Instrument panel leds

[Bison535]

While I was checking the Instrumentation Panel, because the illumination LED’s are not working, a slight whiff of hot electrics came from the back of the panel, although I could not pin point anything obvious. I removed and tested the white led above speedo and it was ok. I put a temporary 12v supply to the pcb at an led connection to try and get the lights to work, but they didn’t!?
I have now reassembled the Instrument Panel and the following defects have shown up :-
The temp gauge red warning light is constantly flashing when running and the needle rises above its normal position, just under half way.
The fuel gauge moves up and down slowly not registering the correct fuel level.
The yellow Glow Plug led does not now come on !?

I have driven many thousands of Km’s prior to this Instrument Panel electrical fault of today and I’m very confident of the cooling system and it’s sensors being ok.
I have had a look through The Forum and Wiki and it seems I may have an issue with the blue pcb tape which runs around the led’s etc
Would appreciate any constructive comments and or thoughts on what to check? Investigate and repair ?
Also, I need to continue motoring under these prevailing fault conditions for a while; can I do so without detriment to the instruments etc ?
Because I’m confident of the cooling water system I am not concerned re water temp/alarm etc.
Cheers

1990 T25 VW Campervan - replacement AAX 1.9 TD 2017

[Cecil]

Sounds like you have applied your testing voltage with reversed polarity. you may have blown the voltage regulator and your glow plug LED or glow plug relay.Replacement Voltage regulator is available from brickwerks and others but you have to mount it upside down due to different lead arrangement! LED s need the positive / negative the right way round !
Maybe your “slight whiff” came from the instrument dimmer built into the headlight switch!
Important to Check the Earth connection to the pcb is good ( could be the cause of multiple defects )

[AngeloEvs]

The main failure with the membrane PCB is at the edge connector itself, usually broken or worn tracks or just oxidisation. Another weakness point is the copper tracks under the Dash Illumination bulbs (or LEDs in your case) which can fracture when trying to replace them. In both cases, visual inspection can identify any potential issues.

The difficulty here is that your Dash problems have started after attempting to isolate a problem with the LED dash lights and hooking a 12v supply to test them. A small puff of smoke could be a sign of a ruptured track. Your best approach is to remove the dash and carry out a visual inspection for any damaged tracks, particularly earth (Pin 3 on the edge connector, and the 12V supply track (pin by following the tracks around the pcb. After that you will need to do some tests with a multimeter and then powering the dash from an auxillay supply and checking the regulator outputs 10V. you will need the relevant information regards the 12 pin connections which I should be able to upload if it helps......

[AngeloEvs]

Dash Schematic for later Petrol/Diesel vans with DOPS PCB and LED Dash lights with Picture of rear auxillary 12V test points below.




dashschemwp by Angelo Evans, on Flickr


The centre Nut of the Temperature gauge (B) can be used to provide a 0v connection (check this goes to pin 3 (left to right) on the edge connector).

A 12V aux supply can be connected to pin 8 (shown with a crocodile clip) or preferably, solder a small fly lead to the input side of the regulator as shown (red lead)

At point A should read 10v with a 12v aux supply connected.

Point C is the output side of the temp gauge, connecting a 100 ohm resistor between points C and B should cause the temp gauge to settle at the middle point (coolant LED will not flash except for a few seconds after first connecting the 12v supply.)



rear90v4 by Angelo Evans, on Flickr

[Bison535]

Hi guys, thanks very much for you very helpful replies, much appreciated. I’m on the road at present in Portugal so will have to wait until settled to start further investigation. The diagrams most helpful as ‘sparks’ not my best subject