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Old 1st January 2013, 01:37 AM   #11
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There is no normal condition where the focus coil drive transistors should be getting hot in this player. In stop mode, the output voltage of the drive pair should be 0VDC, + or - 100mV, so neither xstor should be warm. In play mode, unless the platter height is way off, the mean average voltage should be under 1V, so should run no more than a little warm. If no abnormal voltages seen, remotely possible it could be a leaky npn xstor in the pair. If only hot in play, with normal voltages, it may be the focus gain is turned way too high(causing loud hissing from pickup) or the focus coil is partially shorted(never seen that on a kss152).
As for the STK6922/BX1201 thing, that was an IC failure issue that would cause the focus coil to melt down, not vice versa, and only seen on the very early players.
Must add that this whole generation of Alpine-Luxman players were pretty darned crappy and unreliable. I would not invest much time or money into this one.
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Old 1st January 2013, 07:32 AM   #12
Tomom is offline Tomom  Australia
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Thanks for input stephensank.

I guess that you may be right - I compared voltages from manual to the ones I measured (ah, I should have done it earlier!) and got the following:

Manual specs.: Q1302 (NPN) My measerement
B= 1V B= -0.6V
C= 11V C= 12V
E= 0V E= -0.03V

Q1301 (PNP)
B= 1V B= -0.6V
C= -11V C= -12V
E= 0V E= -0.03V

There is obviously a problem! It seams that you have been working on these units; does it mean that Servo processor is at fault (pin 11, FE0)? As I mentioned before, I replaced all 8 transistors with new ones.
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Old 1st January 2013, 07:36 AM   #13
Tomom is offline Tomom  Australia
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It didn't come out very clear; BCE on the left are manual specs. BCE on the right are my measurement (with negative voltage on bases and emitters...
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Old 1st January 2013, 08:04 AM   #14
Tomom is offline Tomom  Australia
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Forgot to say, they get hot only in play mode...
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Old 1st January 2013, 10:23 AM   #15
Mooly is offline Mooly  United Kingdom
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I honestly think you are imagining a problem where one doesn't exist.

How hot are they really ? Can you hold a finger on them for 10 seconds. Does the solder of the transistor leads sizzle water ? I know its difficult gauging temperatures but if it passes those "tests" I would say it was OK. If its as hot as a domestic radiator on full then thats not over hot for a transistor.

Look at your figures and theirs.
The manual says there is 1 volt across the base emitter junction of the NPN. That's not possible as a DC reading because the base emitter junction appears as a diode and limits the drop to 0.7 "ish" as a maximum.

The emitter voltage is really the voltage that appears across the coil. You measure 30 millivolts. That gives a DC current of 4 milliamps into 7 ohm. The transistor would be cold at that. Was that in stop mode ?

Unfortunately service manuals often give hugely inaccurate or just plain wrong information sometimes.

I honestly think your chasing something that doesn't exist
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Old 1st January 2013, 10:53 AM   #16
Tomom is offline Tomom  Australia
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I would describe my knowledge of electronics as "basic". I measured about 30 millivolts, that was in STOP mode. In PLAY mode it climbed up to 4 Volts.

I just try temperature test; both transistors have metal tab on the back (BD139/140). The one that is not as hot I can hold finger on, and I measured about 60 deg.C

The other one I could not hold finger on for more then a second, and I measured temperature of 110 deg.C (using multimeter and K type probe).
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Old 1st January 2013, 10:54 AM   #17
Tomom is offline Tomom  Australia
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Yes, they are cold in STOP mode, get hot in PLAY mode...
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Old 1st January 2013, 12:29 PM   #18
Mooly is offline Mooly  United Kingdom
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That does sound hot I must admit. Well it is hot, too hot really although such things do occur in commercial gear.

Have you had the player from new or might it have some history ?

It obviously all works OK... and 110 degrees is still technically OK for a silicon device but at those temperatures other effects may be noticed. Has the board discoloured around the transistor or its leads ? That would indicate long term running at high temperature which may suggest its normal.

Just to be sure on the info The focus drive showed 4 volts on the emitter of the driver pair of transistors ? That sounds high enough to be driving the pickup out of the block (and yet its all working) and would also pull nearly half an amp through the coil. I wonder if you are getting a true reading on the meter because the presence of high frequency AC (the focus error waveform) might be confusing the DVM.

After its been playing for a few minutes is the pickup (the top of it) hot ?

Have you tried as Stephen suggested and turned the focus gain down ? It's not a hugely critical adjustment. Note the position of the pot first. Be sure it is focus gain and not focus bias or offset you adjust (assuming it has those adjustments)
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Old 1st January 2013, 10:47 PM   #19
Tomom is offline Tomom  Australia
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There is no signs of discolouration or burns on the board. And the top of pick-up does not get hot?!

What precaution should I take if high frequency AC is suspect to confuse the DVM? As transistor is getting so hot, I think reading may be close to correct.

I have attached two pages of adjustment procedure that can be done, and I will do it when I get test CD (is it possible to copy such CD from somewhere - it will cost me $50 to buy). Step No. 4 is not exactly clear to me; it requires CD and Oscilator as input, what is monitor, and I do not have 2 pointer AC voltmeter (or I don't know what it is...).

The player does have a history , I know just a part of it. I bought it from a guy on eBay for $10, and I think he got it on some kind of market or so, he said he didn't know how to fix skipping problem (which we managed to do) so he was selling it as it is.

I haven't try Stephen suggestion yet, as I said I would like to do it properly, not just by "feel" so I would prefer to have that test CD...
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Old 1st January 2013, 10:49 PM   #20
Tomom is offline Tomom  Australia
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Here is adjustment procedure...
Attached Files
File Type: pdf img050.pdf (473.0 KB, 16 views)
File Type: pdf img051.pdf (557.2 KB, 7 views)
File Type: pdf img052.pdf (928.1 KB, 7 views)
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