Oddball one on my repair bench for a flat screen tv repair - Page 1
Forum section: electronics / repair

author: tedybear315
author_rank: Contributor
timestamp: October 25, 2015, 01:30:17 am
content: Hiya guys and gals!Have an interesting one on my repair bench.It's just a simple 32" flat screen TV made by a bad company for a big box store (bestbuy) and it's a few years old.I might wind up parting this out on eBay if I can't work out an audio issue it has. Namely it has no audio. Dead as a dodo. Here's the rub!If I unplug the connector to the speakers and then plug it back in, the audio comes back to life and works normally until it's powered off...and then it's back to the fun again!There's little to nothing on line about the main board (DYNEX DX-32L150A11 569KS0169B) Last set of numbers and letters is the board itself. And it looks like a limited production run--as my usual source for assemblies (shopjimmy) states little to no chance of it coming back to stock. The parts all look fine from a physical inspection, and sense this is a stereo TV, I've been trying to trace back things common to both left/right channels.Has anyone seen something like this where it's unplugged and plugged in for the audio--and that fixes the no-audio issue until the next time you go to turn the set on?Kinda scratching my head on this one.Ideas are welcome--but I might just part it out at this point. It's been taking up bench space for a while now while I worked out the issues with the scopes a short while ago. (I've been using the old military one with the slot adapters from the 7704a. Interchangeable LOL. So I've been playing with a 4 channel scope <G>)Thanks again!S-

author: tautech
author_rank: Super Contributor
timestamp: October 25, 2015, 02:44:25 am
content: Wild guess.Audio output stage going into self protect as a result of failing local supply or coupling caps.Feed it a test tone and trace it.

author: tedybear315
author_rank: Contributor
timestamp: October 25, 2015, 12:10:10 pm
content: Currently my idea of a test tone is feeding the set with a dvd player. Still trying to find a signal injector of some type that can be used for this purpose.If it's a good movie (maybe "Back to the future" LOL) that will give me something to listen to when I poke around.I followed it around a tad with the scope. Very cool operation O0 However there's not a lot online for this--actually nothing.... Most of the time these things are considered disposable and I'm trying to keep 'em out of the landfill.I was able to ID the audio chip. So I'll start there. I also might try a gentle re-flow with the hot air gun on that chip. I used my El Cheap'o USB microscope and found the bulk of the pins look like they where soldered by a blind monkey with a severe case of monkey-butt roids. 1/2 of the pins look great--the other 1/2 looks like they used 80% flux and 20% solder. Kinda crusty looking. Another wild guess.S-

author: tautech
author_rank: Super Contributor
timestamp: October 25, 2015, 12:28:21 pm
content: Use a 1KHz sine wave set to a similar amplitude of the audio.

author: Rasz
author_rank: Super Contributor
timestamp: October 26, 2015, 08:01:57 pm
content: Quote from: tautech on October 25, 2015, 02:44:25 amwas my first thought as wellon start by uploading a photo of the board