Wadia 21 Dead laser or servo problems?

[Zero Cool]

I need to take a close look at the laser block assembly. Pin 6 is labeled as ground but it is tied to -5v on the servo board. I am assuming this is just a typo, but if the laser is running on +5 and -5V it would explain the over heating! the trimmers were locked in place (before "I" messed with them) so I don't think that this is from anyone messing with them. so it's really puzzling. I will try and get a picture if i can zoom in close enough.

[Zero Cool]

Not sure how clear these are going to show up, but this is the transistor on the back of the trimmer PCB. the board is charred and bubbled in between the transistor and the resistor.

[Zero Cool]

Now looking at this picture leads me to believe that they might have Gnd and -5V mixed up. This photo shows Pin1 as VC and Pin 6 as GND. VCC being +5v it would be a logical guess that VC should be -5V and Pin 6 really should be ground!

[Zero Cool]

you can see here that Pin 6 is shown connected to -5V and Pin 1 is connected to Gnd

[Mooly]

Same goes for me.
I think I would do a quick of the rails with the old laser still fitted. Maybe look for any drys on regs anywhere.

[Zero Cool]

OK well some success tonight and some problems. 1- I replaced the laser and it fired right up, read the disc and appears to play. But the unit has other problems as it will not come out of mute and the volume control doesn't work but I will get to those issues later.

What I did discover is that the servo board does have -5v on Pin6 and ground on Pin 1 just like the schematic shows and that the laser block is connected as show where Pin 6 should be ground and Pin 1 should be VC which I am guessing is -5V. I did not get to pin out the chukei board and see if it does a swap but I am guessing not!

I know that in other VRDS transports they used the KSS-151A laser. I can't find a pin out of the 151 and I wonder if they made a mistake and assumed both were pinned the same???

So the question now is should I just leave it as is and hope the new laser last's awhile or should I tear it apart and change it the way it should be??


Zc

[stephensank]

The KSS240 is being "floated" between the rails, so that it "thinks" it's running +10VDC. There is no need for the laser's ld/pd circuit to be "real grounded", so it's perfectly fine running this way.
The damage makes me think that the laser diode catastrophically shorted, frying the transistor that supplies it. This can theoretically happen years after a laser diode has been static zapped, but I never really thought it possible in practice until now.

[Zero Cool]

I wish I could find a data sheet for the M52104FP IC. in all the other schematics I have seen thus far that use the KSS-240A laser, they have Pin 6 grounded and Pin1 tied to -5V and is running from +5V. Running from +10v may be fine but that still leaves the issue of Pin 1 tied to ground and not -5V.

I will leave it as is, but it is something to think about. I need to get the other issues sorted out and that may be a much bigger issue.

[stephensank]

Missed that the pin1 connector through to the main board is also a ground line, which I verified on the full manual schematic. Just checked the Denon DCD-1290 manual, and verified that the VC is not a supply line, but is rather a mid-point voltage bias pin, so using it or not depends on the servo chipset.

[Mooly]

The "virtual ground" thing is a bit weird on these. M52104 ? this is a 52103.

Couldn't find anything on that either...