Need some quick Technics help

[Qwin]

The strobe light firing transistor needs removing from the board to silence it.
Even if you remove the strobe light, the transistor continues to ground the circuit at 50 times a second creating noise in theory when firing, though I don't know if anyone has measured this. The LED's in the strobe only flicker due to this transistor grounding the input at a speed of 50Hz. The trigger/controler for the transistor is one of the large chips on the board nearby, if you look at the PCB layout in the service manual the tracks are pretty easy to follow. I removed this transistor on my 3 modified decks and think I mentioned it in one of my build threads.

Also agree that removing the power supply and making it external should be the first step.

If you don't need the pitch fader or cueing light remove these as well.
When you unplug the pitch fader you need to bridge two of the pins on the board header, this is covered by someone on one of the threads and I may have covered it on my first build. EDIT: Its pin No 6 and 7 you need to bridge (join together). see this thread for details: http://theartofsound.net/forum/showt...its-removal%29

There is a brief summery of my three projects on my website linked at my signature below. But the threads have discussed details not on their, you would have to search for them.

EDIT: I have bumped my three build threads so you can spot them easily. I also cover a straight arm modification.

[Khom]

I can't imagine how the strobe light electrical pulses can affect to mechanical hum. Yes, these pulses have a huge value (I measured approx. 80 mA peaks), but I checked needle positions on the disc (i.e. contact) and 1 mm above - results was different, it means that 100 Hz hum caused by mechanical (more precisely electro-mechanical) issues.

I replaced also some time ago strobe LED's with modern ones and reduced strobe current pulses to 5 mA, so this issue now is theoretical for me.

[Qwin]

I don't think anyone mentioned mechanical hum, more likely introducing electrical interference.
I was making the point that the x4 LED's will not be contributing much in the way of electrical noise.
Any electrical noise produced is more likely to be coming from the switching transistor that dims them, so removing the LED's without removing the transistor isn't achieving much. And yes how much, if any effect any of this has is somewhat theoretical, I don't think anyone has measured it, but in theory it is good practice.

The strobe on a Technics sl-1200 deck is after all a redundant device, the quartz lock guarantees it runs at the right speed. The pitch fader only cons the circuit into thinking it is running at the wrong speed and it increases/decreases speed by the amount set on the slider. The pitch fader needs correct calibration for the deck to run at the right speed when set to zero, but remove it and bypass its input by bridging pin 6 and 7 on the PCB header and the deck reverts to running and maintaining the correct speed.

I simply remove any of the items which are surplus to my requirements, it costs nothing, if I had a valid use for any of these I would leave them in. I suspect any gains by removing these devices would be small anyway, moving the PSU external and upgrading it or the internal regulator should give greater gains.