Interesting S1 PTU repair

Did this TV Repair shop happen to be O'connor Television? Brytech used to own a TV Repair and electronics shop, reminds me of his dodgy work

 

Been there done that. I won't link to the thread because it turned into a fish slap between 2 of my
favourite members ( who have long since "kissed and made up" ) but here's a story about the PTU that
came with my Zed, remanufactured by Automotive Computers Australia

Short version?? Have long since fitted a series 2 PTU but it still intrigues me that the old school "hobby style" rebuild worked quite well.

Almost guarantee that it would never fail from heat or vibration, those semiconductors are HUGE by today's standards, the current paths were
via the thick wires of the components rather than a thin copper track, and the solder joints were all done by hand.

Go figure...

 

That is horrifying.
What sort of pressure was being put on the ECU.
That was like direct hooking up the coil packs to the ECU.
DAMN !

 

Chill Graham, it's not as bad as it seems.

The ECU sends out a low powered trigger signal to the PTU.
This small trigger signal gets amplified by the PTU into something large enough to fire the coilpacks.

I could go on forever here but short version is that the ECU is safe from damage even from a strange looking PTU

Sideways and backwards version - the construction methods used in the PTU that ryzan and myself posted were
good enough to put a man on the moon in 1969

 

LOL
Those old school PTUs may not look like swiss precision engineering,
but has anyone looked inside the S2 ?

 

I did miss the row of transistors which would isolate the ecu.
On first look I only saw the resistors and thought someone had done a direct hook up.
Boy is my face red.

Thanks for clearing that up.

Still learning about these cars.

 

GMB you don't need to be red faced about anything.
1. The pic wasn't that obvious, first glance looks like direct connect wires
2. The description by RyZan who was looking directly at it, seems to support your initial impression. He implies it's just resistors
3. For the benefit of anyone using a browser that does not show pics, there are six flat trannies covered in grey silicon under the barely discernable resistors (almost hiding in the background of the pic)

We should all take comfort in knowing that part of our zeds can be fixed by a TV repair guy.
Unfortunately TV repair guys are rarer than S1 PTUs.

So RyZan are you going to convert your loom to S2 now?

 

Well its the thought that counts.

IMO the idea was there they have just let themselves down with the overall/final arrangement/assembly.

Poor resistors can easily fail as well so I would be using something more like this if possible.



But there are a lot of very good high power switching transistors out there.

My question would be why on earth there units are located in the engine compartment let alone anywhere near the engine.

A lot of transistors are highly prone to failure.

And most transistors have an absolute maximum operating temperature of 150C.

 

I think they mounted the PTU in that position because its high and dry and gets good cooling from the fan, the ouputs would have some nasty EMF noise on them too, keeping in far from other stuff is probably helpful.

 

DC voltages drop over distance so they would need to keep the PTU close to the engine.
Where would you like to put it?
Near the ECU?
That could work

 

Dumb PTU's are nothing more that a switching transistor, or in the Zeds case, a bank of 6 of them biased on and off by the ECU.
Current switching done by the PTU is not that high. 4 or 5 amps as a rule at most.

Some el-cheapo 2n3055 power transistors will easily handle that given that duty cycle is so low and radiating area of a 2n3055 in a metal To3 case ( i think) is so large... however, where things get tricky is finding a switching device that will handle rather high back EMF, induced in the coil primary windings, when power is cut.
This can be in the vicinity of several hundred volts and anybody who had grabbed the negative post of an old points car coil when running will testify, its pretty powerful and the kind of thing that most common switching transistors take a dim view of.

Replacing the PTU guts with appropriate transistors is a perfectly sensible solution to a very simple problem when considering the price of a new OEM PTU.The success of the job depends on whether the approporiate switching transistors were used or some thing less robust was fitted.

E

 

not quite the negative terminal but close...... I am one of those idiots.

 

I've seen a few of these modded units. Not as reliable as the original design, but definitely a lot cheaper fix than a new unit! The originals are a thick film hybrid circuit - a good choice for vibration resistance and heatsinking. Yes, they had a design flaw which was most probably a mechanical failure of the joins to the terminals, more than the electronic components themselves. Let's face it though, most of them lasted many years before failing.

Brisz, I agree with you. The original mounting location puts the PTU near the coilpacks, as all the heavy current (and electrical noise) is from the PTU to the coilpacks, not the ECU to the PTU. It would also assist in cooling, being exposed on the front of the engine and near the radiator fan. I think it was in the right spot.

 

For those that are not familiar, although the hybrid thick film assemblies may look a little clumsy they are actually a very high quality way of putting a circuit together.

Sometimes the printed resistors are laser trimmed in circuit for ultra precision, I do not know if it was done in the PTU's but if gives you an idea or where this style of manufacture fits in.

Comparing the OEM to the farm yard stuff is laughable, it may work but if I was putting a performance car together I know what I would use.

 

I would have to agree the potential generated here would have to be the main argument against relocating the PTU. Ideally I guess you would have them as near to each coil as possible for this reason. But even the majority of industrial transistors I have datasheet on still specify maximum operating temperatures of 150C. I guess the PTUs would have to be based more upon that of most TO-3. Which generally have a higher temperature rating mainly due to heatsink AFAIK. With the 2N3055 I do not think it offers any circuit protection. However I think there are packages out there which do. Some of the IGBT may be good for this reason.

 

Oh come on ladies, think about things for a minute will you.....

The ptu would be mounted onto the engine to expedite original assembly and the further away you can place a PTU out of the hot airflow and vibration found on the front of the engine the better.
You could mount he PTU in the frikken boot and use light wire and not see any appreciable voltage/power loss to the coils.

The PTU is there to isolate the ECU from the noisy and back EMF prone ignition coil system.

There is no "heavy current" necessitating big wire or short wire runs. Coils only draw (inrush) around 4 to 5 amps at most for a couple of Ms each firing stroke/cylinder.

Despite all the funky looking fins and shit on a S1, they dont get hot and they dont need cooling air. Why do you think an S2 is just a plain pack... Hmmm?
they get hot because they are in a HOT environment FFS!

If the ptu gets hot enough to actually FEEL when mounted on a cool surface such as an inner guard, then you have a real problem such as a short somewhere.

Get the PTU OFF the engine and mounted firmly. Anywhere off the heat cycled and vibration prone environment of the engine itself which is murder on electronic components.

E

 

What sort of resistance do the the coil-spark plug packs have? Ie. As in a typical hi-tension lead. I would be guessing the point of the system would be for them to have very little.

 

So Nissan screwed it up again ?

6 circuits switching around 10 amps each 30 times a second is not going to produce heat ?, wow they must have special silicon down your way.

The kind of temps that would bother PTU's is probably around 180C, these temperatures are at the gate deep inside the semiconductor, you do not "feel" that on the outside of the package, using your logic you could touch the heat sink on a computer CPU and on the basis it is cool say it does not need one. Take the heat sink off a computer CPU and see how long it lasts. You are a nuts and bolt man and a pretty good one but you think of things like an engine at 80C, the whole block is at 80C but in semiconductors it is like the gudgeon pin is at 80C and the temperature is dissipated through the rest of the engine. Like putting a lighter flame under a brick there are very high temperatures but in general the brick will be cool, that just means the heat sink is working, a heat sink does not need to be exceedingly hot to be deemed necessary and or working.

What is going to bring the semiconductors in the PTU to its temp threshold is dwell, the period that each ignition signal is held on for, the longer the dwell the stronger the field in the primary winding and therefore the stronger the resulting spark from the secondary winding and also the more heat that is created in the PTU, excessive dwell will fry semiconductors and threaten coil life.

Nissan/Hitachi/Jecs/Bosch have plenty of bright sparks in lab coats that work out all the details to make a performance system work reliably.

Again I will say when you see the likes of these people doing something that looks strange like exposing electronics to vibration, look at it this way, there is most definitely something going on, and what you are looking at is the short side of the triangle, try not to see it as "Nissan screwed up" because you will be wrong 99.99% of the time.

In Nistune there are dwell maps for voltage and RPM. As voltage drops dwell increase, this is the same in both NA and TT, just a pure energy correction to get the spark required. In RPM you see a small difference between NA and TT pretty much when a TT would be boosting, a higher density charge in the cylinder requires more energy for the spark to jump the gap, sometimes a smaller gap is used, but Nissan got in there and did the single figure percentage changes to dwell so it works reliably.

When you look at something like this and realise the detail Nissan went to I don't know where people get off thinking the work experience kid was the one who slapped the PTU on the front of the engine.

The red line is TT on top of pink NA.

 

Thanks Briz.
So we will keep our heatsinks and even the location
But I might put a vibration dampening mount under it.

So why did the Non Turbo graph have to be pink
Why not blue?