NAD 502+512+514 - Burned Transistor from Focus Power Buffer Output Stage (pos. Half)

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This is to observe in general by all devices of the above mentioned models.

At least there must be resolder at solder side of the main board in this aera.
Better solution is the replace of this transistor to a version with TO-126 outline (e. g. BD139) and heatsink (or electrical isolated mounting on chassis).

Who knows the reason for the enhanced power loss in the upper half (positive rail) ?

BTW - The laser unit (optical pickup) is the KSS-210A from Sony.
And the Transistor is Q608 (2SD1858, ROHM-MPT3) by NAD514 and Q102 by NAD 502.
 
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+14V

I have problems with the +14V power too.
Symptom: Drawer didn't open any more.

Changed fuses IP101 and IP102 (N10 fuses) and swapped Q102/104/106/108 against BD139 transistors.
Now the drawer opens/closes again.

Unconfirmed suspicion: the fuses blew once the drawer got "stuck" and therefore drew a too high current. Might that have been the cause for you too? The +14V seem to be on all 4 transistors so I could imagine that to happen.

However the beast still doesn't want to read a CD and the motor spin doesn't seem to work.

NB: The PCB around these transistors is of really poor quality. Be careful when unsoldering them, you risk to have the copper going off the PCB. Unbelievable poor for an "audiophile" class of device IMHO and makes me doubt overall NAD is really what they claim to be.
 
Here are to find good pictures.
NAD 502 - Le forum Audiovintage
NAD 502 - CD does not start to spin | AVS Forum
Repairing a NAD 502 CD Player - Commented Out
Main reason for the burned focus transistor is the not perfect height of the motor pulley from spindle motor (discmotor).

The adjusting procedure is very difficult (pulley is pressed on shaft of spindle motor without grub screw for adjusting).
One have the correct height, if the lens of KSS-210A don't change the position from "PLAY" mode to "Off" mode after pulling the power plug from mains socket.

Then is the difference of temperature between the both PP transistors from the focus driver stage only small.
One can see the lens position clearly while "PLAY" mode when a compact disc with the maximum possible playing time is in use - if near the end of the playing time is reached.

The disc should not have a vertical stroke or curls so that the lens goes up and down while "Play" mode.

Another deficiency is the too hot shiny natural heat sink for the voltage regulation by closed cover. This issue isn't longer present after removing the heatsink and mounting the parts therefore at the back plate.

I have problems with the +14V power too.
Symptom: Drawer didn't open any more.

Changed fuses IP101 and IP102 (N10 fuses) and swapped Q102/104/106/108 against BD139 transistors.
Now the drawer opens/closes again.

Unconfirmed suspicion: the fuses blew once the drawer got "stuck" and therefore drew a too high current. Might that have been the cause for you too? The +14V seem to be on all 4 transistors so I could imagine that to happen.

However the beast still doesn't want to read a CD and the motor spin doesn't seem to work.

NB: The PCB around these transistors is of really poor quality. Be careful when un-soldering them, you risk to have the copper going off the PCB. Unbelievable poor for an "audiophile" class of device IMHO and makes me doubt overall NAD is really what they claim to be.
Check out and clean the contacts of both loader position switches for "tray in" and "tray out"
For troubleshooting I have forget any details (my last repair work is long time ago). Best way is to purchase a second device of the same model for compare all values of DC-voltages.
 
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OK thanks - now that I also swapped the IC CXA1082BS the spindle spins up again and the optical mount is moving. However... it spins up to a (very high) speed and apparently is unable to read the disc. When I then open the drawer, the speed of the disc turning was so high that it was "ejected" towards the side of the unit (i.e. the spindle didn't slow down before opening the drawer).

Also... confirming what you wrote, pressing on the metal bracket going over the whole drawer I feel that it was slowing down the spindle (i.e. when I turned the device on without a disc loaded spindle mechanics makes a sort of scratching noise when turning the spindle motor for some seconds).

From this description, do you think this could be the adjustment you describe?
Or an indication something addition could be broken, i.e. laser unit not getting correct signals?
 
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