Great reply, thanks ricardo.....tomorrow's job is to open up both coils, just as you have shown in the pictures, will take some pictures and post on here .........thanks for your help......going to search youtube now for soldering tips...

Edited 19 March, 201610 yr by morrispaul

Start by opening the old coil. Use that experience to do the best job on the new coil, as you want to use it on your pickup. Have some silicon handy too for assembly phase.

Drilled the rivets this morning, before I drilled them I tried both coils on the car too double check the faults, both coils are not sparking on cylinders 1 + 4.

Drilled the rivits on the old coil and parted the two halves, bit messy with all that silicon but got there in the end, broke the join on one of the transistors in doing so and also on of the linking tabs to the 2 fat transformers...this will be my spares coil, will be more carefull with the good one....

a question for RICARDO, you have mentioned replacing the "power transistor" would that be one of the small black boxes soldered to the circuit board at the 4 pin plug end of the coil pack ?, see pic 2

Edited 20 March, 201610 yr by morrispaul

a question for RICARDO, you have mentioned replacing the "power transistor" would that be one of the small black boxes soldered to the circuit board at the 4 pin plug end of the coil pack ?, see pic 2

Yes, Paul. I thought you know how a transistor looks like. But nevermind, we'll take it slowly. First of all, I need you to tell me if each transistor is marked VB921ZV. Then tell me why the heatsink of each transistor is so clean and shiny. There should be thermo-conductive white grease for good heat transfer. If there was and you cleaned it, it's OK. But you have to smear the heatsink with thermo-conductive white grease before reinstall. If you haven't any, you can find at any computer parts store in a small tube. It's very cheap.

 

Now, to have the confirmation of a burnt transistor, you need to use a digital or analogue multimeter on resistance scale to measure the resistance in a few points (between some terminals of the 4-pin connector). We will use the photo bellow as a reference. Before doing that please tell me if you own a multimeter and know how to use it.

 

morning ricardo......as you can probably already tell,iam not too good at electrics.....i cleaned the white grease off so i could see what i had,the circuit board was also incased in what i think was black silicon,cleaned that off as well,yes i have a multimeter and will be able to do a few resistance tests,will check the transistors for markings later when i get in from work.

 

what i will struggle with is the soldering,will need to buy a new soldering iron and teach myself how to use it,ive broken some of the joints on one of the transistors so guess this will have to be soldered before i do the resistance tests.

 

many thanks for you help on this one,most helpfull.....and i learning at the same time 

many thanks for you help on this one,most helpfull.....and i learning at the same time 

That is the spirit. Be patient, methodical and you'll be able to sort this job. Parts changer can be anyone. Repair man, a few.

 

What I would like you to measure is the resistance between each connector pins as follows:

 

 

Note: The multimeter has two leads: a red one connected to terminal marked VΩ, and a black one connected to terminal marked COM. In the above table I've colour-marked which lead goes where. Basically we are looking for shorts.

 

When you start measuring, the range selector switch should be set on continuity (marked with a diode symbol and/or a beep symbol). If you get a 1 symbol to the left of display that means in fact I (capital letter I) from infinite resistance. Then switch to higher resistance range to see if you get a meaningful value. I have assumed you own a regular digital multimeter.

 

Do the same measurements on the newer coil.

How to Use a Multimeter for Beginners - How to Measure Voltage, Resistance, Continuity and Amps

 

Soldering

Paul

One of my previous photos had the pin numbering of the coil connector reversed by mistake. Sorry. Please use the photo below as correct reference for your measurements.

Hi ricardo.....thank you for the links and your time for putting that chart together , think I'll be ok with the multi meter, used it before for various tests but nice to have a reminder, need to get myself a new , suitable, soldering iron,that will have to wait until the weekend, very busy at work at the moment , no time for shopping trips but easter weekend this week which means a couple of days extra off work.......

a piccie of my multi meter, will need to re-solder the transistor on the old coil but I will try and test the newer coil before the weekend and post the results on your chart......thanks again for your help

The multimeter will do very well for our purpose.

Paul, could you take very good close up photos of parts I circled in red? Is there any marking on them? Any signs of cracks or arcing? If possible use a better camera because the focus on previous close up photos is not too good.

 

Oh, and don't forget my previous question about the markings on transistors.

 

Edited 25 March, 201610 yr by morrispaul

hi ricardo.......ive done a few tests this morning and also taken a few pictures,origanal pictures i took with my tablet these pictures ive taken with my digital camera,a lot clearer    

 

 

 

first the test results,used the new coil as ive not yet soldered the transistor back onto the circuit board on the old one...mullti meter set on 2k

 

 

pins                   resistance                                                            pins                      resistance

 

1r - 2b                       I                                                                     1b - 2r                       0.704

1r - 3b                       I                                                                     1b - 3r                       0.704

1r - 4b                       I                                                                     1b - 4r                       0.634

2r - 3b                       I                                                                     2b - 3r                           I

2r - 4b                   1.257                                                                 2b - 4r                       1.239

3r - 4b                   0.652                                                                 3b - 4r                        0.675

 

 

pictures are from the old coil,not looking good                                           

Edited 26 March, 201610 yr by morrispaul

pictures are from the old coil,not looking good                                           

I thought I see something on previous picture and now we have the confirmation. Those components are diodes. At least one diode look shot from 1) dirt and moisture forming a conductive bridge and 2) the intermittent short circuit in connecting cable. They need to be removed. There is a big chance that both 'transistors' are good and only one diode was shorted. In fact there is no need of diodes. I have photos of a coil without them (from factory). To me it was a surprise seeing them. See note below. By adding those diodes conditions are met for a 'programmed' failure. They short easily and people buy new coils

 

Note: I called the 3-leads black components 'transistors' for simplification. In fact they are power Integrated Circuits. You can see from the datasheet that they don't need external components (no diodes) and that they are very rugged and well protected.

 

 

The measurements confirm that one diode and/or a junction of one transistor are shorted. I attach the schematic of the 'coil' for better understanding.

 

 

Bottom line: desolder both diodes, solder back the transistor exactly how it was and repeat the measurements. Chances are the coil will be 100% functional. Same thing for the newer coil. You might end up with 2 working coils. Remember that you have to assemble the coil exactly how you found it. The transistors need to have good thermal contact with the metallic heatsink to stay cold during operation.

Thanks for that ricardo........ok.i'll remove the resistors, re-fit the transistor and see what happens, bought a new soldering iron and solder yesterday but forgot some de-soldering braid, will get some tomorrow.....

ok.i'll remove the resistors

 

Diodes. SMD rectifier diodes.

Edited 27 March, 201610 yr by RicardoM

Ooooops.............diodes....I'll take the diodes out tomorrow ......

Thanks for that ricardo........ok.i'll remove the resistors, re-fit the transistor and see what happens, bought a new soldering iron and solder yesterday but forgot some de-soldering braid, will get some tomorrow.....

Re  soldering out/in transistors. Something to be award of is that mains soldering irons need to be earthed to stop transient currents damaging electronic components.

Soldering braid is good, but you will need some form of heat shunt on the transistor legs. A large pair if long nose pliers is great, but often you will get away ( both for removal and installation ) with a large crocodile clip on the legs. Transistors are best tested out of circuit. There's three legs- base/ emitter and collector. Most modern digital multimeter have a diode test facility, and as a transistor id simply a pair of diodes, this will do the job. Base-Emmitter ,one lead on each= conductance ( or if diode test available, usually 1-1.4 v). Reverse leads and no conductance. Repeat for base /collector junction. Emmiter - collector junctions are usually open circuit ,both ways.But certain meters need consideration when testing transistors, on other ranges. The low ohms/diode est range is possibly OK, but on other ranges, either voltages or currents can destroy an otherwise good electronic component. De soldering components from a board I wish to junk, I do in the heat solder and thump fashion, or remove leg through board with large nosed log nose pliars.

That is not a transistor, it is a power IC. Read all posts carefully. As for the "heat shunt"... that is stuff from 30 years ago when Germanium transistors were high-tech. I know you are old school, probably in your 70's, but don't make things look more scary as they are. I am sure Paul will do well. It's an easy job, not an impossible one like putting a man on the Moon.

Thanks for your input guys, iam a complete novice at this sort of thing so a lot of what has been said is going straight over my head, on the plus side I am picking up a few bits and pieces.i really do appreciate everyons help.so a big thank you to everyones whos posted....

So.....been busy this morning, a trip to maplins to get some de-soldering wire, I bought a new soldering iron and solder the other day so time to start work.......iam a bit heavy handed and managed to break of one of the transistors so first job was to remove the solder and the legs of the transistor, put up a bit of a struggle but I managed it in the end, I removed the circuit board at the connection to the transformers to make it easier to hold, removed the two diodes, came off easy with gentle heat from the iron and use of the desoldering wire........slotted the transistor in place and soldered in place, resoldered the circuit board back onto the transformers...the most ive done with solder in the past is simple wire connecting but iam reasonably happy with the way things have turned out, not the neatest but strong with a good connection..

was thinking of trying on the car before putting the outer cover back on.....would it be ok to do this ?

Edited 28 March, 201610 yr by morrispaul

was thinking of trying on the car before putting the outer cover back on.....would it be ok to do this ?

Probably you already did that by now... but the answer is "absolutely not!". You are negating the purpose of a multimeter in electronics. We don't just solder things and hope for success... we measure first. Moreover, the transistors might get hot very quickly and destroy themselves from overheating. They are supposed to work with a heatsink, the cover.

Thought that would be the answer, I remember you mentioned the "thermo-conductive grease" in an earlier post....not tried it on the car yet for that reason........lots of the white grease on the transistors when I took the coils apart and the circuit board was also incased in what looked like black silicone.....if it is silicone do I need to re-pack it the same ?

The short answer is "yes". The white grease is used to dissipate the heat from transistors to metallic cover acting as heatsink. The black silicone is used as protection against moisture / condensation and arcing. But how about measuring this coil as you did with the other one?

Thanks ricardo.......yes will do the same tests again , be interesting to see how the results compare....

Measure resistance on 20k scale please.