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Can i save this 280zx turbo ecu?

rramer56

New Member
Can anyone identify the part in my attachment that looks like a big resister its the one in the middle of the 3 big red parts with black stripes that look like big resisters. Its a ecu from a 1982 nissan 280zx turbo. Also anyone know if im waisting my time trying to fix this after a battery jumper was reversed? I can find no other outward signs of damage after "looking" at it closely. That part ohmed out millions of ohms and can see its cooked on my board while the other 2 were around 2000 ohms. Hopefully i can replace that and luck out. Dont pay attention to the arrow the pic is from another pc. Thanks 4 ECU Full SIZED.jpg
 

DavidW

New Member
Yes, that certainly does look like resistor. I can’t make out the band colors to ascertain the value from the picture - but from the size it would be rated circa 0.25 Watt. As a gross approximation you might expect it could carry a current of say around 20 mA from a 14V supply [ that would dissipate circa 0.125 Watt max with a 1.5K ohm resistor]. It would be unusual to put a resistor in circuit with this size/power rating with a mega ohm value that you measure - because it would dissipate very little power... and it would not need to be nearly as large as it is. So, yes, I would think that component is suspect - especially since the board has been cooked. You may be able to ascertain the correct value from the band colors if you can make them out.
 

rramer56

New Member
Hello DavidW it is red and they all have black stripes, They are all striped differently. That board is from 1982 and from japan. I showed it to an old guy that owns an electronic supply and he never seen anything like those but he thought they were resisters cuz they have R61 and R62 < (the bad one) at the foot of of them. See the one the burnt one the arrow points to? It was replaced with a a .5 watt 22 ohm carbon resister, originally it had a .25 watt 22 ohm in it.
 

rramer56

New Member
hello debe , how do you check it? I do basic electrical work on cars in my job but this is mostly over my head :) I do have automotive scopes and multimeters to use. Have you ever seen that middle red resister with 4 black stripes ? it is blown open internally on my board.
 
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rramer56

New Member
Thanks debe, i guess you dont know what that red resister like thing is either. I find it strange that with all the electronic experience in here no one can identify what that is. That is in at least every Nissan 82,83 280zx turbo ecu sold, possibly non turbos and many other ecus. It might not fix the ecu changing it but its worth a try if i can find out what it is and replace it.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
The burnt resistor should be 22 Ohms.

I found an article relating to that exact fault, here:

(Though resistors are not polarised. Orientation is cosmetic, it's just easier to read them if they all face the same way).
 

rramer56

New Member
hjello rjenkinsgb that article is where i got the pic from. I say dont pay attention to that arrow cuz thats a different ecu. That post is where i got my incentive that i might be able to fix this. The resister it points to in my ecu is 22 ohms. If you read my post you will find im trying to identify a different resister (the middle one) that is in a group of 3 and are all big red all with black stripes.
 

rramer56

New Member
hello les jones the part i need identified is right above the circle and right below the back of the lower arrrow in this pic, red with 4 black stripes.
120526
 

DavidW

New Member
Hiya rramer56,

all black bands on a resistor makes little sense because you would expect some colors to denote the value of resistance - but it could possibly be some kind of fusible resistor inserted as a link of zero ohms [noting also the code for black is zero]. However, I would have expected the bands would still have been used to denote a value. Without a schematic/wiring diagram you cannot be sure of anything unless you trace some of the circuit around R62.

I have repaired a few Nissan ECUs - but not this model. That said, the problem you describe has been reported by others. This pic was posted back circa 2007 on zcar.com that also has the failed larger red middle resistor (R62):

DSC00646.jpg

I don’t know how/if that ECU problem was solved - but there is another pic that shows Q705? got toasted along with R62:

DSC00643.jpg

Q705 is the green transistor on the picture that you originally posted. It looks like a stock Hitachi A780 (2SA780) PNP power transistor: Beta (gain) around 30, and max ratings around 1A, 50V and 10 Watt. R62 might be configured as some kind of pass resistor for a series regulator/switch using Q705 - so I would check that transistor's junctions with your multimeter too even if yours 'looks' good.

Hope that might help.

Regards
 

rramer56

New Member
Hello again DavidW, I dont understand how all that works or how to test it. All that is noise if i cant find and replace that red with black striped thing. I absolutely know that it is bad. It wouldnt read ohms till my meter was on the 2m scale,Its not as bad as that one in the pic but you can see the coating was starting to bubble, the other 2 read on 2k or lower scale. If i replace that bad part and it still dont work then what you were saying might be relevant here :)
We have to make sure not to put them cart before the horse. Thanks for putting your time and effort in to this.
Is it ok for me to post again in a more generalized forum just asking if someone can identify that bad part? I dont want to break any rules.
 

Les Jones

Well-Known Member
Does the left hand end of the large diode connect to the supply negative (The car body / negative battery terminal.) ?
Does the right hand end of the large diode connect to one end of the suspect resistor ?
Does the other end of the suspect resistor connect to the positive supply to the ECU ?
If the answer to all these questions is yes then then the suspect resistor will be a low value fusible resistor.

Les.
 

rramer56

New Member
Hello Mike ive never hooked it up to the car with the cover off so i dont know. Wouldnt t all that resistance be considered an open curcuit
 
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rramer56

New Member
Les jones, When i look at the backside of the board it looks like it isnt hooked to anything. so shows what i know :) Could i assume that it has power and ground on each side of it cuz hooking up a jumper backwards is what blew it along with the main fusible link. ? Are you saying that if its low value it was put there to blow first in case something went wrong? would that somehow help to figure out a replacement. Also I dont know what diode you are talking about. I cant test it cuz its at work and i can only sneak a few minutes here and there to test it more. if a few tests can determine what can be used to replace it i sure will try to do some but would need detailed instructions. would a pic of the whole board front and back help? Also I dont know if the other board that is attached by a ribbon would have anything to do with blowing that resister. Thanks
 
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DavidW

New Member
Because the bad resistor appears to have unusual [non-standard] markings it will be difficult for anyone to specifically identify it without access to other information - like the actual schematic/circuit/parts-list of the ECU... bear in mind that the ECU design is around 40 years old and information is likely to be as rare as hens teeth as the ECU was probably intended to be repaired by ECU replacement. Maybe some kind soul measuring a known good ECU resistor for you is a possibility?

Saving other possibilities of finding an answer, you will need to do some circuit tracing!
I am thinking along the same lines [and related components] as Les Jones – although there may some additional insights to be gained considering:
(1) the Electro Magnetic Interference [EMI-B] subassembly located at the near lower left in relation to the three largish resistors. Note this ‘appears’ to just be three wire links threaded through ferrites standing up as isolated components in some kind of casing.
(2) Internal ECU Interfaces to its connector, and the car harness to sensors/actuators and battery.

The large diode (D60) below the three large resistors on the PCB is a 5 Watt, 27 V Zener. This particular device (Toshiba T5Z27) is/was commonly used for automotive transient overvoltage suppression against spikes when jump-starting etc. Zener diodes are designed to normally operate ‘reverse biased’ [connected in reverse to other diodes] around the Zener voltage [i.e. the diode would normally sit at battery voltage with almost no current, and only start conducting if voltage went above 27V to quench any jump starting spikes]. This diode would also have been ‘forward biased’ temporarily had a very high current when the battery was reversed - until the cars fusible link blew. D60 could be toast – but it is more likely not affecting operation of the circuit other than it may not provide much protection anymore. Unless it has failed short cct [unlikely] I would just leave the diode D60 alone for now. I have only ever replaced these diodes when I thought they could be degraded after protection has been activated - but they do usually seem to keep working OK.

Because the D60 diode would have been forward biased [and only dropping around 0.6V or so] when the battery was reversed the diode would have provided a low impedance ‘supply’ to anything that it was connected with. The thinking is that if R62 was connected, it could have had almost all of the battery voltage across it… and yes cooked. But I suspect this may not be the fault mode.

Each side of R62 WILL have circuit board traces/tracks to other components - on the PCB rear, or the component side. It would be good to establish what other components [including ECU pins] that it connects to so people could help you much more!

I think you should possibly have a close look around EMI-B. The proximity of those three ferrites to the three largish resistors may be relevant. Though an over simplification, ferrites are often used to suppress higher frequency noise on interface lines. The proximity is suggestive that the resistors might trace through the ferrites to the ECU connector and vehicle harness as part of the vehicle sensor/control interfaces it provides.

This diagram of vehicle wiring & harness to the ECU connector/s may be of some value:

ECU Wiring.jpg

You could get lucky looking at what is connecting/tracing to particular ECU connector pins.
For example [this is NOT based on anything but a guess]: do those three largish resistors somehow interface/trace through to the three crank angle sensor/s via ECU pins 8, 35 and 17 (?). I would be especially focused on anything that connected to pin 35 as that also provides a path through to the the ECU via the cars EFI relay from a car fuse separate to the cars fusible link. If the three resistors are associated with the crank angle sensor it would indeed be a reasonable start to replace R62 with a similar [nearest standard preferred] value as the other two. If R62 traced through to other sensor/devices you would need to consider the characteristics of the sensor/device involved.

Anyway, there are some more thoughts and info for you. I hope it might be helpful.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
I've found another photo that shows one either from a different batch, or that has been repaired - it has standard colour coded components rather than the multiple black band ones.

The photo was of the whole thing, I've zoomed & cropped it to just the resistor area. trying to zoom more just makes it fuzzier.

The centre one appears to be green-black-silver, which would be 0.5 Ohm

The top one looks like 470 or 4700 Ohm, depending if the third band is brown or red.
Lower one 2 Ohm possibly?

Probably 2W or so rating, estimating the size compared to other resistors.

I'd be tempted to lift the top one out (at one end, at least) and measure the resistance out of circuit. If it's 470 or 4700, the centre one is likely to be 0.5 ohm.


ECU.jpg
 

DavidW

New Member
Concur with rjenkinsgb that the middle resistor R62 does look like 0.5 Ohm [Green-Black-Silver] 2 Watt on the new pic posted.

The values of the other two large resistors don't really matter if they are undamaged and working. However, the top resistor is probably 4700 Ohm rather than 470 Ohm noting that in the first post rramer has measured [in-circuit] both the upper and lower resistors at around 2000 Ohms. Also, if the lower resistor is still good then it can't be as low as 2 Ohm if it measures [in-circuit] at 2000 Ohm.
 

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