JoshuaMonger
New Member
I have two JVC-R-S33 units, and originally I bought one to fix the other as the original one was my fathers and I was repairing it for him. Well I actually decided I like the sound enough that I want one myself. The parts one I ordered I ended up finding a loose ground on the main board and it works great, well... except the phono pre stage has a 50hz hum (I measured it to be certain). Interestingly the hum is only there when I plug in turntable, and the ground wire slightly softens the hum but it is still pronounced. The volume turns up the hum and it is present in both channels. I know the turntable is not the problem as it works with other amplifiers just fine with no hum.
I started by replacing the caps in the power supply board. No avail, however, this actually was the problem with the previous (my father's receiver). I decided to replace a few electrolytic caps on the stage itself and it didn't help so I swapped them back as most of the originals tested better than the replacements I had. I didn't do all of them though and there is a lot of them!! I will get some photos here later today.
So I noticed most threads try and point these problems at the turntable but this definitely is not what is going on. I don't own or know how to use a scope but I could certainly try if I had some idea what to look for. I saw a thread somewhere where people suggested replacing diodes on the ps and i have no idea if that is something I should try. I do have an ESR and a capacitance meter and have no issue pulling and testing caps. I am suspicious of all of the small ceramic caps. There is one on the ps board that I haven't replaced and several on the pre. I also have not replaced the mains caps but I did do a couple of the small electrolytic ones on that main board that I had lying around just to test. The big mains caps are impossible to source and if it's those it's more like just buy another unit. I did also check some grounds continuance on the boards and they seem okay. I did find one interesting area on the pre board where the negative side of a cap ends up have 15-ohm resistance to the ground, but it almost looks intentional as it goes back to the dc-side of the ps and is resistor fed i believe.
I wonder if anyone has any tips or experience for me with this! Any help would be appreciated. I could just get another unit, but at this point I am super curious what is really going on here. Thanks everyone!
I started by replacing the caps in the power supply board. No avail, however, this actually was the problem with the previous (my father's receiver). I decided to replace a few electrolytic caps on the stage itself and it didn't help so I swapped them back as most of the originals tested better than the replacements I had. I didn't do all of them though and there is a lot of them!! I will get some photos here later today.
So I noticed most threads try and point these problems at the turntable but this definitely is not what is going on. I don't own or know how to use a scope but I could certainly try if I had some idea what to look for. I saw a thread somewhere where people suggested replacing diodes on the ps and i have no idea if that is something I should try. I do have an ESR and a capacitance meter and have no issue pulling and testing caps. I am suspicious of all of the small ceramic caps. There is one on the ps board that I haven't replaced and several on the pre. I also have not replaced the mains caps but I did do a couple of the small electrolytic ones on that main board that I had lying around just to test. The big mains caps are impossible to source and if it's those it's more like just buy another unit. I did also check some grounds continuance on the boards and they seem okay. I did find one interesting area on the pre board where the negative side of a cap ends up have 15-ohm resistance to the ground, but it almost looks intentional as it goes back to the dc-side of the ps and is resistor fed i believe.
I wonder if anyone has any tips or experience for me with this! Any help would be appreciated. I could just get another unit, but at this point I am super curious what is really going on here. Thanks everyone!
