Something blown up in ECU!

alinton · Post by **alinton** » Sat Jul 19, 2014 8:40 pm

Yes you're right, it's Q29 not 30.

D1780 probably means 2SD1780, which is a Jap transistor number, an npn tranny with an integral 60v zener diode b-c, which is unusual. They're only a fiver to buy anyway.

If you can, can you see what value the emitter resistor is?

Thanks!

Andy

wurlycorner wrote:Interesting... I didn't expect there to be much difference between that ECU and another, but I've just opened up a spare UKDM manual ECU I have lying around (xxxx-P13-G01) and I have Q30 fitted but nothing in Q29

FWIW, all the transistors in that batch have the same code on them;
Top row: "D1780" (or "D178D" difficult to tell through the lacquer)
Bottom row: "45"

If that's burnt out, you should check any bias resistors and any components after the Emitter too, in case one of those has gone down and that was causing excessive current draw through the transistor itself.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Mon Jul 21, 2014 2:19 pm

Just seen this, will check later on and let you know...

alinton · Post by **alinton** » Sun Aug 10, 2014 11:51 pm

Just to follow up, I got a replacement transistor and installed it, and the ECU seems to be working fine.

I reckon the transistor is something to do with the lambda sensor, following the pcb traces it goes directly to a pin designated as connecting to the heated O2 sensor.

Strange though that the car wasn't throwing any errors, I'd have assumed that the lambda wasn't working, but I would then expected an error light and some flash codes.

Hmmm...

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Mon Aug 11, 2014 7:21 am

Glad that's fixed it. It probably wouldn't have known that the circuit was faulty though - I'd assume that the self diagnosis is more designed to test/monitor the inputs from the sensor and if they're ok, then everything would appear normal to it?

Froidas · Post by **Froidas** » Mon Aug 11, 2014 7:38 am

I am pretty sure these are responsible for IAB. I had such a JDM P13, but never tested, if it really was IAB, because my Prelude doesn't have them.
It should be quite easy to verify, because on idle IAB must be closed.

alinton · Post by **alinton** » Wed Aug 13, 2014 10:02 am

And the IAB is? And where is?

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Wed Aug 13, 2014 10:28 am

Intake Air Bypass
It opens/shuts the dual runners in the inlet manifold to alter torque at high/low engine speed.

I thought everyone knew that!

(that's a mickey take of myself btw - I had no idea either, until I asked earlier this year

)

alinton · Post by **alinton** » Wed Aug 13, 2014 9:08 pm

Everyone does now!

So, does everyone except me also know where the actuator is?

mercutio · Post by **mercutio** » Wed Aug 13, 2014 9:11 pm

its on the cambelt side of the intake manifold