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Can i save this 280zx turbo ecu?

rramer56

New Member
WOW DavidW, do you know what that board was off of or did the rest of the board pretty much match up with mine? When i was rating those resisters in my first posts i didnt know what they were exactly when i wrote this only that they were on one of the lower scales of my meter while the bad one was on one of the top scales. The board is at work so i had no way to be exact, i was just pointing out the huge difference. I know that resisters are made with different materials and properties even if they are rated the same. Can a small resister be put there thats rated the same or is there a reason those are so big?
 

rramer56

New Member
I guess it would be smart of me to let you guys suggest a resister to go there cuz you realy dont want me to try and figure it out lol. Also i can take a pic of the backside of that board, post the true ohms of the other 2 resisters monday and post it after work if that would be helpfull. Where did you find that pic of the board?
Thanks you guys are fabulous :)
 
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Pommie

Well-Known Member
Most Helpful Member
If any resistor is 4700Ω then it would require about 70V across it to dissipate 1 watt. Doesn't seem reasonable. More likely 470Ω?

Mike.
 

DavidW

New Member
All of the pics that I have posted to date were purportedly for 82-83 280ZXT. Within the archive of material, I have collected I do have another car wiring diagram that shows the ECU connections for this model – but the detail is the same as the other diagram I posted.

I have no idea if the pic posted by rjenkinsgb is from the 82-83 model – but it does look remarkably close to the ECU pic I posted save those resistor markings. That said, it is not unusual for manufacturers to use the same printed circuit board for a time over subsequent models – even if they need to change components. For example, different injectors, sensors and actuators might need slightly different interfacing components in the ECU. The Z cars did have a few technology jumps where things changed, and there are also a cadre of performance enthusiasts who developed ECU mods over the years – though I doubt yours has been modded unless you can see that extra diodes/resistors/wires have been added.

In general, it’s a good idea to keep with the size/rating/technology when you replace components. Different sized film/carbon/wire resistor may have the same/similar power ratings – but the size and technology has likely been selected for some particular reason. Fusible resistors are a different kettle of fish again… a fusible resistor is more like a standard resistor with an internal fuse that will blow [open circuit] above some voltage/power. Some modern fusible devices are semiconductor-based and very small – whilst older larger devices are based on an area/surface of conductive film that essentially gets destroyed as the device heats. Apart from size, there are big differences. For example, a 0.5 Ohm 2W resistor will quite happily continuously pass 2A [and a bit beyond], whilst a 0.5 Ohm fusible resistor might be designed to open circuit at 1.5A (1.5W). Sometimes, you will be able to reasonably insert one or the other – it depends on what a component is included to do [function] in the circuit.

Usually you can get circuits working again with pretty gross repairs like bypassing fusible resistors [certainly NOT recommended] or just selecting a resistor to allow a ball-park current – though that will/may compromise the design intent and protections. To date there is not really enough information to make good evidence-based decisions on those resistors. Also, there are some seemingly conflicting observations. For example, as Pommie points out it would be kinda unusual to have a 4700 Ohm 2W for the top resistor (R42) on the board with the voltages that are present. Remember also that you have a damaged ECU – it’s possible that all three of those largish ‘resistors’ may be flakey albeit only R62 shows evidence of overheating damage!

Yes, you should post some photos of your ECU, measurements – and some tracing. People will be able to help you much more if you do!
 

DavidW

New Member
That last pic with the two boards is interesting - the upper ECU board in the pic has the strangely marked components.
There is another pic with it on forums.hybridz.org that has a little better resolution of board with color banded resistors - see crop below:

Another1 cropped.jpg
 

rramer56

New Member
i do have a few pics of my board on my phone that i sent to my pc but when i tried to post them here they were way to large.Does any one know of free software i can use to reduce them?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
i do have a few pics of my board on my phone that i sent to my pc but when i tried to post them here they were way to large.Does any one know of free software i can use to reduce them?
Paint comes with Windows, and if not is available as a free download from Microsoft - and does what you want.
 

rramer56

New Member
The ohms on those 3 resisters on my board are
the first one towards the middle of the board is .470 on my meters 2k scale,
the middle one which i think is bad is .312 on the 2m scale and
the lower one is 1.5 ohms on 200 scale.
Seems that what you were thinking the ohms those other 2 good ones are in the alternate pic match up to mine. If so maybe the middle one in the pic is what i need? Seems that a .5 ohm 2 watt resister is very rare from my searches.
 

DavidW

New Member
Resistors are usually made/sold in several series of “preferred values” - each with an associated tolerance; see Wikipedia if you want more detail. Generally, you select the nearest preferred value within acceptable tolerance. E12 Series (10% tolerance) 0.47 or 0.56 Ohm resistors would be more common than say an E24 Series (5% tolerance) 0.51 or 0.56 Ohm resistors, and a E48 (2% tolerance) 0.511 Ohm resistor would be quite rare, and so on…

The resistor you are trying to replace looks as though it is: Green (5), Black (0), Silver (1/100), Gold (5%)….
So, 0.5 Ohm 5% is between 0.475 and 0.525 ohm. 0.51 ohm would be closest standard value you will see available.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
[See post below - somehow duplicated rather than edited..]
 
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rjenkinsgb

Well-Known Member
Most Helpful Member
0.51 ohm would be closest standard value you will see available.
???

0.5 Ohms is a standard value - Farnells list several different 0,5 Ohm 2W resistors:

Looking at the photo of the back of the circuit board, that group of resistors is fed from the EMI suppression block next to them & so almost certainly power feeds.

The centre resistor does connect to the power transistor in the middle of the board, the one that's shown as cooked out in another photo.
It is definitely worth testing or just replacing that as well as the resistors.

The lower resistor is connected directly to the big diode, which does appear to be configured as reverse polarity protection.

That resistor will need replacing as well, if it's supposed to be two ohm and reading high it has burned out.
If it is still two ohms leave it, it is fed via the centre one so that blowing may have protected it.

The other (470 / 4700) is probably high enough value so it was never subject to overload.

Edit -
Other suppliers - Mouser and Digikey
 

DavidW

New Member
Just looking at the measurements rramer56 reported yesterday. Probably would have been better if the DMM was on the lowest scale for all of the measurements… but the measured values are not extraordinary:

* R42 (Upper of the three large resistors on component side) measured at 0.47 Ohm. That makes some sense given the first two bands on the component are Yellow (4) and Violet (7).

* R62 (Middle of the three large resistors on component side) measured at 0.32 Ohm. That is not far off a value to limit the maximum current through D60. So plausible… despite some damage being evident. Also, pics of other boards have resistors with bands that look like 0.5 Ohm, and some in-circuit load would also bring this down closer to 0.32 Ohms.

* R61 (Lower of the three large resistors on component side) measured at 1.5 Ohms. That is plausible with some in circuit loading… especially if the resistor bands in those pics were for 2 Ohm 5%: Red (2), Black (0), Gold (1/10), Gold (5%).

Is it possible those resistors may all still be OK ??

rrramer56: The car has a fuse on the line that runs power to the EFI relay switch and through to the ECU pins 35/27. This fuse is separate to the main fusible link that provides power to the ignition switch. Did you check/replace that fuse in the line to the EFI relay? That fuse possibly blew in addition to the main fusible link. Just checkin to see if you might be pulling your hair out with the ECU for no reason!

The transistor that was shown toasted and burnt part of its own PCB label away is not actually Q705. That burnt transistor [fed through R42] is actually Q50. R61 feeds another similarly rated power transistor Q61 that is standing upright on the near the lower left corner of the PCB component side. R42 & Q50 look like a ballast regulator that use R50 and D50 as a voltage reference/control. The R61 & Q61 combination is likely to be similar, but I did not try to trace that through, include other components, or check any detail. See below for quick partial markup & sketch.

partial Trace & cct.jpg
 

rramer56

New Member
hello DavidW. Actually the fuseable link that blew was the black one 80amp that feeds the white wire, It feeds the alternator and everything except the ecu and related systems.
I have power to all of the inputs going into the ecu plus all grounds going in are good. Have power to the injectors and the coil. The fuel pump should turn on for a few seconds with the key on but does not. The pump should turn back on when the ecu sees the CAS signal. When i crank the engine i do get a CAS signal to the ecu but no output to the fuel pump relay. When i energize the ecu control wire pin 16 to the fuel pump relay the pump turns on.I dont have the ecu outputs to the coil, injectors or to the fuel pump relay.

My boss had someone look at it that works on ecus among other things related. We were told that the power supply in the ecu was bad and had to fix that before anything else could be checked. Do you see anything that could be considered a power supply? Maybe thats not the technical name for it but maybe he said power supply to keep it simple. I just got the news over the phone.
That middle resister didnt measure .32 ohms, it wouldnt register till i was on the 2 million scale. i got .312 on 2m scale, wouldnt that be about 312,000 ohms? i think the next lowest scale was 200k and it didnt register at all.
 
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rramer56

New Member
heres a wiring diagram thats easier to read except for the dotted lines that kinda make you crazy following them, they are the turbo wiring.


G96045.gif
 
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