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Old 16th Nov 2015, 11:29 pm   #1
1955APREN
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Default Philips PM3240

I have a Philips scope PM3240. A few days ago the unit stopped working, no power light and no screen display including the illum. I removed the power supply board. One of the capacitors near the mains input socket, a .22uf 250v x rated
had burnt up, and one leg of the bridge rectifier was o/c. The PCB had an oily looking substance on it. I did not know if this had come from the main ht capacitor or from the .22uf. I have replaced these parts, also a 100uf 25v. and cleaned the board. Sorry I cannot give ref No.s as there are no No,s on the PCB. I would be pleased to hear if any one has had this fault, or has a circuit digram of the power supply. Thanks for any help that can be supplied.
regards Derrick
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Old 17th Nov 2015, 12:46 am   #2
karesz*
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Default Re: philips PM3240

Hallo Derrick- for your solution...
Karl

Last edited by karesz*; 17th Nov 2015 at 12:56 am.
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Old 17th Nov 2015, 1:48 am   #3
Maarten
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Default Re: Philips PM3240

The RIFA (or sometimes WIMA) x-rated impregnated paper capacitors always fail, and chances are the oily substance is the residue of its impregnation
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Old 17th Nov 2015, 2:27 am   #4
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Default Re: Philips PM3240

RIFA, WIMA and the US Bonbon
were already defective when they left the factory gate 50 years ago.
When we repaired Radio + TV in the 60th - first order check these caps
And after 50 years - move them all ,-)

Peter
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Old 17th Nov 2015, 9:10 pm   #5
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Default Re: Philips PM3240

Thanks ever one for your quick replies
KAREST the circuit diagram and the lay out are just what I required . I shall now spend time fault finding.

Maarten and Chaparal
Yes you where right cap was a RIFA type it did seem strange that the 1.6a main fuse had not blown looking at the state of the cap I would have thought that this would have blown
Thanks again for all your help , I will let you know how I get on with the repair.
Regards Derrick
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Old 17th Nov 2015, 9:26 pm   #6
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Default Re: Philips PM3240

Derrick, you`re welcome.
Quote:
the 1.6a main fuse had not blown looking at the state of the cap I would have thought that this would have blown
Clear, than it`s an "X"-type (and new one must be i.e. an X2 -or safety type too and min. for AC 250V ...), for that reason is his "selfhealing" - can not go in short!
Best greetings Karl

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Old 2nd Dec 2015, 1:01 pm   #7
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Default Re: Philips PM3240

Progress so far. Due to other comments I did not spend a lot of time on this till just a few days ago. At first the power supply was in trip mode, the voltage on the the collector of TS1807 was varying between 274v and 300v. I spent a lot of time looking for faulty part in the power supply, then I did something I should have done in the first place, checked the output lines. This showed that the 45v line out was s/c (2 ohms). This was traced to TS1402 being collector /emitter short. I have replaced with a TIP50. I now have a working p/s and a - voltage high going out on BU601 (not measured did not want to damage meter) the lumll now works and the power light is now on. But I still have no display and I cannot see the CRT heater glowing. Can you please help with information regarding where the CRT heater supply comes from, and the pins no's of the CRT heater.

Last edited by AC/HL; 2nd Dec 2015 at 1:34 pm. Reason: Stuck shift key
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Old 2nd Dec 2015, 2:05 pm   #8
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Default Re: Philips PM3240

DC CRT heater is supplied from the main power supply transformer T1802, winding between pins 17 & 18, via rectifier GR1822.

You have the scope in front of you.
The CRT type.no. should be on a label attached to the CRT.
Now use Google to find spec's which should be do-able.
Just as do-able as Google+Philips PM3240 =Service-manual in pdf.
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Old 2nd Dec 2015, 6:09 pm   #9
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Default Re: Philips PM3240

Hi Derrick,
PM3240 has originally an CRT Type of D14-125GH/37_to find -only- in part of specifications_in 1.2.1..._ and pls find the complete SM to download here.
Regards, Karl

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Old 3rd Dec 2015, 4:56 pm   #10
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Default Re: Philips PM3240

PM3240. You really must get yourself the manual. This scope uses a direct mains switching supply, and everything around your TS1807 is floating anywhere up to 600v away from ground. You should use an isolating transformer to do any testing on these supplies. It was not an entirely successful idea, and Philips kept changing the design for about10 years in the 1970's, each model different..
Be aware the tube heater on pins 1 & 14, each side of the gap in the base pins, floats at -1500v. But you often cannot see the heater glow anyway.
If no trace, consider the tube Bright Up (Zmodulation) circut. The high voltage transistors there frequently fail.
A quick test is does the brilliance control alter the voltage at the collector of TS1308, which drives the diodes through the high voltage capacitor C1309. It is a sophisticated circuit, and you will need to study the description of how it operates p3.2.9.1.

You will be lucky to find any data on the web about any instrument CRT tube types. I have data of many of those produced since 1939. Very useful for identifying suitable alternatives from other makers when one has failed.
The tube D14-125 seems never to have been available commercially. If Karesz has the detailed data sheet on the D14-125, I would be very grateful for a copy.
Identical as far as I can tell is the D14-121 or low heater current version D14-123. The GH/08 or whatever merely indicates the screen phosphor characteristics and the style of the internal graticule.
If you are stuck, I have the full data sheets for these, and also the full service manual for the PM3240.
A high voltage adapter for your meter is useful. I and others have posted details, using a string of resistors in an insulated tube, with the method (almost a trick given by Tek or HP) used to calibrate it. For a few pence of 10M resistors, worth having.
wme_bill

Last edited by WME_bill; 3rd Dec 2015 at 5:01 pm.
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Old 3rd Dec 2015, 7:23 pm   #11
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Default Re: Philips PM3240

Hallo Bill,
tnx for your queshtion, but yet seems for me inpossible to be, but I`m working an that. Btw a good link...
Sincerely, Karl
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Old 4th Dec 2015, 11:41 pm   #12
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Default Re: Philips PM3240

Hi karesz
thank you for directing me to manual i have been able to down load this.

Wme bill
thanks for your inf about ts1308 , i have cheeked collector voltage and have the following
min setting o.63v on brightness
max setting 0.46v
i have also carried out the following measurements on the tube base pins 1/14 6.4v heater with one pin disconnected tested current 100m/a
pin 3 g3 -900v
pin 6 g5 0v
pin 7 k -1380
pin 8 g3- 980
pin 9 g2 44v
pin 11 g7 74v
also noted that b1301 neon light is on
these voltages taken with digital meter on 600v dc range.
I would very pleased for any further information on this fault
thank you for your help so far.
Kind regards derrick
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Old 5th Dec 2015, 8:16 pm   #13
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Default Re: Philips PM3240

PM3240.
Now you have the manual, look as the description of the Bright-up circuit operation.
More tests: does the voltage on emitter of TS1306, the brightup driver vary with the intensity/brightness control . The manual says between 4 and 40v, which will change with the sweep. So be sure to set the TB to XY operation. Your previous test onTS1308 will also have been AC at 100Khz. The DC readings are not helpful.
Don't confuse Intensity control with the preset R1327 Brilliance control controlling the variation of brightness in dual trace operation, which you can forget for now.
Now, more importantly, the grid of the tube (g1) on pin3 should always be negative of the cathode (k) on pin 7. Your figures indicate it is +480v. That is why the neon is on. The neon (ZA1004 85v, 1ma) is a safety valve to prevent the grid going positive and ruining the tube. With the grid as positive as that, there should be an impossibly bright trace.
The other tube voltages look about right. Even if the PDA 8kv has failed, you should see something if the rest of the tube is working.
I suggest to limit any further damage to the tube, disconnect the heater.
Then look at the brightup circuit and diodes. Keep to XY mode. Note that C1309 and C1308 are the high voltage isolating capacitors. Safe to poke about on the LH side, but be careful on theRHS, which is at-1600v.
Make the high voltage probe. It only has to be accurate to 10%. A string of ten 10M and a 100k. Earth at the bottom, probe at the top, and your meter at the 100k. This will give you 1:1000. On ten volt range of your meter, you have a 10kv tester. Calibrate against any other known supply.
I assume your reference to pin3 being g3 is a typing error.
The Philips description of tube grids is rather confusing compared to usual English terms.
G1.p3. or Wehnelt cylinder = Grid. Controls brightness
G5. p6 = interplate shield or screen. Can correct raster/background
K.p7 = cathode
G3.p8 = a2 focus anode
G2-4 p9.= a1,3 main anode or accelerator. Also astigmatism
G7 p11 = mesh. Also geometry
I am a bit gloomy about the tube I am afraid, but lots of near alternatives offered on ebay. Ask if you want suggestions.
wme_bill.
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