Technics SL7 Troubleshooting

[Mohan Siribadda]

My Technics SL7 Direct Drive Turntable works intermittently. For example, when I press the starter switch (after the player is powered) its turntable momentarily rotates and stops. Some times, when you press the starter switch, it works perfectly, but most of the time the turntable momentarily rotates and stops.

Since, it is a direct drive TT, I do not think it has a belt drive. Is it due to poor electrical contacts or defective switch.

Can DIYer help me to overcome this problem?

Cheers

 

[kstagger]

the problem with many of the DD turntables (heck - just about any late 80s mass turntable belt or otherwise) is the extra complexity. Cracking open my old Hitachi L55 to fix a problem was a nightmare with the speed controllers, servos, and whatnot in there.

It _could_ be a defective switch... or perhaps an aged capacitor? or bad solder joint or cracked PCB.

Maybe it's time for another turntable or else you'll have to get in the Technics and start measuring and experimenting.

 

[kevinahcc20]

You don't indicate the age of the TT but I will assume it has a good number of years on it. I would do the following:
1. VinylEngine has the service manual - download it
2. Get a list of all of the electrolytic caps in the power supply & order them & replace them.
3. Clean all of the control pots and board interconnect pins with DeOxit
4. If the problem persists see if the service manual troubleshooting guide addresses your problem...if yes follow the instructions.
5. Still no luck come back here with what you have done & found & seek further guidance.

 

[Mohan Siribadda]

Technics SL7

Dear Kevin & Kstagger

Thanks for your response, it was one of the award winning TT produced by Technics in 1983. Upto now it was working flawlessly, except changing the arm control belt. It's a linear tracking, DD turntable. Sound seems very good.

I have down loaded the service manual, I will go through it and see whether there any troubleshooting pertaining to present issue.

The specific problem is when I press the start button, the turntable rotates momentarily. Some time it works, but most of the times it doesn't.

Thanks for your kind response.

Best regards

 

[Shaun]

I have owned Technics SL-7 and SL-10. Of the two, my fondest memories are of the SL-7.

Have you had a look under the hood? The most likely fault with intermittent operation is poor (or intermittent) electrical continuity somewhere. The first I would suspect is a solder joint failure on the PCB assembly. See the following links for more info and pics:

Soldering - Wikipedia, the free encyclopedia
Failure in solder joints

 

[Mohan Siribadda]

Technics SL7

Dear Shaun,

Thanks for your suggestion, I am going to check the PCB connections. Also, I will clean all the connections and revert back.

I really appreciate your support given to fellow DIYer.

Cheers

 

[Number13]

IF I recall correctly, that table also has two small idiot-proofing
switches. In the back of the platter area there is a switch that senses the edge
of the record and one that senses that the player is closed. Be sure to check and clean those.

 

[Mohan Siribadda]

Technics SL7

Dear Number 13,

Thanks for your suggestion, I will make sure to clean these switches to see whether the TT will operate smoothly. Kindly let me know your referred switches are the sensor slits on the platter? or something else?

I checked, I find some slits (six no) on the platter located symetrically.

Kindly advise me.

Regards

Mohan

 

[Number13]

The sensor slits on the platter tell the table what size
record is being played. The likely culprit, the "cover closed"
switch is at the back of the player. It is easy to get to once
you have the bottom off.

 

[Mohan Siribadda]

Technics SL7

Dear Friend,

Thank you for your detailed explanation. I will take into account of your suggestions when I troubleshoot the TT. Yesterday, I cleaned the all switch contacts using camera lens cleaning liquid, I found the TT was working without a problem, I have not come to any conclusion yet, I will continue to check the TT operation for few days.

I will revert back.

Cheers

 

[aardvarkash10]

try here - worked for me.

I think Shoji had an inside line on the technical aspects...

 

[OXAUDIO]

I am attempting to repair a SL-7 in which the brass pulley had dropped off the worm drive assembly's shaft, in the process throwing off the small drive belt, with the result that, although the turntable ri=uns at the correct speed, the PU arm doesn't track across the record. Having refitted the pulley and attemped to secure it in place with a dab of superglue in the pulleys centre hole, only to have it fall off again, does anyone have any suggestions as to how this fault can be rectified. It would have been better, IMHO, if the pulley had been held in place with a circlip, but there is no provision for this. The drive shaft, as some will know, is highly polished steel,so there is no grip between this and the metal pulley.

 

[OXAUDIO]

Since my previous post, I've secured the pulley to the iworm drive shaft with Loctite 2700, checked that the arm is correctly positioned and is free to run along it's track, so every thing is mechanically OK. However although the turntable spins with a record in place and the lid closed, the PU arm doesn't move from the start position. In addition, the stylus will only lift and lower if the lid is open and the 'lid closed' switch manually pressed and held in. This could, I guess indicate that said switch is intermittent, so a clean or replacement is needed, but the arm still doesn't move from the rest position even with the lid open and switch manually operated as above. The forward search doesn't work, either, so could it be a problem with that switch? I've had the turntable and bottom cover off and can see no evidence of bad solder joints, so am beginning to suspect one or more of the control ICs (101, 201, & 301) Incidentall the main PCB layout on the SL7 on which I'm working differs from that shown in the service manual on the Vinyl Engine site, although, AFAIK, the circuit is the same.