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Old 22nd December 2006, 01:45 AM   #41
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Hate it when that happens.........NOT!!!!!!!!! LOL
Dave
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Old 3rd September 2007, 09:19 PM   #42
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Default Nakamichi oms-4a

I just finished a repair on Nak oms-4a. I wish I would have perused this thread before I rolled up my shirtsleeves. Bought one used (non-working) on eBay for US 27.00. You guys described every issue my unit had. Oh, the frustration that could've been avoided!
Plays and sounds beautiful. BTW, mine had static on right channel output due to brown glue appled liberally on d/a converter solder connections. Cleaned it off and static vanished.
Thanks, all!
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Old 3rd September 2007, 10:20 PM   #43
tvi is offline tvi  Australia
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Can I join the que for a copy of the service manual?
If so may email is:
tvi at iinet dot com dot au

Regards
James
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Old 4th September 2007, 12:45 AM   #44
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Well I tried the heat soak-cold soak x 2 on the belt...It worked
Well , It worked for a short time anyway...I ended up purchasing a new belt and removing the loading tray assbly. --cleaning and relubing with a little white lithium grease.Now it works like a champ. TVI I will e-mail you the manual shortly.

Cheers Dave
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Old 4th September 2007, 12:50 AM   #45
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Default Re: Nakamichi oms-4a

Quote:
Originally posted by audioprobe
I just finished a repair on Nak oms-4a. I wish I would have perused this thread before I rolled up my shirtsleeves. Bought one used (non-working) on eBay for US 27.00. You guys described every issue my unit had. Oh, the frustration that could've been avoided!
Plays and sounds beautiful. BTW, mine had static on right channel output due to brown glue appled liberally on d/a converter solder connections. Cleaned it off and static vanished.
Thanks, all!
Thumbs-up on your successful recessitation of your Nak.Personally I prefer the OMS-4a over my OMS-7 these are real nice sounding units.

Dave
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Old 4th September 2007, 02:55 AM   #46
anatech is offline anatech  Canada
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Hi Dave,
Quote:
Personally I prefer the OMS-4a over my OMS-7 these are real nice sounding units.
Now that is weird!
Not only do I also own an OMS-7, but also an OMS-4! What are the chances of that??? My preferences are reversed to yours.

The alignment of the OMS-5/7 laser heads are normally out of kilter. When you dial these in the results are stunning. There was also a servo modification for the OMS 5/7 as they were originally designed to reject discs that were not up to redbook. Guess what? Yup, most CD's are not up to scratch.

So I don't know how much work you have done to yours, but you may have a machine there that you have never heard before. Also remove the "Sony bond" glue that we all love.

-Chris
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Old 21st February 2010, 09:23 AM   #47
Salar is offline Salar  Germany
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Uhm... is it possible, that I get the oms-4 service manual as well?
I would like to compare the servo circuitry of the OMS-4 with my OMS-5AII.
Thanks a lot,
salar at snafu dot de
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Old 23rd June 2010, 07:12 PM   #48
Salar is offline Salar  Germany
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Got a broken OMS-3 today. The resistor-fuse R260 is blown as well, as being described earlier in this thread.
It feeds the positve supply voltage of a transistor driving the disc-motor. I bridged R260 for testing purposes, the motor spins, and at least the first track can be played.
But some weird effect: Connecting the IR Diode board and the phototransistor to the main PCB will prevent the disc motor from spinning.
Disconnecting them (connectors 404 and 405 on the main board) makes the player play a disc and almost function normally
It also takes some time, until the player accepts "stop", like the disc motor was not able to spin down properly
Any ideas on that? But I have not removed the glue yet.
Also, I measure +/-21V before R260/R261, should be +/-15.
The voltage for the analogue output is around 13 to 14V...

Are the OMS3/OMS4 completely Nakamichi-homebrewn? (Except the PCM54HP)
I do not find the usual CX1018/CX1019 IC-combo from Sony for the RF amp and servo circutry, like in the OMS-7II/OMS5II
(As we all know, the OMS-7 / OMS-5 are N.E.C and Philips)
In the OMS-3, these circuits are on a sub-board beneath the transport, made from usual opamps and transistors...
All the best,
Salar

Last edited by Salar; 23rd June 2010 at 07:16 PM.
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Old 24th June 2010, 09:14 PM   #49
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It's very, very common for the IR disc detector to be oversensitive, making it give a no disc signal when a disc is present. The quick & easy, and usually permanent, fix for this, which still allows it to function as intended, is to simply wrap the top IR device board(forget if that's the led or the photodiode) in two or more layers of scotch tape. Works like a charm.
The OMS-2/3/4 players were largely made by NEC(boards by Nak in the OMS-4), with NEC borrowing heavily from Yamaha. The OMS-5/7 units were made by Kyocera, with boards by Nak and laser by NEC.
BTW, these units always need a healthy shot of silicone spray lubricant up into the platter motor to decarbonise them, which sounds very much needed in your case.
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Old 24th June 2010, 09:45 PM   #50
Salar is offline Salar  Germany
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Hello Stephen,
thanks a lot! I am not sure about being oversensitive, because removing the plugs of diode and LED with a disc inserted and the unit powered on makes the player play a disc immediately. But maybe the logic does not look for the drawer being opened/closed before to play a disc.
Any idea, why the player does not stop playing immediately when the stop-button is pushed?
The mechanism makes some noise after pushing the stop button, sounds like it tries to speed up the disc and stop it the same time so this could be a carbonmized contact/brush of the motor?
BTW, what is the exact height of the adjustment-gauge fo the disc-platter? 18.8mm as stated here before?
All the best,
Salar

Last edited by Salar; 24th June 2010 at 09:47 PM.
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