PS-8750 : speed issue solved !

turntables, tonearms, tuners, open-reel & K7 recorders...

Re: PS-8750 : speed issue solved !

Postby Sam Z » Sun Apr 26, 2015 3:49 am

So to be clear, the switch isn't the issue, but there's a bad component or connection somewhere else that only works properly after the TT has been powered on for a while...right?

Next step is identifying what it is.

Or maybe life's too short and you can just keep it powered on.
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Re: PS-8750 : speed issue solved !

Postby Axel » Sun Apr 26, 2015 8:12 am

Sam,

At least on mine the switch didn't do anything... I think I've cleaned it enough so that germs and oxidation wouldn't creep up before at least 2056 !

But changing the two SN7400N frequency dividing ICs did 80% of the job ; keeping it powered on will do the other 20%...
Or just wait about 45 minutes after power-on before playing a record :)

Now on to that auto-return belt & motor.
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PS-8750 speed issue solved... for real !

Postby Axel » Sat Sep 26, 2015 8:17 pm

Ok - final episode of the series.

After a few more hiccups and erratic behaviors popping up (and down), the speed problem wasn't solved : when cold it would still go too fast ; after some time time warming up, it would at last work ; then, when too warm... again it would speed things up.

So ambient humidity and temp and ICs in need of heat (but not too much) (and not all) (or not always) (it depends) (is it the first of the month ?) led quite naturally, after a few more in-depth tests by Pat66 to that one bloody crux of so many mid/late 70s Sonys : the pass-through soldering on the X'Tal board.
And indeed : when that one board has been entirely cleaned-up and resoldered, its caps all exchanged for new ones, everythings works as it should : cold, hot, rainy, first of the month or not.

So, to sum it up :
1. Get rid of the old solder, traces and residue and resolder everything (absolute utmost necessity),
2. Change all caps (necessity),
3. Change the two dividing SN7400N ICs (just in case),
4. Plug, and play.
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