Transmission Control Units

[Shrewz92]

If a Transmission Control Unit is bad, and it's dismantled to look at the circuit board, will there always be a tell-tale burn or resistor/capacitor leakage on the board?

[AccordCodger]

No.

[Shrewz92]

Any idea what on the board would need replaced to make a 'bad' unit 'good'?

[AccordCodger]

Unless you have specialized test equipment to test the TCU, then I can't see any way you could repair it yourself. There is no way to "know" what to replace, even if you are comfortable with repairing PCBs.

Go buy another one from a junkyard.

[Shrewz92]

I did find a TCU at a junkyard for $45. It's something that I don't know about and I love to experiment to learn (thus my love of repairing my accord). I've seen pics of burnt boards and read posts of x-guy replacing a series of resistors and capacitors in the lower right hand side of the PCB, close to the plugs. I've cracked this replacement part and saw nothing on the pcb, neither. I do the transplant tomorrow.

[Shrewz92]

So...guess what? The salvage yard unit is just as bad, actually, WORSE than the one that's being replaced. I opened the case. Resistors in positions 41 & 42 are burnt to a crisp. There're no bands nor coloration left to figure out what the ohmage is. Anyone know what their resistance values are?

[AccordCodger]

You're kidding, of course. The folks here are mighty good mechanics, but they probably don't repair TCUs (even if they could get schematics for them - and I have no idea how you'd pry those loose from Honda).

The TCU is a unit assembled in an electronics factory somewhere. I'd be amazed if Honda makes them themselves.

Play around, by all means. If you can find a hacker site that has all the info you need - sure. But IMHO a junkyard replacement (or several of them) is the way to go. (You're forgetting that not all blown electronic components show any external signs of damage. e.g. semiconductors).

[dlarrimo]

Just wondering if you'd found the values for those resistors. Apparently, this is a common problem. 1993 Honda Accord LX with a damaged R41 and probably R42. Thanks!

[ProMan]

R41 & R42 are always the 2 got burnt. But it's not because they are bad, the cause is something else. If you just replace these 2 resistors, it will burn immediately after you connect.

I heard the real cause is a dried capacitor, but I am not very good at these electronics stuff and never got a chance to find out. I have the resistor color code, will post it later. See if you can find out what's really going on.

[ProMan]

The 2 resistors are the same. 15 Ohms.