Adjusting EF tracking KSS-240a TEAC VRDS - diyAudio
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Old 1st August 2013, 02:58 AM   #1
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Default Adjusting EF tracking KSS-240a TEAC VRDS

Does anyone know how to adjust the EF Tracking on a KSS-240a Laser head in a TEAC/Esoteric VRDS-T1??

The Esoteric service manual isn't much help as it only states how to adjust settings on the Teac Servo board. I found a service note that talks about adjusting the Focus bias pot for the clearest eye pattern. but nothing about the EF tracking.

I replaced the laser assembly and adjusted the servo board as per the service manual. and the unit would play a cd but would skip badly once it got past track 9 or 10. I adjusted the Focus Bias pot per the service bulletin for the cleanest eye pattern and it got a bit better. but not much. then out of frustration i tweaked the EF tracking pot and it hasn't skipped since. I figure i must have it close at this point. but I would like to adjust it the proper way before buttoning it up.

In other service manuals I have seen section where you look at a specific test point and then adjust the EF while fast forwarding or fast reversing for even tracking above and below the zero line. I would assume something similar but I can find no information on the subject anywhere. even reading other VRDS service manuals. they seem to get less detailed in each one. some don't even state what track to use for adjustments!
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Old 1st August 2013, 03:08 AM   #2
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I think i found my answer...sort of...

Sony CDP790 and KSS240 Restoration Project - diyAudio
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Old 1st August 2013, 03:11 AM   #3
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Ok Stephen Sank's note here I think is really critical.

The other two pots on the 240 are EF balance & Focus Bias. The latter is correctly set by clearest, max rf pattern, but the EF bal can't be precisely set that way, often not even close to best. The best way to set EF bal on virtually any player is to put a cd on pause, then look at the tracking error output signal(TE or TER, usually). If you slow down your scope a lot, you will see the kick pulse, as the laser is told to jump track to stay on the same point on after each revolution. Proper EF balance is set by having the positive & negative going peaks of this pulse at equal length above & below the signal mid line. This is perfect EF, and is critical for proper tracking.
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Old 1st August 2013, 10:22 PM   #4
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There's a picture of E-F balance procedure in lots of Sony manuals...see below. The basic principle is as you describe.

Is it best set at a particular point on the CD, such as half-way maybe? I don't know what's on YEDS-18. Note it says it (and the focus bias) should only need adjusting for a new mech, which I guess is why they moved the adjuster to the mech itself.

After an epic trudge through fixing every problem a CDP can have, I discovered my 101 has run out of adjustment on the E-F pot . Fine until the last track. I hate it when that happens.
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Old 1st August 2013, 11:06 PM   #5
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well Track 1 of the YEDS-18 test disc is listed as:
01 - Air Glow-Theme of CD, emphasis on


while the adjustments in the VRDS T1 service manual say to use track 4
04 - 100Hz Sine Wave, 0 dB, L & R, emphasis off

I don't know what difference it makes?

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Old 2nd August 2013, 01:34 AM   #6
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A themed, impressionistic test disc...Sony is endearingly considerate at times

I don't understand, either. Does the alignment of the error signal vary, or does the player's tolerance of misalignment change? One or other reason must explain why later tracks are the first to suffer. If the alignment varies, then adjustment should be done half-way through the CD. If not, then it shouldn't matter.

AFAIK the adjustment is to the gain applied to either the E or the F photodiode, to make the peak amplitude of the two signals equal. This seems simpler than it is, considering that the laser head is supposed to move to make them equal anyway. I assume the head seeks equal area, rather than equal amplitude.

Misadjustment leads to physical misalignment. The signal remains centred with respect to area as a result, but not with respect to amplitude.

Even if all this is true, it still doesn't directly explain the symptoms. As the CD plays through, the curvature of the track reduces, and so does the average rate of radial movement of the head. Why should either make a difference to the E-F balance, or the player's sensitivity to imbalance?

Anyway, the sure option would be to adjust half-way through the CD.
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Old 2nd August 2013, 02:14 AM   #7
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The VRDS service manual has a section on adjusting the Focus Gain adjustment. using track 4 (100hz) inject a 1.05khz 10V P-P signal into the FE2 pin on the test connector through a 100K resistor. then observe the signal and the FE1 signal on a dual trace scope and set the F.Gain so that the phase of the 2 signals is 90 degree's apart.

The Tracking gain is similarly adjusted injecting a 1.09khz signal into the TE pins.

So I have no idea how or why the 100hz signal on the disc has anything to do with those adjustments?

Then I found a separate service note about adjusting the Focus Bias pot on the laser block. but there was never any mention about adjusting the EF pot. and my unit would not track the last few tracks on a disc after replacing the laser assembly. Tweaking the EF control has fixed that problem but I need to get back in there and adjust everything correctly.

I found a local service dept friend that will lend me the TEAC MCD-111 disc so I can do the adjustments per the service manual at least.
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Old 2nd August 2013, 02:59 AM   #8
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Your symptom does NOT suggest a servo misadjusment fault at all. It is much, much more suggestive of a mechanical problem. First check the obvious- drive gear teeth, gear axle grease hardening, guide rail lub, cable interference. Then check that there is no warpage or other defect in the guide track opposite the rail or with the rail mounting.

As for the adjustments, it does not matter what disc or where on it that you do the EF/tracking balance, unless the disc is just plain defective. On the focus & tracking gains, IGNORE the manual. The best way to adjust, which I've written here on other threads, is to turn each gain down(i.e., less coil noise), while playing a known good disc, any good disc, until you see the RF waveform start to collapse, then turn gain back up about 1/6 to 1/5 of a turn. Focus bias/offset just requires going for maximum height and clarity of RF waveform on ANY disc. Tracking offset can, most of the time, be done in stop mode, just going for 0vdc on the TE/TER output test point, or can be set during my noted-above EF procedure, simply planting the average center line of the waveform on 0vdc line on scope, with scope in dc coupled mode, of course.

Honestly, I don't know of ANY cd player/transport that actually requires a proper test cd to do proper alignments, and I've been in cd service for as long as cd has been around. I have not used a test disc since 1984. Literally.

The only special tools generally ever needed are the optical laser power meter(e.g., Leader LPM8000) for laser power adj., and an accurate >/=10mHz frequency counter for VCO adjust(rarely needs adj on most players).
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Old 2nd August 2013, 03:55 AM   #9
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I can't see how the frequency of the signal on the disc is significant. More likely is the position of track 4? Phase difference at a particular frequency is a measure of delay...the reaction time of the control loop. I wonder why the focus and tracking frequencies are so close, and yet not the same. Curiouser and curiouser.

I generally end up going through all the adjustments at least twice, and then tweaking the focus gain to minimise mechanical noise from the head, but I've never worked on the later types with adjusters on the mech.

I've learned to appreciate the old Philips single-beam, swinging-arm system.
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Old 2nd August 2013, 04:14 AM   #10
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Quote:
Originally Posted by stephensank View Post
Your symptom does NOT suggest a servo misadjusment fault at all. It is much, much more suggestive of a mechanical problem...
Generally I agree, and respect your experience. However, my CDP101 definitely begins to skip on later tracks when E-F balance is misadjusted. It is especially prone to suffering drag from cables to the head that can cause similar problems, so I've been scrupulous in eliminating that as a cause.

It is quite possible that the problem adjusting E-F balance, and the skipping, have a common cause, like storks and babies. However, when Zero reported that adjustment cured his problem, I'm happy to suspect a direct connection. I guess we'll soon find out.
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