[Andy Cousins]

I made some progress. A cheap ebay digital oscilloscope proved that the main IC isn’t dead (I could see activity on the System Ocillator Output and Input pins), but something didn’t seem right with the Reset and Voltage Reference signal.

Digging around, while checking the power supply output current, I found a diode that tested bad. Replacing that, a whole load of functionality woke up, but it’s still not working correctly yet.

It will now ‘play’ once (I don’t yet have a cartridge and I’m not going to buy one until I have the unit working correctly).

Pressing play, it’ll move the arm to the relevant place for a 33 or 45 and lower the arm. Nudging the arm to the left will engage the tracking motor and move the arm in to the centre. Pressing play lowers it again in the new position.

The forward and reverse buttons will trigger the unit to raise the arm and move it left or right. The play and move left and right buttons will also make the light come on for four or five seconds. The 33/45 LEDs are working and the speed selector buttons change the speed of the main motor speeds up or slows down and the LEDs switch over as appropriate.

Allowing it to ‘play’ and tracking the arm in to the end of the disk, it’ll get to the endc centre, raise the arm and start to return it, but it always returns it to the start point of the disk, not to the far right ‘home’ position.

Once it’s done that once and the arm has reutned to the start point on the disk, it won’t play again and the main motor continues to rotate the platter.

Pressing play, stop or the move left and right buttons after the arm has returned to the start point on the disk causes the the light to come on and the tracking motorto runs for several seconds, but the metal lever doesn’t push the tracking worm gear in to contact with the main bobbin that the tracking wire is looped round, so nothing moves.

So, it seems to have the potential to work correctly, but it’s almost like it doesn’t know how to go through the start and end part of the cycle. I’m still thinking that something is amiss with the input signal to the Reset pin. The voltage on it and the Voltage Reference pin are constant 5.4V, unless I unplug it and the input voltage to it slowly drops. Plugging it back in doesn’t cause the main motor to spin up and reset the arm though

Any pointers?

[Andy Cousins]

Thanks.

Yes, I’ve tried it with 7″ and 12″ records. It doesn’t respond to inputs in any case.

I need to keep notes about what it does in each test, but I’m pretty certain that whichever size disk I put on the platter, the tone arm LED displayed ’33’. Without a record I think it displayed both speeds, or neither.

I’ll trace back through the schematic and test the transistors that control the light as well.

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