A Couple of More AIU Questions & Comments

Some AIU's have 5A relays, we had this discussion before.  I posted some pictures of one I took the cover off with the 5A relays.

I also suspect the traces probably would be straining with 10 amps.

There's no reason that the solution for the MTH uncoupling track wouldn't work for the Lionel one that I can imagine.

Other than different specifications of the relays, I don't know of any operational changes. 

There is a modification for the AIU dated 1/26/2012 to prevent damage if you happen to plug the TIU cable into the output jack instead of the input jack.  If that mod is not in place, U3 will probably be cooked by an incorrect cable connection.

There is a modification for the AIU dated 1/26/2012 to prevent damage if you happen to plug the TIU cable into the output jack instead of the input jack. 

JOHN: since I did that once and fried mine, what is that mod???  Thanks - walt

It involves some soldering and component replacement on the AIU board.  I don't have it in machine readable form it would appear.

gunrunnerjohn posted:

It involves some soldering and component replacement on the AIU board.  I don't have it in machine readable form it would appear.

GRJ; do you have it in paper form that could be scanned and posted by chance?

Rod

Well... that could be difficult Rod.

OH, OK, here it is.

I should have known John, coming from you and all, that there was no simple answer!

- walt

John, I'm not near my AIU to take a look:  Can you tell me which of those IC's in your picture is U3?

walt rapp posted:

I should have known John, coming from you and all, that there was no simple answer!

- walt

It's not my answer Walt, it's MTH's answer.

EscapeRocks posted:

John, I'm not near my AIU to take a look:  Can you tell me which of those IC's in your picture is U3?

I don't have one open either.  However, U3 is silkscreened on the board, so it shouldn't be that hard to find.

Have screwdriver, will travel

Perhaps versions with the 10A relays already have the mod installed.  Mine has the 10A relay (different relay part number than in GRJ's photo).  D4 and D8 are missing, R54 is 1K, and there's a 0.01uF capacitor across R54 (attached on bottom of board).

U3: 42 cents at DigiKey.

1/8W 1K 5% leaded resistor: 10 cents at DigiKey

0.01uF (10,000pF) 50V radial capacitor: 19 cents at DigiKey

And for anyone attempting or thinking of attempting the repair and/or mod, the AIU opens easily by removing 6 small Philips screws on the bottom of the case.  And once open, the circuit board lifts straight away from the case to gain access to the bottom of the board.

I suspect new ones received the mod at the factory, but I don't know for sure.

FYI.  U3 is top row, 2nd from the right in the top picture in this thread.  

I just bought a couple locally.  Going to dig in shortly 

GRJ & Stan; all good info. Thanks for posting!  Even though U3 is only $.53 I think the biggest problem for most of us would be the R&R!

Rod

I just checked my other AIU pix and it appears that D4 and D8 are not present. These were bought new stock in 2010, so I suspect as grj says all newer AIU's have this mod. as well as 10 amp relays. Seems funny that MTH did not rev up AIU's with this mod, as they have with modified TIU's?

Rod

Just for fun, here's my AIU with U3 removed.  Patience and a solder sucker.   Now it's time to install the new one. 

Not the absolute cleanest, but this is my first time removing a soldered IC from a board.   I know my way around soldering, etc..  I simply watched some brief how-to videos, and went for it.

I didn't have one of those blade things, so I did this:

Put the board in my electric project "vise" to set it on end.

Cocked the solder-sucker, and placed it over the leg on the back side.

Used my low watt soldering pencil and touched one leg on the bad IC.  Released the tool.  Then moved on to the next one.  Tedious, but it worked.

The new one slipped right in and is soldered in.  That part was easy.

Apparently this old AIU's issue was a bad U3 after all.   I just plugged it in, and the sweet sound of switches switching from my DCS remote filled the air.

Next time you do this kind of repair, I have a tip.  Before firing up the soldering iron, just clip all the pins off the IC right at the IC body.  Then you can just heat the back side and pluck the leads out of the PCB one at a time grabbing the individual pin.  Cleaning out the holes without any pins in them is much easier after that.

Thank you, John.   It was a fun learning exercise, with the payoff being it worked!

Here's the new U3 IC chip 74HC138.   Cost me $1.25 plus a little time to fix my AIU.

Shipping was probably more than the chip.

   Luckily, I have a local store that stocks all manner of components, this being one of them. 

Gas and maintenance on the car was probably more expensive than a few dollars shipping.

hahahaha  we can play this all day

IMO the real story is you took the bull by the horns and attempted the repair in the first place.

I updated my previous post to include DigiKey links to a suitable resistor and capacitor to make the protection mod.  I'd think anyone with a damaged AIU attempting this "U3" repair would also make the mod at the same time.

gunrunnerjohn posted:

walt rapp posted:

I should have known John, coming from you and all, that there was no simple answer!

- walt

It's not my answer Walt, it's MTH's answer.

Meant as a compliment John, not a sarcastic criticism!

- walt

No problem Walt.

I agree with Stan, if I take the thing apart, I'd certainly apply the upgrade to prevent that from happening again.  It's very easy to stuff that connector into the wrong hole, and the smoke release is pretty quick if you do that!

Since I only use one AIU, I put a temporary stop gap measure on mine to prevent another U3 failure:   I cut a small section of gaffer tape and covered the phone jack.

EscapeRocks posted:

Since I only use one AIU, I put a temporary stop gap measure on mine to prevent another U3 failure:   I cut a small section of gaffer tape and covered the phone jack.

 

 

A nice simple preventative measure. Ya gotta love it.

Rod