Notes: typo on the 'reapair' sorry.
Got this one in for repair, the owner said it makes spatter distorted sound when the audio is applied to the any inputs and does not matter if the volume is up or down.
I found that the +/- 30V power supply are not balanced, the +VCC is about 5V lower than -VCC, these are supplies for OPAMPs.
Inspect the board and found that the center tap pin of the dual supplies was never soldered to the board, there was no solder applied.
Soldered it and the voltages are reading fine now but the distorted sound is still present, I did more research on the non-opamp IC (there are two 16-pin ICs, one is for Volume control, and another one is for Tone control) so I can get the pin out for the voltages feeding the ICs, I was suspecting the Volume control IC since turning the Volume control knobs has no effect on the level of the distorted sound. The -VCC is showing -12V, but the +VCC is showing <1V, check the resistance reading on the +VCC and it shows < 5 Ohms. The +/-VCC pins are fed through 100 Ohms resistors and small lytics cap for filtering. Removed the filter caps and it still shows <5 Ohms, so I cut the +VCC pin then the 5 Ohms reading went away. check the +VCC pin and GND pin of the IC off the board and it shows <5 Ohms. Luckily I still some of these Toshiba ICs in stock, now it is running, it sounds pretty good.
Got this one in for repair, the owner said it makes spatter distorted sound when the audio is applied to the any inputs and does not matter if the volume is up or down.
I found that the +/- 30V power supply are not balanced, the +VCC is about 5V lower than -VCC, these are supplies for OPAMPs.
Inspect the board and found that the center tap pin of the dual supplies was never soldered to the board, there was no solder applied.
Soldered it and the voltages are reading fine now but the distorted sound is still present, I did more research on the non-opamp IC (there are two 16-pin ICs, one is for Volume control, and another one is for Tone control) so I can get the pin out for the voltages feeding the ICs, I was suspecting the Volume control IC since turning the Volume control knobs has no effect on the level of the distorted sound. The -VCC is showing -12V, but the +VCC is showing <1V, check the resistance reading on the +VCC and it shows < 5 Ohms. The +/-VCC pins are fed through 100 Ohms resistors and small lytics cap for filtering. Removed the filter caps and it still shows <5 Ohms, so I cut the +VCC pin then the 5 Ohms reading went away. check the +VCC pin and GND pin of the IC off the board and it shows <5 Ohms. Luckily I still some of these Toshiba ICs in stock, now it is running, it sounds pretty good.
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