Hey everyone, so i successfully swapped my caps for the ECM...
BUT... i believe at some point during the process, a resistor was either knocked off, or was already broken prior. *i prob knocked it off*

I only took pictures of the caps prior to ECU surgery, but not the backside where the smd resistors are...

Does anyone here know which resistor or other component was suppose to go in slot "C190" for a 1996 Lexus LS400 ECU Model : 89661-50304, 175200-0930 12v
It's on the right side of the back of the PCB, directly under the lid with the label towards the left 8:30/9 o clock

I could really use some help :3, i tried searching for the info but i honestly don't know where to start, i tried googling "1996 LS400 PCB Layout slot C190" LOL, much that got me >_> among few other variations of that.

Its against the edge at about 8:30/9 o'clock

Any help would be GREATFULLY appreciated, i want to get her running beautifully :3


Attachment 487103

 

C190 looks to be missing. It's going to be a capacitor with the "C" designation. It looks to be surface mounted and would be very small.

 

@jaaa , thank you! so it will be a capacitor.. so from looking at the rest of the board on that side, the only capacitors i can tell from so far have "A4" and "A5" marked on them.... would it be safe to just throw a A5 on there? and would anyone know how to go about finding said capacitor? O_O

i'm guessing to search for it, would be considered a "SMD Capacitor" with a5 marking? or a4 marking?

 

More than likely it will look like C206, C207, C208, C209- thats my best guess. Have no idea what the capacitance will be. Too bad, as of a couple month ago I had a spare ECU and could have looked on mine and told you what it was, but I just sold it.

 

i appreciate the thought... thank you though!

 

Looking at the placement of the cap C190 on the board, it's a bypass, not a coupling or RF cap. A bypass cap is a filter which is used to filter (eliminate) any ripple voltages (noises) riding on the DC (Direct Current) line whereas a coupling or an RF (Radio Frequency) cap is used to block a DC signal i.e. 5.2Vdc & allow the RF signal to pass through. Another application of the coupling cap is also used as a timing circuit in electronics. Anyway, the right & left sides of the C190 is soldered to a Vcc (5.2V) & ground, respectively. It would be very difficult for you to accidentally knock it off the board because first of all, it's small & it's a surface mounted components. Secondly, in order to get it off the board, you will have to de-solder/wick off the solder on both sides of the cap so if you didn't put a soldering iron there on purpose then it wasn't you that did it, however there's a possibility that the previous owner may had "tampered" with it. Thirdly, if you had accidentally bumped & knocked it off, the end-bells of that cap would still be there as they're being held w/ solder & based on what I can see from your photo, both end-bells aren't there & the solder on both sides appears to be intact without any signs of it being missing or disturbed. Now, since it's a bypass cap, you still be able to power on the board (you just don't have any DC filtering) & chances are it'll work without it.

 

thank you for that info!!

I should have added in the OP that there was some piece there in the center but it was like little tiny brown shrapnel, 90%+ of the remainder was missing, so I cleaned it up to replace whatever was on there.

what type of part should I be looking for to put there by chance?

THANK YOU @Superfast1 !!!

 

^ awesome answer superfast! i'm an electrical engineer by day and agree with his full assessment that it will likely still work.
in looking at the pics, there are other Cxxx positions that don't have any components on them either so it is likely C190 never had one to begin with. does the solder pads look round or does it look like something is missing?

i've personally knocked off surface mount components off boards before due to my mishandling during reinstallation *ashamed* ...thankfully i've always found the missing component and they are usually intact. the pads were not as shiny as the rest since the component was sheared off.

 

I was a Senior Scientist at an Aerospace Company in Southern California specializing in Communication Satellite designs for 36 years so I've considered electronics is one of my expertise. Last year, I've decided to retired early so my wife & I can travel to see the world. So far, we've spent 5 months travel throughout Europe & another 4 months in Asia. We would have been on the road again if not because of the current Coronavirus pandemic situation. There are just so many beautiful places & wonderful people that God has created for us to enjoy & meet so we've planned to keep going full blast for the next 10 years while we're still being able to walk . Highly recommended to anyone thinking about retirement and/or approaching the retirement age. Don't stay home & always be active as that's the only way for you to stay in good health.

Anyway, in regards to the C190 cap, as stated, it's a bypass cap so there's a very good chance that your ECU still work & you won't see any electrical performance degradation due to the facts that there are other bypass caps are also on the board so any ripple voltages/noises had been attenuated/reduced or even completely filtered/eliminated so you should be fine. If, however if you really want to find out if the cap was there & what's the value of that cap then you'll have to look for the schematic & parts list of the ECU. You can find it but it can be very time consuming so my recommendation for you is to go ahead, put everything back then power it up. Assuming there isn't anything else wrong with the ECU, it'll work just fine so you should proceed & try it out. Good luck.

 

Retirement IS everything its cracked up to be.Enjoy,your lifetime of hard work has paid off.Wishing you and the Mrs the very best.

 

Thanks Spuds.

 

Without it, there remain high frequency ripples and noises. I'd simply add a ceramic capacitor 0.47uF/16V X7R selecting one of these for the stable ECU operation.

 

thanks for the link! after replacing the caps i tested the ECU, still getting those misfires, haven't test drove it yet to see if knock sensors are still going off.
Although my TRAC control light is flickering now, it use to do that before, until i replaced the alternator. then it stopped, but it came back. I wonder if that capacitor is at fault for that? and maybe the misfires?

what could possibly cause a cylinder 3/4 and 7/8 misfire in harmony? they are taking turns, cylinders 3/4 will misfire 227, then 7/8 will misfire 227. very odd... with a random misfire here and there in a different cylinder, but a low number like 7...


Ordering those ceramic caps on digikey now, i love that site, it has 1 day shipping and they process QUICK

 

Perhaps someone already made the recommendation, but consider looking at another ECU board for the capacitor...and whether a part number or value mark on the component.

Anyone with an image to share with OP?

If you have an experienced electronics technician with SMD desoldering/soldering equipment, then possibly the component can be unsoldered from donor board and reused on yours...(however this is not best practice if a new replacement component is available)

My sense is there's more to the story here, so consided replacing your ECU with one professionally recapped.

it will reach a point where other components, in addition to simple capacitor replacement, will become necessary.

Perhaps someone familiar with Denso ECU's predicts which component set(s) are next in the replacement progression.

 

So i've replaced the missing Capacitor, and all the other larger capacitors.

Although i'm still receiving a TRAC OFF blinking light, misfires alternating between bank 1 and bank 2 in alternate identical misfiring values.

Current known issues with the car :
Misfires
(I haven't seen the P0330 and P0325 code yet, but will take a longer test drive today)
TRAC OFF light blinking

I've tested the camshaft position sensor with my oscilloscope and the wave form looked normal.

The car does have a slight exhaust leak coming out somewhere close to the engine, i will attempt to fix that today, but i don't believe that exhaust leak would cause such drastic misfires in the pattern it is happening.

@Yamae suggested i check the CKPS and CMPS, so far the camshaft position sensor seemed to be normal.

to fix this problem so far i've tried :
Spark Plugs
Spark Plug Wires
Re-soldering new capacitors
Lab Scope the Cam shaft position sensor


Would anyone here know what could solve my misfires? i'm not receiving any codes for the misfires, they just show up in the live data.
The misfires happen in order like 7/229/229 in cylinders 2 3 4 and 6 7 8 in alternating order as you can see in the two misfiring live data feed.
here's a pic of the scanner data :




Attachment 487083
Attachment 487084


THANK YOU EVERYONE FOR ALL YOUR HELP!! SO MUCH!!