Nakamichi OMS-7 CD Player from 1985

[Smoky]

I get a call saying that a broken CD player was put on my front porch and it doesn't work and you can have it. "Thanks Bob" I said.

It turns out to be a Nakamichi OMS-7 CD player from 1985 and it looks practically new.

I call Bob back and asked him if this thing was used much. He said rarely and the last time would've been around 1994. He tried a CD recently, the door opened, he put in a CD, the door closed but nothing would happen after that. I asked him if the door opened automatically after a short time and he said no.

I have not lifted the cover yet but peering inside the vent holes on the top of the player I see corrosion going on near a capacitor where the power cord comes in

From what I've read about these older CD players is that the laser fades away and they pretty-much transform themselves into doorstops. I see a lot of electrolytic capacitors on the top PC board and many near the power cord inlet. I'll take more pictures when I lift the lid.









Thankfully, no batteries were left in the remote control

[Haenk]

Nice machine, but unfortunately very dated (1540 DACs). And if the laser is dead, a replacement is probably impossible to find or very expensive. More on the "impossible" side.
However if it does work, some enthusiast might pay good money.

[wasedadoc]

Laser lifetime is much more dependent on operating hours than age.

A dead laser would not prevent the tray opening or the motor spinning up at least briefly when the tray goes back in.

[Zenith]

There's loads on the web on this from places like Audiokarma, including the service manual and discussions of repairs. If it really hasn't had much use, I doubt the laser is dead. It might be simple problems such as switches needing cleaning, belts replacing and electrolytic capacitors needing replacing.

In a working condition they sell for a decent price on ebay USA, and as parts only they are not given away.

[Haenk]

Laser lifetime is much more dependent on operating hours than age.

A dead laser would not prevent the tray opening or the motor spinning up at least briefly when the tray goes back in.

Sure. But this laser unit is not like a modern laser unit. The optics might have unglued itself. But that's something to check after the other stuff is running again. Might need a recap as well.

[Manolo Mos]

Hi. It's laser pickup is a KSS-123A, but can be KSS-120A, 121A and 122A too, they are equivalentes.
The CD player can be some problems, but the most probably in  a KSS-123A is mold in the lens. I've cleaned a KSS-120A with fungus, and its labour is workly. Then, when the laser pickup is cleaned, you have to check the adjusts, and adjust if it proceed.
Maybe the problem is a bit of dirt in the lens, in this case, you're in luck.
Don't waste time in capacitors issues. The people are focused in capacitors, nor in search the real cause of the failures.

[Smoky]

I lifted the cover and took some pictures. What looked like leaking capacitors is something more related to the glue used to hold them down:





The glue is what looks to be corroding the small wire jumpers nearby. Here you can see a strand of it crossing two jumpers:



The rest of the machine has just a light layer of dust on it:



Here's the power supply schematic. I'll check all of the voltages once the power supply board is cleaned up:



I read that the laser pickup in an OMS-7 is NEC part number HLPL 030020 (Nakamichi CA80255A).

The later Nakamichi OMS-7II used the SONY KSS-123A.

Btw, does anyone have a laser power meter that I can borrow

[wasedadoc]

J5 looks badly corroded.  Is it actually functional as a conducting link?

[Manolo Mos]

Be methodical and logical. Be the fault and search the cause of the fault. The capacitors are not the cause malfunctioning. If you replace capacitors, you waste time, money, and the fault still.

First of all, look RF signal, diode laser current.

[Gyro]

Do however check for excessive ripple on the supply rails.

[Smoky]

I'll check the voltages and ripple tonight after I clean the PC boards. If it wasn't for the power supply board being fastened from top and bottom I could have easily removed it from the chassis since cable connectors are all that attach to it. No soldered wires.

So it seems that determining if the laser is working is step #1. The service manual reads that the laser must measure .27mW with a laser power meter. So I'm dead in the water until I get one or borrow one because it must not be adjusted beyond .30mW or damage will occur to the pickup, plus, if the laser is borderline and barely reaches .26mW or so, performance will probably suffer. It would be nice to know if the laser will adjust to say .28mW brightness giving me an idea of its age.

There is one belt in the player and it looks to move the laser assembly across the disc.  If the laser checks out as being good I'll spring for a new one. There is a company in Germany that sells a silicone belt for this player and many others. They claim that they never stretch or lose tension and are far superior to black butyl belts. Has anyone dealt with this company before?

https://dindiki.com/?belt

Thanks for all of the replies too

[Manolo Mos]

Laser power meter is only orientative, RF signal and laser diode current are more important parameters.

[Smoky]

So if that's the case, the service manual shows a second procedure to set the current of the laser without a laser power meter by measuring across a 180 Ohm resistor (RM09) on the Auto Power Control PCB.

I was just imagining that it would be possible that even though the current feeding the laser circuit could be set correctly, that the laser could still be weak and that using a laser power meter would be the end-all and more accurate procedure.

So Manolo Mos, you're saying that the proper current level can never be reached if the laser is weak?

[wasedadoc]

Unless the laser is completely dead you should be able to see its red spot on a CD. Do you?

[Gyro]

The laser will only show as a dull glow to the human eye (it's an IR one). You should be able to see it more clearly with a mobile phone camera (it will show white).

Normally it's a bad idea to (re-)follow the service manual laser current adjustment procedure. This is intended for setup adjustment of a new laser. If you start playing with the laser current of an old laser you will will most likely shorten its life - if it's output has dropped over time, turning up the current isn't the solution.

[Manolo Mos]

So if that's the case, the service manual shows a second procedure to set the current of the laser without a laser power meter by measuring across a 180 Ohm resistor (RM09) on the Auto Power Control PCB.

I was just imagining that it would be possible that even though the current feeding the laser circuit could be set correctly, that the laser could still be weak and that using a laser power meter would be the end-all and more accurate procedure.

So Manolo Mos, you're saying that the proper current level can never be reached if the laser is weak?

Yes, the laser diode is subject to aging. While the laser diode is aging, the current needed for keep the same power is increasing. The laser diode has a servo circuit that keep the power at the same level, for this, the laser current is increased or reduced. Temperature affects too laser power. But I've observed another effect and is the following: I suspect the laser diode, while is ageing, loses the "laser" propierties, and the most important is Phase purity. Why do I think it? Because a lot of times, the laser keeps its power, however RF signal is low and noisy. I do not have optical instruments for to assure it, but I'm almost sure of it.

But, going to the problem to your cd player Nakamichi, be methodical. Try to see laser diode current, RF signal if it appears, check the laser optical if it is not clean.

The worst problem in KSS-121a and similar is fungus at optical.  I hope your laser pickup is free of fungus.


One question. Does the cd player lights the display when you power on?

[Smoky]

I cleaned the PC boards and removed any corrosion looking stuff on the jumpers. Whatever that glue is made of, when I peeled it off of the plated jumpers, copper shined out from under it So the glue eats through the plating and polishes the copper?

Anywho, I powered-up the player and the display came to life. It doesn't look very bright but it reads well:



I next went to reading the voltages and measuring the ripple on the power supply board .

The -24v rail measured -24.6v with 10.92mV of ripple.

The -12v rail measured -12.2v with 212uV of ripple.

The +12v rail measured 11.9v with 200uV of ripple.

The -7v rail measured -7v with 540uV of ripple.

The +7v rail measured 7.4v with 512uV of ripple.

The +5v rail measured 5v with 224uV of ripple.

The -17v rail measured -18.3v with 300uV of ripple.

The +11v rail measured 12.9v with 96mV of ripple. Yes, 96 millivolts of ripple:



But if you look close at the power supply schematic the +11v rail has no smoothing as it comes directly off of the bridge rectifier.

As for the laser pickup, the part number is stamped on it:



More to come...

[Smoky]

The door of the CD player opens, I put a CD in the tray and then close it. The CD spins. I see no light coming from the laser because it's hidden sitting parked close to the spindle. I press the fast-forward button, I key-in selection 10, I key-in selection 20, no movement whatsoever of the laser from its parked position.

So I turn over the player and remove the bottom cover:







Time to place an order

[Smoky]

One last thing. Look at the black pulley on that small motor shaft.

Well, it's not a black pulley! The belt has turned back into its gooey state and part of it spun around the small shaft.

When I went to throw out the old belt it stuck to my fingers, it's all over my phone, Jesus!

[Haenk]

I put a CD in the tray and then close it. The CD spins.

I'd say that's a good sign. I'm not sure if the power up flow chart is in the manual, but I assume the spin up happens after the laser detected a medium - so the laser might be OK. Don't fiddle with pots etc. for now, the new belt might be all it needs.

[Smoky]

Thanks Haenk. I'm not going to fiddle with anything until the belt arrives. Btw, in this CD player there is a hole in the tray where a separate sensor detects a disc.

But I do have some good news

I was able to turn the cogged gear and move the laser all of the way out of its parked position to the end where it would be tracking the clear edge of the CD.





With the CD in the tray, I can see a visible dot coming from the laser

[Zenith]

I suspect there's nothing wrong with this apart from the decomposing belt and the mess it's left. Are there any more belts to replace or other parts which haven't faced the challenges time presents well?

Apart from that, after maybe a bit of careful cleaning and lubrication, you will most likely have a hi-fi classic which you can either enjoy, or pass on via ebay to a true connoisseur who can even better appreciate its virtues.

I certainly don't believe you should be messing with presets, unless you absolutely have to and all alternatives have been exhausted.

[Smoky]

I'm hoping you're right Zenith. The belt arrived yesterday from Germany. It took nine days to make it to North Carolina USA:



I noticed that the end bumpers of the bar that guides the laser across the disc are soft and sticky too. Nothing is getting stuck to them though so I'll measure their thickness and find replacements. Maybe black rubber faucet washers might work



Anywho, if the new silicone belt works, I'll see if Dindiki sells belts for my Nakamichi LX-5 cassette deck because that repair is coming up   I hope the belts inside of it aren't gooing-up

[Smoky]

I tell you what, there is no black belt that grips like these silicone ones. Wow. Perfect tension and I don't think this belt will let go from the plastic pulley or the metal shaft for a nano-second. If Dindiki's claim of them never losing tension or stretching or slipping or drying-out, I'm sold



I hope they have belts for the LX-5 and my old Thorens turntable!

[andy3055]

Where did you say you got the belt from?