CurtPalme.com Home Theater Forum

stefuel

I have a LCD touch screen monitor that I'm trying to repair after a failed power supply. I repaired the inverter for the back light power source. The panels OSD now works but I can't get it to display a image. There is a 5V power regulator that is getting smokin hot within a few seconds of powering up along with 3 capacitors that surround the reg (85c 25V 100uf). You can't put your finger on the tops of them within 30 seconds of power up. Does that sound normal. Both the input and output of the regulator are normal.

Yes Heywood, I'm still putzing around with it Laughing

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Id need a schematic or a pic of the Circuit to help better. But the caps.... are they polar caps? if so they may be bad and thats why they are getting hot, they may have shorted. And no they should not get that hot!! Is there any Diodes nearby? It could be one of those too. I'm still learning this stuff myself so hopefully Curt or McGyver will chime in.

Athanasios

tse · Joined: 03 May 2006 Posts: 1014 Location: Sweatbucket, Fl.

Caps should not get hot. If it is taking 30 secs for them to heat up and the regulator gets hot immediately then there is a chance the caps are getting hot from the heat conducting through the PCB traces from the regulator. The caps are near the regulator?

Scott

stefuel · Posted: Sat Feb 28, 2009 1:16 am Post subject:

They actually all seem to be heating up together. Perhaps the regulator a bit faster. I have never touched the top of a capacitor that felt like it was going to burn me. The three in question are about 1/4 to 1/2 inch away from the regulator.
It cought me by surprise YOWZA hot.

jkruger · Joined: 24 Oct 2007 Posts: 2435 Location: Carlsbad, CA

A Barco is only a AmPro with training wheels... but they don't catch on fire!

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Are those caps in the trace on the 5v side?

beun · Joined: 28 Jun 2006 Posts: 676

Capacitors can only get hot when they are extremely leaky and thus need to be replaced, or they carry an enormous AC current which means that the regulator oscillates. Are they bulgeing like canned meat gone bad?

Kim

**Curt Palme** · Posted: Sat Feb 28, 2009 4:52 am Post subject:

What Beun said.

Change all three caps, if they've heated up, they are bad, or are heat damaged. Change the 5 volt regulator, then measure the 5 volt output to make sure it's 5 volts. Manufacturers now make everything to really tight tolerances, so the caps could be rated at 6 volts, and if the regulator has a lifted ground, it could be putting out 8 volts, bad news all around..

stefuel · Posted: Sat Feb 28, 2009 10:37 am Post subject:

I looked up the specs of the regulator and it's a fixed 5V. I have 12VDC in and 5VDC out. The caps show no visual sign of
failure. It has not been allowed to run long enough to physically blow the caps. I noticed the extreme heat right away. I'll try replacing the three caps and vr as it's only about $5.00 worth of parts.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Its normal for some of those regulators to run very hot. If its output is 5 volts and it is a 5 volt regulator it should be fine. If it was being loaded down the voltage would be lower. As far as the caps, they should not get hot on their own but if they are near a filter coil or something else that gets hot the heat will be transferred.
I have a flat panel here that I just finished and the regulators are hot to the touch but not smoking. Some of the caps in the P/S are super hot also but its being transferred from a near by coil.
But again, depending where those caps are in the P/S, I would at least check them for continuity. That would be the only reason they would get hot on their own.