EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: 90skidjohnny on July 04, 2021, 01:33:48 am
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Howdy Everyone :)
I recently picked up a HTR-5280 for a fiver at a thrift store. I cleaned it up and powered it on, and everything seemed fine. Had it on for say, an hour or so. No issue.
Next day I go to power it on, it stays on about 5 minutes, then powers off. I power back on, again the same. Eventually the time it would stay powered on would become shorter and shorted. So now, it powers on (ie, lights up) then quickly turns off. I learned that these units have a protection mode that you can bypass for further testing, but even with it bypassed, it would quickly turn off.
So i opened it up, and started testing things. I have limited knowledge with stereos and the like, but tested the voltage regulators. I really couldn't get the unit to stay on long enough to test in circuit, so I decided to remove them and test with a power supply. Sure enough, on of the 7805's was only outputting around 1.5volts instead of 5v. So i ordered some of them up. (I actually ordered them all to just go ahead and replace them all, but only the 7805's have shown up. The other did test ok)
I then reassemble and power back on, same thing. Darn. However this time, when i power on with the protected mode bypassed, it stays powered on. So that's good.
But, if i disable protected mode and power on. then power it off, and power on normal, it stays on. It only seems like it wont power on when its been cold for a bit. and when it does, if i bypass that protected mode, power on, power off, power on.. it stays on.
Again, I'm pretty new to electronics in general, but for some reason, I'm thinking there could be a capacitor issue? And the reason why I say that is, its almost like if i force it to power on, it charges up that capacitor enough to bypass the protection mode kind of thing. I might be completely barking up the wrong tree though.
Any ideas of what should be checked next? I appreciate any info. Thanks all! :)
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Just update, through the protection mode, the first screen that flashes is PS PRT 033 , apparently looking at the service manual, this is the last fault history, where the Power Supply recieved "33%" of "100%" of the voltage normally expected. Where 100% is 5v. Theres another 5v regulator which is a 7905 (which i believe outputs negative 5 volts)
Unfortunately, testing this in circuit is near impossible, as its at the bottom of a vertical board. The board can be , repositioned, but then the regulators wont be on the heat sink. Im wondering if it would be ok to remove the heat sink temporarily to test as then i can reposition the board.
More Edits! :)
SO i was able to get to the regulator, and tested fine. However, On the outputs, of that board, I am not getting the correct voltages.
I was trying to add an image of the schematic for this board, but essentialy, the Regulators lead into a capacitor, and then out to another board, and from the looks of it, only the capacitors could effect the output.
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Heres the schematic. Voltages test at the regulators, not sure how to test the actual voltage over the capacitor. I have one of those cheap Chinese capacitor testers somewhere tho.
[attach=1]
Edit: My multimeter has an option for testing caps, and most of them tested ok, slightly low tho. Ie, 100 uf cap would read 95ish etc. I replaced those caps on the board, and now, i can see all the correct voltages leading into the board from here, however, still getting a read about abnormal voltage.
Since it seems to be underpowered, instead of overpowered, I am at a loss, as I cant see anywhere the fault is occuring.
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Pictures could be useful. And FYI, capacitors have a 20% tolerance up or down (so there's nothing wrong with a 100uf measuring 95)
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Try resetting it. If the "last fault history" has any effect, that might help.
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You should also make sure that you correctly set the speaker impedance on the amp to match connected speakers. It's probably not the cause of your issues, but if not set correctly, it can trip the protection mode.