DVD player won't power up

[kenshi]

A friend gave me a DVD player (with speakers so I guess it's an amplifier too) that quit working on him. He said at first, the problem was intermittent and it would occasionally make a pop from the speakers and stop working until he unplugged it for a few seconds and restarted it. At this point, when you plug it in, the red standby light comes on, but when you press power, it just goes black until you unplug it and plug it back in, no noticeable pop or anything. It's no big deal to him if I can't fix it, but I would like the learning experience and would feel a bit proud if I'm able to get it going again.

My first thought was power supply. After taking off the cover, I carefully looked over the electrolytic caps but didn't see any that appear blown. I checked the power supply output with my voltmeter and oscilloscope. One output is labelled 38V and it's only about half a volt off. The others are unlabeled, but measure +/- 12V, +5V, and +2.8V. The noise on the line doesn't exceed about 100 mV, most of them are around 50.

So far, that's all I've thought to do to it. I was wondering if anyone has any suggestions for fairly simple things to check. The device is an RCA RTD325W if that helps.

[mengfei]

try to do some isolation, if it has a built in amp isolate that section first. the popping sound could be a dead transistor/IC or cap. If it was totally dead you could suspect the PSU section but you said it has a red light when plugged in but dies when you switch it on, it could b the protect circuit is kicking in.

I remember the days when we where repairing electronics/ appliances, it's so fulfilling when you get it to work. One time it took us weeks to power on a National TV & the problem was just an itsybitsy SMD resistor which changed value.

[McBryce]

I fixed a TEAC Amplifier lately that did exactly the same thing. In my case the amplifier Micro-controller checked the outputs before powering up the output stage. If a short-circuit is detected the amplifier shut down. It was a short in the speaker that was causing the issue. Check that the speaker +/- outputs aren't shorted (ie: see if it powers up when the speakers are disconnected). If that's not the problem, it's probably an IC or transistor in the endstage that's died.

McBryce. 

[Skimask]

Or throw it in the junkpile and spend $20 at the nearest Walmart for a replacement.

[kenshi]

It's not the speakers as I haven't even had them plugged in on most attempts. I'll do a little checking on the amplifier circuitry.

[kenshi]

Well I went to the store and bought some Chip Quick and pulled the amplifier chip. It was the first time I desoldered an SMD chip, so I've learned something from it already. However, when I try to power it up, it does exactly the same thing. I don't think the amplifier circuit is the problem. Any other ideas of easy things to check before we scrap it?

[mengfei]

see the MCU that controls the power up of your unit, it may not be triggering on coz of some open/ short parts