Hey gang - I'm a total newbie trying to fix a Philips 212 turntable I found in the street. The turntable uses a fairly unique "flip flop" mechanism to choose Stop/33/45 modes, with touch sensitive capacitive buttons acting as the selectors.
My problem seems to be in the very early stages of the circuit. The AC transformer is putting out 14.4 VAC without a load. When I connect it to the board and turn the turntable on, input voltage drops to 13.6 VAC.
I have tuned the resistor at R472 to get an exact voltage of -9.0V DC on the top rail. The problem is at the bottom, where the other output for the bridge rectifier goes into the transistor TS405 (which is PNP). The schematic says I should be getting +7.6V there at the emitter side, but I'm only measuring +6.6V. (I checked my DMM against a voltage reference and it's bang-on, so I know it's not the DMM.) And on the base side, the schematic says +7.4V, but I'm only getting +6.3V.
Interestingly, over at T441, the NPN transistor, I'm measuring -0.75V (pretty close to spec) on the emitter.
This problem is either carrying through the circuit or is a symptom of a different problem -- because the main problem I face with the turntable currently is that the lamp for the 33RPM touch switch is underpowered when activated. It's only getting 4.3V or so -- meanwhile, the stop bulb seems fine and is getting 5.5V. The motor runs when I push the buttons, but the 33 and 45 bulbs just don't seem to be getting the right voltages.
With regard to that TS405 transistor, I checked it out and using the diode mode on my DMM I get these fwd voltages: Veb of 0.129V, a Vcb of 0.125V, and a Vec of 0.332V. All other combos measure O.L.
I have replaced the C734 470uF cap, and also pulled the resistors R582 and R583 and checked them, and get good readings there. I also replaced all the internal light bulbs with bulbs I got from the UK that match exactly the specs in the service manual. (I had read in other forums this was important for the circuit to work correctly.)
Does anyone have any ideas of areas to investigate or further check to help diagnose what's going wrong? I'm really tearing my hair out!
I've attached a zoomed in pic of the circuit diagram where the power input is. I've also attached the complete circuit diagram and the PCB layout.
Thanks!
-Steve