Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Dreaded PCB Stikes Again

Hi Nick,

Thanks for your input, until recently all I'd actually lost was the seatbelt warning tell-tale, this never worked since I bought the car and was never an issue for me as I'm perfectly capable of knowing if I've put my seatbelt on thank you very much Morgan!

However, more recently my Speedo and ignition tell-tale dropped out, TBH I can live with a few missing tell-tales, but I'm not keen on driving without a speedo so I needed to investigate why it had sudenly dropped out?




To get the speedo working again my first thought was to check the fuses, and as expected I did indeed find one had blown in the main fuse board under the dash in front of the heater, it was fuse 4 which according to my laminated fuse diagram is a 5a fuse responsible for the dash module. An interesting point to consider here being that it clearly does not protect the entire dash module as a lot of other elements connected to the PCB continued to work just fine despite the blown fuse!

However, my first replacement 5a blew immediately, then another in quick succession, so clearly there was a deeper issue. I then did what one should never do, while lying on my back looking up at the fuse board I noticed there was a spare 7.5a fuse staring right at me, the temptation to try it was overwhelming. I fitted it justifying my actions by convincing myself an additional 2.5a was minimal, it is of course in percentage terms quite a jump in value.

Anyway, hey presto, as soon as I fitted that spare 7.5a fuse the speedo, the handbrake tell-tale, and the ignition warning tell tale all returned and have remained reliable ever since. Unfortunately, while I was delighted to see the return of the ignition warning light and most importantly the essential speedo, the two green indicator direction tell tales, the green headlight tell tale and the blue high beam tell tale did not return. I believe this is also when I lost the illumination to the fog light switch and heated screen switch, looking back at the chain of events it would seem my ill advised fitment of the 7.5a fuse must have blown the tracking on the PCB.

That aside, these Morgan PCBs are definitely unreliable with some owners reporting up to four consecutive failures, it seems to have been built with tracks that are only just heavy enough to carry the expected loads, there appears to be no head space to deal with any small increase in resistance or current spike. Now, as it stands I could simply have the burnt track repaired and re-fit the correct 5a fuse, but for sure it'll blow immediately again and I'd be back to the unacceptable situation of being without a speedo.

In my defense and even with the benefit of hindsight, I would probably do the exact same thing again as I can live with a few missing tell-tales and some switch illumination, what I can't live without is a speedo, I also fear the issue may have nothing to do with the speedo, it could just as easily be blower motor or heated screen related. I strongly suspect the track that burnt out is a shared ground for some, but not all of the tell-tales, which is why I've only lost a few of them and only some switch illumination too, the handbrake & ignition warning tell-tales still remain and we now know that 5a fuse 4 only protects certain circuits on the PCB, the way it's wired and fuse protected follows no logic ????




As I say, the board only seems to be just about man enough to take the expected current, with a bit of age, vibration and moisture it's inevitable there will be a certain amount of increased resistance and this will vary from car to car based on use, climate, storage conditions and the 'law of sod' of course. The Carebont made instrument MFU is also a long way off what we would consider modern car maker quality, as Roger points out above its function seems to introduce unnecessary complication for no real benefit, it also has to work perfectly with the PCB that as I understand it was not made by Caerbont.

To my mind as Caerbont supplied the speedo, rev counter and multifunction gauge but Caerbont did not make the PCB, Morgan should have wired the gauges completely separately to the switches and tell-tales. Either way you look at it the setup is a bit of a pig in a poke, expecting a small company like Caerbont to work with the manufacturer of the PCB to deliver one integrated reliable system was a bit of an ask. I very much doubt either company had the kind of development budget and working practices to make a collaboration like that work, for example the Caerbont MFU could easily be overloading the PCB and it certainly seems possible this could be my very issue.

Anyway, it's all a lot of speculation, some definitely seem to have solved their issues by replacing the board mounted relays with a bank of traditional 12v automotive (diode protected) relays that are mounted remotely. This will be my starting point as even if the board mounted relays aren't my issue, going with the remote mounted relay solution should help to make the system more robust.... hopefully!

Certainly toggle switches are an option but my dash uses push buttons similar to the ones used on the Morgan original dash. They are not the same exactly as the type of switch needed to be changed from momentary to latching (if I recall correctly) and also I ordered a number of warning or indicator lights from a Chinese supplier. I did have to order a minimum quantity as some were custom. I kept spares and passed the rest to Borghi.

This is the original dash (for sale if anyone wants it )



And this is the new dash.



All the LED warning and indicator lights with chrome bezels are the ones I ordered to replace the original light strip.

Oh! I also got Smiths to make a few new gauges for me and new faces for the speedo and tacho.

The 2008 4/4 was fitted with horrid perishable rubber windscreen washer tubes that sit immediately above the circuit board. Mine leaked and were quickly replaced with neoprene tubing. I recommend double checking if your tubing is of the black rubber type. If the car is rarely used in the wet you may not notice any leakage for a long while but then get cought out a few years down the road.
Mentioning this as a possible cause for the circuit board failure.

Cheers Rog, some straightforward bridging tests there I can attempt at the weekend

That looks lovely Peter, I have sent you a private message.

Kind regards, Dave.

Good
Whilst in testing mode it might be prudent to do a bit more checking on the car? Probably worth probing the PCB's flying 15 way header connector with a multi-meter. These are the inputs coming into the PCB so may help indicate if there is a fault elsewhere in the car. Maybe worth checking at least your suspect functions.

Say…
Power (1)
Ignition light (13)
Seat belt (8)
Handbrake/fluid (9)
Indicators (2&3)

That's very interesting Rog

It got me thinking, so I've just mentally ticked off everything below:



Which confirmed all the circuits on that connector that I would expect to be working, are indeed currently functioning correctly on Monty.... with the help of a 7.5a fuse

The remaining circuits I would not expect to work are the aircon lamp as I don't have aircon, and anything ECU related (PATS LED & ENGINE MANAGEMENT LAMP) as I no longer run the Ford/Visteon ECU. This also tallies with the three circuits I lost when the 5a dash module fuse blew (fuse 4), as we know I was able to reinstate these three circuits (and the speedo) by replacing the 5a fuse with a 7.5a fuse.

9. Handbrake/Fluid switches

13. Ignition lamp

15. The ground

The above three circuits (and the speedo) continue to function perfectly with the 7.5a fuse fitted, but the continuous blowing of the correct 5a dash module fuse under the dash does seem to indicate the resistance, and therefore the load on one of these three circuits must have recently increased.

However, I'm also now left wondering if the following six circuits I've lost are even protected by the 5a dash module fuse (fuse 4), or any fuse at all for that matter!!!!!!

1 - No illumination of the fog light switch - Rear fog light still works
2 - No illumination of the heated screen switch - Heated screen may not be working?
3 - No indicator tell tales - Indicators still work
4 - No headlight tell tale - Headlights and sidelights still work
5 - No high beam tell tale - High beam still works
6 - No seat belt tell tale - This light never worked in my ownership

If the above circuits I've lost are not fuse protected and there's been a recent increase in resistance somewhere, then the weakest point in the tracking would indeed blow just like a fuse.



The investigation continues, but it does seem odd I can lose the above six circuits without any fuse blowing, are these circuits simply passing through the other 20a dash module fuse (fuse 6) in the small fuse box mounted under the bonnet on the scuttle by the ECU & MFU?



And why would Morgan choose to protect the dash module with a second 20a fuse, surely 20a is way too high to offer any protection to the feeble PCB tracking

I appreciate I've introduced more questions than answers here, but I have an inquisitive mind and the way Morgan wired the dash module currently makes no sense to me, or should I say the way they fuse protected it follows no logic!

Perhaps someone can enlighten me

1 - No illumination of the fog light switch - Rear fog light still works
2 - No illumination of the heated screen switch - Heated screen may not be working?
3 - No indicator tell tales - Indicators still work
4 - No headlight tell tale - Headlights and sidelights still work
5 - No high beam tell tale - High beam still works
6 - No seat belt tell tale - This light never worked in my ownership

Could the bulbs have blown/failed.

The higher current scuttle fuses in the 2006 -2014 cars are the first in line from main battery feed Dave and there to protect wiring as much as anything else. There are other fuses further down the line to protect individual circuits fed from same. The collective main feeds to PCB relays when all energised would probably require such, noting that the heater fan alone is fused at 15 amps further along.

Note also fuse 4 in main group to dash module is a more modest 5 amps. This would likely be the one supposedly protecting the PCB control circuits including feeds to relay coils.

Many thanks Richard, it now makes sense that the 20a scuttle fuse (fuse 6) is protecting the main +12v supply cable to the dash module, like you say if all the relays are energised simultaneously a 20a fuse value would be about right too.

However, it still seems odd that the 5a dash module fuse (fuse 4 under dash fuse box) is not protecting everything connected to the PCB, can you confirm where I might find these other fuses further up the line that you refer to?

The laminated fuse ID card that came with Monty clearly just shows two fuse boxes, plus the expected 80a battery cable fuse.



Also, there's absolutely nothing in Monty's owners manual referring to additional fuses

Thanks again, Dave.