These days I'm playing with an old cassette player, a TEAC W-485C. It's a lowish end model but currently the victim of my diy fever. 🙂 Although it has a regulated psu there is an annoying 50Hz noise. Moreover, this noise gets louder through the speakers when the deck is turned off. Sniffing around I found two wires coming from the PCB to the power switch and connect some kind of load when the switch is off. The user's manual says "The equipment draws nominal nonoperative power from the AC outlet with its power switch in the off position". Does anyone know what is this?
BTW, if anyone knows where I could find a schematic/service manual, it would be much appreciated.
BTW, if anyone knows where I could find a schematic/service manual, it would be much appreciated.
You may have some kind of ground loop.
Try plugging the deck into a wall switched AC outlet.
Here you go.
Try plugging the deck into a wall switched AC outlet.
Here you go.
Thanks for reply! It is a ground loop, no doubt. I don't have a switched outlet but the noise goes away when I pull the plug. I forgot to say it's a class II appliance.
Unfortunately, the attached is user's manual. I have that but it doesn't have a schematic or belts size etc.
Unfortunately, the attached is user's manual. I have that but it doesn't have a schematic or belts size etc.
Hi kostas
Many of low power audio gear had the power switch at the secondary of the power transformer, leaving the primary always connected to the mains. In OFF position, it draws from the mains the magnetising current of the transformer.
If there is hum, try to reverse the mains plug to see if the noise weakens.
If there is buzz, you have to start investigating for ground loop problem.
You may also check the ceramic capacitor from one of the RCA barrels to chassis.
I can't find a schematic of your model (or one close to it).
George
Thank you George!
It makes sense. The problem is that in this case is badly implemented. Two 30cm long wires going from the PCB ground to the switch. I cut them and -together with twisting all AC wires- hum is gone. Anyway they were out of the circuit when power on. So, is it mandatory at power off?
It makes sense. The problem is that in this case is badly implemented. Two 30cm long wires going from the PCB ground to the switch. I cut them and -together with twisting all AC wires- hum is gone. Anyway they were out of the circuit when power on. So, is it mandatory at power off?
It's not clear to me what these two 30cm wires are for.
The power switch should be in series with the secondary of the transformer.
The power switch should be in series with the secondary of the transformer.
Here is a picture. The area of interest is to the left. The power switch cuts the secondary. All AC wires were twisted by me, previously were loose like the purple and grey wires that I cut. I placed them like they were before. The purple takes the PCB ground to the switch and the grey returns it when the switch is off to some kind of load. Like if it had a stand by function but there is no such thing in this. I'll need to lift the PCB to trace that.
Attachments
That takes me back:
'In the UK this device is sold without an AC plug'.
What fun when inept people without tools would connect a plug by stripping wires with a kitchen knife and tighten the terminals with a table knife.
'In the UK this device is sold without an AC plug'.
What fun when inept people without tools would connect a plug by stripping wires with a kitchen knife and tighten the terminals with a table knife.