Electronics > Repair
Roland E-35 keyboard with temporary noise/hum
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marcinado:
I couldn't capture the problem by oscilloscope probe because of high noise floor on idle signal. I've made another test. I've recorded signals from three different audio outputs. Speaker out, phones out and line out. As you can hear, noises on speaker output are most hearable. Phones out is much better, almost free of problem. On line out problem doesn't exist.
I've connected external speakers to speaker cables instead of internal 4 ohm speakers. On speaker with 4 ohm impedance noise is the same as on internal speakers. With 8 ohm speaker is better but not very much.
Internal speakers and phones out are connected in the same place. The only differences are resistors and ferrite beads in serial for phones output.
I have another keyboard Roland E-15 which has almost identical Power & Amplifier Board. There are only two differences between them. E-35 has additional resistor 2.2 ohm instead of jumper in power section (maybe because of different voltage value on input? E-15 9V and E-35 12V). And another difference is 18k resistor and 27nF capacitor connected to TDA IC. What's strange it's only on the right channel. On left channel there are empty pads like on both channels on E-15.  And problem with temporary noise doesn't exist on E-15 keyboard.
Do you think it's worth to replace TDA1905 chips? I can't spot another source of the problem different than TDA1905 chips.
pinkeye:
Hi
Did you ever find the cause of this?
I just got asked to repair one of these keyboard and the hum is very loud on all outputs....
marcinado:
Hi.
I couldn't find the cause. But I have only problem with internal speakers sound. Headphones out and Line out is clean.
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