ENG: 90-93 TCU Fix / Preventative Maintenance

[cloudasc]

Hello Everyone! It is HIGHLY recommended if you have a 90-93 TCU that you replace all the capacitors listed in this guide as preventative maintenance, otherwise you may have to get creative in your repair (if even repairable), and the area of the board that gets damaged could be different from this case. I only paid $5 from a local electronics supplier for all the parts replaced in this guide, as I already had access to the tools.

Description:
A very common problem alot of 90-93 accord owners suffer is their tcu computer going bad, which restricts the driver to 2nd and 4th gear; the sport light comes on, and when you try and pull a code you either get 0 or no codes (My case), or 6+ different codes at once. In my case, either a Capacitor leaked, or shorted, which caused 2 resistors to flare, burning out, which resulted in some damage to the board.

Tools:
Soldering Iron
Solder
Desoldering Braid or Solder Vacuum
Wire cutters
Hot Glue (Not required for preventative maintence)

Parts List: (Less than $5 from a local electronic component supplier)
Capacitors:
1uf 50V
330uf 10V
33uf 35V
220uf 35V
4.7uf 50V

Resistors: (Not required for preventative maintence)
2x 15 Ohm 1/2 Watt



I replaced all the capacitors on the board, and since the original mounting holes for the resistors were covered in carbon, I had to be a little creative in the repair job. The two resistors are suspended in Hot Glue, which act as a vibration dampener, while holding them in place, plus it can easily be peeled off later if needed.

Here are some pictures of my fried TCU:




Here are pictures of my TCU after being repaired:

[real_mckoy]

stupid question is that A/T or M/T TCU?

[dj_ender]

Originally Posted by real_mckoy

stupid question is that A/T or M/T TCU?

TCU denotes transmission control unit, which means it's an auto.

[cloudasc]

I thought I would post up another example of a users (Tippey764) 92/93 tcu going bad:


In this case, the repair would be as simple as cleaning up the electrolytes from the leaking capacitors with a q-tip and some isopropyl alchohol, then replacing all the capacitors on this board; which should return the tcu to "like new" condition.

This issue isn't just related to 90/91 TCU's anymore, its all of them... old age is catching up, so anyone with an Automatic should have this procedure done.

If you think you can just get a replacement from the junkyard, just remember this, it will fail, its only a matter of time, so your best option is to REPLACE ALL CAPACITORS before putting a replacement into use... otherwise the cycle will continue.

Heres a cool video to help you understand capacitors:

[lucifer1]

I would also add that capacitors that are not leaking can also be bad. If the top is puffed out like a dome it is a sign that they are most likely bad.

I fix a 32" lcd tv and Casablanca fan by simply replacing capacitors. Both times they were not leaking but were puffed out.

[cloudasc]

Originally Posted by lucifer1

I would also add that capacitors that are not leaking can also be bad. If the top is puffed out like a dome it is a sign that they are most likely bad.

I fix a 32" lcd tv and Casablanca fan by simply replacing capacitors. Both times they were not leaking but were puffed out.

Yep, and they were only designed to last so long, they have managed over 15 years in most cases, and the ones blowing out now are 20 years old. All the caps on my tcu looked fine, there was no leak or anything, but it probably shorted and thats what caused the two resisters to go up in flames, and deposit all the carbon on the board.

Its way better to fix these before they go bad, as the chance of damage to the board and other components is drastically less, and if we can keep as many of them out of the landfill as possible, its that much better for the environment. 5 caps vs a whole circuit board.

[cloudasc]

I really think a link to this DIY should be added to the READ HERE FIRST threads, preferably in both the beginner and regular tech sections.

I just thought I would give this thread a bump, as more and more cases of tcu's going bad, and I would like to report that at least one other member that I know of has saved their tcu by following this guide. What brought the issue to attention of the owner was the horrible fuel economy they were getting. 150 miles to tank due to ecu/tcu only using 2 of the available gears!

Reference: Still Getting Bad Gas Mileage

[Bad_dude]

I have 2 questions for you sir:
1) If your TCU isn't bad yet, should I just replace the caps or do I need to replace the resistors too?
2) Does brands of capacitors matter?

I know a bit about capacitors as I used to modify sound cards to make them sound a lot cleaner and better audio quality. I do the capacitors replacement to improve sound for audio equipment dramatically. For audio, the best are Blackgate(out of business but you can still find), Nichicon, Elna, Nippon Chemi, any other brand is not worth it for audio.

Thanks.

[cloudasc]

Originally Posted by Bad_dude

I have 2 questions for you sir:
1) If your TCU isn't bad yet, should I just replace the caps or do I need to replace the resistors too?
2) Does brands of capacitors matter?

I know a bit about capacitors as I used to modify sound cards to make them sound a lot cleaner and better audio quality. I do the capacitors replacement to improve sound for audio equipment dramatically. For audio, the best are Blackgate(out of business but you can still find), Nichicon, Elna, Nippon Chemi, any other brand is not worth it for audio.

Thanks.

1. Correct, all you need to replace is the capacitors for preventative maintenance. No resistors required.
2. I do not believe so for this application. All I cared about when looking for the caps was getting the correct rating. I am pretty sure I used 2-3 different brands of caps to repair my tcu.

[Bad_dude]

Two more questions if I could please:
1) The capacitors you listed are they exact match to the TCU or they are within specs?
2) This question is unrelated to the TCU but the solenoid, I don't have any problem right now, but should I remove it for cleaning as a preventive maintenance? If remove, is there any gasket or o rings that I might need to replace?
Honda's transmission diagnostic
With the TCU having bad caps, what are the chances that the ECU might have this too?
Thanks again.

[cloudasc]

Originally Posted by Bad_dude

Two more questions if I could please:
1) The capacitors you listed are they exact match to the TCU or they are within specs?
2) This question is unrelated to the TCU but the solenoid, I don't have any problem right now, but should I remove it for cleaning as a preventive maintenance? If remove, is there any gasket or o rings that I might need to replace?
Honda's transmission diagnostic
With the TCU having bad caps, what are the chances that the ECU might have this too?
Thanks again.

1. Yes they are an exact match, so if you can't find the exact one, you can always substitute (within reason).
2. I've never messed with the solenoid. As for the question about the ecu, there are technically alot of capacitors on the board, they come in a bunch of different shapes and sizes (2.03 Capacitor types), but its mainly the big round ones that you would have to worry about, and from looking at the pictures on my wiki, theres at least 6 of the ones you might be concerned with.

[Bad_dude]

Thanks. I have never come across a bad ECU with leaking capacitors. But then again, most just replaced and not repair leaked capacitors.

[blackoutt]

this should mos def be a sticky..pmed

[Cb7GHOST]

great post

[Raf99]

Great post indeed. I just wanted to add that one can test capacitors with a multimeter/voltmeter. Using the appropriate Ohm setting for the voltage of the capacitor. It should increase from 0 at a steady rate to infinity which means the capacitor is working. If the meter sits at 0 and nothing happens then it is faulty (dead, bad connection, etc). There are also ways to test a capacitor while supplying a voltage to the unit but its more technical.
http://m.wikihow.com/Check-a-Start-Capacitor

But as cloudasc pointed out, it's HIGHLY recommended to replace them all.

Cheers

[Bad_dude]

Has any one seen those solid type new capacitors of the same specs to our applications any where? Those solid ones are put on new motherboards now days and last almost forever. Very solid and low noise too. I am thinking if it would work as the solid ones are surface mount.

[cloudasc]

Originally Posted by Bad_dude

Has any one seen those solid type new capacitors of the same specs to our applications any where? Those solid ones are put on new motherboards now days and last almost forever. Very solid and low noise too. I am thinking if it would work as the solid ones are surface mount.

They make the same rating capacitors in several different Termination styles, but if you use anything but an Radial, you would have to figure out a way to adapt it to mount to a through hole.

[Bad_dude]

Got my capacitors. I didn't want to spend the extras for the exact match. Total $4.95 for all 5 in quantities. Here's what I got:
-4.7uF 50V qt:10
-33uF 50V qt:10
-1uF 50V qt:10, smallest in size
-330uF 16V qt:5
-220uF 50V qt: 5, Rubicon brand.
They only sell in quantities. They came in various brands but the best quality I think is the Rubicon ones. Do the physical size really matter? The sizes are very little difference. The uF are exact match but the voltages are higher for 3 of them.
Cloudasc, when you had your TCU burn, which capacitor was the culprit? I know you replaced all for precaution.
Thanks.

[cloudasc]

I am not sure what capacitor was the culprit. According to my father, who is an engineer, and would be an expert in the field of electonic engineering, especially communications components, said he didn't notice any of the capacitors had leaked, his guess is one internally failed/shorted. You could just follow the traces on the board for those two resistors to find out. That's his handywork in the photo, I am still a novice when it comes to soldering. He did however give me an dead old digital telephone brain to practice on, as soon as I get the proper soldering iron/tip, I plan on honing my skills before butchering a pt3 soon for development purposes.

[Bad_dude]

Soldering isn't hard when you got the right iron. It's the removing the solder that is harder with the silly pump.