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Old 24th September 2005, 08:08 AM   #1
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Default Akai GX-95

This Akai GX-95 which is the first generation GX-95 from Akai and does any one of you know its bias frequency?
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Old 29th September 2005, 03:40 PM   #2
anatech is offline anatech  Canada
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I don't know the frequency but 105 KHz was popular. The best way to figure it out is monitor the record traps on the audio side and tune the oscillator up and down (note the starting frequency first). Note the frequency of minimum output for each channel. The proper frequency should be close and would be an integer value.

I hope there has not been too much "gerfingerpoken" already.

-Chris
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Old 1st October 2005, 06:12 PM   #3
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Thank you anatech for you information and as I know from the Service manual that the GX-95Mk2 is having a bias frequency of 105khz but the the tuning range of GX-95 doesn't go over 102khz!
That's the problem, it seems that the value should be lower than this and I don't have any information for this.

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Old 1st October 2005, 06:18 PM   #4
anatech is offline anatech  Canada
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Do you have any way of testing the capacitors? I have found in servicing that the caps in this circuit can either open partially or short. The circuit does run somewhere around 60 ~ 90 VAC. That can be hard on the caps.
It's not unusual to see the bias oscillator dead either on the older machines. Same cause. A defective cap may take out a transistor as well.

-Chris
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Old 4th October 2005, 11:52 AM   #5
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Today I checked the cap and even subtitute with a new cap having the same value that`s 150 pf and checked that the adjustable frequency range is around 82khz-95khz,and the previous value 102khz posted should be incorrect.
And 95mk 2 should be an improved version of this earliest 95 version and usually having a higher bias frerquency in this case 105khz.
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Old 4th October 2005, 12:45 PM   #6
anatech is offline anatech  Canada
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But where do you see the minimum signal on the audio side of the traps? That will be very accurate, no matter what anyone says.

-Chris
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Old 5th October 2005, 10:55 AM   #7
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Default apples

The lowest mean value as I measure the bias traps is -6.7V!
at 90khz.
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Old 5th October 2005, 02:31 PM   #8
anatech is offline anatech  Canada
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This would be an AC value. I use an oscilloscope as the average meter will not indicate a null easily at that frequency. If you can't get an oscilloscope, you can make an RF detector probe for your meter. Essentially it's a signal diode in series with your probe and a small (0.001uF) cap from the probe to ground. Have a look on the web to make sure I have it right.

So you need to find the lowest point, or null. 95KHz was another common frequency used.

-Chris
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Old 16th October 2005, 01:58 PM   #9
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I did solve the bias problem for Akai GX-95.
Now I have to bring out another problem found in the other GX.95 mk2 that's during calibration,the level functions but the bias has no response!?
and I have checked against another working GX.95 mk2 and found that the measured voltages are correct and I just couldn't get it right.
And I suspect the problem is caused by the calibration switch.
Any comment.
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Old 16th October 2005, 03:37 PM   #10
anatech is offline anatech  Canada
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Hi Mike,
The bias control should vary the bias level to the record head. You can see this with an oscilloscope or an RF probe for your meter.

Your calibration switch should be working or you wouldn't see the record level change. Can you post a picture of the front panel controls? This might give us a clue how it's set up.

So how did you figure out your bias problem and what was the frequency?

-Chris
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