Pioneer SX-1000TD

[scorpio333]

Found this other day and it followed me home. Was a horrendous sounding mess when I first powered it on. Deoxit'd everything and dusted it out. All knobs are smooth with no noise. FM sounds very good, I just never listen to FM. All the lights work. It plays loud and doesn't break up at all.

When I switch to Phono, Tape or Aux there is an audible hiss like FM static. Turning the volume knob slowly with no source playing, right about 11 o'clock there's a dip in volume then it kicks right back to where it should be. Any ideas what could be causing this hiss?

There's also a bit of a blip or thump when powering on.

[Dicky]

Grab a schematic from hi fi engine.  I glanced for a second, looks like a little more cleaning should do something since they (Tuner and aux) all end up on a selector switch with nothing in between, but again i looked real quick.  If i have time later Ill try to evaluate more.

[scorpio333]

Just poking around it sounds like a pre-amp issue since the volume knob will increase/decrease the static. I'm a noob in this area, so I could have that all wrong, but want to learn this.

Here's the diagram for the pre-amp

[Sir Thrift-a-Lot]

Turning the volume knob slowly with no source playing, right about 11 o'clock there's a dip in volume then it kicks right back to where it should be.

I would DeOxit that pot again.   I've had ones where two or three cleanings were needed to get it to 100%.

[Anders]

Yes but any dc on the pot will cause it to act up.

[scorpio333]

Cleaned this up some more and got 50% of the noise to go away. Doesn't get noisy until volume is half way up. Not too shabby. Not my favorite sound. Will work nice in garage with old JBL 2500s.

[Mongojustpawn]

The 2sc458 transistors might be causing your hiss, according to many posts on audio karma they are prone to failure.

[scorpio333]

Swapped it into main rig and it gets weirder. When the TT is running and hits the run out, the amp is pretty silent. As soon as the TT shuts off, it's a snowstorm.

The AUX is pretty quiet, the tape inputs (with nothing connected) are crazy snowy.

Satisfied for now, it'll get some use as is.

[Sir Thrift-a-Lot]

Maybe there is a bad grounding issue somewhere inside.

[scorpio333]

Maybe there is a bad grounding issue somewhere inside.

Without the bottom cover on while sitting on the table I got it to act like a theremin. Waving my hand over certain spots would increase the snow. Doesn't occur with the bottom cover in place.

[MacGeek]

A couple of suggestions-looking for easy stuff.  Check and tighten all screws.  Take the eraser end of a pencil and try gently pushing on and flexing the boards, while listening for changes in noise/hum, etc.  Be careful as this requires the unit to be on.  This may expose a cold/loose solder joint or a crack in the boards.  If you hear changes a strong magnifying glass may help to locate the problem.  While the unit is off, unplug and reconnect any internal jumpers; remove and reinsert fuses.

Basically move everything that can be moved in an effort to identify anything weird or that changes.

[scorpio333]

Thanks MacGeek, great tips, especially the pencil eraser. I like learning as much as I can about this stuff. Lots of great old stuff out there that is deserving of continued use. Since I don't have a lot of the basic electronics training I've been trying to go through some online training.

I tried one more thing. These old Pioneers have a voltage selector on the rear. 110, 117, 130, up to 230 I believe. I tried the first three, when I tried the 130 things settled down a great deal. Phono has a bit of ground hum up about 75% volume, which is way too loud to listen to at that level. AUX is almost dead silent, slight white noise over 50%. Tape is noisy as all hell at any volume, but no plans for tape listening anyhow. We'll see how it reacts to getting more use, but for now it's a rocking little unit.

[MacGeek]

I have no formal electronics training and know only what I picked up along the way.

It seems odd that any one high level input is noisier than another, they all pass through the selector switch.  Or, does this unit not have tape inputs on the input selector, rather having it/them via monitor button(s).  If it has buttons, try cleaning and exercising them again.

If the phono doesn't hum until the volume control is past the 2:00 position, I think you are doing fine