I‘d like to repair my interface unit, the black box in the trunk, 7EM or DAC2586 as Walmart offers one for $18, but that is far away and the others available to me now are more expensive.
If it’s just a transistor or the IC it might be a few cents.
Reason for asking, the trip computer shows everything but the fuel related data. The board is quite beautiful, but I have no idea whether there’s a way to test it (preferably without oscilloscopes). If someone here says that the IC is usually done after 30 years, I‘ll get my hands on one, it’s just that there’s barely anything to be found online on repairing it - all I know is that it converts the fuel injector signal into a trip computer format.
Thankful for any input.
David
This is the best I found and it gives pinouts; it says in his case the IC was broken, but how do I find out? http://backglass.org/duncan/jag/ifu/
If available, David - I would rather change the whole interface unit…
While new parts doesn’t necessarily work, but if they do get rid of the problem; they are confirmed working. That does of course apply equally to the IC, but working inside electronics is always a bit iffy. And ‘fiddle factor’ may work against you - and if problems stays; you are left with more doubt…
If a new interface works; you positively know that the old one does not - and you can go about work on that with the some certainty that working on it will eventually solve the problem - and not wasting work…
By and large; ‘a few cents’ versus ‘18 dollars’ (or whatever in that range) is not a hill of beans. These days I rather throw money at a problem than work…
Sure enough. You understand my worries. I’ve always been good at soldering, and have not seen an european trip computer interface for less than $50 (shipping from the usa is expensive, takes time and there’s no guarantee it works) and those are from wreckers, not necessarily confirmed working - I’d need SIII friends to swap with.
I was hoping for somebody pointing out a failure mode, but if it’s not the chip I will go through the transistors and the wiring before I throw it out.
The battery’s been out a few times and the fuel data never worked, but I believe I have measured continuity of the wiring both from the ECU and to the trip computer as well as power and ground… and I tested a substitute trip computer. I’ll look for the IC tonight.
Quite simple to replace- cut the IC legs as close to the body of the IC so you have something to grab as you unsolder each leg individually. Might be a good idea to replace any electrolytic capacitors (ones with polarity marks) as they go bad over time. I have done 2 of the V12 units with success.
Precisely what I needed to hear. Good idea about cutting the legs, much easier than desoldering individually or pulling up piece by piece. Luckily no electrolyte in sight, just diodes, resistors and a little ceramic capacitor.
The parts finally arrived. None of my sidecutters at home - so I just heated all the solder carefully and pulled the chip out. The new one was soldered in and what I got was this:
Success!
Somewhat. Either the chip was a dud and crapped out or something fried it.
Lucky me, because I bought 6. Can’t wait!
So I‘d say always replace the op amp before suspecting anything else if all fuel values are zero.
The situation that I had/have with my 88 XJ-S was that the fuel interface was bad; I replaced the IC which restored the fuel used readings on the travel computer, but the distance functions were also inoperative. I traced this to the speed interface module (was able to feed a square wave signal at the interface which made the travel computer register distance).
Part number for the speed interface on mine is DAC4864; have been unable to locate one at a reasonable price and cannot remove the PC board in the interface for repair as it is glued in it’s case. If I find one (even dead) I would cut it open to see if repair is possible.
Luckily my distance and speed functions work.
Another chip yields nothing but the instant hovers at „1“ now.
I might leave it at that or find out why some other time. I consider any change a (part) success, though!
I’m curious as to why you didn’t replace the whole unit? I know that David @ everydayxj has a couple. I have a couple. Just curious.
I’m happy to see you got it working; that’s cool! I have a ecu that I have to replace a couple mosfets. I haven’t done it yet; mainly because I don’t know what size. .
I don’t want to waste too much on the trip computer and there is nothing in the rest of the unit itself that seems at all fragile. With my luck I‘m replacing the whole car to get this working and that’s not worth it to me. Three good years without it!
And they’re not cheap enough here, at least not on ebay.
INST 1 - AVG 1.1 from previously 0 in all three - the numbers don’t change.
