Turn the balance toward the speaker you have plugged in. On this Sony HP-510A one speaker plug was broken, so the whole early diagnosis used a single cabinet. Balance was parked at full right, which is where that speaker was connected. Full right was audible and quiet. Full left was silence. That is a working balance control doing what it was designed to do, and it looks like a weak amplifier if you only listen at one setting.
One speaker, two ends of the knob
| Balance | What you should hear | What it means | Shop |
|---|---|---|---|
| All the way toward the connected speaker | That channel, as loud as it can be | The knob was the quiet, if this is suddenly loud | — |
| All the way toward the empty side | Silence | The control works. You are listening to a jack with nothing in it | — |
| Centered, and one side still crackles on AM and FM | The crackle stays with the channel when you swap speakers | Stop buying knobs. The channel is the fault | View Centered, and one side still crackles on AM and FM (affiliate) |
Affiliate Link • Earns Commission
Center it, then listen. If the one speaker jumps in volume, you have the answer and you do not need a part. Move that speaker to the other channel before you go further. On this unit the left played clean once the speaker was on the left, and the right crackled on both AM and FM. The crackle followed the channel, not the cabinet. Phono was silent on both at that point. Two faults, neither of them the balance knob.
A knob that crackles as it turns is dirt, and that is DeoxIT, with the stereo unplugged, a short burst, and the control worked 20 to 30 times. A knob that is merely turned the wrong way does not need the can.
Set mono off before you trust a one-channel result. Mono copies the bad side into the good speaker and makes a balance problem look like two dead channels. That switch, on this stereo, is its own guide: both channels crackle. The channel that survives the balance test and the speaker swap is the one-channel fault.