Vintage Sony discman d-7 dead

[Mike]

I got my hands on a discman D-7, I like older toys, and its got the classic
dead symtom. No nothing.
Well, I got a steady 12 volts in, but everywhere I probe, even the power
switch, 0v. nadda.

In the power regulator area, I got 12v going to a few select transistors,
and I got 6 to 8 volts comming out of one, and different areas I got
1.2volts to zilch. Nothing getting to the power switch.

There is also a big silver box like thing that has leads soldered in the
board around that area, Is this the voltage regulator box? Im thinking about
cutting that away and finding out.

I took readings on those pins, got about 10 volts in from the b+ supply, and
no other voltages elsewhere on the outputs.

Also, Does anyone have service info or schematics theyd like to send?

 

[jango2]

The silver box might be a dc to dc convertor. You could start by
confirming the door close switch is ok. Next , if the function pcb is
on top of the lid , i'd look for a break in the connector or flex pcb
linking it to the main circuit board. I had a case once when the faulty
component was simply a defective play switch.
Jango

 

[Mike]

it is a PWM dc-dc converter.

I tore into the box, and the outputs have 6.3v caps, so by that, im juding
the ouput is +/- 5v.

one pin is hooked to ground, the top pin is negative of the set of caps, the
other is on the positive. Just like you would setup a rail on a power
amplifier.

The other side has 4 pins. One is VCC, I know that, The other I have no
idea, but it goes through a resistor to the VCC of the PWM IC. So, Im
assuming thats also VCC.

and there are 2 left, one I have no idea, it goes to the main cd micro.
(standby enabel?) and the other one goes to the base of a transistor. So, i
guess when it is held high, it switches on that transistor which maybe turns
on the Dc-dc? well that transistor has a 25 marking on it, SMD, and it reads
nearly open. same on the other 2 that are on the DC DC.

hmmm. I assume the standby circuits get power, and when you press play, it
toggles those pins high on the DC dC, causing it to switch on, and provide
power to the LCD and the rest of the circuits?

Also, i have no idea, but when you flip the power switch, does the LCD
immidiatly come on? or not? does the LCD only come on when you press play?

I got nothing out of this player. I see VCC on my required pins, but no
output. so the DC DC isnt runing, maybe because those SMD transistors inside
the module are reading about1.5 to infinate drop. supposed to be .5 to .7??

 

[Mike]

I fixed it. 2 bad transistors, the shunt regulator driver, and a STROBE
switcher in the DC-DC box.