Audio-GD R28 Dead Left Channel

wang890

Member
2019-10-04 5:33 am
i got this knowing problem with left channel.
opened to see and found 4 caps bulging/leaking and 2 SMD resistor burnt. see images. i ordered parts from Kingwa and replaced those and when switched on, very quickly i can see the new resistors started smoking. the left cap gets hot fast and the C5171 transistor below it even on it's heatsink, gets hot fast. the other are warm. kingwa said those caps are "power filter" and suspect some kind of short. i looked at the board all other components sees fine. right channel works perfectly fine. this thing is very well made and i got it very cheap so if i can get it working would be great. i can provide higher resolution images some of these are taken with phone.

First time posting here and seems to have lots of great experts from me reading on this site over the years. i fix some electronics here and there, this one probably a bit more complicated than i thought it is. i don't think there is some major problem with this since one side works.

any suggestions on what to check next would be great. i am thinking maybe should replace the hot transistor.

first owner bought it and left side have noise and he send it back and then they sent it back and he got the same problem.
 

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wang890

Member
2019-10-04 5:33 am
Hi,
When the capacitors they get hot means you are feeding them with AC. So the first think to look into would be the rectifiers. Possible you have a short bridge.

thank you for your reply. would it be any of of these components? the leftmost C5171 is the super hot one somehow that is causing the capacitor above it to get hot and the two resistor right of the last A1930 where it says +15v to smoke.

someone said if those power transistor fail it will get hot.

this device looks like it has power going to 2 x 20v and 2 x 10v. can you tell which one controls the left side amp? i could remove the power to this side and try using it see if it still works. my educated guess is two are for amp and two are for those resistor ladder dac north of all these components. the usb Amanero Combo384 connects to computer fine.
 

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jean-paul

Ex-Moderator
2002-09-20 7:20 am
Germany
First: don't power it on anymore till you have checked the following. Remove the hot capacitor and measure if it has become a low impedance resistor thingie. If so replace it. Remove the hot transistor and measure if it is OK. Check both diode bridges and check for shorted diodes. It seems like a defective diode bridge to be honest but I can be wrong. If so it is quite logical that caps and transistor become hot.

And ask Audio-GD for a schematic. That will help tremendously finding the fault(s).
 
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