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Attached is a photo of the wire I have to work with :
20 awg ; 16 awg ; 12 awg // 12 awg seems awful big but if you think that is best then that is what I will go with. For the other connections would 20awg be ok? It is bigger than the 24 or 26 gauge that was used on the previous repair but to get the smaller gauges I have to buy 100ft when I only need 18 inches. Also, my stripper only goes down to 22 gauge.
Last edited by greenforest56; 11-06-2017 at 10:19 AM.
I take it having an over capacity on voltage is ok, it is under capacity that is a problem? I note that all your recommended replacements have voltage capacity higher than stock capacitors.
Oops! I reckoned to have measured that, but on re-checking there's around 30mm between the pcb and the top of the case.
It's OK to go higher on the voltage up to a point, provided the larger physical size doesn't cause problems.
I'll review my list as I got a bit fixated on the temp. ratings.
12awg is quite stout, but bear in mind that the inline fuse is 30A - take a look at the green/yellow wires on the other half of the connector. The jumper attachment points to the board connector pins and the link (marked R751) are also reasonably sound mechanically.
Not sure why you need 18" of thinner wire - do you have an issue with something other than the track that runs by C721? You could probably salvage some short pieces from an old radio or similar.
Got the new capacitors and went right to work. I installed six new ones. All six of the old ones I removed were only rated at 85c. Two were supposed to be 50v but they were only 16v. Two others were supposed to be 63v but they were only 16v. So, looks like the tech who worked on this just grabbed whatever was handy around the shop and installed them.
Good news is six correct capacitors are now installed. Bad news is I am the worse tech in the world when it comes to soldering / desoldering. If the ECM wasn't ruined before - it is now.
However, let's continue to proceed. You wanted a photo of the small 0.1uf capacitor that I am going to replace to see if the pcm was ok. I have removed the 0.1uf capacitor and attached is a photo of the area. Now that I have removed it, it looks like the diode?
next to it might be burnt as well. What do you think?
Hey Charlie,
I imagine that the previous repairer was working on the assumption that because the ECM is fed from a 12V battery that 16V caps would be OK. They have obviously been working up to now so he's got away with it, but it's not always a safe assumption to make.
The diode looks fine to me:-it's a Toshiba 5Z30 zener and it's there as a surge suppressor. Only check you can easily make is that it's not short-circuit. I've attached the datasheet and Mouser has them if you're worried/encounter any problem.
I see that you have sourced a replacement ECM and are back up and running other than the P0741. She's not cutting you any slack
However, onward and upward. You're working with a scorch-damaged area making the best of a tricky job. I don't see anything that you have done that has made matters any worse, other than you've slipped a few times with the soldering iron tip! You may not have had enough heat to that area when removing the blue cap. That's OK:- you're concerned about not getting things too hot, but a soldering iron tip won't reach the temperatures that the burnt cap did.
If you can lay hands on a circuit from an old radio (or whatever), you can practise with the iron and solder. Make sure it's fairly thin multicore solder - you might be able to blag some (you don't need much) from a radio repair shop if you don't have any suitable.
Here's how I would approach the rest of what you have to do:
On the topside of the board, remove the remaining lifted copper track. Cut carefully with a modelling knife along the green lines on picture 1 and peel the remnants off the board. Pay particular attention that there's nothing bridging to the connector pin circled in red, and ignore the blue circle
Replace the missing copper tracks with stout copper wire as in the earlier pictures.
You can now fit the new caps.
You only have the one intact connection on the underside of the board for both of them. For the small blue cap, probably the easiest solution is to solder it across the two links R751 and R752 on the top side of the board. Note that cleanliness of the areas to be joined is key when soldering.
Now fit the large electrolytic though the holes on the board, remembering that the -ve mark on the can should be closest to the connector pins.
Solder the cap lead to the intact connection and snip off the excess. For the other lead, I'd suggest soldering to the underside of the link as shown in picture 2 (I think it will be long enough). Slip a short piece of insulation over it so there's no risk of a short to the track in the middle. (The yellow bit in the picture).
Finally, do a double-check for any shorts.
I came across this the other day on the Bad Caps forum (yes, there really is one). It's not car-related, but an interesting discussion about the types of caps fitted to our ECMs - particularly post #3. As you will see, the problems aren't confined to Jaguar... https://www.badcaps.net/forum/showthread.php?t=63896
Shame we're not closer as I'd be happy to do this. Shout if you need anything..
11-06-2017, 10:14 AM
