Technics SL-1700 no arm return help

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Tom_Technics
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Re: Technics SL-1700 no arm return help

Post by Tom_Technics » 22 Sep 2019 14:09

paddypaws wrote:
22 Sep 2019 06:51
Hi Tom_Technics, no as far as I can tell i'm the first person to take it apart judging by all the dirt that is inside. Are there any places to get a full service done on this deck, I might just do that. There seems to be loads of places that will do 1200's but obviously a 1700 is more complex. Its cosmetically excellent so would be worth doing.
Dirty insides are the number one sign that the machine has never been serviced. Unless your willing to send the deck via courier, you'd probably want to find someone fairly local to you. Where in the UK are you?

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Re: Technics SL-1700 no arm return help

Post by paddypaws » 22 Sep 2019 21:19

I’m in Fleet Hampshire between Basingstoke and Farnham.
I am willing to spend some money on it, and send it off, but I’m quite enjoying working on it. I can replace the electrolytic caps. I’ve got good soldering ability. I just wish I could get to the bottom of this arm problem. Looks like I’ll have to stumble across the problem rather than work out which part of the logic is faulty.

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Re: Technics SL-1700 no arm return help

Post by paddypaws » 24 Sep 2019 17:12

Japi Roelofs wrote:
16 Sep 2019 20:53
Hi paddypaws,

if you look at the SL-1700 page in the Library, you'll find —next to the user- and servicemanuals— the 'Technical Bulletin' that I uploaded a while ago. It describes a couple of types of 'misbehaviour' that can occur on both the SL-1700MK2 and it's fully automatic brother the SL-1600MK2.

The tonearm's automatic function works with sensors (for tonearm position detection), switches, and a small motor that drives a couple of gears. In the bulletin it is described how mis-alignment of the switches can cause trouble. For example Symptom B: "Cueing (UP) and auto return do not operate but cut operation is normal". ('cut operation' means pushing the Stop button, and tonearm returns to rest).

While this does not sound exactly like your problem, it could have something to do with the alignment of those switches.
Japi Roelofs , I may have not adjusted the switches properly. The technical bulletin is a little vague in how to adjust the switches 407 and 408 correctly. Am I right in thinking that when the arm is down and parked on the arm rest both switches are just closed by their respective shoulders on the cam? Any pointers greatly appreciated.

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Re: Technics SL-1700 no arm return help

Post by Japi Roelofs » 24 Sep 2019 17:27

The drawings in the technical bulleting are indeed a bit vague. Fig. 1 shows how the switches are supposed to be sitting when the arm is in the armrest. Fig. 2 and Fig. 3 show deflection of the switch position. I think in both drawings the deflected switch is shown in straight line as well as dotted line. So different faulty positions. But I might be wrong.

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Re: Technics SL-1700 no arm return help

Post by paddypaws » 24 Sep 2019 18:59

Japi Roelofs wrote:
24 Sep 2019 17:27
The drawings in the technical bulleting are indeed a bit vague. Fig. 1 shows how the switches are supposed to be sitting when the arm is in the armrest. Fig. 2 and Fig. 3 show deflection of the switch position. I think in both drawings the deflected switch is shown in straight line as well as dotted line. So different faulty positions. But I might be wrong.
Thank you! I’ll double check my switches.
I’ve bought all the capacitors for a recap which is next on the list.

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Re: Technics SL-1700 no arm return help

Post by paddypaws » 30 Sep 2019 15:52

I've checked the arm switches and replaced all the capacitors on the logic board and arm driver board and still no auto arm return! Grrrr. I'm going to throw some new CMOS chips at the logic board next. Any further ideas would still be much appreciated.

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Re: Technics SL-1700 no arm return help

Post by Tom_Technics » 30 Sep 2019 16:26

paddypaws wrote:
30 Sep 2019 15:52
I've checked the arm switches and replaced all the capacitors on the logic board and arm driver board and still no auto arm return! Grrrr. I'm going to throw some new CMOS chips at the logic board next. Any further ideas would still be much appreciated.
I did say quite some time ago that your symptoms indicate failed IC's in the arm control circuitry.

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Re: Technics SL-1700 no arm return help

Post by georgesgiralt » 01 Oct 2019 08:28

Beware, Those IC are static sensitive. So try to not replace fried ones by fried ones. Use proper handling and soldering procedure. Just my 2 ¢

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Re: Technics SL-1700 no arm return help

Post by paddypaws » 10 Oct 2019 18:13

Fixed!
Just to complete the thread as I've seen other threads with the same problem that did not report back the solution. I replaced ic458 and ic459 on the logic board (TC4023 and TC4011) CMOS chips. This fixed the auto arm return.
I'm very pleased I have a perfect SL-1700 MK2 now as I've serviced it mechanically and electronically.

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Re: Technics SL-1700 no arm return help

Post by Tom_Technics » 10 Oct 2019 19:17

paddypaws wrote:
10 Oct 2019 18:13
Fixed!
Just to complete the thread as I've seen other threads with the same problem that did not report back the solution. I replaced ic458 and ic459 on the logic board (TC4023 and TC4011) CMOS chips. This fixed the auto arm return.
I'm very pleased I have a perfect SL-1700 MK2 now as I've serviced it mechanically and electronically.
Congratulations Paddy! Early MOS technology is regularly troublesome. The most notable example in the world of Technics is the MN6042 Pitch Control IC as featured in the SL-150MK2 series and SP-10MK3. Did you find suitable modern substitutes or new old stock parts?

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Re: Technics SL-1700 no arm return help

Post by paddypaws » 10 Oct 2019 20:05

Thanks! I got some Toshiba chips from eBay. I guess they are new old stock.
I’m thinking I might replace the strobe LEDs as they seem quite dim (after all they are nearly 40 years old)

I’ll also replace the rca leads.