P38A HEVAC screen light issue

kermit_rr said:

Have you done the obvious and checked the connectors between the holder and the board? Tabs on the holder could be loose

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Grrrrrr said:

As above. Or if the ribbon connected is worn then Marty does a refurb kit on his p38spares website.

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Grrrrrr said:

As above. Or if the ribbon connected is worn then Marty does a refurb kit on his p38spares website.

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P38Seb said:

Evening all, you were incredibly helpful last time I posted so I hope you can help again.

My HEVAC screen has an annoying bulb issue. Most of the time it doesn’t illuminate, yet at seemingly random times it’ll light up - such as a trip to Bristol it lit up as I parked up, but hasn’t since, it might tomorrow though?

I’ve changed the bulbs with a new kit, I’ve done the zebra cable fix and that’s solved the stuck pixels, I know the screen works as I can shine a torch on it and see the info, but for the life of me I can’t seem to work this out. I’ve fiddled with the wires and tried to check they’re in securely which it appears they are.

What’s the next step? Whole new HEVAC unit?

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Datatek said:

Check the metal strips from the bulb holder in the plastic housing where they solder into the pcb for cracked joints.
Check for corrosion on the HEVAC connectors or loose pins.
Do the dash lights respond to the dimmer control?

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P38Seb said:

So I’ve pulled the unit apart and taken a look:

The solder appears okay - no obvious signs of cracked solder.

No corrosion in the connections. I have sprayed these with contact cleaner to hopefully rid anything that may have been there out.

All the lights respond to the dimmer control as well, including all the bulbs on the HEVAC, except for the screen bulb as it doesn’t illuminate at all.

I’ve looked at the connection between the green bulb and the tracks and it looks like they are slightly scored from previous bulb figments, could this be the issue? If so what’s the solution, contact cleaner and the Mrs’ credit card as a scrubber? I’ve attached a photo.

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Datatek said:

You can clean up the contact surfaces with a pencil eraser, a fairly coarse one does the job.

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P38Seb said:

Thank you! I’ll dig out my pencil case. I’ll give that a try as well.

I’m going to pop to a local Landy specialist tomorrow after I’ve got it regassed and see if they can shed any light before I buy a unit of eBay.

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Datatek said:

If you cannot find the fault, assuming you can solder, it would be possible to rewire the feed to the bulb.

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P38Seb said:

That was something I considered. I’d seen someone wire in from the other bulbs, but that then only worked when side lights were activated.

Is there anything that’s an ignition 12v I can run a wire off?

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Datatek said:

I'll take a look at RAVE and see what I can find.

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P38Seb said:

Appreciate it, thank you!

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Datatek said:

OK, on the HEVAC, there is a white connector, Pin 1 = aux power supply; #2 battery power supply; #ignition switched supply; #4 earth. I f you look at the connector, one row has only 3 pins, with this at the bottom as you look at the connector, pin1 is the first on the left of the 3 pin row, then #2; #3. Top row the first on the left is pin 4 then #5; #6; #7; #8.
Check you have power between earth and the 3 power inputs. You could then add a pair of wires from #3 and #4 to the bulb. YOU MUST DISCOONECT THE METAL STRIPS FOM THE PCB if you do this.

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P38Seb said:

Amazing! Really appreciate the effort you’ve gone to here!

Best way to removed the metal strips, would heating up the existing solder and removing them that way? Or just snip them?

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P38Seb said:

Awesome. I’ll try the eraser mentioned further up first before I go grab the solder iron.

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