D-15 repair (wrong polarity damage?)

Hello,

(I posted this in the new member/introduction section before and I think, like suggested its better to post it in the specific discman section.)


I recently came across a (dead) D-15 and I payed just 30 bucks for it, but unfortunately (it was offered as dead) it does not play.
The D-15 is in a perfect condition and I think nobody has ever opened it.

I think there could be a reversed polarity damage because I could identify a little dark, burned spot right after the first flex cable that delivers the power. I have some tools (oscilloscope, DE-5000 esr/lcr meter) and soldering/desoldering experience so I hope, that I may find the problem and finally will get the D-15 running again.

I did not desolder anything, I just took pictures. The 9V input jack measures 600K Ohm in one direction, 22K Ohm in the other direction. The diode test shows in one direction 1,78V/ OL in the other direction.
The D-15 now does not do anything at all when power is plugged in(lcd dead, no spinning motors, nearly zero current consumption).
On the lead acid battery pins I can measure arround 2V. 5V should be the right voltage (thank you Jorge).

Jorge already mentioned that Iam on the right track and I will continue the repair as soon as I know how to seperate the boards(hopefully I can do this without desoldering a flex cable).
The biggest burned spot is like you can see on the attached pictures (on the mainboard) at the other side of Q434/Q409, arround Q417/Q437. To get access I may would have to take it apart somehow. Is there a more easy way to get to the underside without desoldering any of the flex cables?



Best regards and thank you very much

Alexander

 

Hello,

I now finally managed to get some NOS transistors(2SB798s).
The only problem is, I dont know how the pcb looked before Q417 burned out.

It looks like there may happened a trace missalignement (cut trace/loose piece of a trace). Does anybody know where exactly the traces under Q417 go?
There seems to be a little metal trace piece arround the middle pin of Q417 which is cut and hangs loose.
Where does this belong to?
Was Q417 even attached (it looks like there couldve been a solder blob before) to the additional little sandwhiched board (nothing about it in the service manual, but why?)right under Q417?

Could somebody take pictures from an intact or broken D-15 mainboard? Just the spot where Q417 is located is important.
Unfortunately I cant find any pictures of a D-15 mainboard (on the whole internet) to compare it how it should look originally.
Are there any detailed pictures of a D-15/150 mainboard here on the forum?


Best regards and thank you very much.
Alexander

 

Hello,

Ok, I got it, no photos needed.
I overlooked the little extra pcbs on the manual and its clear that the edge at D415 goes to the collector of Q417.

If I see this correctly, Q417/Q436 are in parallel without any resistor on the emitter. I would try to add 0,1-0,8 Ohm /2W (voltage drop too high?) so that the currents will distribute more evenly on Q417/Q436.

Brgds
Alexander