Sl-7 Disassembly Problem

turning japanese
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xactifan
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Post by xactifan » 22 Jan 2010 17:41

Hello,
I used your precious procedure. I 've tested the two sides of power transformer:
one with two yellow wires:continuity ok
other with four wires: blu blk wht brn, I found continuity only between
blk and wht. Is it normal? Where do I mesure the values , at the same place?

hunter on the way...

Athermos
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Post by Athermos » 22 Jan 2010 18:03

Hi there,

You will have to compare the values you get from the other SL7 in this regard.

Go on to the next step, power it up and check for the rectified DC value and the value of the supply that is being fed to the motor PCB.

Check in particular for blown fuses and/or transistors in the power supply.Compare the voltages at various parts of the power supply and elsewhere with the values obtained from your other SL7 under similar conditions.

Above all, proceed logically and try to pinpoint the cause of its recent behaviour.


Cheers,

Shoji
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Post by Shoji » 22 Jan 2010 18:28

Hello. Is sad to hear you are having this problem. Is necessary to make the check of power supply for correct level at the regulator IC1 plus also regulator IC2. Only make check if have competance for check or else ask technician to make such check. Regulator IC1 input to pin 1 18 Vdc with the output to pin 2 12Vdc. Regulator IC2 input to pin 1 12Vdc with the output to pin 2 5Vdc. Make also the double check for all correct with ground line in this circuit. Take much care when make this checks as easy for test probe to make slip for short circuit of component plus also take much care as live AC power in circuit.

xactifan
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Post by xactifan » 25 Jan 2010 18:04

Hello,
I could not find anyone to do the thing ,so finally I have tested IC1 and IC2

IC1 pin 1 input: value fluctuates around 2-3V with peaks at 12,14,17V(rarely) who fall immediately
pin2 output: around 2V

IC2 pin 1 input and pin2 output around 2V

For IC1 and IC2 pin 3 and ground gives 0

I have not used the Multimeter so I verified by testing a battery that I got a fixed value
Was does that mean this is the fault , or may be an index ?

Cheers

attached photo which shows the condition of welds
12186
12187

Shoji
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Post by Shoji » 25 Jan 2010 18:24

Hello xactifan. With low value and fluctuate on IC1 pin 1 is require to make the check of circuit before this. Make temporary remove from circuit of the capacitor C3 and make check of figure again. If still make problem make good for C3 connection and make temporary remove of C6 and make check of figure again. If still make problem look to correct function of recitifier D1 plus also the input from CN1. Again please to remember to take much care with such check. From photgraph you show is look like IC1 plus IC2 have been make with solder before. Is idea to clean residue of flux and make good this solder connection. Please only make this attempt if have the experience for makeing good solder connection. Is very quick to make plenty of damage to circuit board if not have solder experience :(

xactifan
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Post by xactifan » 27 Jan 2010 18:22

Hello shoji, Testing again IC1 and IC2 I found lower values, I had to set the multimeter in the lowest range position 200m. I noticed about IC2 that pin1 was broken and replaced by a soldered wire. The mainboard seems to have been removed in the past,it is fixed with only one screw and the cover on the cushion of the tonearm's motor is missing.

Now I'm faced :? with my soldering inexperience and after your warning caution it would be wise not to remove the capacitor. I should learn and try before first, I think. Although I suppose there is a hierarchy in testing the components is it possible to test rectifier and the input from CN1 and how to measure values?

Athermos
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Post by Athermos » 28 Jan 2010 09:19

Hello xactifan,


Nice to to hear from you again. Your diagnosis clearly indicates that the rectified and filtered voltage going to the 3 terminal regulator ICs (78xx, or higher current variants)is below the value expected. There is a provision for running the turntable off 12 Volts DC. Please try it to confirm that the fault is in the power supply only.The IC with the broken pin can be easily procured from a nearby electronics parts stockist if the jointed pin (soldered) is problematic. But before soldering on the turntable PCB you must properly ground the iron, connect a length of insulated copper wire from the iron (nearer to its bakelite handle where it is least hot ) and ground the same physically (the actual grounding area must be wet to ensure good electrical conductivity). This is of utmost importance so as to prevent new damages (inadvertent) because the PCB has CMOS devices.

Check the rectifier diodes , the incoming low voltage AC.


Cheers and keep up your spirit.

Athermos
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Post by Athermos » 28 Jan 2010 15:30

IC1 pin 1 input: value fluctuates around 2-3V with peaks at 12,14,17V(rarely) who fall immediately
pin2 output: around 2V

Yes, there is a broken soldering joint waiting to be spotted. It is very difficult but try tapping every possible place on the PCB to see if the voltage rises to say 17 volts.

Cheers!

xactifan
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Post by xactifan » 28 Jan 2010 17:35

Hello Athermos :idea:

I think you're right because the problem happened just after disassembly/reassembly the turntable,it was running just 10 mn before. . I've then noticed that spacer IC1 IC2 was hanging ,this has been a little twisted the pins. The soldered wire does not seem broken.Continuity of the rectifier is good,is it the right test?
Now I'll strum gently on the PCB hoping soon listen to music! :)
Always grateful for your insight to resolve the investigation

Athermos
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Post by Athermos » 29 Jan 2010 07:18

Hello there,


I believe the broken solder joint is somewhere between IC 1&2's (78xx's) input and the (raw) low voltage AC supply coming to the main PCB. Always work on this PCB with a grounded iron.



Cheers !

xactifan
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Post by xactifan » 31 Jan 2010 18:33

Hello Athermos,
Unfortunately I did not find the broken soldering joint, now the values fluctuates around 2-3mv with no peaks. To test further I've no experience to measure the values ,I don't know exactly where take them.
:( I should expect more learning about this and be careful I think and I regret not knowing follow this good advice.

cheers! :)

Athermos
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Post by Athermos » 01 Feb 2010 00:02

Check the incoming AC (low voltage) , which is coming from the transformer onto the PCB. Also check all the fuses.


Cheers !

xactifan
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Post by xactifan » 18 Feb 2010 17:45

Thanks to good advice Athermos I do not abandon the party :D ! Now I have to replace IC1 and IC2 which the pins are broken. ,they are manufactured by NEC but obsoletes: SVIUPC7812H and SVIUPC78M05H. I searched with Google but without success There are many 7812 and 78M05 without H, but I'm too ignorant to find the exact equivalent. Other problem, sales are not for individuals but for companies and sending to France is often impossible. Here I am! I will be happy if someone can give me information on what or where to buy this...

Athermos
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Post by Athermos » 18 Feb 2010 17:54

Hello,

Nice to hear from you again. Please try 7812 and 7805 as substitutes and see whether the ICs can withstand the peak power dissipation, use heatsinks (and heatsink compound) if necessary

Regards,

fscl
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Post by fscl » 19 Feb 2010 03:32

fscl wrote:DiGreen writes:
If I understood this problem better, maybe I could come up with an idea. Is it just the small "ears" on the clear plastic cover that break off, or is there more to it than that?
That's it 2 tiny ears.

I was thinking of putting metal corners in on both sides with the ear shape, but then I thought of the plastic latch on the bottom and after use, the plastic catch would eventually let go.

My thinking is to "JB Weld" / fill in that area, take a tracing of the intact one and then try milling out the bad side in the same shape with a Dremel :?

However, the last time I tried a Dremel to buff out some deep scratches on a dust cover, I ended up melting it.... :oops: :?

I'm going to have to make a lump of JB Weld and then practice on shaping it......

Fred and that's the best I can come up with.....at this time :-k
Just for fun, I poked around the Partstore website again today.....

Was curious to see what parts were available for the newly fleabay acquired SL 10. For some reason, this model was not in Partstore so I then entered the entire compact footprint Technics linearage :)

When I put in the SL 7, the "dustcover" part is once again listed and "available" so I purchased this (price is the same as last time) along with belts which show as an "available part" under the SL 5.

The dustcover is also listed as being used for an SL 6000? too. Is this tt the same as the SL 7 sold under the Panasonic brand? I pulled the trigger based on the cartridge replacement part the "TM-14".

Anyway, we'll see what happens / what I get.

Edit: I've been notified that the dustcover is going to ship at the end of
Feb.

Fred and looking at my lump of kneaded and hardened charcoal gray Quick Steel and going to attack with my Dremel tool for ear shaping for dustcover repair...... along with receiving a "new" one.... :) [-o<

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