Author Topic: Philips PM 3232 repair  (Read 25000 times)

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Offline Heribert Hechtersheim

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Re: Philips PM 3232 repair
« Reply #25 on: October 14, 2013, 11:58:36 am »
I assumed that the voltage multiplier is broken, so I decided to look what's inside the black box. Getting to the pcb was not very easy, after I removed the outer plastic layer with a simple wood saw, a very bad smelling block of nasty synthetic material appeared.



 I got it off the pcb by using a screwdriver and pliers. I accidantally damaged some caps by doing it so I wasn't able to determine what components were causing the voltage multiplier not to work correctly.



Then I desoldered all parts and cleaned the PCB in the sink with warm water. After that I had to decide what components I should use to substitute the old parts. The diodes were not labeled at all and the caps had an uncommon labeling.



It was "W470 4kV". I think the "4kV" stand for 4 kilo Volt maximum voltage. But I was not sure if the 470 stands for 470pF or 47*10^0pF = 47pF. I decided to use my new Fluke 17B DMM  but I was not able to measure the capacitance. Every time I added another of these caps in parallel to my test leads, the difference between the capacitance was not constant but dropping.
However, I bought 470pF 4kV caps and GP0240 diodes, which are rated for 4kV and 250mA:



By the way, here is the schematic I figured out for the multiplier:



Then I soldered all components on the board. It wasnt so easy for me because I had to keep the old solder in the holes liquid so the legs of the new components could slide through. I kept the little ceramic rings at the legs from the old caps and used them again. Maybe they will prevent arcing. I reused the old resistor because it wasn't damaged.



After I finished the soldering I hooked it up to my scope and secured it with a peg so the board was floating in the air and could not create any shorts.



Much to my astonishment a trace appeared, which made me very happy.



Next I wanted to put the pcb back into a secure casing. I decided to use some old silicone rubber I found in our basement. I made a little cardboard box with the backside of the old case attached to it which had the clips on it so it can be connected to the body of the scope.





Unfortunately I used to much binder when I mixed the silicone rubber, which caused the material to get stiff very fast. I had just enough time to fill the box and stuff the PCB in it. The result was not perfect so I used tape to seal everything up.





Then I read the first chapter of the calibration in the service manual and adjusted the pots so the traces were equally bright and focused. I did not continue with the next chapter because I am not sure if I can adjust it without any other equipment than a second scope and a multimeter. Is it nevertheless possible for me to calibrate the scope? Could it be done with the calibration voltage of my second scope?



 

Offline grumpydoc

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Re: Philips PM 3232 repair
« Reply #26 on: October 14, 2013, 12:39:51 pm »
Quote
Nice job. I think you are right, the -1500V is a low impedance point so -1527 could be correct

-1527 reading on that rail completely OK (as deminstrated by sucessfully fixing the multiplier - nice job BTW).

Just under 30V out in 1500 is 2% out which is fine.

That said the actual reading may well be a bit higher - there's 1% tolerance in the resistors, but having 100M/.991M in the divider makes it read about 2% low - having 9x10M plus a 9.1M and adding a 10K to the 1M+100K series combination would reduce the systematic error to less than 1% (not much point aiming better because of the resistor tolerances).
 

Offline Heribert Hechtersheim

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Re: Philips PM 3232 repair
« Reply #27 on: October 14, 2013, 01:29:15 pm »
-1527 reading on that rail completely OK (as deminstrated by sucessfully fixing the multiplier - nice job BTW).

Thank you very much!

That said the actual reading may well be a bit higher - there's 1% tolerance in the resistors, but having 100M/.991M in the divider makes it read about 2% low - having 9x10M plus a 9.1M and adding a 10K to the 1M+100K series combination would reduce the systematic error to less than 1% (not much point aiming better because of the resistor tolerances).

Oh! I totally miscalculated that when I choosed my resistors. But I think I will not change it because I hot glue everything and now I know the ratio so I can calculate the voltage ;)
Like PA4TIM said, adding a pot would be the best solution. Then the resistance error percentage would not matter. But therefore I need a reliable voltage source to calibrate the probe or a Multimeter which can read those high resistances.
 

Offline Bryan

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Re: Philips PM 3232 repair
« Reply #28 on: October 14, 2013, 08:49:25 pm »
Good job, enjoyed the thread. I would have given up a long time ago. :D :D
-=Bryan=-
 

Offline PA4TIM

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Re: Philips PM 3232 repair
« Reply #29 on: October 14, 2013, 09:23:58 pm »
Nice Job.
Do not mess with the calibration unless you have the tools.
You can check amplitude with a DC signal (set trace at centre, chose for instance 1V/div, measure the output of you psu at 3V with your multimeter and set the scope op DC and connect it to the psu. You must see the trace now go up 3 divisions)
Timebase: build a Xtal oscillator with a 10 MHz Xtal. Use things like 4013's to divide it a few times and you can make a standard with several frequencies that will be good enough to get a decent amateur calibration.
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
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Offline Satbeginner

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Re: Philips PM 3232 repair
« Reply #30 on: May 13, 2017, 04:24:54 pm »

I've recently also repaired 8 Philips PM3211 scopes and all of them emit this high pitched whine when starting up. After a few seconds the caps charge up and the frequency is beyond the hearing range so it seems quiet. Looks like all of these Philips scopes had the same power supply topology. The audible whine in your scope may be a problem with a power supply overload.


Hi, I know it's an older thread, but I also bought a PM 3211 as a repair project to keep me busy.

Mine does not power up and blows fuses.
Is there an obvious thing to look at with these power supplies?

I did a basic check of the blue caps, and none of them shows a short.
One of the BD237's was shorted out, so I replaced that, but so far no luck.
After the replacement of the BD237 at least the fuse stays ok for about 20 seconds, so I have some time to test things.
I replaced the 3.6V sender, that seems broken too.

I temporarily disconnected the two caps to the HV tripler, but still no change.

I would be happy with some suggestions.

Un saludo,
Satbeginner (Leo)
You need a scope to repair a scope, and you need many multimeters to repair another multimeter!
*Tek 2467B, Tek 2465B, Tek 2465B, Tek 485, Tek 475A,  Keithley 175A, Keithley 2000, HP 3468B, HP 3457A, HP 34401A, PM 6671, PM 5716, Fluke 45, Fluke 75, Fluke 77, Fluke 79, AFX 9660BL, KPS 605D, etc. *
 

Offline ACruz

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Re: Philips PM 3232 repair
« Reply #31 on: April 24, 2019, 07:14:54 pm »
Hello to all,
    I hope someone out there is willing to give me a hand on fixing my vintage scope...

I have a Philips PM3233 with a power supply board issue that I'm fighting with for the last 3-4 days!  |O |O |O
I know it is related to 1500v rail that is shorting to ground somewhere...

So far I found t800 transistor to be faulty and that along with it R829, R830, R802 and R819. I've replaced all of them except for the transistor.

When I remove the transistor T800 I have all power supply voltages OK. When I place it back (note that I know it is shorted between emitter and collector) the voltage drops from 1500v to around 900v and I have a voltage drop in R830 of 100v and R829 of 200v this will cause them to burn after a few seconds. What I don't understand is why this is happening cause even if it is shorted the current increase shouldn't be enough to burn the resistors... I might be wrong  :-//

Any suggestion?

 

Offline ACruz

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Re: Philips PM 3232 repair
« Reply #32 on: April 25, 2019, 10:11:51 pm »
No one willing to give me a hand on this?  :box:

I've red that cathodic tubes can sometimes short internally. Although I don't believe this is the case can someone tell me how can I check this?  :blah:

An other possibility that I've heard of is that the tube will short if the focus voltage gets higher than tolerance in this case higher than 650V and will become conductive to the astigmatism regulation grid. This might happen if the t800 is shorted wish is my case. Does anyone agree with this?   :blah:

Best regards;
Alcides Cruz
 

Offline PA4TIM

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Re: Philips PM 3232 repair
« Reply #33 on: April 26, 2019, 11:52:16 am »
No use in going on burning things or test things like crt's when you know a tranny is dead. First replace that.
What is the value of those resistors. The voltage over them and their value give you the current. The current and voltage give you the dissipated
power. You only need little current at 400V to get a lot of power. 100mA at 400V is 40W ! In EVERY repair you first test and if needed repair the power supply. A psu problem can cause all kinda weird problems.
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
www.schneiderelectronicsrepair.nl  repair of test and calibration equipment
https://www.youtube.com/user/pa4tim my youtube channel
 

Offline ACruz

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Re: Philips PM 3232 repair
« Reply #34 on: April 27, 2019, 04:30:27 pm »
Thank you for your reply! :-+

I know I should replace it and I've already ordered it. It will take 1 week or 2 to arrive.

What I want is to understand why the CRT is shorting. I want to learn a bit about CRT's and thermionic valves. This old technology is new for me and I'm sure there are some old school guys out there from which I could learn some tricks.

Best regards;
Alcides Cruz
 


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