sl1200 does not spin

turning japanese
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paulmarinis
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sl1200 does not spin

Post by paulmarinis » 16 Apr 2019 09:34

hello
i got an old sl1200 that was not working for many years and had a blown fuse.
i replaced the fuse it worked for 5-10 mins and then i popped up the popup light and the fuse burned again.
I have replaced all the electrolitic caps, all the transistors ( q2, q3, q202, q201) the zener diode and the bridge on the board.
now it does not spin but the fuse does not blow anymore (i have disconnected the popup lamp completely.).
when i power it on it makes maybe 1/8 or 1/16 of a full spin and stops.
also the stroboscope flickers periodically and slow.
the transformer when not connected to the board outputs 30V AC and when i connect it to the board outputs 18V AC.
The an6675 gets very hot from the start.
im thinking an6675 maybe needs replacement, but as it is the most expensive part on the board i thought i should ask first here, any help?

sylvain999
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Re: sl1200 does not spin

Post by sylvain999 » 16 Apr 2019 18:58

It does seem like the AN 6675 is shot, since you changed most usual suspects parts, and the IC gets hot. I would also check the stator coils with ohmeter to see if they all have the same value, maybe one has shorted. If the coils are good, I would isolate the pins of the I.C. one by one by unsoldering the pins that draw current and dips the voltage, then measure your power supply voltage. I'd begin with the voltage supply pins, pins 19 - 20 -21 and 23.

I have scored a couple of working boards on Ebay for around 100$ CDN you are not that far of just buying the I.C.. Also your board may need the AN 6680 replaced too, you never know.

paulmarinis
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Re: sl1200 does not spin

Post by paulmarinis » 16 Apr 2019 19:33

hi, thanks for your reply.
Do you think it might also be something with the regulator q1?
im in EU and the cheapest board i can find is 90-100eu , while the an6675 is 40eu, so if it is only it , it is worth it, plus i gain some knowledge:)
thanks for your advise, i will try it tomorrow and see what happens!

sylvain999
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Re: sl1200 does not spin

Post by sylvain999 » 23 Apr 2019 21:07

Did you put the zener diode the right way? IT's easy do get confused. Can you tell me what are the dc voltages at all pins of Q1 Q2 and Q3?

paulmarinis
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Re: sl1200 does not spin

Post by paulmarinis » 24 Apr 2019 09:34

Good day
Yes i double checked , the zener is ok.
as i have reassembled the turntable many times i have made an external power supply as per the below link

https://theartofsound.net/forum/showthr ... Supply-DIY

i also put the sockets for both chips for easy removal, and replaced Q1 as well.
when i remove the an6675 chip the voltage at the dc input of the board (where the bridge was) drops to 9,8V.
when there is no chip the dc voltage is 27V DC approximately.
I will check the q voltages today or tomorrow and will reply.
Thanks

paulmarinis
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Re: sl1200 does not spin

Post by paulmarinis » 24 Apr 2019 12:19

sorry i meant when there is the an6675 on board the voltage is 9,8V while when there is no an6675 on board the voltage is 27V dc

paulmarinis
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Re: sl1200 does not spin

Post by paulmarinis » 06 Aug 2019 15:11

just to update , the problem was the chip an6675 after all , i have replaced it and now everything is fine.

sylvain999
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Re: sl1200 does not spin

Post by sylvain999 » 12 Sep 2019 17:24

Glad i could help If you (or someone else) ever need parts i recently scored a huge stocking of parts. Many boards, pitch controls for mk2 and MD3, spindles platters, tonarms....you name it.

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