Philips 212 renovation

[Lennie.no]

Hi all,

I have an old Philips 212 which I have been using on and off since I bought used it in the late 80ies.
I have been satisfied with its sound and have had little trouble with it.
I have changed light bulbs and belt a couple of times, changed from DIN to RCA and gotten rid of the grounding hum.

I have other turntables that I am using now, and want to get it in as good shape as I can before handing it on to my 12 year old daughter.

I have read up on others restoration of this model here at AK and other forums, and understand that working, correct spec'ed electronic components are essential to get it working as it should.
I therefore replaced the electrolytic capacitors C730 and C734.
Everything seemed to work after this replacement; all bulbs lit up as they should and the touch buttons worked.

Nevertheless I went on to check the voltages as per the service manual, and found that the supply voltage was a little more than -10v in regard to the chassis.
I therefore wanted to adjust this to the SM specified -9v by turning the (potmeter) R472.

When I did this, the light bulbs went dark, and the player was no longer operable.
No burned component smell emerged, and I hope it still is possible to salvage the TT.

I now have spent some time measuring the resistors of the PCB, and found a few that are not as specified in the schematic diagram.

The most obvious discrepancy is that R472 now has 272 Ohm as maximum value, as opposed to the 1K specified.
I suppose I have to replace R472 with a new 1K pot to be able to get the supply voltage right.

- In regard to supply voltage: Here in Norway we get 230V out of the socket. On the 212 trafo I see that the in-leads are soldered to the 220V pin. Measuring the ACV out of the trafo, I get 15V, as opposed to the schematics 14V. Could this explain my 10V + supply voltage?
- I read that some people opt for an external, balanced power supply. If so, what voltage and amperage should such a PSU have? And were do I connect the + and - to the PCB?

Some of the carbon resistors have two different values, depending on which side I put the leads of my DMM! Resistors are nor polarised, are they?
See the values I measured for R583, R582, R541/R546, R566/577 and others in the attached photo here under. Specified values in parentheses, measured without.
Is this 'polarity' an indication of a defect resistor?

Other resistors have measured values far from the specified. See for example R584, R543.

PCB mirrored:


Since so many of them have measurements so much off, my inclination is to replace all resistors, minus the variable ones, and would like your opinion on if this is a sensible path to pursue.

I am up for replacing whatever it takes to get the TT up and running, but have both limited knowledge in electronics and limited tools to help me decide what to replace: With my DMM I can measure resistance, volts (ac/dc) and amperage (ac/dc).
I understand that capacitors need a special instrument to measure their values, but is there a way to confirm whether they are blown or not with a standard DMM?

For the transistors, I understand that I need the correct supply voltage (and the correct values on the resistors, I suppose) before I can check the transistor voltages stated in the schematics?

The diodes? Can I somehow determine if they are OK, or should I just replace them all along with the resistors?

All suggestions as how to proceed are much appreciated!

Regards,
Lennie

Wiring diagram:


Schematic diagram:

 

[klamsoss]

It would be good to have a DMM that can test diodes and capacitors as well. For around $125 (US) on the used market you can pick up a fluke 117 which would do most anything you'll need. It'll test diodes, capacitors, and will auto-range for resistance, voltage, and capacitance.
You can construct a basic leakage detector with a dc power supply and a current meter. You'll be limited to the voltage your supply can generate. There are threads on how to set something up like that.

A few notes:
If you aren't lifting one end of the component, you'll have sneak circuits that affect your readings with your DMM.
Using the shotgun approach to repair isn't the best way to get a good result. I've worked on several of these and have never run into one with very many parts out of spec. I can't remember having to replace any diodes in any of them. Transistors, maybe, but I'd need to go back and check the parts list against one of the various lists of usual suspects (There's a thread that I think is called "top ten worst offenders" that I have referenced dozens of times).
I generally always replace all of the electrolytic capacitors in these because replacements are cheap and once you have it apart, it's not a lot more work if you are competent with soldering.

As long as the turntable is properly wired for 220v (i.e. it's not meant for the U.S. or Japanese markets) the fact that you get 230V should be fine. Much of my stereo equipment was made for 115V which was standard in the U.S. in the 60s, but my wall voltage is around 122V most days.

One other general suggestion I have is to build a dim bulb tester. These are useful for more than just amplifiers. I use mine every time I power something on after doing any kind of work on it because it shows if there is a short circuit. Your turntable may have a shorted component or there may be wires, traces, or solder bridges that cause a physical short. You'll most likely be able to identify the short by the bulb staying bright, and shut it down before anything else lets go. I have saved myself many times, even with turntables, by always using the DBT for initial power up.

Start from the transformer and check voltages against the spec as you work your way deeper into the schematic. Specifically, start and look for 14V AC between the transformer outputs (marked 6 and 7). If that's correct, look at the DC voltage that comes out of the rectifier. In theory, it should be around 14VDC. Then check TS405 and TS441 voltages. If that's way off, the rectifier may be bad or the transistors. You already understand that R472 is supposed to drop the voltage down to 9.

Get there first and you'll be in good shape to move on.

 

[klamsoss]

One other thing, and really I should have started with this, but what were the initial problems? What about the turntable was not working properly and caused you to open it up and have a look?

Not holding speed properly? Erratic function on the touch lights? Auto stop and lift not working.

As you will find in many threads here on AK (welcome, by the way) it's normally good to establish a baseline, then work towards proper function, and only after that do you really go in for a full restoration. If you start throwing new parts in before you know what the problem is, you can't be sure the new parts aren't contributing to the issues.

 

[MacGM]

Excellent advice from klamsoss above.

After a quick glance at the scheme, that 14vac should be around 14.8vdc just past the rectifier, and 9v after the last leg of R585 and D457.

As long as you get 9vdc at that point, the power supply should be good.

If hazard a guess that you've got
dirty trimpots in that part of the circuit, I'd switch it off, clean them with isopropyl while moving them side to side, and set them back close to where they started and then set the voltage so you see 14vac pre rectifier, 9vdc where I mentioned earlier and work out what's going on from there.

 

[klamsoss]

Yeah, as Mac says, once your get the 14.8VDC it would be a good idea to hit the trimpots with isopropyl or a dab of faderlube works, too.
Power off, unplugged while you do the cleaning, and drain the main cap, too (or let it sit for a couple hours and check that you dont have any meaningful DC voltage anywhere).

 

[MacGM]

Re reading the original post, you're waaay overthinking this.

You don't need an external power supply, you've already got the correct one built inside the turntable.

Your 230v at the wall isn't going to be 230v. It's going to be anywhere between 210 and 250 and swinging somewhere between those two values depending on the time of day and how much solar output is in your neighbourhood, and still be happily in spec.

I'm also in a 230v country and just put my DMM in a wall socket to check. The voltage out of the wall here is swinging between 245v and 252v with the solar array switched on, and 241v and 245v with the solar off. It's a sunny day here so there's a surplus of power, as 80% of the neighbours have solar arrays on their roofs. I've seen it as low as 211v on a cold rainy day, when not much was being generated and everyone was running heaters.

Point being, those capacitors in the power supplies of your hifi equipment are there to smooth these fluctuations out and provide a stable current for the motor of that turntable to work at the right speed, as well as keep volumes from fluctuations in amplifier circuits.

I'd clean the trimpot that I mentioned earlier, and only that trimpot, and set your 9VDC on the correct side of resistor 585 and leave the rest be. If it ain't broke, don't fix it.

Resistors do what they say on the tin.
They slow the current, so of course you will see one voltage on one leg and a different one on the other directly proportional to ohm's law and the value of the resistor in question.

I'd also consider replacing that one 25v electrolytic, but only if I had a spare at hand, I wouldn't go out of my way to change it. I'd probably jot down the value of that cap and order a couple spares next time I put in a bigger order with digikey, but I'd be in no hurry to change it.

Leave well enough alone if it's working okay.. Make sure your voltage is close enough to spec and close it up and play it.

 

[Lennie.no]

Thanks guys for all your guidance and suggestions!

The start-off point for my dive into the circuit board, was to get the TT ship-shape before handing it on to my daughter. I haven't used it for a few years now, and when I powered it up again, it worked OK-ish.
That is, it has always had it's peculiarities, such as having to hold the speed selector buttons for a long time before letting it go in order to make it turn on the selected speed.

Reading up here at AK, and VE, I understand that the electrolytic caps (C730 and C734) often are the culprits for strange behaviour on these old Philips's, I decided to swap them before they got the chance to act up even more - as klamsoss and MacGM also suggests.

After replacing these, I wanted to check if the voltages were correct, as I read in the SM, and in forum posts on the 212, that the supply voltage is critical.
I found that it was a little high, and while trying to rectify this, the bulbs went dim.

So, if not too many things were off prior to my attempt to fix something not that broken, things sure are now.
- Another reason for my diving in to the innards of this TT, is just simply that I would like to learn and understand electronics better. In this respect you guys' comments are gold! So are other members of AKs sharing in other threads.
klamsoss; you are entirely right: I lifted one leg of R546 (47K) and I now measure 47.6K both directions.
Still the 22M R576 and R577 give strange values: I lifted one leg on R576 but can't get any value. Neither can I get any continuity using my DMM.
Measuring R577 I get 0,6 Ohm, but suspect this is not through the resistor.

I will lift the legs of the resistors that had strange values on my initial measuring, and hopefully be pleasantly surprised...



I have cleaned the pot R472, but still can't get higher Ohm value than 272 (R472 is rated 1K)
The supply voltage is way too high, 16,4VDC.
The VAC out of the trafo is 15,7.
To me this indicates that, at least, R472 needs to be replaced - or am I missing something?

klamsoss: I see the value in a Dim Bulb Tester, especially for an amateur like me!

MacGM: Thanks for reassuring me that an external PSU is unnecessary - quite a few posters do think that it is the only way to go...
My concern with the 230VAC on the 220VAC pins on the trafo was that the VAC out was to high, and could explain my initial 10+V supply voltage...
As you say, the VAC in our domestic outlets vary, and the Norwegian electric power suppliers claim that this variation is no more than +-10%.
By the way, in Norway we are not bothered with neighbours covering their roofs with solar arrays and messing with our voltage - this is the North of the planet and we don't get much chance to get sunburnt!

From both your suggestions, I think I will concentrate on getting the supply voltage right and take it from there. Hopefully R472 will do the trick.

I have other issues with the TT, and would for instance like to convert to LED bulbs, but I'll leave that for a later date.

Ta' once again!
Lennie

 

[CT Jim]

Before you jump on the LED bandwagon, get the TYT to work properly with the regular bulbs, even if you have to switch them around from say 45 to 33. Those bulbs have a certain amount of resistance which helps the circuit.
Considering that when the table runs only one bulb is lit, what do you think you will gain by going to LEDs? It’s not a bunch of ceiling lights?????

 

[Lennie.no]

Before ordering a replacement for the R472, I desoldered it and measured its value: It is indeed 1K, and I suppose the value I got when on the PCB was due to my 'shotgun' approach.
So my hope for this easy fix is now gone.
I have searched for other posts on the 212 where the supply voltage is way off, and have found that some TTs had faulty power supplies, and a new PSU, internal or external, did the trick.
My PSU seems to be ok with its 15.7VAC out.

An another forum I came across an interesting post, that I hope you can tell me could apply to my problem too:

That posters supply voltage was not as far off as mine (9.7V opposed to my 16.4V) And was told to check the voltages of TS 441 and the voltage across D458.

The schematics tells us that these should be:

TS 441: e: -0.78V, b:-071V, c:+7.4V;
D458: 7.5V


My TS441 values are: e: -0.69V, b:-0.62V, c:16.36V

The voltage across D458 is just 63mV!
Measuring voltage from Anode leg to ground shows 2.73V, and from Cathode leg 2.68V.
- Am I measuring the voltage across the diode wrongly? I find almost the same voltage on either side of R583: 2.75V, 2.69V, and suspect it is that value I get from my measurements on D458...

Where should I go from here? Replace D458 (and TS441)? The poster on the other forum fixed his supply voltage with a new D458.
Since my supply voltage is far more off, could the problem lie an entirely different place?

After a quick glance at the scheme, that 14vac should be around 14.8vdc just past the rectifier, and 9v after the last leg of R585 and D457.

I get 19.7V over the +- legs of the rectifier (lead A14 and top end of D456)

I suppose you refer to the right hand side of these components, as seen in the wiring diagram above- and in relation to ground/chassis?
For the R585 I get 1.9V, for the diode 3.3mV (wich i suspect is actually 0.0V) on the left hand side.
On their right hand sides I get R585 2.77V and D457 0.69V

P.S.
Measuring the TS441 collector I accidentally touched the housing. The stop and auto-stop bulbs lit up to their normal brightness...

P.P.S.
Reducing the resistance on R472 makes the voltages reported here decrease - I hope this is correct.

CT Jim:
These bulbs are getting increasingly difficult to get a hold on, and having to wait for 2-3 weeks to play your records while waiting for replacement bulbs, is a drag.
Philips thought it was a good idea to switch to leds in the late 70-ies: The later 312s came with leds, and you can find a Service Manual Supplement for the 312 from Philips in VEs library, where Philips qualifies this change with "for increased reliability"

Regards
lennie

 

[Lennie.no]

Hi again.

I left my quest to bring my 212 back to life on hold for a while now, hoping to get some more tips as how to proceed on this forum.

I am stumbling in the dark, and suppose the lack of feedback has much to do with me asking the wrong questions...
I have therefore tried to read up a bit, and although I have a long way ahead of me, I hope the shimmer of light I see is indeed daylight.

I found that I should be able to determine if transistors and diodes are faulty with my digital multimeter (DMM) and its Diode test function.
There are several 'How to'-s out there, and I followed this for transistors and this for diodes.

The first guide says that there should be a voltage drop from Base to Emitter and from Base to Collector between 0.45V and 0.9V on NPN transmittors.
On PNP transistors there should be the same voltage drop from Emitter to Base and from Collector to Base when the transmittors are good.
Collector to Emitter and Emitter to Collector should read 'OL' (Over Limit) for both NPN and PNP, as should all other measuring combinations.

On the Diode test guide we read that
"A good forward-based diode displays a voltage drop ranging from 0.5 to 0.8 volts for the most commonly used silicon diodes.
Some germanium diodes have a voltage drop ranging from 0.2 to 0.3 V."

On another forums thread on testing germanium transistors, I read:
"what you are basically looking for is two diode junctions, one between the base and collector and the other between the base and emitter. With the diode test feature of a DMM, you would expect to get a reading of around 0.2 when the test probes forward bias each junction of a germanium transistor, and a reading of OL, infinite, or the whatever the meter does to indicate an open circuit when the junction is reverse biased. Some germaniums have slight leakage so you might get a very high resistance reading in the reverse direction"

With the above in mind, I went on to measure the suspects, TS 405=AD162 (PNP type) and TS 441=AC127 (NPN type).

TS 405:
(Positive test probe to the first letter. Voltage, resistance)

eb: 0.158V , 468 ohm ------------ be: OL , 187 Kohm (and sinking value)
cb: 0.154V , 451 ohm ------------ bc: OL , 133K (and sinking value)
ec: 1.756V , 1.5K (sinking) ------ ce: OL , OL

TS 441:
(Positive test probe to the first letter. Voltage, resistance)

be: 0.167V , 507 ohm (sinking) ----- eb: OL, 70K (rising value)
bc: 0.164V , 490 ohm (sinking) ----- cb: OL , OL
ce: 1,9V (sinking _, OL ---------------- ec: 0.95V (rising_ ____, 1.48K (and rising)
_____ after 1 min. --------------------------_ after 1 min.-> 1.01V)
w/probe at leads:1.8V)


D458=BZX79C7V5 (Zener type):

positive probe to Anode: 0.03V
positive probe to Cathode: 0.03V


Bridge rectifier D456=BY164
I get forward bias values from the AC inlets to the + outlet of 0.58V and 0.55V; from the - outlet to the AC intakes 0.56 and 0.57. Across outlets, - to +, I get 1.03V.
All other paths read "OL".


From the test guides I refer to, I am pretty sure the D458 is gone.

For the transistors I am somewhat bewildered: The forward bias (PNP: eb, cb; NPN: be, bc) could be said to be in the expected "around 0.2" range. So is the reverse bias (OL or high K-ohm readings)
What makes me uncertain is the readings I get on ce and ec: For silicone transistors I would expect "OL", but since germanium transistors can have some leakage on reverse bias (as my specimen does), could my readings be OK?

The Bridge rectifier looks fine to me.

Searching for replacements for these transistors, I find them hard to get hold on, and relatively costly as well. If I need to replace these, I would be grateful for suggestions on sources.
The D458 zener diode is available as NOS, but a 'cousin', BZX79C7V5-113, is readily available in most electrical components stores
Are these compatible? I can't find any difference looking at the specs given in different stores.
Are there other, perhaps better, modern diodes I could use without having to replace other parts of the power supply circuit?


All the best!
Lennie