Philips GA212 turntable - power supply issues

Thread Starter

magicwindow

Joined Oct 7, 2020
10
The service manual states that the turntable has a supply voltage of 9v, but upon measurement it's sitting at 9.7v. A little high for my tastes... and I'd be fearful of this causing damage over time. It also states that this rail can be adjusted by turning R472, which is a 1k ohm trimpot. It was replaced somewhere down the line with a modern multiturn Bourns type. I started off making small adjustments to it, but this is actually increasing the supply voltage! So I turned it back to as low as it can go (measuring the resistance in-circuit it appears to be at 0 ohms...) and the lowest voltage I've achieved is again 9.7v.

I'm guessing there is an issue elsewhere - but I don't have an idea of where to start to troubleshoot this. If someone could point me in the right direction, it would be greatly appreciated.

Service manual with schematic can be found here (I would add this as an attachment but I'm unsure if this would violate any site rules)
 

Thread Starter

magicwindow

Joined Oct 7, 2020
10
Am I correct in saying that the blue dot on these germanium transistors indicates the collector lead? If so I think whoever last worked on it changed the transistor and installed it the wrong way round. The resistor that you see immediately beside one of the legs of the transistor is R583, which is meant to be directly connected with the emitter lead.

_DSC0013.jpg
 

MrChips

Joined Oct 2, 2009
23,204
Ah! The good old AC127. Brings back memories.
I have a copy of Philips Transistors Theory and Applications if there is any technical information that you need.

1602173039220.png
 
Top