Replacing the dashboard plastic PCB

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CJH
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Re: Replacing the dashboard plastic PCB

Post by CJH »

AngeloEvs wrote:Worth evaluating. How do the other commercially available repair kits connect to the DOP's board?

From the photos and videos that I've seen, they don't seem to be very clear on this point. I think I'll go with those Dupont connectors for now, as they can be bought cheaply in bulk and they're guaranteed to fit. They're even cheaper if you crimp them yourself, but they're extremely fiddly and difficult to do properly without the right crimper. The drawback is they could be connected up in the wrong order, but anyone attempting this will surely check the order carefully. If I buy ready-made 40cm female-to-female multicoloured Dupont connectors in ribbon strips 40 wide, I can peel them off in strips of 6 and cut the 40cm pairs in half to give me 2 sets. If I then put a ribbon connector on the cut end, the order becomes fixed. I'll put a 2x3 pin header on the connection board for that ribbon connector, instead of (as well as perhaps?) the screw-down terminals, and it should be fairly fool-proof.

The multiplug connector is about ready to order - just need to check a couple of measurements to make sure the two slots in the board will ensure a tight fit. I did away with the zip tie holes, as I think a zip tie running the other way (from the long edge of this board to the back of the multiplug) is simpler and better, if needed.

Image

Image

I checked under my dash binnacle again, and of course the hydraulic fluid reservoir takes up the space between the dials behind the LEDs, so there isn't really room for another board to stack behind the LED panel. So for this first go I think I'll stick to a single all-in-one board, while I iron out the niggles, and then consider splitting it in a future iteration. A few more things to finish on the layout but hopefully it should be ready to order this weekend.
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Re: Replacing the dashboard plastic PCB

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AngeloEvs wrote:Worth evaluating. How do the other commercially available repair kits connect to the DOP's board?

From the photos and videos that I've seen, they don't seem to be very clear on this point. I think I'll go with those Dupont connectors for now, as they can be bought cheaply in bulk and they're guaranteed to fit. They're even cheaper if you crimp them yourself, but they're extremely fiddly and difficult to do properly without the right crimper. The drawback is they could be connected up in the wrong order, but anyone attempting this will surely check the order carefully. If I buy ready-made 40cm female-to-female multicoloured Dupont connectors in ribbon strips 40 wide, I can peel them off in strips of 6 and cut the 40cm pairs in half to give me 2 sets. If I then put a ribbon connector on the cut end, the order becomes fixed. I'll put a 2x3 pin header on the connection board for that ribbon connector, instead of (as well as perhaps?) the screw-down terminals, and it should be fairly fool-proof.

The multiplug connector is about ready to order - just need to check a couple of measurements to make sure the two slots in the board will ensure a tight fit. I did away with the zip tie holes, as I think a zip tie running the other way (from the long edge of this board to the back of the multiplug) is simpler and better, if needed.

Image

Image

I checked under my dash binnacle again, and of course the hydraulic fluid reservoir takes up the space between the dials behind the LEDs, so there isn't really room for another board to stack behind the LED panel. So for this first go I think I'll stick to a single all-in-one board, while I iron out the niggles, and then consider splitting it in a future iteration. A few more things to finish on the layout but hopefully it should be ready to order this weekend.
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Re: Replacing the dashboard plastic PCB

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Question about the 10V regulator: On the original flexible PCB it seems to earth by screwing the backing down onto the circuit board itself. But the regulator has an earth leg as well. Is the backing used instead of this leg simply to aid heat dissipation? Does it get particularly hot? I'm wondering if I can just use the earth leg, or whether I should additionally clear a patch of the ground plane for it to screw down onto, and would that provide enough heat dissipation.
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Re: Replacing the dashboard plastic PCB

Post by MidLifeCrisis »

CJH wrote:Question about the 10V regulator: On the original flexible PCB it seems to earth by screwing the backing down onto the circuit board itself. But the regulator has an earth leg as well. Is the backing used instead of this leg simply to aid heat dissipation? Does it get particularly hot? I'm wondering if I can just use the earth leg, or whether I should additionally clear a patch of the ground plane for it to screw down onto, and would that provide enough heat dissipation.

Yes - serves dual purpose as a ground and a bit of a heat sink
I’d suggest you have some sort of heatsink - not sure that regulator is working very hard but it’s going to help - you can get small bolt on metal heatsinks with little fins that would work if there isn’t a good metal ground base to attach it to
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Re: Replacing the dashboard plastic PCB

Post by boatbuilder »

I mounted my 10v regulator on a separate small circuit board (veroboard) attached to the top surface of the clocks. I have it mounted on those little green screw terminals so its easy to replace. It does get a bit warm, but nothing terrible. Biggest danger is blowing it up by shorting out the wrong pins. Thats why I have a few spares on hand.

I recently changed the connectors on my diy veroboard system. I had used a motherboard atx male and female connector but I don't think its up to the job. The pins aren't robust enough and I was getting intermittent connections, so the coolant light was flashing all the time as a result. I cut them off and replaced them with a multi connector off a Vw that I got at a scrapyard. They were from the engine bay of modern vw. Much better but you need twonof them because they are only six wires each.

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Re: Replacing the dashboard plastic PCB

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Thanks folks. I cleared a patch of solder mask away from the ground plane where the regulator will lie. The ground plane covers most of the component side of the board, so will give some heat dissipation effect. If necessary I can stand the regulator up and use a separate heatsink.

Had a bit of a shuffle round - removed the holes that won't be used as screw holes. Changed the DOPS connectors to a 2x3 pin header arrangement to suit a ribbon cable and moved it to the edge closest to the speedo. Moved the gauges terminals so that the wires won't have to pass over the regulator, in case that needs to stand up (might look at using angled terminal blocks to make them easier to connect up). Still need to increase the physical size of the resistors, add those missing components, adjust the track width for the alternator and add the extra paralleled resistor to split the power in the alternator circuit. Getting there.

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Re: Replacing the dashboard plastic PCB

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I added a jumper, so that the dash lights can be configured as 'always on' or as standard, via the dimmer. And I turned the power connector because it might be a bit cramped between the dials to access that connector.

Image

I made a cardboard mock-up, to check for blunders. I'll offer it up to my own dash later, to make sure everything's going to clear. I had some 5.08mm screw-down terminals, so I checked access - it's a bit tight, but quite doable.

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Re: Replacing the dashboard plastic PCB

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I had laid out the 'spare' LED to have the same configuration as all the other signals, i.e. the LED comes on when the corresponding signal goes to earth. The High Beam circuit is the odd man out, in that the LED lights up when the High Beam signal goes to +12V. So I wondered whether I could make the 'spare' LED flexible, so that it could be configured either to work when the signal goes to earth OR when it goes to +12V. I added a couple of jumpers, so that the 'Spare' anode can be fed by either the 'Spare' signal wire or IGN+, and the 'Spare' cathode can be connected to GND or the 'Spare' signal wire. Obviously the jumpers would have to be set as a pair.

Image

I can't decide whether this is useful or necessary - I guess it depends whether the circuit it's going to monitor is switched-live or switched-earth. In fact maybe my jumper labels should say 'Switched +ve' instead of 'Spare +ve'.
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Re: Replacing the dashboard plastic PCB

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I checked the clearance in situ:

Plenty of space for the dash light connections at the top edge:
Image

...and plenty of space for the all-in-one board behind the LED sockets. I was worried that it might foul the hydraulic master cylinder, but theres plenty of space down there (not visible in the photo). But there clearly isn't room to stack another board behind the LED PCB - it would foul the reservoir.

Image
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Re: Replacing the dashboard plastic PCB

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AngeloEvs wrote:The clock below the LED display is a standard 52mm Tachometer.

You can use 1/4 W resistors for most of the circuit apart from the Alternator charge circuit LED. The introduction of the horizontal dash connector saw an increase in the Alternator exciter current (doubled in fact). Two 120 ohm resistors are used in parallel, these need to be at least 2W each to handle a max current where V/I = 12.7/60. Tracks need to be bit wider for the alternator LED to pin out on the edge connector. If the ignition is left on without starting the engine these resistors get quite hot. A frequently used method is to to tin the tracks along their entire length to increase the track current capability if track width is a problem.

Same goes for the tracks to the Fuel and Temp tracks, nominal resistance of both guages where coolant temp is normal and fuel tank half full is 100 ohms each, the regulator limits the voltage to 10 so V/I = 10/100 for each track.

Can you check my maths?

For the alternator, worst case, as you say, is when the ignition is on and the alternator isn't turning, in which case the battery is 12.7V above the alternator (let's say +14.5V for the really worst case in which the battery is fully charged and the engine has just been turned off). So current through the part of the circuit with the two parallel 120 ohm resistors is 14.5/60 = 0.24A

Using this online trace width calculator, to cope with a current of 0.24A in a trace that's the standard 1oz thickness, a couple of mil is all that's required. It depends on how much temperature rise you can tolerate, but allowing, say, 10 degrees in that track, that calculator says I need 1.65mil for an external layer (which they both are in a 2-layer board). I've been laying the board out with 10mil tracks as standard, and by a bit of iteration that calculator says 10mil will handle 0.24A and only warm up by half a degree.

Using the nominal resistance that you mentioned for the two gauges, the current of 0.1A is even less of a problem, but do you have any idea what the minimum resistance of those gauges could be?
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Re: Replacing the dashboard plastic PCB

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ZsZ wrote:Just traced my late diesel clock PCB:
Image

Can anyone explain the purpose of the upper of the two diodes in this diagram? It seems to sit between GND and Ignition. It's not there on the earlier drawing that didn't have the DOPS circuit, so it's probably something to do with that circuit. The diagram suggests it lets current flow from the DOPS ground pin to the multiplug ignition pin. Why would that situation ever arise? And if GND ever got to that potential, wouldn't it cause a problem for anything else that expects GND to be 12V or so below Ignition?

I added it to my circuit diagram with exactly the connections shown in the diagram, but when I placed it on the PCB it became obvious that it's just sitting between my GND plane and my IGN plane.
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Re: Replacing the dashboard plastic PCB

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I think I'm about done. I shuffled things around again to make more room to access the screw-down terminals. I also added the same configuration jumpers to the glow plug LED as I'd earlier added to the spare LED. This will give those without glow plugs a second 'spare' LED to use on either a 'switched-live' or 'switched-earth' circuit. I do hope I'm right with the configuration!

I still don't understand that second diode. I've left it in, but as far as I can see it's totally redundant and could be left off the PCB entirely. It prevents current flowing from Ignition live to Earth (exactly as if it wasn't there), and it allows current to flow from Earth to Ignition, and I cannot imagine a scenario where that would be necessary. I'd love for someone to point out my error.

I've beefed up the two gauge circuits, the dash lights circuit and the alternator circuit, even though they appear to be over-specified already. I've also increased the physical size of the resistor locations to allow 10mm resistors in most locations, and 12mm for the two higher power resistors.

Here's the component side:
Image

and the LED side:
Image

And here's the track layout, in case anyone feels like pointing out any obvious blunders!
Image
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Re: Replacing the dashboard plastic PCB

Post by CovKid »

When you think you're there Chris, let me know how much. Happy to test as I'm pulling the clocks out for another project shortly.

The only other mod I'd make is to add in another smaller circuit on the board for those (like me) that use LED dash illumination and need a section on the board to add dropper resistors for these.
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Re: Replacing the dashboard plastic PCB

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CovKid wrote: The only other mod I'd make is to add in another smaller circuit on the board for those (like me) that use LED dash illumination and need a section on the board to add dropper resistors for these.

I wondered about that. Do you think a single resistor shared between all three would work? I could squeeze in another jumper to select routing the dash lights through such a resistor.
I think it should - it's there to limit the current through the LEDs, so it would just need to limit the current to 3x what each LED needs. The only danger would be if one LED failed, then the current through the other two would increase.

Actually, I think there's a better way. Back in a mo....
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Re: Replacing the dashboard plastic PCB

Post by CovKid »

https://www.ledsupply.com/blog/wiring-l ... explained/" onclick="window.open(this.href);return false;
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