Sony HiFi broken [Protect mode] Need diagnoses.

[Mac_Black]

Ok my Hi Fi is a LBT XG500, as pictured
https://www.avshop.ru/fotolib/LBT-XG500.jpg
Now it has'nt been working for a good few weeks and I haven't got around to posting this but I've realised I really miss the sound of it
I thought there's bound to be someone on here who is quite clued up on the matter and might be able to advise me on what is the matter.

Think back to the creation of the Metallicawhich... Well basically after 3 hours non stop of Metallica playing at about volume 21,
I turned off the unit and the next time I tried to use it made a buzzing sound and then displayed "PROTECT PUSH POWER" as in the video.
https://www.youtube.com/watch?v=KTN8U15x2kU
The buzzing sound appears to be coming from somewhere around the fan- fuse- tape deck... well the amp circuit really.

I've attempted to investigate myself by removing the heat sink and fan to get a better look but I really don't have a clue what I'm looking at,
the only thing I feel important to add here is that the fan doesn't work.
I looked into the Protect mode on the net and I understand what it's doing,
I think it's possible that I might need to replace the Black thing against the heat sink, which I believe is the amp circuit fuse.
But what I'm not sure about is the noise...
Yeh ummm please do help if you can, sorry for the wall of text, I just figured I should give as much info as I can, maybe a bit to much.

[neil.]

Ok... (this is all pure speculation and guesswork on my part by the way...)

The black component has 3 legs right? If so, then it's a transistor, or FET (or MOSFET, depends on what they used) in the power output stage of the amplifier. If the fan has failed, the device may be clever enough to monitor it and simply not allow the amp to power up without it. In this case, replace the fan. Otherwise, chances are the transistor overheated and burned out, going open or short circuit. De-solder it, and look for a replacement. Maplin or Farnell are good places to start, and it should be a relatively cheap component. It may or may not have taken other components with it, depending on how quickly the protection circuitry kicked in. Examine the board for scorching as well as things like capacitors to see if they are bulging or have burst (there will be white powdery splatters underneath/around them. Also go over every component with a multimeter to check for things like continuity where there shouldn't be (like a diode both ways). The problem with consumer electronics these days is that mostly everything is bloody surface mounted and therefore very difficult to repair (throw-away culture and all that), but the big daddy components can still be dealt with.

Of course, if it isn't the transistor that has failed, then things that tend to go are electrolytic capacitors and bridge rectifiers. Also, if there are any power transformers in there, they are worth a look at as they can burn out when at when being run with a high load for a long time, especially if they have been underspecified by the manufacturer.

Good luck!
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CBT February 2008 | A2 June 2008 | Yamaha YBR125 (written off) | Honda CBF125 (current)