Pioneer CDJ-400 - Output Quiet and Distorted

[dazzler22]

Hi All,

Just found this forum on the hunt for an audio/electronics guru, im in the process of learning by doing! have a couple of electrical bits that need fixing and figured the best way to do it is to get right in there.

so the situation, I bought a pioneer cdj-400, the seller told me that it was not reading CD's, no problem i thought, I have replaced optical pickups in several device's and as it happend i was looking for one of these players.

so paid the guy and the player arrived, plugged it in to test and the unit did not power up (seller tells me it must have had a knock in the post and he wants nothing to do with it), so I got hold of a copy of the service manual with a circuit diagram and started checking resistance's on the board.  What i found was some really dodgy soldering where someone had tried to repair the board before, clearly the seller was lying to me! 

one of the dodgy bits of soldering was so bad i removed it and replaced and viola! the unit now powers up, all buttons working the display is working, great i thought! untill i plugged it into my amp.....

the sound output is very quiet and very distorted.... so clearly something else is not quite right....

My question is where do i start testing? can anyone point me in the right direction?

the service manual is http://www.maetech.it/docs/datasheets/pioneer_cdj-400.pdf

any gurus on here care to share what they would do in this situation?

the original problem that i fixed was an issue with the +5v circuit, there was some solder linking the +5 to the ground....

I hope this makes sense, any help is greatly appreciated.

Cheers
Daz

 

[gswan]

Start by checking the supply voltages from the PSU board, to make sure they are all OK.
Then check the ALO and ARO test points with a known source (say a 1kHz test CD). Pgae 50 of the pdf doc shows the circuit. The buffers are NJM4580 devices, so check the output of these as well, until you see a point where the audio is distorted or attenuated where it should not be. Also check the audio mute transistors on the outputs (page 59) and teh protection circuits. Someone may have popped one of those, and/or a protection diode.

 

[dazzler22]

Thanks for the response, on further testing and some info from another forum I have found that the -5v rail is not working.

this is used to power the mute circuit which is now on at all times making the analogue output quiet and distorted. I have plugged in an external DAC and it is working fine.

it looks like there is a transistor cooked on the -5v DC converter....

if i can get hold of that part (and don't have to order 10000000) hopefully i can get it fixed, failing that i will just use it with the external DAC.

Cheers
Daz