Open it from the top. On this Sony HP-510A the screws you can see from underneath are not the ones that free the chassis. Wait on pulling the case if FM, the mono switch, and contact cleaner have not been tried. Those checks are the first crackle guide.
This is an early-1970s all-in-one: tuner, amplifier, and turntable in one wood cabinet, bought on Facebook Marketplace, with the matching SS-510 speakers from eBay. The left channel and the phono input were already working after cleaning. The right channel was still crackling on every source, and the wires to that speaker jack could not be followed from outside.
What each screw on this HP-510A actually held
| What you see | What it held | What to do |
|---|---|---|
| Screws through the rubber feet | The feet, into the wood | Leave them. They did not release the chassis |
| Small screws in the back corners | Wood screwed to wood | Leave them. The cabinet stays together |
| The turntable, from above | The deck over the amplifier | Lift the turntable out. The board is under it |
What did not work
The usual guess for a wood-case all-in-one is that the foot screws pass through the cabinet and thread into the metal chassis. On this HP-510A they do not. Take one out and it is a short screw for the foot.
The other guess is the small screws in the rear corners. Those hold wood to wood. The cabinet does not split there, and the chassis does not slide out the back.
What did work
The turntable comes out from above. Once that deck is lifted off, the amplifier is in the open: the board, the wiring from the speaker jacks, two speaker fuses, and a metal heatsink with the large output transistors bolted to it.
Both speaker fuses on this unit were intact. A fuse that is still good does not explain a channel that crackles, so the next job is identifying which parts belong to the bad channel. That split, including the parts marked SONY D291, is the transistor guide.
The speaker-wire path on the right was hard to see even with the deck off. Continuity from the right speaker jack to the fuse clips is the way to name the right-channel fuse without tracing a hidden wire by eye. The meter for that check is the same Klein already used on the speakers.
Once it is open
Unplug the stereo and leave it before your hands go near the board. The large filter capacitors can hold a charge. Stay off the power switch, the transformer, and those capacitors.
Power goes back on through a dim bulb tester, not straight into the wall. Owners of the related HP-511 have described output transistors failing on a first power-up with no limiter. The bulb is the cheap version of that protection, and it belongs in the circuit again after any part is changed.
The fault this opening was for, one channel crackling after the controls were cleaned, continues in the one-channel guide.