Technics SL-1700 MK2 No auto-return or Stop, but Cue working

[KeithD]

Recently picked up one of these. The cueing motor belt was disintegrated. So, put a new one one and the cuing now works; however, the table does not auto-return at the end of a record, and when pressing the Stop button, nothing happens. This is a bit of a mystery to me since these seem to be two separate activators. The auto-return is activated by an optical switch sensing how far the tone arm has moved to the center, as far as I can tell. While the stop button should activate the cue and return feature anywhere on the record. It seems odd because the first function for both return features is for the cue motor to lift the arm. So, I'm suspecting this is a signal in the circuitry that is not getting through to turn the motor on to cue the tonearm and then return. If I manually move the belt the tonearm cues up and if I continue moving the belt, the tonearm returns, so I don't think there is anything mechanically wrong. Any insights as to which electrical component (transistor or IC) that might be the culprit? Most threads I've seen on this the table doesn't cue or auto return, and usually the fix is just a new belt. Not the case here. Any help appreciated.

 

[KeithD]

Well, just to wrap this up, the issue seemed to be with IC456. The issue with following the test procedure in the SM is you have to detach everything screwed to the bottom of the plinth so that all the boards remain connected electrically and you can measure the test points. A hassle, but the attach points are fairly obvious and everything is screwed in place. No plastic holders or other troublesome hold downs.

Once I had the boards/PS/transformer detached I was able to do the first test: pin 10 on IC456. I was not getting the square wave pulse as specified in the SM on page 6. I was able to trigger the auto return by touching pin 10 with a screw driver, probe of a DMM, etc., though it was a bit random what would trigger the auto return. I figured it was the tiniest amount of charge picked up by the metal probe. Pressing on the IC made no difference, so cold/cracked solder joint seemed unlikely. There are several identical ICs on the board. IC455 controls the cueing, which was working and is the same IC as 456. So, I decided to swap the two ICs. I figured either the problem would move with the IC, or I'd get lucky and the faulty part of the IC would be unused in the new position. Fortunately, it was the latter, and once the ICs were swapped I had full auto-return functions working along with cueing. A nice ending for this wonderful table.

 

[Monicker1]

I have the same TT and I have discovered the same issue. Just had it serviced a year ago. I was wondering if I physically damaged it.

 

[KeithD]

I have the same TT and I have discovered the same issue. Just had it serviced a year ago. I was wondering if I physically damaged it.

Seems doubtful that just having it serviced would do damage. It's been well-documented that ICs go bad on this table (same with the 1600, I think). If you are having an issue with cueing and/or autoreturn, you first have to confirm the motor for the auto functions is turning on when called for. If it is, then the issue is mechanical with the gearing or limit switches in the tonearm mechanism. If the motor is not turning on, then you have an electrical issue: either a connection is bad, or (as in my case) a signal is not being sent to turn the motor on. This needs troubleshooting by someone who can read a schematic and has some experience with the automatic functions of a turntable.

 

[Wayne Tj]

I had the same problem and couldn’t figure out what component was bad so I decided to start replacing boards, luckily there was someone on eBay parting out an SL1700 MKII. I don’t recall the name of the board, but it was the one on the left side opposite the arm.

It worked great until one of the gears in the mechanism that returned the arm wore out. I bought a 3D printed gear and it’s been working solid now for 2 years.

 

[picturesd]

Well, just to wrap this up, the issue seemed to be with IC456. The issue with following the test procedure in the SM is you have to detach everything screwed to the bottom of the plinth so that all the boards remain connected electrically and you can measure the test points. A hassle, but the attach points are fairly obvious and everything is screwed in place. No plastic holders or other troublesome hold downs.

Once I had the boards/PS/transformer detached I was able to do the first test: pin 10 on IC456. I was not getting the square wave pulse as specified in the SM on page 6. I was able to trigger the auto return by touching pin 10 with a screw driver, probe of a DMM, etc., though it was a bit random what would trigger the auto return. I figured it was the tiniest amount of charge picked up by the metal probe. Pressing on the IC made no difference, so cold/cracked solder joint seemed unlikely. There are several identical ICs on the board. IC455 controls the cueing, which was working and is the same IC as 456. So, I decided to swap the two ICs. I figured either the problem would move with the IC, or I'd get lucky and the faulty part of the IC would be unused in the new position. Fortunately, it was the latter, and once the ICs were swapped I had full auto-return functions working along with cueing. A nice ending for this wonderful table.

Hi KeithD, I read about your problem with the Technic SL 1700MKI. I have the following symptoms on mine: when the record ends, the tonearm lifts and the record continues to spin but the autoreturn does not work. When I press the STOP button, the tonearm returns and the record stops spinning but the cueing motor continues to run, then I press the cueing button and the tonearm down to the rest position. Should I swap ICs it too?

 

[KeithD]

Hi KeithD, I read about your problem with the Technic SL 1700MKI. I have the following symptoms on mine: when the record ends, the tonearm lifts and the record continues to spin but the autoreturn does not work. When I press the STOP button, the tonearm returns and the record stops spinning but the cueing motor continues to run, then I press the cueing button and the tonearm down to the rest position. Should I swap ICs it too?

Your description does sound like the mechanical parts are working, but the signals are not being properly sent for each function. That does seem to be an electrical (IC) issue. However, be aware there is no guarantee swapping ICs will solve the problem. Not every circuit in the IC is used in each position, only some to perform the needed function. It seems to me your table has circuits in more than one IC not functioning: I don't think one IC controls all of the functions that are not working in your table.

 

[picturesd]

Thank you very much, I am a beginner at this and I want to fix my turntable. Are ic458 and ic459 on the logic part of the control board (TC4023 and TC4011) CMOS the same thing or are they four different things?

 

[KeithD]

Thank you very much, I am a beginner at this and I want to fix my turntable. Are ic458 and ic459 on the logic part of the control board (TC4023 and TC4011) CMOS the same thing or are they four different things?

Do you have the service manual? The block diagram for the TT is on page 5, and will allow you to see which components are involved in each circuit:



Additionally, page 6 has a trouble shooting flow chart that tells you which component to check and tests to perform for each type of problem.



I found these pages and understanding them crucial when finding the fault in my TT.

 

[KeithD]

To answer your question about the IC's more directly, IC458 and 459 are different chips (different supplier numbers), so I assume they are not the same. I have no idea what the internal logic is on those chips.

By studying the diagrams in the SM, I was able to narrow down where the problem was on IC456 (SVITC4011BP). It appeared to me only some of the circuits on each chip on the board were being used, so I determined swapping two identical chips might give me working circuits where I needed them. Had the swap with IC455 not worked, I would have tried one of the other identical ICs.

 

[picturesd]

Ok guys. What I noticed on the entire board on my SL 700MKI are Integrated Circuits with mostly the same markings. I marked in the last photo whether I need to replace these ICs, or replace them all. Of course not me because I would screw everything up with soldering, but my good electronics friend. Thanks everyone for the great help. If everything works out as it should, I'll open a bottle of red wine with some good Progressive Rock.

 

[picturesd]

Thank you very much @KeithD . After your advice and the advice of other friends I succeeded, the main culprit is the ICs. I replaced 6 ICs and did not replace the three ICs that have capacitors on them. I am very happy because now everything works on my turntable which is literally new. thank you for all.