Amp-11-lv THWARN led illuminated

[thor.heglund]

I bought a pair of Amp-11-lv a year or two ago, after stuffing up one of the boards soldering one of the chips on I boxed them up and forgot about them. I decided to revisit my undamaged board and put it together for "practice" over the weekend. All appeared to go well. Passed the 9v and 5v tests, adjusted the DC-offset, hooked it up to a speaker and it sounded great. No hums, it would pop a little when I unmuted it but I think that's normal? I'm running it at about 14V.

I played music through it for a couple hours, then turned it off for the night. Yesterday after work I came home and powered it up, put some music on then noticed that the THWARN led was on, it hadn't been on previously. I don't have a heatsink yet but the chip isn't really hot to the touch, it gets warm after a while, and it hasn't shut off on it's own like it's supposed to when it get's too hot. The led comes on right as it's powered up, even after sitting powered off all night so I don't think it's actually heat that's triggering it.

I tried googling the issue but it doesn't seem like anyone else has experienced this. Any suggestions?

Thanks

Thor

[V-bro]

If you google to find the TK2050 datasheet you'll find a pin-out of the TP2050 chip. There is a pin called THWAR, which is high/low to indicate a thermal warning. AMP11 uses a little fet (Q4) to whichs' gate the THWAR pin is attached and this fet will then start to conduct the 5V through a resistor (R84) towards the LED indicator.

There is a possibility this fet has gotten damaged and is in conduction mode (shorted) all the time, which is a typical way for fets to die....

Here's the schematic:
http://i.imgur.com/zDArj.jpg

Another chance is that a current through R45 is somehow pulling Q4 up and makes it conduct. To investigate this you could desolder R45 to make sure of this. R45 is connected to the gate of Q4 and on it's other side connected to the IBIAS pin on the TP2050.

There are more possibilities, but these only count when the fet is pulled up by a current through R45....

[thor.heglund]

Howdy,

Thanks for the detailed help. I haven't had anything to report, tested the FETs etc. as time permitted but really hadn't found any clues. In preparation to look into things today I cleaned w/ isopropyl and a toothbrush. No more THWARN led. I was hoping to learn a more interesting lesson but apparently I need to clean up better.

I've examined my other board and don't think I'll be able rescue it. I see the TP2050 is available in the store (the chip I need), but the Amp-11-lv is out of stock, I wonder if the circuit board is available by itself? I'm very pleased with the amp I have working and can only imagine how much better my music would sound in stereo!

Thanks again,

Thor

[V-bro]

Check again in a week or so, Jan's working on getting everything back in stock and sales up and running again...

Cheers by the way for solving the problem!