Tennesseejed Posted August 5, 2008 Share Posted August 5, 2008 New guy here. I acquired a '75 280Z yesterday. Haven't owned a Z since a '73 240 back in my college days long ago. I was told the car needed a new transistor control unit. I searched these forums last night and didn't find what I needed so I figured I might ask for an opinion or two. With the ignition on, coil gets no voltage on the contacts. Using the trusty Haynes maual, I tested the leads to the transistor control unit and determined that 12VDC is getting to the black, black/white (x2) and blue wires at the control unit harness. (Car is the California verision without the brown wire) The only thing I can think to do before I buy a new control unit is test continuity between the control unit and the coil. I have read much about these fusible link things. Neither wiring diagram I have shows a fusible link in the ignition circuit, but one of the pictures I found linked on this site does. My questions are: 1. Which wires am I testing from the control unit to the coil for continuity? The blue wire appear to go from the unit to coil +. I don't know which black/white wire goes from the unit to resistor/coil -. 2. Are there any other checks or test I can do before I start buying parts which will confirm that the control unit is bad? Thanks in advance for any feedback. TJ Quote Link to comment Share on other sites More sharing options...
Tennesseejed Posted August 8, 2008 Author Share Posted August 8, 2008 Update: I pulled the brain and removed some transistors in hopes of finding a bad component. [Alaska is pretty much BFE for finding used Datsun parts]. Turns out all the transistors were good but several of the solder joints lacked continuity. So I resoldered all of the control unit leads as well as the connectors to the PC board. After reinstall, coil had no spark. Checked the coil wiring and moved two wires. Still wouldn't start. Checked the spark plug firing order and found all the wires one off. Changed the wires around and *drum roll* She started right up. Woot!!! Now the real work begins. Clearly needs a tune up. Runs fine but a little rough; idles at 1300rpm. Lots of obvious electrical issues too like fan motor not running and wipers not working. Once I get the tune up behind me all the fluids will be changed to syn. After that . . . hello money pit! Quote Link to comment Share on other sites More sharing options...
woldson Posted August 8, 2008 Share Posted August 8, 2008 Great job!! Quote Link to comment Share on other sites More sharing options...
m4xwellmurd3r Posted August 9, 2008 Share Posted August 9, 2008 wow dude, you must know a little bit of electrical work to tear one of those open to repair haha. Good job on getting it started! It looks REALLY clean too! Quote Link to comment Share on other sites More sharing options...
Tony D Posted August 9, 2008 Share Posted August 9, 2008 Cool, that tidbit about bad solder joints in the box will be filed in my vault! You MAY want to get yourself a late-model ZX Distributor assembly. It's a drop-in for what you have, and I ran my 75 for months till I found the correct transistor unit for mine (from a California 77 model...the 75 I had was a JDM FairladyZ!) Would make for a nice roadside bail out should the need arise. Quote Link to comment Share on other sites More sharing options...
Tennesseejed Posted August 9, 2008 Author Share Posted August 9, 2008 Thanks guys. I get around pretty well with electronics, but think I mostly got lucky to stumble on the solder joint solution. Really, the test and solution are very simple. And you don't have to do anything more than to remove the back cover of the brain. Remove all the wires/wiring harness and back panel on the ecu. Set your multimeter to ohms and test the resistance between the harness contacts and any point in the circuit beyond the solder joint where each wire connects to the PC board. If the resistance is more than a few ohms, the solder joint is not good. Visually, a bad or "cold" solder joint may have a brown bubbly/oxidized look to it. The fix is simply to apply a hot solder iron to melt the existing solder while wiggling the wire to ensure a good connection. I also resoldered the harness leads where they attached to the pc board. Even if you have no experience with electronics and soldering irons, if you are convinced a brain is bad and needs to be replaced, nothing is lost by trying to fix it yourself before you pay good money for a new one. Hey, it's going in the trash anyway. Not sure what I'm going to do with the car. It's not as clean as the pictures. I tried to check the timing yesterday and found the timing mark on the crank pulley is about 180 degrees out. Yikes! I'm in denial of shredded crank key syndrome for now. Engine has 20K on a rebuild and pulls strong. Hope to do valvle lash, check dash pot and distributor advance today. Yesterday, replaced diff fluid with syn and learned that the tranny fluind cannot be changed without having the car on a lift. (can it?) I'll probably just drive the car for a couple of months before I decide which way to go. I probably won't go the resto way. My gut tells me I'll likely probably strip it and turn it into a NA road racer. Glad I found this site. Tons of info and knowledgable people. Hope ya'll will let me jump on the Z-car bandwagon and ride along with you. TJ Quote Link to comment Share on other sites More sharing options...
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