Mac2

Great advice, replaced all 8 ECU capacitors in my 1992 SC300 last month, and I am no soldering expert. A desoldering iron from Radio Shack helped a bunch.

Rough running-gone, smoking gone. My car never ran better.

special thanks to Yamae and LSCowboy.LS

LScowboyLS

yay! woohoo!

Yamae

You are welcome, Mac2.
Thanks for informing your result. It is important that a no soldering guy can fix his ECU and his car runs good now.

The result may affect many others who try to replace capacitors by themselves.
There are many those who hesitate to replace due to the no soldering experience.
It would be very nice if you'd show the detail of your way to do the replacement for no soldering guys.

gphilemon

yamae indicated some capacitors may look good, replace them anyway, and why the recommended CAPS are larger than original for LS 400 1996

LScowboyLS

because they are all of the same make amd model with the defect - Nichicon PF (M) series - and will all be leaking soon enough, and if that were not reason enough, they are all nearly 20 years old, and beyond their service life


larger voltage rated caps can give additional protection against ripple current and typically have improved specifications all around, such as lower ESR (although ESR being too low would not be a good thing either) - the list of recommended caps has been thoroughly vetted for quality, size, specifications and availability by Yamae and myself.

higher voltage rating on a cap is fine, the capacitance itself is what must match, and the ESR must be in a specified range

Privateer

I have a 94 ls400 ecu that I'm working on 89661-50142. The only symptom it exhibits is the AC fails to operate. I have it dismantled atm and discovered there are a number of traces damaged between C832 and the connector block.

Sorry I didn't crop it to just that area. If you look directly below where 623 is printed in reddish pink on the connector block you will see the damaged traces. Is there a wiring diagram to be had that I can use to make the appropriate repairs?

LScowboyLS

are you sure they are actually in need of repair, the first level of damage is when the electrolyte eats the solder mask off so what I am trying to say is that some discoloration of traces is not sufficient enough damage to worry about - try to see if any are actually severed

now a real problem is getting the damaged areas that need a capacitor installed to accept the new solder without ruining the solder pad, it takes some super fine 2000+ grit sanding (almost like using paper to sand with) and lots of flux to get solder to make a good connection after electrolyte corrosive damage

can you take a close up - macro shot pic of that area? - a digital camera that is not in a phone would be great

PS - how did your can of flux get so dirty inside? - keep it clean! - nothing should go into the flux container besides clean fingers!

also, anytime there is damage to traces like this, you also need to track down how & why they got damaged!

Privateer

The flux is dirty due to it being left out in my garage for a long time without the lid on it. I'll be getting a new container of it in the morning.

Here is a new shot, close up.

Several appear to be damaged completely through. I cleaned off quite a bit to get a good look at them, and I'm of the opinion the damage was the result of the cap at C832 leaking out in that area. The ecu runs great otherwise, in terms of engine performance, though I'm going to replace the rest of the caps after I get some new flux.

The top hole of c832 was completely destroyed and I can't tell if there was a trace coming off of it leading elsewhere. I need to clean up the flux I left behind from removing the cap that was there.

PS. As to cleaning a trace, have you tried using a pencil eraser? I found them to be very useful and as long as you don't get too aggressive they work rather well.

LScowboyLS

yes, was gonna suggest an eraser as another option, it is a good abrasive level, just clean off any residue it leaves before fluxing

I would clean the really bad areas on this board and reassess the damage.

If an ECU requires trace repair work, then not only would that be a real pain, but it also probably means there is a lot of oxidation of many of the pads, you sometimes have to remember that discretion is the larger part of valor and before you spend too many hours on an ECU that is this badly damaged, you might want to find a "virgin" (never repaired before) at the junkyard or on ebay that hasn't leaked yet and then just proactively fix that one.

because the original chocolate brown Nichicon PF (M) capacitors have been discontinued for many years, that is how to easily spot a "virgin" ECU - just read the cap markings!

Privateer

Well, i was unsuccessful in my initial attempt at a repair on this ecu. The engine still ran great as before, but the damage to the traces and whatever else I am not able to diagnose still prevented the A/C from running. So I took the spare ecu which presented issues when accelerating heavily and performed the same procedure. This one took quite well, and after several test drives I've not experienced any sign of the previous problem. When I have more time, I'm going to try to identify and reroute the traces as best I can and see if I can repair the first ecu fully, but I'm not going to hold my breath.

Thanks for all the information about the ecu repairs that have been posted in this thread. Time well spent in reading it, and my hat is off to those who have contributed. Who knew the soldering class I took while in the Corps twenty some odd years ago would come in handy?

LScowboyLS

glad to have helped!

Mac2

As posted above, my 1992 SC300 now has all new capacitors in the ECU and never ran better. This are a few of the details about the repair:
1. About 4 months ago the SC300 began to run rough especially at idle, and the exhaust smoked badly.

2. Couldn't find a problem, so I did a little research here.

3. After finding this information about bad capacitors leaking I removed the ECU.

4. Sure enough, I wiped the circuit boards with a Q-tip and alcohol and found a yellowish residue around two of the caps that were mounted together.

5. I cleaned the board good and put the ECU back, and all problems were solved for several weeks, but then returned with a vengeance.

6. Removed the ECU, and found that the oily residue had returned around the same 2 caps.

7. Then I knew that I would have to follow LScowboy and Yamae's advice, and replace the caps

8. I have soldered before but not much and not lately, soooooooo I found an old PCB from an old portable radio and practiced removing and installing components

Mac2

9. what really helped was the desoldering iron from radio shack with the red rubber bulb attached.

10. When I felt confident, I replaced the 2 bad caps and reinstalled the ECU. Problem solved for months, but I believed the wisdom here was to replace all caps as strongly advised.

11. So I went back and replaced all of the caps. as directed and could not be more pleased with the results.

For me the practice was time well spent, after the practice 8 out of 10 of the replaced solder joints were hard to tell from the originals, The other couple were pretty fair, maybe a bit more spherical than conical but still shiny and sound.

Hope this may help others.

Dutchy

Hi Yamae, sorry but i don't have that multimeter any more. I changed job a few months ago I will try to borrow a good one.

The capacitors have arrived from the states, soon they wil be replaced and i'm very curious about the changes.

simrx3

ah crap mines doing some of these things.. 1993 aussie delivered LS400

Might be time to haltech and supra stick her