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Old 3rd May 2021, 6:55 pm   #1
samjmann
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Default Technics SL1700MKII from Hell!

Whilst I'm asking for some advice from the wise, I thought I might post details of the repair on this lovely old(ish) turntable.

First switch on - dead. No 12Vdc due to O/C 12v regulator.
Supply then normal, but PU arm motor (this is semi auto deck) running CCW all the time. This was due to every 4000 logic IC on the control board being defective in one way or another. Replaced the IC's one by one and the voltages in the stop mode all came back to normal bit by bit.

After this the deck would spin the turntable motor, the PU arm motor would lift the arm for cue, but not lift off at the end of a record. At this point the speed display was doing odd things, but this seemed a minor issue at this stage.
There was another 4011 in the record-end circuit that I had missed, this was defective too. As all of these IC's had one thing in common - the 12V supply, I thought I'd better check the Ic's in the speed display circuit - all of them were defective. This includes the LED driver and the AN6552 op-amp.

The deck now started, stopped, arm up/down, parked, but would lift off at the end of a record. This was due to a slight misadjustment of the gain preset on the arm control pcb. The test points were marked wrong in the service manual, in the end I set as I thought best which seemed to work.

I changed 12 IC's on this deck!!! It's very difficult to work on running, has any any experience of this type of mass failure on these before?

After re-assembling, I noticed on the end of the arm tube where the counter weight is, there seems to be a thread for a screw/bolt. Is this normal? Is something missing?

Regards, SJM
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Last edited by samjmann; 3rd May 2021 at 6:58 pm. Reason: Typo error.
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Old 4th May 2021, 9:13 am   #2
Alan SP15
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Default Re: Technics SL1700MKII from Hell!

Quote:
Originally Posted by samjmann View Post
After re-assembling, I noticed on the end of the arm tube where the counter weight is, there seems to be a thread for a screw/bolt. Is this normal? Is something missing?

Regards, SJM
The thread is to accept the extra weight SFPWG17202 if using a heavy cartridge/headshell.

Alan
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Old 4th May 2021, 2:20 pm   #3
G6ONEDave
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Default Re: Technics SL1700MKII from Hell!

Perhaps the faulty CMOS was caused by either an over voltage well beyond 18v or someone reverse connecting the supply. The supply reversal is my bet.

Dave
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Old 4th May 2021, 8:48 pm   #4
samjmann
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Default Re: Technics SL1700MKII from Hell!

Thanks Alan for the guidance on the arm weight and going to the trouble of even quoting the part number.

Thanks to Dave, yes I think that looking at the quality of repair to the rest of the unit, wrong or missing screws etc, a reversed supply or similar could have been the culprit.

I should have mentioned that the deck light had been changed to one of the new blue LED types. This is also fed directly from the 12vDC supply. Maybe this was the start of it all.

There was lots of odd cosmetic things done wrong as well, even the return cut switch had been fitted 180degrees out!

These are the domestic version of the SL1200/1210, same motor and arm, but with suspension, and auto return and motorised cueing. Top quality deck that deserves to live!

SJM
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Old 5th May 2021, 10:55 am   #5
qualityten
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Default Re: Technics SL1700MKII from Hell!

Great to hear of these 'repairs' gradually getting repaired! Is this an economic repair, or a labour of love?
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Old 6th May 2021, 6:50 pm   #6
samjmann
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Default Re: Technics SL1700MKII from Hell!

I do have a bit of a penchant for Technics gear of this era. Once fixed it looks and sounds very nice. For the most part, Technics items are quite serviceable, although I'll admit to a few notable exceptions. I ended up making a few extension cables for this one and sitting the entire control board and pu arm control pcb's on a bit of vinyl flooring on the top of the deck. I was then able to fault find without adding any more faults

I have had an odd 4013 logic chip fail before in the speed display circuit, but the arm control has normally being fine. I sure someone had an accident during fault finding on this - hence the extensive number of failures.

At least all the 4000 series Ic's are cheap. If it had been a specially masked micro, it would probably have been game over.

Regards SJM.
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Old 7th May 2021, 8:34 am   #7
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Default Re: Technics SL1700MKII from Hell!

Just out of curiosity, what's the motor like in the SL1700 Mk 2? I had an SL1700 Mk I for a while and found that the motor's behaviour was considerably different from the SL1200 (Mk 2 - I've never used an SL1200 Mk I). Though it had almost as much torque and would bring the record up to speed in less than half a turn from rest, it had no ability to brake the turntable, so if the turntable was spinning too fast as a result of cueing, scratching or otherwise manipulating the record, it had to slow down to the right speed itself. That made it pretty difficult to use for DJing.

Chris
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Old 8th May 2021, 3:59 pm   #8
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Default Re: Technics SL1700MKII from Hell!

From what I can see, the motor in the MK2 is the same as the 1200/1210. It is a much heavier motor altogether, and is PLL, whereas the MK1 just uses the mains as a speed ref via a strobe and neon lamp.

The strobe is much more complex on the MK2, it is an LED strobe from the control circuit, and you can 'see if the turntable is running 3 or 6 % fast by different bands on the turntable edge.

Overall the MK2 is the one to have, the fact that it's semi-auto shouldn't put you off. The arm height is adjustable whereas on the MK1 it's not. I'm not bashing the MK1, I've owned mine
since 1978 and I'm not selling!

SJM.
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