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Hacking up Honda's ECU
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 Post subject: ECU lost 5v supply
PostPosted: Tue Dec 16, 2014 1:47 am 
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Joined: Mon Dec 15, 2014 11:18 pm
Posts: 3
Hello all,
I'll try to keep it short. I've been running a chipped OBD1 ecu for over a year. One day, the engine wouldn't start and when cranking I could hear the main relay click on/off a few times in rapid succession while cranking. On turning the key back to off and back to on, I got a solid CEL and no fuel pump prime. Swapping the main relay made no change, and bypassing the relay to run the fuel pump resulted in a no-start condition. Upon jumping the service connector, I simply got a code 0. Next I checked under the hood for 5v reference voltage to the MAP/TPS, but would only get ~ 0.5 volts.
Taking the ecu out of the car and checking it on the bench, there don't appear to be any leaking or blown capacitors. I burned another chip but got the same result. Upon powering it up on the bench I found I'm only getting about 1.6-1.7v to the 5v reg input, and the 5v output is giving me the same 0.5v I was measuring under the hood in the car. Next I rigged up an LED as a CEL and grounded the service connector pin on the ECU - same result, solid CEL. I added another jumper to provide 12v to the 5v regulator Vin, and the Vout came right up to 5v. With the 5v supply at voltage again I tried to ground the service connector and got the CEL LED to blink out codes (as would be expected for not having any sensors or simulator connected).

So my question is, where to start. In the mean time I've ordered another chipped OBD1 ecu as I don't have a spare and I'd like the car running soon, but I'd like to take a stab at fixing my current ecu. From searching, I've seen similar 5v issues referring to replacing the caps as the solution, as well as the Toshiba TA8903 and the STA413A. I can pull these from an OBD2 board I have sitting around. I haven't yet lifted C14 out, but it doesn't appear to have leaked anything on the board, but I figure that will be the first spot to check. I've searched but can't seem to find a good schematic of the power supply side of the ECU, just some handwritten schematics regarding sensor inputs. Has anyone else found other components to check that would cause an issue such as this? Any locations to check voltages at to narrow it down?

Thanks for any insight you guys can provide!
Chris


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 Post subject: Re: ECU lost 5v supply
PostPosted: Tue Dec 16, 2014 6:42 am 
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Joined: Mon Dec 15, 2014 11:18 pm
Posts: 3
Well, I guess I should have done a bit more troubleshooting before I posted, but since I've seen several instances of people with trouble with the 5v supply and not getting 5v back with replacing the capacitors and other components, I figure I'll post what I found.

The issue was with with the 220uF capacitor - the one usually indicated. I pulled it off the board, and noticed that there was a very slight amount of leakage down the positive terminal of the capacitor, but not really anything visible as far as damage to the PCB - a very slight bit of mess on the PCB, but I was able to wipe it away without even needing any solvent (but used some to clean it up as one should) With the capacitor out I tested the + side via on the top of the board and was reading 12v as I had set on my lab supply and was reading on the + terminal on the back side of the board. Seeing I didn't have a 220uF capacitor in my parts collection, I put in a new 330uF 50v I had (plus since it appears to be used for power filtering as near I can tell, the higher rating shouldn't matter really - especially for troubleshooting). I put the capacitor in and tested it out and was now getting .997-1v on the 5v regulator input - I lost nearly half a volt on the input side and dropped even lower on the 5v output. Seeing the only thing I touched was the one capacitor, I knew the issue had to be in that area. I pulled the capacitor back out and took a closer look - darn hard to tell even!

The copper ring surrounding the through hole via was just fine - which is why I was able to read 12v on both sides of the board. I powered the board up w/o the capacitor again and started following the trace on the top side of the board - the resistor right next to the capacitor was only seeing the same 1v as the voltage regulator, even though the trace clearly went to the + terminal of the capacitor which should have been reading 12v. Scratching a tiny bit of conformal coating off the trace just past the via registered the same 1v reading, and with the sharpest probe I have I was able to find that the capacitor had leaked down the lead into the inside of the PCB and under the conformal coating and had eating across the trace surrounding the via. Fortunately, with the damage being so minimal it was easy to repair with a short jumper lead from the capacitor + terminal to the resistor's + lead adjacent to the capacitor. Powering it up with the capacitor back in and the jumper in place gave me a solid 5v again, and plugging it back into the car gives me a happy running engine again.

The board looked undamaged under the capacitor - even had solid ring around the top of the via adjacent directly to the conformal coating. Even the capacitor took close inspection to see signs that it had leaked. I've replaced capacitors on equipment that have leaked much worse than this with more damage to the board and was still working, so for those that end up with a 5 volt issue on the ECU take an extra close look at that capacitor. If you read less than your supply voltage on the + trace side of the resistor adjacent to the capacitor, your board is dropping voltage after the capacitor.

Thanks for the site for those that run and support it. There's a great bit of advice and information here, and hopefully the solution to my issue will help someone else out there! I'll try and add some pictures when I get a chance.


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 Post subject: Re: ECU lost 5v supply
PostPosted: Tue Dec 16, 2014 11:30 am 
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Joined: Tue Jul 27, 2004 2:19 am
Posts: 653
Location: France
99.99% of the problems concerning the + 5V is caused by this capacitor and the destruction of the circuit below.
Image

After replacing the capacitor by a new and repair of the PCB.
Image


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 Post subject: Re: ECU lost 5v supply
PostPosted: Tue Dec 16, 2014 6:33 pm 
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Joined: Mon Dec 15, 2014 11:18 pm
Posts: 3
Perfect pictures - The capacitor shows more signs of leaking than mine had, but the repair executed is exactly the same as I implemented on mine. Thanks dip!


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 Post subject: Re: ECU lost 5v supply
PostPosted: Wed Jun 15, 2016 5:12 am 
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Joined: Sun Mar 08, 2009 11:12 pm
Posts: 101
Location: Malaysia
whats problem if got 5v but still cant start( solid CEL and no fuel pump prime). I got two ecu, p30 and p27. I already change ic12,ic17(TA8903) and QM3 ..


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 Post subject: Re: ECU lost 5v supply
PostPosted: Sun Nov 20, 2016 8:37 pm 
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Joined: Thu Jan 15, 2015 11:59 pm
Posts: 2
gee wrote:
whats problem if got 5v but still cant start( solid CEL and no fuel pump prime). I got two ecu, p30 and p27. I already change ic12,ic17(TA8903) and QM3 ..


You change all the caps?


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