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 Post subject: [LD-700] Tilt motor and belt
PostPosted: 27 Oct 2023, 17:20 
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Thought I would post a few "learnings" after a successful LD-700 repair recently. There are a few threads here that begin "my LD-700 has stopped working," which are followed by the advice "clean the lens, if that doesn't work chuck it in the bin."

I think I can add another stage to that, pre-bin - check the tilt mechanism and belt.

My LD-700, used only very rarely, was working fine until a few months ago when it started skipping crazily whilst making a squealing noise. I left it until last weekend, tried it again and, although it still span up, the laser would scan quickly across the whole disc, with no picture displayed.

Given the earlier squealing, assumed it was something mechanical, so first thing I noticed was the little drive belt that is driven by the tilt motor. It looked loose and, after removal, retained the 'egg shape' of its path between the two sheaves. So obtained a replacement (25mm diameter, 1.2mm thick square section). Tricky to thread it back on, but after 20 minutes of struggling, managed it.

But - no improvement, player still not showing a picture.

Tried rotating the tilt motor with a finger, and noticed that the sheave+gear it was driving wasn't rotating. Tried rotating that with my finger (a rather tight squeeze, could only use my little finger) and found it was almost completely seized up. So that was the root problem.

Guided by the service manual, removed the four screws holding the two 'tracks' for the laser carriage (also removed the little hatch in the back panel to give more space). Decided not to try to disconnect the ribbon cable, so had to be very careful not to damage it.

Then removed the four screws holding in the 'tilting' part of the assembly, and the washer circlip holding it in the carriage from underneath. Could now see the various worms and gears of the tilt mechanism. However the problem wasn't there, so that step should be skipped if you're trying this yourself.

The actual problem was with the sheave+gear being driven by the tilt-motor, on the outside of the laser carriage. Removing the circlip holding it in place, and sliding it off its spindle, it was the grease there that had become incredibly sticky. Polished the spindle, washed the nylon piece, put a bit of lithium grease on it and reassembled. Now it turned freely.

Then reassembled the rest of it, following the service manual - it's important to line up the potentiometer gear correctly when doing this.

Powered up, and, lo and behold, a picture! Fine-tuned the tilt using the VR1 pot on the tilt board (I don't have a test disc or oscilloscope to do proper adjustments sadly, just did the best I could with a freeze frame on a CAV disc.)

Picture not great - slightly poorer than my LD-1100 I'd say - but it was never that good since I bought it a few years ago. But the LD-700 is the machine I dreamt of owning when I was a youngster, so happy to have given it a new lease of life.
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