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DI cassett repair

1K views 11 replies 6 participants last post by  djtaylor 
#1 ·
Can DI cassett,s be repaired & if so where / who stocks the bits, anybody done it
 
#5 ·
Yes, I've repaired several.
If the problem is misfires, it's usually a coil or two that have obviously lost oil. The coils simply unplug so you can easily make one good DI out of two.
If the problem with the cassette is that it stops working when hot (or randomly), it's usually the circuit board, cannot be repaired, but is a good source of coils.
 
#6 ·
Jim Mesthene said:
Yes, I've repaired several.
If the problem is misfires, it's usually a coil or two that have obviously lost oil. The coils simply unplug so you can easily make one good DI out of two.
If the problem with the cassette is that it stops working when hot (or randomly), it's usually the circuit board, cannot be repaired, but is a good source of coils.
Jim, I have a DIC that misfires under high boost (runs fine otherwise) but hasn't lost any oil, actually it worked fine before I put it in my trunk 1 year ago, apparently it failed while being carried around in my trunk. What can be the problem, then?
Also, how do you remove the coils? any special technique? I revode the lower black cover but found no obvious way to remove the coils.
Thanks.
 
#7 ·
Thanks Jim, I suspect this subject may pick up some interest, would really apreciate if you could fwd some maintenance detail
how I did it, what materials was used, what inspection crieria was used ( coil resistance, capacitor checks etc....
Thanks again
 
#8 ·
Jim Mesthene said:
it's usually the circuit board, cannot be repaired, but is a good source of coils.
Anything can be repaired ;)

For one thing, I note there's an electrolytic capacitor on the DI. These are typically not great at high temperatures as they dry out. This is a common fault with switched mode power supplies which work fine as long as they're not turned off, then once turned off and on again, all it does is click because the capacitor isn't storing any charge.

Probably the biggest challenge is that most of the electronics if I recall is embedded in potting compound.

David.
 
#9 ·
Stefano said:
... but found no obvious way to remove the coils.
Just pull on them, they plug in.

Norman Lovie said:
....if you could fwd some maintenance detail
how I did it, what materials was used, what inspection crieria was used ( coil resistance, capacitor checks etc....
I never measured anything, it didn't do much good; they failed under load, you'd have to put them under load to test.
If you remove the obvious screws and remove the plastic cover, to reveal the coils, you can usually see some sign of failure. Look for oil leaking or missing. Also look for carbon tracking at the coil output end. Other than that, it's trial and error.

DISCLAIMER: I've only done this with the red DI units; I retired before the black ones started to fail.
 
#10 ·
djtaylor said:
Probably the biggest challenge is that most of the electronics if I recall is embedded in potting compound.

David.
Probably the earlier (89-92) DIs were not filled with resin, hence easily accessible and repairable, but the later ones (93+, Trionic ones I mean) are definately filled with solid resin. I don't know a way to remove it without damaging the electronics, maybe somebody does...?
 
#11 ·
djtaylor said:
Anything can be repaired ;)

For one thing, I note there's an electrolytic capacitor on the DI. These are typically not great at high temperatures as they dry out. This is a common fault with switched mode power supplies which work fine as long as they're not turned off, then once turned off and on again, all it does is click because the capacitor isn't storing any charge.

Probably the biggest challenge is that most of the electronics if I recall is embedded in potting compound.
I'm just a humble mechanic, I don't know a whole lot about circuit boards.
The electronics of the DI cassette run 12v (from the ECU) through an occilator, then a transformer, then back through a rectifier, to step up the DC volts to 400v. This 400v potential is what's used to measure ionization in the cylinders to sense knock, and is always present across the plugs (this is why the DI uses resistor plugs).
All of that stuff is embedded in the epoxy you see on the inside. Fixing that stuff is beyond my skill level.
 
#12 ·
Jim Mesthene said:
The electronics of the DI cassette run 12v (from the ECU) through an occilator, then a transformer, then back through a rectifier, to step up the DC volts to 400v. This 400v potential is what's used to measure ionization in the cylinders to sense knock, and is always present across the plugs (this is why the DI uses resistor plugs).
All of that stuff is embedded in the epoxy you see on the inside. Fixing that stuff is beyond my skill level.
Yep, it's a standard way of generating a higher voltage through a coil. You have to have an alternating current in order to drive a transformer which is why the oscillator exists and thereafter rectification again to get back to DC. General problem is how to unpot everything in the first place :)

The three general ways are either heat it up to soften it and tear it off but if it's a high temperature one then that won't work so cool it and smash it. Not going to be a great solution either. Chemical removal is an option using solvents designed for the job but they're toxic. If there's a general component failure such as a dried out electrolytic, it could probably be accessed by some careful drilling/grinding. It's a pity really because the fixing would otherwise be fairly trivial.

David.
 
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