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 Post subject: Philips TT
PostPosted: Feb Sat 16, 2019 10:58 pm 
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Joined: Jan Mon 24, 2011 7:21 am
Posts: 696
Location: saint clair shores, michigan
I am looking at a Philips model 312 turntable for my buddy. This semi-auto TT uses touch buttons to turn on either at 33 or 45 rpm. Intermittently the on button won't latch. As long as your finger is on the button, the platter turns, but as soon as take your finger off, it stops. Sometimes it functions correctly. Seeing as how the circuits for each speed button are separate, it seems the problem must be elsewhere, or just the bad one would not work. Any suggestions? I have included the part of the service manual that describes the touch circuits, and the schematic.


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2019-02-16-0001.pdf [98.67 KiB]
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2019-02-16-0002.pdf [54.71 KiB]
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2019-02-16-0003.pdf [53.58 KiB]
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2019-02-16-0004.pdf [36.89 KiB]
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2019-02-16-0006-min.pdf [148.56 KiB]
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 Post subject: Re: Philips TT
PostPosted: Feb Sat 16, 2019 11:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 262
Location: Arlington, TX, USA
I remember having a model 212 years ago, and the light bulbs under the touch switches had to be working or the touch switches themselves would not work correctly. Not sure if this is the problem you are having with this one. The bulbs were some kind of oddball low current types similar to the old stereo indicator bulbs in 1960s solid state tuners, but with a screw base.


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 Post subject: Re: Philips TT
PostPosted: Feb Sun 17, 2019 12:00 am 
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Joined: Jan Mon 24, 2011 7:21 am
Posts: 696
Location: saint clair shores, michigan
This model uses 3 LEDs for the speed and stop buttons, and a fourth as part of some kind of detector circuit under the base of the tonearm. I was told if that one was weak it could cause problems. I swapped that one out. No help. I also checked the -10 volts as described in the service manual and replaced capacitor 728.

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 Post subject: Re: Philips TT
PostPosted: Feb Sun 17, 2019 2:49 am 
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Joined: Nov Fri 06, 2009 1:04 am
Posts: 2446
Location: Rochester, NY 14425
Check the transistors described on page 8 of the service manual. One may be (starting to) short or open?

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