1G TCU...limp mode

[THEHOUND]

Hello,
I'm having limp mode issues with my 1g. I have looked at numerous threads, read many articles online. I'm just trying to hone in on the potential issue.
Obviously as stated she's in limp mode...I removed the TCU and opened it up. I looked at the usual suspected issues. None of the caps are blown or leaking. However, I noticed discoloration on top of the chips. Along with discoloration, I noticed that the tops were also bubbled and cracked in a circular patern.

I've looked online and found minimal information on whether or not this is normal, or a sign of failure. Given that it's 30 years old. It could be a sign of age. Cycling on and off for its life, maybe it's normal??

Before I try and hunt down a new TCU or forced 4 box. I want to make sure it's shot.

Any direction anybody can point me to would be great.

Thanks

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[petrosian]

Did you test it to see if it responds when being queried for fault codes? (See pic). If it doesn’t, (and it’s not a fuse issue) it’s most likely dead.

The transmission’s limp mode is 3rd gear because that’s the default gear the transmission is in when no input signals are given to the transmission solenoids. If you tried driving with no TCU, it would be the same result. So either you’ll get some error code(s), telling you why the TCU chose limp mode, or you’ll get nothing, indicating either a dead TCU or a blown fuse (check fuse #7, interior driver side fuse box).

As you’ve probably read, if that large capacitor fails, there’s a chance 12V gets fed to 5V components, and poof.

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[steve]

It's dead. You can see both the heat mark in the center of the microprocessor and you blew up the port expander and cracked the casing. That's what usually happens when the +5 volt regulator fails and pumps 12v to the chips.

I'm pretty sure if you removed the large capacitor with the blue dot on it you'll find it leaked and corroded the traces under it.

 

[1990TSIAWDTALON]

I have a couple MD750092's. If you need a replacement hit me up. I need to post them in the classifieds since I run a shift box now.

 

[THEHOUND]

I figured it was shot, but wanted some more experienced eyes to confirm it. Thanks for the offer Marty, but I'm leaning towards running a shift box as well. Probably a forced four. Is that what you are running? If so, how has your experience with it?

 

[1990TSIAWDTALON]

Yes, a SmartShift 100.1 which they don't make anymore but it works very well for me. I set it up to shift at a certain RPM and I DRIVE the car.
HERE is a short clip from the track. I couldn't get out of the hole to save my life, but it was still fun. It does all of my shifting for me if I want or I can use my pushbuttons on my steering wheel to change gears (which I also like). Even with a shitty 3.xx 60', I was trapping 117 out the back door. I don't have the NOS setup on the car yet (and the trans has a broken main shaft at the OD end).
Marty