Nakamichi OMS-7 CD Player from 1985 - Page 1
Forum section: electronics / repair

author: Smoky
author_rank: Frequent Contributor
timestamp: March 08, 2024, 02:23:10 am
content: 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 inFrom 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

author: Haenk
author_rank: Super Contributor
timestamp: March 08, 2024, 09:42:31 am
content: 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.

author: wasedadoc
author_rank: Super Contributor
timestamp: March 08, 2024, 10:05:21 am
content: 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.

author: Zenith
author_rank: Frequent Contributor
timestamp: March 08, 2024, 10:16:06 am
content: 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.

author: Haenk
author_rank: Super Contributor
timestamp: March 08, 2024, 03:34:19 pm
content: Quote from: wasedadoc on March 08, 2024, 10:05:21 amSure. 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.

author: Manolo Mos
author_rank: Contributor
timestamp: March 08, 2024, 04:12:40 pm
content: 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.

author: Smoky
author_rank: Frequent Contributor
timestamp: March 08, 2024, 05:17:51 pm
content: 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

author: wasedadoc
author_rank: Super Contributor
timestamp: March 08, 2024, 05:34:28 pm
content: J5 looks badly corroded. Is it actually functional as a conducting link?

author: Manolo Mos
author_rank: Contributor
timestamp: March 08, 2024, 06:31:50 pm
content: 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.

author: Gyro
author_rank: Super Contributor
timestamp: March 08, 2024, 07:52:13 pm
content: Do however check for excessive ripple on the supply rails.

author: Smoky
author_rank: Frequent Contributor
timestamp: March 08, 2024, 08:58:48 pm
content: 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/?beltThanks for all of the replies too

author: Manolo Mos
author_rank: Contributor
timestamp: March 08, 2024, 09:01:52 pm
content: Laser power meter is only orientative, RF signal and laser diode current are more important parameters.

author: Smoky
author_rank: Frequent Contributor
timestamp: March 08, 2024, 09:26:45 pm
content: 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?

author: wasedadoc
author_rank: Super Contributor
timestamp: March 08, 2024, 09:48:22 pm
content: Unless the laser is completely dead you should be able to see its red spot on a CD. Do you?

author: Gyro
author_rank: Super Contributor
timestamp: March 08, 2024, 10:21:23 pm
content: 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.

author: Manolo Mos
author_rank: Contributor
timestamp: March 09, 2024, 12:39:37 am
content: Quote from: Smoky on March 08, 2024, 09:26:45 pmYes, 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?

author: Smoky
author_rank: Frequent Contributor
timestamp: March 09, 2024, 02:57:39 am
content: 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 itSo 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...

author: Smoky
author_rank: Frequent Contributor
timestamp: March 09, 2024, 03:08:46 am
content: 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

author: Smoky
author_rank: Frequent Contributor
timestamp: March 09, 2024, 04:13:16 am
content: 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!

author: Haenk
author_rank: Super Contributor
timestamp: March 09, 2024, 05:12:10 pm
content: Quote from: Smoky on March 09, 2024, 03:08:46 amI'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.

author: Smoky
author_rank: Frequent Contributor
timestamp: March 09, 2024, 08:54:35 pm
content: 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 newsI 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

author: Zenith
author_rank: Frequent Contributor
timestamp: March 09, 2024, 10:44:13 pm
content: 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.

author: Smoky
author_rank: Frequent Contributor
timestamp: March 22, 2024, 01:53:35 am
content: 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 workAnywho, 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 upI hope the belts inside of it aren't gooing-up

author: Smoky
author_rank: Frequent Contributor
timestamp: March 22, 2024, 02:18:20 am
content: I tell you what, there is no black belt that grips like these blue 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 soldI hope they have belts for the LX-5 and my old Thorens turntable!

author: andy3055
author_rank: Super Contributor
timestamp: March 22, 2024, 02:26:27 am
content: Where did you say you got the belt from?

author: Smoky
author_rank: Frequent Contributor
timestamp: March 22, 2024, 02:34:35 am
content: That'shttps://dindiki.com/Click on belts for CD players or turntables.

author: Smoky
author_rank: Frequent Contributor
timestamp: March 22, 2024, 03:01:51 am
content: She livesLast week I burned a new CD of test tones fromhttps://www.wavecor.co.uk/testdisk.htmlAt the bottom of the webpage, I downloaded all 80 tracks to one CD. Tomorrow, I'm going to see how well the CD player responds to it. I'll try multiple frequencies while the outputs are connected to the oscilloscope. I want to see how well each channel is balanced.The Test CD's website even has a cover-art file for the CD's jewel case

author: Haenk
author_rank: Super Contributor
timestamp: March 22, 2024, 06:08:31 am
content: Great. Happy to see another Oldtimer brought back to life 😀

author: Smoky
author_rank: Frequent Contributor
timestamp: March 23, 2024, 01:33:20 am
content: I just connected the oscilloscope to the outputs of the CD player and inserted the Test CD and and pressed play.Both channels of the CD player are working and the oscilloscope picks up the signals very clearly.I then switched the oscilloscope to DC coupled, and with the CD player sitting at idle with no CD playing, I did notice that the right channel has about 6mV of DC offset:The left channel has about -108uV of DC Offset:Is this a level that I should be concerned about?

author: akasaka
author_rank: Regular Contributor
timestamp: March 23, 2024, 02:29:56 am
content: Given most amps have decoupling capacitors on their inputs, I'd not stress it much. Though also, given that the line level is 775mV for 0dB, that might take out some dynamic range...Could there be a trimpot somewhere on the board nearby to set the centerpoints of the output buffer opamp?

author: wasedadoc
author_rank: Super Contributor
timestamp: March 23, 2024, 06:39:40 am
content: Measure again with a 22k load resistor.

author: Smoky
author_rank: Frequent Contributor
timestamp: March 24, 2024, 12:29:41 am
content: Thanks Wasedadoc, I'll do just that. I'm going to try modifying some older 75 Ohm dummy loads that I have into values that I can use in the future. The ends look just like 50 Ohm typesMy old Rockwell router has a spanner wrench that matched the flats:Using the hot air station and the soldering iron, the parts fell away:I found a 1w PR01 resistor that measured 22K ad soldered it on the end:I inserted the contact into the body of the BNC and tightened the cap back on with the loose lead coming through:I used hot air station and the iron to flow fresh solder:I'll use this load in a BNC "T" to run the test again on the CD player outputs

author: wasedadoc
author_rank: Super Contributor
timestamp: March 24, 2024, 10:24:11 am
content: Words fail me!