Philips GA 312 Cue Switch

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gfreek1
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Philips GA 312 Cue Switch

Post by gfreek1 » 14 Dec 2018 20:31

So the the problem is I push the cue switch down, it stays down for a few seconds, maybe longer then pops back up on its own. Power switch off. Not much on the web about this specific problem.. I'm thinking that its worn and it won't stay in place..Tried a fix from another site but no go...Wondering if anyone has seen this and a fix for it .. Thanks

Japi Roelofs
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Re: Philips GA 312 Cue Switch

Post by Japi Roelofs » 14 Dec 2018 20:35

The cue down will only work when the platter is spinning. It's some kind of safety device.

gfreek1
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Re: Philips GA 312 Cue Switch

Post by gfreek1 » 15 Dec 2018 02:01

Even when the platter is turning playing a record it does it..it lifts and the platter keeps turning. From what I understand, please correct me if wrong, it is supposed to raise the tonearm when the cue switch is energized. De-energized is supposed let the Cue rocker to stay depressed.

Japi Roelofs
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Re: Philips GA 312 Cue Switch

Post by Japi Roelofs » 15 Dec 2018 18:20

Ah OK, I guess I misunderstood your first post where you said "Power switch off". I thought you meant you had the turntable power switched off. Do you mean the tonearm raises, and then the platter stops rotating?

The Cue switch activates a solenoid, which keeps the arm in the 'up' position otherwise. The solenoid can only be activated when the platter is turning, so then the arm can come down. Once the stylus reaches the end of the record, a sensor triggers the mechanism and the solenoid is de-activated, so the arm goes up again. This mechanism works with a light source (LED), a sensor (LDR), and a device connected to the bottom of the tonearm that gradually blocks the light shining from the LED into the LDR. So when the arm moves towards the end, the device starts blocking the light and the mechanism is triggered. What could be going on is that the LED light doesn't have enough power anymore, so not enough light is picked up by the LDR. It therefore thinks the end of the record has arrived, and the mechanism is triggered.

LED's that are dimmed because of their age are a common problem in Philips turntables.
You could try to replace the LED bulb with a fresh new one. Part # LED402 in the service manual.

gfreek1
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Re: Philips GA 312 Cue Switch

Post by gfreek1 » 15 Dec 2018 18:34

Yes I did mean power switch "off". I guess i misunderstood how that worked.. With the power switch "on" the arm raises on it's own, platter keeps spinning. Thanks for explaining how that works. I have the service manual, but understanding it is another thing...Thanks, I'll look into the LED bulb

reisod
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Re: Philips GA 312 Cue Switch

Post by reisod » 17 Dec 2018 03:07

I'm just finishing up refurbishing a GA 312 I picked up at an antique store as a Christmas gift for my father.

The table had been subject to previous "servicing", meaning that the power switch and the auto-lift had both been bypassed, as well as some janky fixes to the suspension. I'm still resolving some light rubbing issues due to the suspension, but I seem to have gotten the controls operating appropriately.

The LED is coupled with an LDR. The tonearm has a mechanical 'flag' that breaks the light path between the LED and LDR as the cartridge approaches the end of the record. Once the path is broken, the solenoid is activated and the lift mechanism re-engages the tonearm.

Insert standard disclaimer here: only work on live circuits if you are trained and knowledgeable. Proceed at your own risk!

Page 4 of the Service Manual under "Electrical Adjustments" asks you to check voltage across two points on the LDR while shielding the LDR from direct light. This voltage should be 2.5VDC, and there is a trim pot for adjustment if your value is something else. Using this test, you should be able to check if the LED is emitting enough light for the LDR to respond as designed.

It's also worth noting that the previous owner of my 312 defeated the auto lift by cutting the single brown lead that ran between the tonearm lift switch and the main circuit board (without opening the table again, I believe this was either B/24 or B/22 in the service manual). By breaking this connection, the LDR no longer triggers the solenoid. One option would be to temporarily break this connection to isolate whether or not your issue is coming from the LED/LDR control cluster, or the solenoid / mechanical switch cluster.

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