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Nakamichi MR-2
Nakamichi MR-2
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Old 18th October 2009, 04:18 AM   #1
gain wire is offline gain wire  Canada
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Default Nakamichi MR-2

Hi there, does anyone have a service manual/schematic for the Nakamichi MR 2 cassette deck? It's a professional version with balanced ins/outs and pitch control.

That's actually the problem, and yes I've cleaned the little 2K potentiometer, it didn't help.

Thank you
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Old 14th November 2009, 02:15 AM   #2
thinkzinc is offline thinkzinc  United States
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I have the same problem on the same deck! I just got one today in the mail from an ebay auction. Here's what I did. I'd rather have no pitch control and a working deck. So I pulled the second connector out (the bigger one) of the pitch board. The sound slowed down. Then I noticed that if I ground the board, the music slows down even more. So I connected a wire between the chassis ground and the board. Then I dialed the little black pot on the top until I had the right pitch. Done. Perfect.
To recap:
1. Disconnect the lower, bigger connector from the pitch board. You can find it by taking the lid off the deck and looking right behind the pitch knob.
2. Connect a wire from the chassis ground to the pitch board. There are two screws to choose from on the pitch board.
3. Adjust the little black pot on the top of the pitch board to the correct pitch.

I hope this helps!
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Old 25th May 2015, 06:05 AM   #3
selberg is offline selberg
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Hi, I discovered that my MR-2 developed the same problem and I know my Dad's had develop it earlier, but I'd like to shed more light on a solution than thinkzinc's answer.

The root of the problem is the 2k center-tap pot used for the pitch control went bad. I should have four connections - each side of a 2k resistor, one fixed in the middle with 1k to each of the sides and the last is the wiper which depending on the position of the knob will move from the one side to the other. By going bad, what happened is the wiper was no longer making contact for whatever reason.

The really bad news is that center tap pots are no longer commonly made - so it's near impossible to find a replacement part.

Inside the unit, there is a small PC board that contains the pitch control circuit. The chip is a quad switch. What is supposed to happen is that if the record line goes high, it flips the switches so that the center tap of the pitch pot is used. If the record line goes low, it uses the wiper of the pot. This was done so that you always recorded at the 'proper' speed and could thus use the tape on other tape players, but could adjust the speed on playback. Thus, people with this problem will find that an MR-2 can record just fine, but playback goes way to fast.

My solution was to remove the broken pitch control pot and insert a fixed 1k resistor. With this fix, the unit works fine minus the ability to adjust the pitch.

Here are the specifics of what I did.

First, I used the free open source software "Audacity" to generate a 5 minute 440 Hz wave file which I played out and recored onto a tape. 400 Hz is the common tuning value for concert A. I did this so I can use a guitar tuner to calibrate the playback speed. I had another tape deck at my disposal, but because the record functionality of the MR-2 is operation you could use it as well.

Then I opened up the MR-2 by removing the side screws. This was followed by removing the front cover which is attached by 8 screws (4 on top, 4 on bottom) and some plastic latches. With the front and side covers removed, I was able to remove the single screw holding the pitch control board, and then the board itself.

After seperating the metal bracket from the board, I desoldered and removed the pitch control pot - VR602. On the board, one of the leads from the removed pot went to R664 (It goes through two jumpers). I then soldered in a 1K resistor between the hole going to R664 and the neighboring hole. This is an identical configuration as provided by the center tap of the original part. I then shorted the other two holes to the lead of the resistor. So, you should have the three holes shorted together, then go through the 1k resistor to the last hole which continues to R664. With the soldering work complete, I put the board back in, reattached the connectors and turned it on.

At this point, the unit was operational, but not quite on pitch as the 1k resistor was slightly different than the original center tap value. So, I put in my 440Hz reference tape and plugged a guitar tuner into the headphone out. (I have a nice TC polytune tuner that emulates a strobe tuner. There are a number of apps for iPhones and the like that could be used as well. I do prefer the strobe to the needle display as it's easier to see very slight deviations from perfect.) I then used a screwdriver to adjust the trim pot (VR603) till the tuner locked in on "A".

I then put the front panel and cover back on and the unit is good to go. I suspect that the trim pot has enough range that adding the 1k resistor is not necessary. I just don't really know and wanted to keep the unit as close to factory specs as I could.

Hopefully this helps somebody in the future.
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