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RE: P-700 Service Manual?

Posted by mr.bear (A) on July 22, 2017 at 10:17:07

In Reply to: RE: Speed adjustment? posted by flood2 on July 22, 2017 at 00:52:28:

Closest I could find was for the P-751, from the same vintage roughly. Vinyl Engine. Looking at the schematic for the 751 it appears the entire motor speed control is in 2 IC's with just a few external components, no speed adjustment trim-pots. The speed lock LED is binary, on=speed locked to xtal reference, off= not. Its kinda useless.

The 751 service manual shows only how to connect an oscilloscope to see the speed control waveform (you need to build a little buffer amplifier with one transistor to make the 'scope connection!) and there is no way to adjust or fix it in the manual. You just look at it see if it's sour and start replacing components till it's pretty, I guess.

The entire speed control (for the 751, possibly the same for the 700?) is on a single PC board attached to the motor coils. It's a very basic system. That board has several electrolytic capacitors it's possible that one (or more) of them is dead. It does not appear that there is an external speed sensor, the servo is established from a coil somewhere in the motor PC board.

I hate the words "no user serviceable parts inside" but in this case it seems true... short of looking for fried electrolytic or replacing them systematically. A couple things you might try first, beyond looking for obvious busted stuff, fuzzballs, and dead bugs might be 1. check the voltage from the power supply is reasonable (the 751 is 24v), 2. see that the motor turns freely (if not, de-gunk the bearing) and 3. spray contact cleaner in the motor speed switch in case it is erratic. Otherwise, maybe start thinking of saying goodbye to the ol' 700- on eBay the dustcover should be worth something.

Bear sez: "Don't electrocute yourself"

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