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Can i save this 280zx turbo ecu?

rjenkinsgb

Well-Known Member
Most Helpful Member
The three red resistors are a key part of the power supply to the rest of the electronics.

Those need replacing if showing high resistance, plus the power transistor needs testing.
 

DavidW

New Member
Yes, I agree with rjenkinsgb. If R62 is measuring 312,000 Ohms that circuit is not going to work properly.

It looks as though there are at least two [and possibly three] power supplies. R62 is critical to at least one of them, and protection functions. Some quick points that might assist:

Protection. First R62 limits the maximum current through D60 if the battery voltage has a high voltage spike it tries to clamp it to 27 volts in the ECU. Secondly, when the battery voltage is reversed, D60 conducts with a low negative voltage across it, but a very high current in the opposite direction through R62 [intending to blow an external fuse, but in your case probably toasted R62 instead]. As R62 currently has a high resistance, these protections cannot work as intended until R62 is replaced.

PS1. In operation, current would normally flow through R62, through R61, and onto Q61. Almost no current will flow through D60 in normal operation. However, because R62 appears to be high resistance [and needs replacement] little/no current flows via R62/R61 and Q61 cannot work as intended [and some of the ECU functions may not be working]. Before you replace R62 you should also consider an ‘in circuit’ test of Q61. If you replace R62 first it could make testing Q61 more difficult than it needs to be. If initial/basic tests of Q61 look dodgey you can always remove it for a more conclusive test/replacement. There are many guides around on how to test a transistor with a multi-meter (MM). It’s easier to do with a Digital MM that has a diode test feature as you can read the junction voltages - but there are instructions to use an Analog MM too. You will need to confirm what type of transistor Q61 is [PNP or NPN] as the test changes for each type. Transistor Q61 is possibly PNP, noting that is what Q50 is [and Q61 might be the same device] – but I could not see what Q61 actually is. To test Q61 you will need to look at the device number and find the associated data/sheet to: (1) ascertain if it is PNP/NPN, and (2) determine which pins are emitter/base/collector from the device case layout. If you are lucky Q61 will still be OK, and simply replacing R62 may fix your circuit.

PS2. R42 supplies current to Transistor Q50 emitter (e). Some current also flows down via R50 and through D50 [probably a zener diode] that attains its ‘zener’ voltage. This voltage is also the Q50 base (b) voltage that essentially ‘controls’ how Q50/R42 conducts/regulates the load of other components that are connected to the Q50 collector (c). Q50 is the PNP power transistor that was toasted on the other persons ECU board. You should check the transistor noting it has been seen to fail in similar [reverse voltage] circumstances previously. However, there is a fair chance Q50 is working as some of your ECU is partially functioning, and you say your Q50 looks undamaged.

PS3? The PCB also has another ‘power transistor’ next to Q61 that could also be controlling power, and it may also have failed. That said, I would try replacing R62 and check Q61/Q50 before moving to this additional transistor.
 

rramer56

New Member
rjenkinsgb I was told it would cost $100 to change the supply cuz it wasnt powering up. Would that bad resister prevent the power supply from working or is it after the power supply?
 

rramer56

New Member
DavidW all that is over my head. I only know basic auto electricity. I understand inputs and outputs of an ecu and how to scope them but im lost when it comes to the internals what they are and how they work. Where are the 2 power supplys and if you can tell which one is the main one.Is that middle resister connected to a power supply. Could that bad resister be why the power supply isnt working?
 

Les Jones

Well-Known Member
R42 being faulty would prevent the top power supply working.
Either or both R61 and R62 would prevent the lower power supply from working.
If D60 is still good or has failed short circuit then it has probably prevented damage to the lower power supply but it is unlikely to have protected the upper power supply.
If D60 has failed open circuit then there has probably been a lot more damage done to the ECU.

Les.
 

DavidW

New Member
The 'power supply' involving R62, R61 and Q61 cannot be working. Because R62 appears to be high resistance [and needs replacement] little/no current flows via R62/R61 and Q61 cannot work as intended. If you are lucky Q61 will still be OK, and simply replacing R62 may fix your circuit.

If you are unlucky, one/more of the power transistors [Q50, Q61, Q60] and/or other semiconductor/other devices may also be failed. The transistors are prime candidates for failure in reverse voltage scenarios, and that is why it is suggested that you check them.
 
Last edited:

rjenkinsgb

Well-Known Member
Most Helpful Member
rjenkinsgb I was told it would cost $100 to change the supply cuz it wasnt powering up. Would that bad resister prevent the power supply from working or is it after the power supply?
The simplest analogy is to think of those resistors as being fuses (though they are not, really),

One or more "fuses" have blown and the power is cut off from some sections of the ECU board.

They are just about the first thing in line with the power connection in to the ECU. Parts after them may also have been damaged, depending what happened to burn out first, the resistors blowing or transistors shorting out then resistors blowing...

There is an old joke from when semiconductor devices first came in to use, that transistors were invented to protect fuses.
Under high overloads, few things will fail faster than a transistor or diode.

The rest of the power supply transistors - the parts that regulate the voltage for the rest of the ECU board - also need testing or replacing.
 

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