driver's door one touch?

: P80 Window masterswitch

: Button shafts

The button shaft ends fit into the holes in the center of the sliders

: Connector pins and circuit board

: Connectors pins for window control

: Connectors for door lock control?

: Control spring for door lock switch

The silver 'ball' to the left of the plastic rod holding the LED bulb is actually a spring and metal cap. There is one either end to give the control 'feel' to the door lock master switch and the override switch for the rear windows.

: Contacts for rear windows and override switch

: Contacts for front windows

I think the 'issue' with the driver's side switch may be the contact point for the contact pin closest looks worn with a concave if you compare to the previous picture for the same pin on the rear LH window control.

Neil.

Post by **rspi** » 28 Jun 2018, 16:24

Contact corrosion, tension wear.

Stu70 · Post by **Stu70** » 28 Jun 2018, 16:35

Arcing of contacts - little or no suppression . I’ve found some EBay/AliExpress units with better suppression/capacitors. The rare case of aftermarket better than OEM

configsys · Post by **configsys** » 28 Jun 2018, 17:31

Nice write-up!

MDK · Post by **MDK** » 28 Jun 2018, 18:19

It's probably the most used set of switches being the driver's side. I changed a few. Most just get dirty or the contacts get a burnt spot beyond repair. I've taken them apart just like you have in your photos. Best thing is to go to a junkyard, scrapyard.etc. And try to find a clean set. What I mean is that you can still see the lettering. Any S 70/V 70 set will do. 98-2000. I will usually pay about 50$ for them here in Ohio...MDK

Post by **BEJinFbk** » 28 Jun 2018, 20:19

I’m going with poor design and underated contacts.
These things are a prime example of planned obsolescence...
The 8 track tape of the P80 world!

Post by **SuperHerman** » 28 Jun 2018, 20:53

The board has some electronics on it. Did you take a close look at them? Is that black box a relay? Do a search on the part number - maybe it is a relay that has gone bad on the board.

Otherwise what others described above.

Post by **scot850** » 28 Jun 2018, 21:26

Thanks for all the replies guys. What I am trying to figure out is what does the circuit board do? Is it part of the window control system or is it part of the door lock switch.

If the board has something to do with the door switches does it only work with the drivers door window? The switches for all the other 3 windows work ok.

I think I pay around $15 CDN for the switch, but can't recall. I have a bunch of them scattered around the garage as well as a brand new contactless Switch Dr. I know that one has a mixed review, but when bought many years ago, there were little reviews on them.

At some point I will give it a try and see if it works any better (i.e. at all on the LSF/driver's front window). I suspect it is a worn contact. I know it worked in the down direction but not for the up.

Neil.

Post by **abscate** » 29 Jun 2018, 04:30

The copper cup on the end of the strip corrodes and then arcs , which leads to switch death.

Until P2, the power windows are analog power, that circuit board just provides power for the windows via relay. I think it might be the one touch function , too? Looks like it just runson a timed circuit.

The locks are simple controls signals to central locking module

All the power for all the windows goes through the driver side power window switch.

Post by **BEJinFbk** » 29 Jun 2018, 08:14

I suspect that the electronics are a current
sensing circuit and a relay for the driver’s
window auto-down feature.

There are a multitude of posts across the
Volvo boards going back decades about
contact failure in these switches. Cleaning
can often extend their lives, but the leaves
flex when used and eventually begin to lose
tension. It ‘s a downward spiral from there...