Hi
My Playmaster 200 has an issue with the left channel when it is turned on. I am using headphones to listen to it and speakers are not hooked up. The right channel is fine but the left has hum and some other noises for several minutes before it comes to life and works well if left on. During this time if the speakers are selected, the relays do not activate but work once the channel works fine. Tapping on one of the J49s produces some noises there is hum on the left headphone when the power is turned off at the amp. This only stops when the power is turned off at the wall. Oscilloscope indicates issue is after input from preamp. I have limited diagnostic ability so any suggestions would be very much appreciated.
Have not been able upload schematic but it can be found at Electronics Australia 1985 : Free Download, Borrow, and Streaming : Internet Archive March Edition. Full details of the construction of the amp is in the Jan, Mar, May editions
My Playmaster 200 has an issue with the left channel when it is turned on. I am using headphones to listen to it and speakers are not hooked up. The right channel is fine but the left has hum and some other noises for several minutes before it comes to life and works well if left on. During this time if the speakers are selected, the relays do not activate but work once the channel works fine. Tapping on one of the J49s produces some noises there is hum on the left headphone when the power is turned off at the amp. This only stops when the power is turned off at the wall. Oscilloscope indicates issue is after input from preamp. I have limited diagnostic ability so any suggestions would be very much appreciated.
Have not been able upload schematic but it can be found at Electronics Australia 1985 : Free Download, Borrow, and Streaming : Internet Archive March Edition. Full details of the construction of the amp is in the Jan, Mar, May editions
Check the integrity of all earth connections - solder joint and mechanical fastenings - particularly the 47uF capacitor in series with 1k which decouples the feedback divider network to earth.
Thanks. Since posting, I have pushed and prodded and found one of the J49s reacted to being tapped on. Have just turned the amp on after being off for a day and it worked perfectly. I suspect there is a dry joint so will check the joints. Not sure about the hum when turned off so will also check the active is off when the power switch is off.