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Hi,

I have a TIU Rev. L that only power-up through the USB port. All the fuses are good no visible damage

to the internal components. The led will flash once and stay off when i apply power to the "Aux power input"

with a 18VAC power supply, the same thing if I use the "Fix voltage in 1".

When it's powered with the USB cable I am able to do back-up, upgrade, etc. It was sent to MTH for repairs some years ago.

Any suggestions on what the problem ?

Thanks.

Jean

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Power supply section failure. How and what should be done by a pro. The last thing you want to do is kill your whole TIU.

There are 2 regulators associated, the 1 without heatsink and the one with heatsink. Further, there are 2 TVS diodes that could be shorted from voltage spike failures.

TIU TVS logic

Again, the good- TIU can be powered by 5V input on the USB and logic and main processor still operating.

The bad- both AUX power and fixed1 not working- most likely a component in this power supply section, but this is pretty advanced for DIY repair.

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  • TIU TVS logic

Again, my guess, a component failed. The regulators I believe have thermal protection and shutdown.

The symptom:

The led will flash once and stay off when i apply power to the "Aux power input"

with a 18VAC power supply, the same thing if I use the "Fix voltage in 1".

Again, theory is, say one of those TVS diodes failed. Then the regulator would initially attempt to power the shorted load on first powering in a cool state. The shorted TVS then overheats the regulator or hits a current limit and the regulator shuts down- hence the once and done system. Blinks once, briefly, and then is dead.

If you powered with the aux plug and it flashed once than LED went out, the board has a shorted component on the 5V or 3V buss dragging 5V buss down causing LED to go out.  This is not a hung up Aux jack, nor a TVS diode fault on fixed one which would short your transformer.  Good chance the Transmit chips failed, or there are other faults not repairable that can cause this.  G

Hi,

Thanks H1000.

Thanks John, the diodes are ordered and when they are received and

installed I will follow up.

Thank you to all for your skills and expertise.

Jean

If you removed the diodes that you think are shorted, wouldn't the TIU start up and led turn red and stay red? I would not run trains without the TVS replaced if it is the culprit, however it could confirm diagnosis and expidite repair. Just a thought.

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