Both Transistor legs are as follows
Centre pin B
Outside pin C
Other outside pin E

ZTX650
Red Probe to B and Black Probe to E about 0.6V - 0.75V
Red Probe to B and Black Probe to C about 0.6V - 0.75V
Swapping Probes so Black to B should give no reading or open circuit - correct open circuit 0V
C to E one way will read 0.6V and open circuit the other way - average was 0.25V BOTH ways (high was 0.29 and low 0.21)This was on both diodes

ZTX750
Exactly the same but the probes are swapped, so Black Probe to B and Red Probe to E will give 0.6V etc.Same as above - both read the same.I have no idea which as which.- I read them from underneath the circuit board just in case that makes a difference



Are these the diodes?

Tested the 6 soldering joints.

 

No the 2 on the bottom left of the PCB shown here, The flat ones not the 1/2 round ones They will have ZTX650 and ZTX750 printed on them



Are these the diodes?

 

Thanks - lets try again...

Both Transistor legs are as follows
Centre pin B
Outside pin C
Other outside pin E

ZTX650
Red Probe to B and Black Probe to E 0.6v
Red Probe to B and Black Probe to C about 0.6v
Swapping Probes so Black to B should give no reading or open circuit Correct NO voltage
C to E one way will read 0.6V and open circuit the other way Correct

ZTX750
Exactly the same but the probes are swapped, so Black Probe to B and Red Probe to E will give 0.6V etc.

Black Probe to B and Red Probe to E 0.003v
Black Probe to B and Red Probe to C about 1.47v
Swapping Probes so Red to B should give no reading or open circuit 0.6V one way and 0.003v
C to E one way will read 0.6V and open circuit the other way 0.6v one way and 1.06v

 

The ZTX750 is bad and will need to be replaced. While you are at it test the diodes circled in red, they should test the same as the transistors 0.6V one way and open circuit the other. Post the voltages for each diode so I can see what they are.

 

Hi Warren,

See below picture for results, thanks.

 

Ok they are good. get another ZTX750 and hopefully that will fix your problem.

To replace the transistor cut the legs off, makes it easier to de-solder. Put solder on the iron tip before you put the tip to the work then pull the legs out with pliers.

When you install the new one make sure it goes in the correct way.

 

Excellent Warren, will report back soon.
thanks & cheers

 

Hi Warren... could not purchase in NZ ... obsolete.
Ordered 10 from China for $9 delivered, hope they are ok.

Searched Ebay and even the ones from Germany looked the same, so why pay an extra $10 for 2?
3 weeks until delivery.

cheers

 

Sorry I should have said RS Components have ZTX753 for $1.55 each, but the Chinese ones will work.

 

I tried RS components but their website said obsolete.
Just waiting now....

 

Hi

I’ll start with an apology for this minor hijack

I have done A/C to a buddy’s XJ-SC V12 ‘85. He told me cruise control had stopped working and that the bellow was cracked. Easy to change while I had the compressor out, so I sourced a used unit.
Now fitted, and still no CC

I measure 22-23 ohm from middle connector pin to each of the 2 side pins, and both solenoids operate with a 9V battery.
When I activate the vacuum supply solenoid, the vacuum is not sucking in the bellow. Is the other solenoid normally open and thereby dumping the applied vacuum until it is activated ?
With engine running and CC switch in ON position I have 0V on all pins in the connector.when stationary. Does that sound right ?
All fuses under LH (driver) knee pad checked for continuity.

I have not read manuals or been very systematic, sorry. It’s raining, and I expected it to be a 10 minutes job...

Edit: Forgot to mention my own XJ-S does not have CC, so there is no reference available...

 

Yes one solenoid is NO and the other is NC so voltage needs to be applied to both to hold vacuum.

All which pins the ones at the bellows or the ones on the CC module?

 

HI Leo - how did you get on?

Well my ZTX753 turned up...




Now I need to wait unit the rain stops to try it!
Fingers crossed!

 

Thanks Warren.
I’m working in R&D developing solenoid valves, so the terms NC and NO are clear to me, but I didn’t want to risk getting less answers by using them in my question...
I haven’t located the CC module yet, so I’m measuring at the bellow connector. I guess next step is to make a small test lamp setup as described in earlier post and go for a drive.

 

Leo,
I haven’t located the CC module yet
passenger side foot well look up, its all there.
At the back, black box, two plugs, one big multi, the other a single.
hope that helps.

 

Duke, to get that old ZTX out cut the legs off tin your soldering iron tip then put it on a solder pad and pull the leg out. Do this for the others re-tinning your iron between each.

When you have them all out you will need solder wick to remove all the solder from the board holes before you try to install the new ZTX. Again tin the iron tip as this puts flux on the iron tip. then put the solder wick on the board and touch it with the iron. Be careful not to leave the iron on the PCB too long or you will lift the pads off the board.

I am happy to skype or Whatsapp if you need help.

 

It is on the passenger side under the shin trim, a black box about the size of a 20 cigarette packet, and has a label on it saying "econocruise".

 

I have been repairing electronics most of my life so tend to reel things off without thinking sometimes as I have been doing it so long. lol

You will have no voltage at the bellows pins until the CC is activated. This will not happen until the car is travelling over 40km/h. I would suggest removing the CC unit and checking both ZTX transistors, they are quite susceptible to failure as any high current draw from a short or jammed solenoid valve will have them fail.

 

Thanks All

I will see how far I get into the fault finding, the car is being picked up tomorrow. Faulty CC-module sounds plausible. It’s not that easy to analyze things, that needs to be moving at 40+ kmh to start working...

Leo

 

Econocruise box located and opened. Looked very fine. No testing done to the diodes and transistors.
Connectors was clean, and the fuse was also OK. I cleaned the ends and holder, just in case...

Test drive: no change.

The issue will then most likely be the transistors or the brake switch, which I will check next. If that is not the cause I will tell the owner, that I didn’t manage to fix it this time. He says it’s ok, he’s not using it often. I would, I love to use CC and relax my right foot on long drives...
Thanx for all your input !

Leo