Skip to main content

So I took an AIU apart just to satisfy my curiosity (character flaw, I know):

IMG_1425

Wow, look at all those nifty relays. Too bad I will hardly be using any of the ACC ones.

I did notice that the relays are rated at 10 amps @ 250 V. But from what I understand the AIU circuits are rated for only 4 amps, so is that because the PCB traces are too light, or is there some other reason that I'm missing?

Also the digital input connector is shown in the AIU manual as "for future use". Has there been any indication from MTH as to what future use they are considering?

I read through a lengthy thread from 2015 which discussed at length some options for using an AIU to operate a UCS uncoupling track. The problem seems to be that if the ACC relay latches and power continues to the uncoupler coil for too long, the coil will burn out. On page 6 of the AIU manual there is a diagram for using 2 ACC channels to operate an MTH uncoupler track. I don't have any MTH uncoupler tracks, but can this diagram be adapted for a Lionel USC track?

Lastly, have there been any later revs of AIU's, or have they remained the same since inception?

Rod

Attachments

Images (1)
  • IMG_1425
Last edited by Rod Stewart
Original Post

Replies sorted oldest to newest

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.

Last edited by gunrunnerjohn
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.

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).

AIU 12V Protection Modification

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.

Attachments

Images (1)
  • AIU 12V Protection Modification
Last edited by stan2004

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

IMG_4855

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.

 

 

 

Attachments

Images (1)
  • IMG_4855
Last edited by EscapeRocks

Add Reply

Post
The DCS Forum is sponsored by

OGR Publishing, Inc., 1310 Eastside Centre Ct, Ste 6, Mountain Home, AR 72653
800-980-OGRR (6477)
www.ogaugerr.com

×
×
×
×
Link copied to your clipboard.
×
×