Hi All,
I am back from vacation and will be taking a look at my controller this weekend, or sooner. i have the MOSFETS so I will be asking questions as I go along.
@Inwo
Dave, Per your picture above, you have F F F F A marked but you skipped a MOSFET in the middle, was that on purpose or did you just skip over one. You have three F’s and one A circled?
I am going to jump into this tonight and see what happens, I am just going to replace all six MOSFETS to be safe and save some testing time.
The picture was from another project.
I believe there are for on this side and two on the other, although it seems they should be grouped in 4 or 8.
Maybe the two are for reverse and it would not require as much current? Just a wild guess.
OK Dave,
Looking for direction here…
My guess is that the four Mosfets that are black on one side are what we are looking for.
The two Mosfets on the other side look just slightly different than the others on that side, do you think that would be the other two?
Since forward gives the 66 error and reverse does not, start with the four black ones? or just do all six?
@Inwo
Start with the ones that are shorted. Most likely only one or two.
Follow the field terminals to the correct mosfets.
Should all have the same part number. In a pinch I’ll open one up here.
A full bridge requires only 4. I don’t remember why six.
It is defiantly those six as you can see from this view. You cannot read the part numbers as it looks like they have been replaced before.
There is also a signature CSW 1-3-18, so someone has worked on it before.
I will start with the four, if it goes easy I will replace the other two while I am in here.
OK, it’s done. Got to be honest - if it works it will be a miracle… LOL It has been 20 years since I have had to solder like that. I replaced all six Mosfet’s and I will test first thing in the morning.
Be aware of the electrical isolation from the heat sink.
It look like some mosfets in the first picture are isolated tab to-220.
Is there an insulated thermal pad and paste between Mosfets and heat sink?
See if you can get a part number.
Not that many out there. IXFP90N20X3M is one.
There were no pads on any of the MOF’s I took out, all of them just had thermal grease between the MOF and the heat sink, I put them all back in just as they came out, including new thermal grease.
Oh, I see what you are saying they might be different MOF’s. There are no part numbers on the original ones so I have no idea.
Just went back and verified there are no visible part numbers on them. Here is a picture of the two types.
What do you suggest I do at this point? I have not reinstalled the controller yet.
If there is no pad between tab and aluminum, it will be a dead short. You will need to source insulated tab mosfets, or use pads.
Were the numbers intentionally ground off? Sounds like a RFF repair.
What do the armature mosfets use for insulation?
Also, there should not be two types. I guess that I will need to open one up and see what they truly are.
I expected part numbers to help you along. The odd ones may be diodes, explaining the odd number.
There were defiantly no pads between the MOFs and the heat sink. The black ones appear to be plastic so that is why they might have been fine. But the other do have metal backs and had no pads.
I can go back in add pads if needed. But I think at this point it would be great if you opened one up and took a look. If I have to get back into this thing I would like to only do it one more time.
I don’t know if the numbers were removed on purpose, but like said before some technician has been in this controller before per the hand written CSW 1-3-18 on the heat sink (right by these MOF’s).
I never worked so hard to beat myself out of a $150. 
All 6 are field mosfets.
Mine uses only 4 total. P80NF12
The side with 4 needs thermal pad to isolate tab from heat sink, which is A2.
Mine uses only 2. Might be upgraded devices from original design, or some controllers may supply higher field current.
The side with only 2 need no pads, as the heat sink is the B+ buss. Supplying B+ to the high end of mosfet bridge.
If you have a microscope look for numbers.
Preaching to the choir Dave LOL - I guess we can just rack this up to education?
That design has is obvious has been modified to only use two.
I will open it back up and slide in pads for the side with four and leave the side with two alone.
I have looked with a high power magnifying glass, the only thing I can see is a small emblem in the corner that kinda looks like a “Z” or Zi"
That’s too bad. It would be nice to know if it was an intended upgrade. Those mosfet packages are rare.
On a happy note, it’s good that you asked before connecting.
OK, it is ready - I am scared to put it in… 
@Inwo
Well… it appears we might have fully functional T4 Controller !!!
I have to say that I have only gone forward and reverse about 10ft in my garage but that is 10ft further than before.
I am going to go bolt it down and take it for a full-blown shakedown run.
