PermaTune Schematic Diagram

[MaranderP]

I have a 76 911S with a PermaTune CDS box that is dated May 1976. I am assuming that it was the stock unit. The box has a fried resistor in it.
I have been searching the posted Q&As and have found extensive info on the Bosche CDS unit. All of the threads seem to be from the early 2000s. Is there any new info on the PermaTune CDS unit. Such as, schematic diagrams and parts lists or close up color photos. Since the resistor is burnt I cannot read the color code.
Any help would be greatly appreciated!

[HarryD]

Highly unlikely you will find any info. Most Permatunes come with their electronics "potted" and as a result are not repairable.

[HarryD]

BTW, Welcome othe best Porsche BBS on earth. A picture of your ride would be great.

If you have one of the early permatunes that was not potted, look closely, it may be a clone of the Bosch CDI. If the other part vaues match, I would thnk you would not be out much to replace the burned resistor with ne that is hte same size as the equivalent Bosch one.

Also, the posts you want to look for are from Early_S_Man. While he has since passed away (leaving a great void in our community), his legacy lives on.

[T77911S]

if it has a fried resistor, there is a reason. usually something else more than likely shorted, causing high current through the resistor.

even if it was not bad, i would trash the permatune and put in an MSD unit and coil.

[Bob Kontak]

Originally Posted by T77911S

even if it was not bad, i would trash the permatune and put in an MSD unit and coil.

+1

Cheaper/equal or better/reliable.

[Perma-Tune]

Can you send me a picture of the resistor? I may be able to help you.

T77911S is right, there could be a real good reason why the resistor burned out.

Hey Bob, 35 year old Perma-Tune not old enough? Ever see a 35 year old MSD?

[Bob Kontak]

Originally Posted by Perma-Tune

Hey Bob, 35 year old Perma-Tune not old enough? Ever see a 35 year old MSD?

I have never seen a 35 year old MSD box.

About time you guys get into the thick of things.

Both of my Perma-tune boxes worked great till they died. Did the box fail on it's own? Doubt that very much. Did something in my electrical system or some screw up I did cause them to fail? Surely the case.

Your customer service is outstanding. Your website is very helpful. However, the boxes, at least legacy boxes, are too sensitive to electrical "stuff" and an unfavorable reputation has been created.

Tell us how new ones are resistant to anomalous input.

[T77911S]

bob, thats funny, "BOTH my permatunes worked great til they died"


i had a permatune once. it died too. maybe with a little help from me. but i also fixed it. SCR blew. i had the SCR at work so that was nice. i must admit, the permatune is much simpler inside, which i like, but they epoxied most of them which i dont like.

ever see permatunes in race cars? (yea, i know, there are probably some out there, but not nearly as many as MSD's)

in elctronics, for that matter, anything can break. sometimes things can get a bad reputation for no reason. sometimes things can work longer than normal. each instance can influence us greatly. i drove my BMW for 6 months with no oil in the gear box. (bought it that way). it did not go out intil i took a trip, then i still drove it another 2 months. now i think the getrag 260 is the best gear box ever made.

[Perma-Tune]

We have always been there for our customers: just a click or phone call away. Many years ago I gave up responding to issues on this site because I was simply shouted down. Hopefully, things are different now.

OK, you asked for the information, put on your reading glasses.

IGNITION COILS

The tendency of the ignition coils to short between primary and secondary windings results in the high Voltage pulse going back to the ignition box rather than to the spark plugs where it should go. The legacy Perma-Tunes simply did not have available to them, at the time, components that could withstand the abuse and would burn out. The Bosch units were a little less susceptible to coil fly back shorts because they put out much less Voltage to the coil than the Perma-Tune.

The fix at that time was more of an issue of education than of technology. The analogy of installing a new box and coil together being like replacing the tire and the valve stem together seemed to help get the point across. After years of badgering our resellers they finally got with the program and started recommending replacing the box and coil together. Since not all failures are due to the coil problem we did not feel it our place to force customers to replace the coil and left the decision to them. We also gave them the choice between the stock transformer coil or the blue coil to save money.

Apparently, our competition saw the need for coil replacements too and introduced an inexpensive coil made in Brazil into the marketplace. It was a very poorly made product and ended up perpetuating the coil Voltage fly back failures. There are still a few being sold to this day so beware.

No doubt the fact that the coil is mounted upside down, on a vibrating fan housing near a heat source contributes to the coil failures. We introduced a coil relocation kit that moves the coil next to the ignition box, mounted right side up and away from heat and vibration. It was not well received probably because it changes the appearance of the engine bay. So we started making our own coils (P/N SC010) that are designed specifically for the air cooled Porsche engine: heat, vibration and leak resistant while still looking stock.

In the early 2000's, new electronics components became available and the Perma-Tune was redesigned to be much more robust and more powerful. This is the newer, black Perma-Tune.

The combination of quality coils, informed mechanics and next generation electronics components has gone a long way to reduce the coil fly back problems.

GROUND CONNECTIONS

Another problem inherent in the Porsche engine design is called a ground loop. A ground loop is a condition created when the current path of a ground circuit is prevented from following its intended path and instead loops back through another path, wreaking destruction in the process. There are several possible ground loops on the air cooled Porsche. In this discussion, I will cover only what is relative to the subject at hand.

911, 911T, 911E ect.

The most common ground loop on the air cooled 911 Porsche occurs between the engine and body. Since the entire drive line is rubber mounted, the electrical ground path for the fuel pumps and the starter is through the large ground strap located between the engine/transmission bolt and the body. This connection is prone to dissimilar metals corrosion due to the confluence of the aluminum alloy housing, steel bolt, brass ground strap and high current flow. Corrosion at this connection introduces both resistive and capacitive properties into the ground circuit. The damage done to the vehicle as a result can vary widely in severity and manifests differently on the early 911 breaker points distributor engines versus the later model magnetic distributor engines.

On the breaker points distributor engine, the alternate ground loop path is through the breaker points. The higher the resistance at the engine/body connection is, the more current is diverted through the points. At lower resistances, and therefore lower current flows, this ground loop condition is indicated by burnt breaker points. Higher current flows will additionally cause the signal sense resistor inside the ignition box to heat up. If the current flow is high enough, the resistor will burn out. (Reference the burned resistor in the 35 year old Perma-Tune that started this thread.) In very high current flow conditions, the problem manifests with slow starter speeds and repeated ignition box, fuel pump and starter failures. Since the capacitive component of the ground loop is so unpredictable, other symptoms may include radio noise related to engine speed.

The legacy Perma-Tune used a wire wound type resistor for points sensing. This type of resistor was used so that in the case of a high current flow condition through the resistor, the resistor will act like a fuse. The logic then was that it is less expensive to replace an ignition box than risk the damage a fire can cause. The newer Perma-Tune design can withstand much more of this kind of abuse while still providing the same degree of protection.

911SC, 930Turbo

The later model magnetic distributor engines have a different ground loop path than on the earlier cars. Although the ground loop condition is created by the same conditions and location as on the earlier car, the consequences of an engine/body ground loop can be far more serious on the later model cars than on the earlier cars.

The ground loop path on the magnetic distributor engine is through the ignition system signal reference ground wire. As the corrosion problem at the engine ground strap grows worse, the resistance at the ground strap increases. The higher the resistance at this connection goes, the more current is diverted through the ignition module ground reference circuit. The results of a ground loop are similar in scope and nature as in the earlier car regarding engine electronics and electrical components: burned out fuel pumps, starters, modules and in the case of the Turbo, burned out speed and run on relays.

Herein lies the difference between the Bosch ignition and the legacy Perma-Tune ignition: the Bosch ignition module will continue to pass current until the wiring and/or the module melts down, the legacy Perma-Tune has an internal fusible link that will burn out before the wiring in the engine bay gets hot enough to melt down. The difference can mean an engine fire versus a burned out ignition box.

The newer black Perma-Tune Model 911SC902 and 930902 ignitions are equipped with a fusible link located in the pig tale of the ignition harness. This facilitates repair rather than replacement of the ignition module while still protecting the car from an engine fire.

Best regards,

Lonnie

[Perma-Tune]

There are a whole lot more Perma-Tunes on the track than what you see. They are hidden inside the old Bosch housings.

[MaranderP]

T77911S & Lonnie from PermaTune & all,



It took me a little time, but in order to get a good view of the resistors, I needed to somewhat disassemble the unit. Someone asked for a pic of my car, so it's there also.
As I understand, Lonnie, you are from PermaTune? I haven't digested the info that you listed, yet, I will though. Can you release schematics and parts lists? My Model No. is 11-75 and Serial No. is 3607. I would think that at the bottom of the tag is the Part No. 911 602 702 01.
I have dismounted the Electrical panel from the left side of the engine compartment and I am cleaning all of the components and connections, as Early_S_Man suggested.

[Perma-Tune]

It looks like the resistors that bias the transistor are smoked. That means the power transistor is history, literally. It has not been available for many years. About the only thing you could do is find another Perma-Tune of the same vintage and strip it for parts.

Really nice looking car you have there. Is that a turbo look whale tail or is it a turbo conversion?

[rick-l]

Originally Posted by MaranderP

T77911S & Lonnie from PermaTune & all,
:

It would not be to hard to reverse engineer that board at all. That is old school with through hole parts you can actually see and touch.

Even though that particular transistor may be no longer available a better one has probably superseded it. Does the suspect transistor have a part #

[Perma-Tune]

True that. You got to be good with electronics though. Unfortunately, we do not have the schematics for that model Perma-Tune.

There are a few web sites around that can cross reference the P/N if you can still read the old part.

[MaranderP]

Does anyone have a PermaTune box that has these two resistors intact?
My ignition transformer seems to be okay. My terminals are labelled A, 4, & 1. The resistance readings are: A to 1 = 0.85 ohms, A to 4 = 703 ohms, and all contacts read open to ground.
This is good information; about cleaning the ground cables from the engine/transmission. Thank you.
Let me know if I'm way off on this, because I don't see how to get a ground loop without some catastrophic failure; for instance, the coils of the ignition transformer shorting across.
As I said earlier, I have removed the electronics, the mounting panel, and the cables from the driver's side of the engine compartment. The LT side of the ignition system is isolated from ground, mounted on pretty substancial rubber cushions, and the ground terminal has the shields of two wires landed there. As I was removing the electronics; I thought that since Porsche was a performance minded company, that the reason for isolating the ignition system from ground, was to isolate any interferance from chassis ground away from the ignition system. I don't believe that the Porsche engineers were concerned with radio reception. Now the HT side of the ignition system, the secondary side of the ignition transformer to the spark plugs runs at 20k to 25k volts. So, the plug wire shields and ignition transformer case is grounded at chassis ground. Can you tell me the path that would lead a voltage spike from chassis ground to the LT side of the ignition system?

[Perma-Tune]

The resistor I was talking about is the 100 Ohm, 5W that feeds the points. This is the only one that can be damaged by conditions outside the box. The resistors that are burned out in your box are due to internal conditions, like I said, probably a shorted out transistor.

I looked around here and could not find anything of that vintage Perma-Tune so I cannot tell you what value the resistors are.

[rpmgroup]

MaranderP, message sent

[Linda911]

Rpmgroup, why would you post a message saying let's talk offline? If you have something to contribute to the thread subject, why not post it here for all of us to learn from? I'm new to this forum, and interested in learning about ignition trouble-shooting tips.

[rpmgroup]

MaranderP asked if anyone had a box and I messaged him that I had one for sale. The forum has a classified section for that and i was not trying to change MaranderP's post to my ad space for selling something.

[Linda911]

Ah, ok. Good blog manners.