Beginner trying to fix Philips 212 turntable circuit - Page 1
Forum section: electronics / repair

author: stevedc
author_rank: Contributor
timestamp: April 22, 2015, 11:00:50 pm
content: 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

author: KJDS
author_rank: Super Contributor
timestamp: April 23, 2015, 08:00:32 am
content: Quote from: stevedc on April 22, 2015, 11:00:50 pmThat does indicate a problem

author: stevedc
author_rank: Contributor
timestamp: April 23, 2015, 04:43:19 pm
content: Ah - so should I be getting O.L. on the Vec as well? (btw, am testing the transistor out of circuit)

author: jancumps
author_rank: Unknown
timestamp: April 23, 2015, 05:06:06 pm
content: Hey, I have that table and fixed it. Normally it's only the power supply cap and the bulbs that need replacement. Then dial in all values as per the service manual. i think mine has some annotations from a repair technician.

author: jancumps
author_rank: Unknown
timestamp: April 23, 2015, 05:08:16 pm
content: I can take comparison measures if that helps. Just say where on the schematic you want to see a measurement.fThe bulbs are not critical, just get some that are close. bulbs aren't precision components anyway.

author: jancumps
author_rank: Unknown
timestamp: April 23, 2015, 08:01:07 pm
content: I made this video on my repair work last year September

author: stevedc
author_rank: Contributor
timestamp: April 23, 2015, 08:22:43 pm
content: That's fantastic - I know your video well! That's what inspired me to take on this project. "Thou shalt measure voltages" - I remember that line from your video!Based on your experience first thing I did was Replaced the caps and bulbs and thought that would do the trick, but it hasn't.The -9v rail voltage is rock solid. When I try to play 33, it has difficulty "latching" and the 33 bulb is very dim when it does. 45 bulb is brightest when I play 45, and stop is in the middle. None of the bulbs is as bright as I think they should be.That's a kind offer to verify measuremens. I took a bunch of measurements last night - they are at home.Later I will post a few for you to check if it's not too much trouble.Thanks!

author: stevedc
author_rank: Contributor
timestamp: April 24, 2015, 03:25:38 pm
content: Jan - here are some measurements that would be terrific to have from your working machine. I've also noted the measurements I get. All the transistor measurements are ones that are out of spec from the diagram.Green wire from 33 lamp (in stop and 33 positions) -8.96 -4.50TS405 Vb (in stop, 33, and 45) +6.6; +5.9; +6.0TS405 Ve (in stop, 33, and 45) +6.8; +6.1; +6.2TS434 Vc (in stop): -0.67TS436 Vc (in stop): -8.67TS438 Vb (in stop): -8.67TS438 Vc (in stop): -8.49Also, if you look at the circuit diagrams for each of the touch controls, there's a 10nF capacitor labeled C219, but I can't find that on the physical board. Do you know where it is?Finally, it's interesting if you look at the Vb and Ve voltages for TS405... in the "stop" position, I'm getting almost the exact voltages expected if 33 is pressed (see pg 4 of service manual).Thanks!-Steve

author: jancumps
author_rank: Unknown
timestamp: April 24, 2015, 04:51:05 pm
content: I'll try and check tomorrow (depending on my health state. I'm going out with my wife this evening)

author: mzacharias
author_rank: Frequent Contributor
timestamp: April 24, 2015, 05:08:40 pm
content: I remember from the old days that these units were very picky regarding the touch sensing; the lamps had to be the right type.

author: jancumps
author_rank: Unknown
timestamp: April 24, 2015, 05:12:21 pm
content: No, they are just generic bulbs. Not picky at all.Someone posted that the table needs one particular type of lamps and half the world jumped on that.I yet have to see the first precision incandescent bulb.

author: jancumps
author_rank: Unknown
timestamp: April 25, 2015, 11:46:48 am
content: Quote from: stevedc on April 24, 2015, 03:25:38 pmStarting...

author: jancumps
author_rank: Unknown
timestamp: April 25, 2015, 12:25:03 pm
content: Quote from: stevedc on April 24, 2015, 03:25:38 pmHere are the measurements:

author: jancumps
author_rank: Unknown
timestamp: April 25, 2015, 12:53:22 pm
content: Quote from: stevedc on April 24, 2015, 03:25:38 pmI see that they are drawn on the bitmap schema that you have attached on your first post. They are not drawn in the manual that I used (see second scan in my previous post).They are on my PCB though. Here's a still from my video where you can see them:

author: mzacharias
author_rank: Frequent Contributor
timestamp: April 26, 2015, 03:51:00 am
content: Quote from: jancumps on April 24, 2015, 05:12:21 pmMy experience tells me otherwise. I stand by it.

author: poot36
author_rank: Frequent Contributor
timestamp: April 26, 2015, 04:41:09 am
content: I agree with the above comment. BMW car light bulbs are also very finicky.

author: stevedc
author_rank: Contributor
timestamp: April 27, 2015, 06:08:03 am
content: Jan - thanks so much for taking the time to do those measurements. That's very kind of you.So it's the transistor at TS405 where we really have differences. Is this a sign I have a bad transistor? Any ideas about what could be causing my TS405 to be so low in the stop position?

author: PCB designer
author_rank: Newbie
timestamp: April 27, 2015, 06:16:44 am
content: Maybe i could help you with the circuit board if you have the gerber format .I will help you double check .

author: jancumps
author_rank: Unknown
timestamp: April 27, 2015, 06:53:59 am
content: Quote from: stevedc on April 27, 2015, 06:08:03 amWhat I see as the biggest difference between your and my measurements is that on TS405, your measurements decrease when switching from 33 to 45, and mine increase.

author: SoundTech-LG
author_rank: Frequent Contributor
timestamp: April 27, 2015, 07:12:08 pm
content: Quote from: mzacharias on April 24, 2015, 05:08:40 pmit's all coming back to me.Yes, worked on so many of these back in the 70's, and people/service shops were installing wrong bulbs. Once the correct bulb was back in the circuit... all was well again.

author: stevedc
author_rank: Contributor
timestamp: April 27, 2015, 09:26:35 pm
content: Quote from: SoundTech-LG on April 27, 2015, 07:12:08 pmWhat's so frustrating to me is this is the first thing I did - I replaced the unit with all new and perfectly spec'd bulbs (ordered from the UK) and I'm still running into trouble...

author: jancumps
author_rank: Unknown
timestamp: April 27, 2015, 09:35:47 pm
content: Frustration is not your best friend when fixing 45 year old turntables.The schematic is not complex, and all electronic parts are still available.It's a very fine table when you get it working.You haven't put your location in your profile. If you're from Belgium, feel free to contact me and we can look at it together @jancumps lab.Or we can arrange a google hangout to try and troubleshoot.

author: stevedc
author_rank: Contributor
timestamp: April 27, 2015, 10:47:12 pm
content: Jan, I PM'd you.