Nakamichi CDplayer3 problem

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I've got a Nakamichi CDPlayer3 which I cobbled together (just for interest/curiosity) out of a couple of friends' "dead" ones - one with its laser and stacker n/w and the other with the electronics main board apparently n/w.
Sometimes it won't start playing at all - usually just turning it off and waiting for a few minutes cures this.
When it does decide to start playing it sounds beautiful - like all Nak gear :) - except that playback always stops about halfway through any CD.

I downloaded the pdf of the manual but can't find any way to fix this.
Except that the manual does mention a "RAM reset" procedure which involves shorting out a couple of jumpers - but this apparently only checks that the stacker mechanism is working OK - which, having gone through this procedure, it is.

I was hoping that this RAMreset might also "reboot" the unit's main "OS" - but apparently not - it will still only play up to halfway through any CD.
It then makes two or three small clicking noises - I haven't yet been able to see what is producing these clicks (with the top cover off it of course) in spite of some very careful peering into it while it is doing this.

There doesn't seem to be anything obstructing the pickup head's travel.

With it occasionally not spinning the CD (even though the clamping mechanism and the lifting up of the laser gubbins both seem to be working OK) and it refusing to go past the first half of any CD it seems that its "brain" might have gotten scrambled somehow and perhaps it might need to have its "computer"/"OS" reset.
Does anyone have any ideas on how to do this - or any other ideas about what to try next??

As I say: it's no big deal - it's just a "to see if I can do it" project - but, having got this far, before putting it into the "scrap" pile I would like to nail this if at all possible.

TIA potential uplines

via linux Mint 17.3

Old'n'Cranky No expert but sounds more like a laser / reading issue to me.

focus check for cd.
spin up.
read toc.
starts playback.

if it occasionally wont spin up, possibly not able to see the cd to start with.
if it stops half way through, possibly a weak or mis focused laser.
Yeah [Old'n'Cranky] (but I'm probably older&crankier :D) - you're probably right - according to the pdf of the manual there's all sorts of pots for "laser focus", "tracking gain", "focus gain" etc etc on the mainboard which I haven't got the oscilloscope, test unit (the design & construction of which is well laid out in the manual), or general technoknowledge to be able to re-set for the new "player gubbins".
I was just happy enough that it seemed to work OK after I'd spent a couple of hours changing all the various pieces over :). But for the first half of CDs only, sadly :(.

if it occasionally wont spin up, possibly not able to see the cd to start with.
I would think that if it's lifted the reading laser mechanism and clamped the CD it has probably recognized that there is a CD there - and I think also that there's a little photoelectric unit/PCB that works through a hole in the disctray to check for a disc actually being present.

It's just not as simple as I'd hoped - an electronics repairer with all the gear would only take an hour or so to sort it out I'm sure - but that'd cost more than the unit's really worth now - so I won't be doing that! Ah well, another goodlooking doorstop :).
And, to console myself, I've got other, better Nak CD players (MB-2, MB-10) with the vital "digital out" feeds to supply my excellent AV-10's internal DAC stage.
And, as a linux fan, it's possible that I'd just become overly fixated on the OS aspect of it :D.
Older, crankier, ? nahhhhhhhh that can't be possible :p

Loading and clamping is a mechanical process that has nothing to do with any actual disc being present.
Lid off, no disc, open and close the tray a few times. watch the laser assy. DO NOT LOOK STRAIGHT INTO IT.
when the draw closes youll see the lens move up and down a few times.
It's trying to focus on the disc. if it cant, it thinks theres no disc and stops.
if the laser is weak or non functioning, well, it cant focus, so it still thinks theres no disc.
That it sometimes spins up and plays means the laser has at least some power left.
with experience you can see the laser beam and judge if the laser is dead, passable or really good.
but, this is a super rough bludgeon that im sure others here are ripping their hair out over about now ;)

Have a look at some cd player flow charts to understand the basic flow of actions.
Bit of logical thinking will get you the rest of the way.

If you are resigned to it being dead, you can probably get it running with a little fiddle.
No it wont be right, yes you risk burning out the laser.
But, it may just make it useable for a bit longer...

I had a guy bring me a studer rack mount, told him i didnt have the gear to align it, he didnt care.
poor thing had soooooo many issues. failed back light, leaking caps, almost unusable draw belt, etc and so on.

It would only play a few cd's to near the end and copies conked out have way through.
I manually adjusted the focus and tracking by trial and error little at a time.
got it to a point where normal cds weren't an issue.
And copied or bad cd's would get to within the last track.

Some cd player manuals give you the laser drive current, so you might at least be able to set that.

If it cost you nothing, and has issues, what have you got to loose ?
have a play and try to learn something as you go......
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