Hey there first time posting. I am seeking advice about repairing an amp where the right Channel works but left only produce a somewhat loud Hum. It does not matter what the volume is set to or whatever input i use. The hum stays constant no matter what i do. I think its 120hz hum, my tuner says its between b and b flat.
Its a Sansui G-2000 amplifier i found in the garbage. I collect and fix electronics from the garbage regularly, i just like doing it. When i first got the amp, all fuses were broken and covered with aluminum foil, except the power fuse that was not shorted like that. What people do sometimes....
I replaced all the fuse with the proper ones and now the amp works in the right but left channel is producing the Hum of death.
Any leads would be appreciated.
Its a Sansui G-2000 amplifier i found in the garbage. I collect and fix electronics from the garbage regularly, i just like doing it. When i first got the amp, all fuses were broken and covered with aluminum foil, except the power fuse that was not shorted like that. What people do sometimes....
I replaced all the fuse with the proper ones and now the amp works in the right but left channel is producing the Hum of death.
Any leads would be appreciated.
Assuming a "normal" discrete amplifier the problem is almost certainly failed output transistors, possibly drivers as well plus any other related parts that may have been damaged. See attached... measure TR15 and TR17. Are they short circuit ? Check all the other components marked.
Theres a G2000 listed here,
Sansui G-2000 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
Theres a G2000 listed here,
Sansui G-2000 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
Attachments
Thanks for the reply.
Yes, two of the output transistors are shorted and I also found one busted resistor.
Also, two more shorted smaller transistors on the left channel but that might be because of the two big ones.
Tomorrow ill unsolder all busted parts and check those other transistors after that.
Yes, two of the output transistors are shorted and I also found one busted resistor.
Also, two more shorted smaller transistors on the left channel but that might be because of the two big ones.
Tomorrow ill unsolder all busted parts and check those other transistors after that.
when you've refitted new parts to the faulty side power up with no speaker load and check the offset voltage at the out put. if there's hight dc check all the pre-drivers aswel,, use the working side to compare voltages to 'set up the repaired side.. place your meter across the emitter resistors of the out put transistors on the good channel and set the B side the same..
Finally had the chance to take those parts off the board. My solder sucker broke on me last week so i had to get a new one.
Turns out the the main output transistors are not shorted once out of the circuit, however the plastic washers from heat sink attachment was melted on them, not a good sign.
I did find 3 shorted transistors on the circuit though and that explains why i measured a short on the mains.
Now to find all those parts and put em back.
Just to be sure about the light bulb tester you guys are referring to, its a device like this right? Simply insert light bulb between outlet and amp ?
Light bulb tester (Dim bulb tester) • DIY Audio Projects Forum
Im a noob at repairing amps and have no real formation in electronics. The little i know i know it from reading the internet and experimenting myself, gotta thank you guys so far you have been a great help!
Turns out the the main output transistors are not shorted once out of the circuit, however the plastic washers from heat sink attachment was melted on them, not a good sign.
I did find 3 shorted transistors on the circuit though and that explains why i measured a short on the mains.
Now to find all those parts and put em back.
Just to be sure about the light bulb tester you guys are referring to, its a device like this right? Simply insert light bulb between outlet and amp ?
Light bulb tester (Dim bulb tester) • DIY Audio Projects Forum
Im a noob at repairing amps and have no real formation in electronics. The little i know i know it from reading the internet and experimenting myself, gotta thank you guys so far you have been a great help!
The easiest way to rig a bulb up (taking safety into account) is to have either a bulb in a holder, or (as I do), solder wires to the bulb and then it's easy to solder the other end of the wires across say the main fuse in the amp or whatever. Obviously remove the fuse first 
If the outputs have got hot enough to melt the washers then they should be replaced to do a proper repair.
Shorted transistors won't give a short reading on the mains input side... you'll find that large transformers read almost short circuit on the primary side. That's because you are just reading the DC resistance of the primary winding. On AC its impedance that matters and the transformer presents a much higher ("resistance") impedance than you measure on a meter.
If the outputs have got hot enough to melt the washers then they should be replaced to do a proper repair.
Shorted transistors won't give a short reading on the mains input side... you'll find that large transformers read almost short circuit on the primary side. That's because you are just reading the DC resistance of the primary winding. On AC its impedance that matters and the transformer presents a much higher ("resistance") impedance than you measure on a meter.
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