Home Forums General Discussion Technical Questions US 1220 major headache

I have a US 1220 job that keeps blowing U41 on the A2 card. This is a transceiver chip that controls four multiplexed signals to the car top. The entire set of car top boards have been swapped with another car. The A1 and A2 boards have been swapped on the controller with another car. The 5 volt power supply reads perfect with not a hint of ripple. The +- 12 volt signals look great as well. It is strange to me to keep blowing the same chip on the A2 Mpu card given that this is pretty deep into the signal chain. Any US pros out there. I am dreading the possible backplane switch.

pity you cant blow the whole damn thing up.....US are junk

hey smitty you said you swapped the A2 card with another car, did it blow the u41 chip on that A2 card also?, did you change the multiplex transceiver board on the car top also, you did say the entire cartop boards, just checking, from the prints i have it looks like the travel cable tv11 through tv32 connects the multiplex transceiver board signals to the mother board, then they pass directly to the A2 computer board pins through the mother board, I would look into the travel cables tv11-tv32, or like you are dreading there is a short on the mother board, you may be able to see the tracings on the mother board from the travel cable inputs to the A2 socket pins, I am suprised you are not blowin up the multiplex transceiver board also, although there is a buffer circuit that isolates this from the input output buffer boards. It seems strange you are just taking out that one chip, these are low level signals that i would not see them taking out a chip if shorted together, maybe you are getting a high voltage into the travel cable associated with these signals, or maybe there is carbon tracking on the mother board for these signals, sounds like fun

I may have got a handle on this one. It was weird that it kept blowing not only the same chip but the same gate. I had swapped the TC wire that you mention Scott. After looking at that signal on an oscilloscope I kept seeing large noise spikes when the door relays came into the picture. The original DCR and DOR had only a diode across each coil. I added some MOVs to the door relay coils and saw some improvement but not enough to satisfy me. I started digging through the controller looking for bad grounds, Finally, way over on the motherboard for the power interface card I found an ICOM wire that was not really into it's terminal at all. Apparently someone recently changed that board out a few weeks ago and didn't get the wire all the way back into the terminal. Knock on wood maybe it is fixed. It's actually hard to believe that for all their advanced circuitry US was using at that time, that they never thought to run those multiplexed wires going to the to the car top in shielded wire.

smitty sounds like you nailed it.Just for everyones knowledge the ICOMs on the car top mother board and main controller mother board are tied together with the mounting screws!So a missing or loose screw or varnish on a repaired board can really cause some interestig problems.

Hey smitty, sounds like you have banged your head here quite a few times. I have banged my head so often on elevator controllers, I have lost all my hair, and some of my memory ha ha. you seem to alway post some tough ones keep em coming

Lol they use to be a fun challenge. Now they are just a pain in the ass.

Im still laughing about your post, after 20 years as a trouble shooter, i am seriously pondering taking a hydro route just to relax and forget the pain in my ass. what the hell regular mechanics wages are not that bad, and the work is much more relaxing.

The sad thing is that years ago there was a significant wage difference between what an adjuster made and a regular route mechanic made. That is not true anymore. Most of our guys by the time you add up their perks make close to what an adjuster makes. The difference is, that they get to go home knowing that when the sh## hits the fan they can call me or someone like you and it ceases to be their problem. So I guess we do love this stuff because it would be easier to be a route mechanic. I do feel bad however for the brothers out there being plagued by things such as GPS and total idiot supervisors with no actual field or trade experience.

What gets Me! The new mechanics coming into this trade don't even what to find out "How you fixed it!It's true the new stuff is held close to the vest on information in the field. Most likely your competitor has better tech support than the OEM in some cases... atleast they give you a tool to work on it!, the OEM won't!!!!!The trade is a changing and we must TOO! This next contract is an important one!....

You are absolutely right. I taught the fourth year apprentice program for about three years. Most of what I saw scared me. It's not only that the technology is making the guys more dependent on special tools, but there seems to be a huge lack of interest in what really makes this stuff work. I came up through new construction and did my share of carrying around steel just as I am sure many of you guys did. When you did get the opportunity to work with an adjuster or an experienced maintenance mechanic or service troubleshooter , you tried to learn as much as you could. A lot of these younger guys seem to lack any interest in this stuff. This next contract coming up could potentially change our trade forever.