Clipping/Distortion in a Pioneer QX-4000 Receiver

[wrlampe]

Hello, I am attempting to repair a Pioneer QX-4000 receiver which has a very nasty problem, whenever the volume is turned up more than the slightest amount there is a very large amount of distortion. This problem occurs in both front channels and all inputs. It also is common to the headphone output and the speaker outputs. The problem gets worse when bass is turned up or loudness is turned on making me think that it is clipping the signal somewhere. Does anyone have any idea how to diagnose this? I have a multimeter and just enough knowledge of electronics to be dangerous. Thanks in advance for your ideas.

-Randall

[sakis]

must be like 100 years old

the last time i repaired qx949 was 20 years ago i think ....

start with recaping almost everything ....inside the amp ....

on the other hand you need to be familiar with the procedures, ajustment , tuning , measure ....will require scope signal genarator and goes on.

very possible job to do .... but for shure not easy .....

you might seek expert help ....

[wrlampe]

Nah, It's only a third of a century old. I have opened the case and everything looks good, no leaking capacitors or anything. If it were mine, I would toss it. However, it has sentimental value to a friend to whom I owe a favor. There are probably more than 100 caps inside the amp. I'd guess that the power supply or the preamp are the most likely culprits to produce this sort of problem.

[sakis]

if you listen to this amp after is been cleaned properly .....recaped properly and tuned ..... you will be more than impressed .... wonderfull sonics ...

but dont be sure about that power sup caps might wanted to be replaced ......its more than that .....

DO it DO all of them ......its an timetaking job to do ...but easy ....

all the best !!!

[ChopperCharles]

Hey, old post, but I was the guy Randall was trying to fix the receiver for. It eventually completely died, no sound whatsoever. I ended up buying another unit on eBay, and I opened them both up side-by-side and compared the voltages on every point i could find. Turns out the amp boards weren't getting voltage. Traced it back to the muting unit, it had a bad diode! Replaced it and she worked again!!

Charles

[ChopperCharles]

Now question... I actually bought three units. The second unit gets MUCH better FM reception than the one i just fixed. The second unit gets a five in signal strength, my dad's receiver gets a 3. Stations the second receiver gets in loud and clear my dad's receiver can't pick up at all.

The third unit... doesn't receive FM at all. AM works great, every other function works perfectly, but it doesn't receive even a blip of FM. Any ideas?

Oh and yes, I fixed this in August 2011, after years and years of it sitting dejected on a shelf.

Charles.