Old philips pm3310

[BEripsta]

Hello, I have a question

I am interested in electronics and I have the chance to buy an old philips pm3310 oscilloscope. I can get the device for next to nothing because it is broken. The problem is that when the device is powered on the LEDs light up for a few seconds but then it shuts itself off. If you try to start it directly after this, nothing happens. If the device gets unplugged and left alone for a little while you can try to start it again, but then the LEDs light up and it shuts itself down again...

As I am kind of new to repairing things I did not buy the device but first wanted to check in with people who knew more about these kind of things.

Now my question: Is this a problem common with older devices, what do you guys think the problem might be (I don't really know if there is too little information or not to be able to determine the problem), would it be worth salvaging this device... What are your opinions?


Thanks in advance

 

[kellys_eye]

Power supply issues. There is an X-class capacitor across the mains input that has a habit of 'exploding' and the electrolytics in the PSU module should really be changed.

It's a nice 'scope to work on - if you know what you're doing.....

There is full documentation on the web for that 'scope so no shortage of technical details to help you along the way.

I also have a box full of spare logic cards for that model (they're all plug-in) if you need any......

 

[BEripsta]

Power supply issues. There is an X-class capacitor across the mains input that has a habit of 'exploding' and the electrolytics in the PSU module should really be changed.

It's a nice 'scope to work on - if you know what you're doing.....

There is full documentation on the web for that 'scope so no shortage of technical details to help you along the way.

I also have a box full of spare logic cards for that model (they're all plug-in) if you need any......

Ok so I finally got the Oscilloscope and found an X-class capacitor that I thought was broken (it was a rather small one but I replaced it and I still get the same problem). Upon further inspection I did find a big filter named 'Funk-entstorfilter'. Is this the capacitor that you were talking about? I might have interpreted your post wrongly. And if I indeed understood your post wrongly and you were talking about the big filter, is there a way to test if it is broken or not?

 

[(*steve*)]

Take some well lit (not flash) photos and post them. A picture may give us enough information to suggest where to look.

I posted a thread a while back about fixing the power supply in my Phillips scope. I'm my case the problem was pretty obvious though.

 

[BEripsta]

I have uploaded a few pictures from the power supply (I know a few are with flash, those are older ones that I took for myself, figured it wont hurt to upload them). There is a picture with a 0.22uF X style capacitor, this is the one I replaced with a new one seen in the last picture (with the long black leads). I also measured the voltage at the output of the Funk-Entstorfilter, this was a normal 240V.

If there are any more photos or anything needed, let me know.

 

[(*steve*)]

There is nothing obviously burnt in the power supply. That doesn't mean it's not a power supply fault, but it means we may need to look further.

The fact that the power supply seems to start up then shut down may indicate that either it is overloaded or is detecting something incorrect with the output voltages.

The power supply is controlled by a TDA1060. The datasheet is here.

The datasheet has some useful information.

1. The whole circuit will shut down if pin 1 drops below 8.4V This is typically supplied by a resistor. If this resistor has gone high in value it may be causing the input voltage to drop as soon as the current drain increases (i.e. as soon as the chip starts doing something). Measuring the voltage between pins 1 and 12 may give some useful information. BEWARE whilst the voltage between these 2 pins may be low, they may be at mains potential -- set up the multimeter and don't touch it while the power is on. Also beware of the charge on the main capacitors, they may have 400VDC across them for some time after the mains has been disconnected.
2. Current sense (pin 11) detection can also turn off the power supply. Compare this voltage against pin 12. It should be less than 480mV. If there is something in the circuit that is drawing a large current, this voltage will be higher. See the warnings above.

It may also be useful to measure the resistance across the low voltage power rails (with the power off and capacitors discharged) just to ensure there is no short across these rails. I have had several repairs recently where some components across the power supply have failed short circuit with the result that the power supply was put under a lot of stress. Measure between ground and the rail. The resistance will start low and rise. What value does it rise to?

It will also be very useful to find a service manual for this scope. It may have a flowchart to follow to diagnose faults.

 

[BEripsta]

Thanks for the detailed guide!

I will be checking the voltages later this day and posting the results.
I've also been looking for schematics or a service manual, but without much luck. I can not find it anywhere, so if anybody has an idea where I might find one, dont hesitate to post!

There is one page that looks interesting, but I'm not sure if it is to be trusted or not, here is the link: http://www.jetecnet.com/Scopes/PM3310.html

 

[(*steve*)]

User manual
Service manual

That should help

 

[BEripsta]

Oh wow, thats amazing! I've been searching the internet for days to find a service manual..
I'll be looking into it as soon as possible!

Again thanks a lot!

 

[73's de Edd]

Sir BEripsta . . . . .

Here is a mark up of just the units power supply section.
This unit is a HOT chassis to the AC line of all circuitry, being to the left of the X1604 Switch Mode Power Supply transformer primary.
At schematic, top left, you have the MAIN DC voltage being created by the V1602 FWB YELLOW SQUARE and traveling across to the
#2 primary term of the SM Pwr T-former, passing thru it, and ending up at the collector of the BU208A SM POWER XSTR.
Initially , in a no power condition, see if BU208 is shorted C-E and has blown open its R1627 emitter resistor to the left.
If all is well there, do the powered up voltage testing.

The MAIN DC voltage also branched down above the interlocked pair of V1621-1622 via a RED arrow path and upon power up, there
is a "kick start" voltage that passes down the PINK arrow line , to the pin 1 power input of the SMPS IC TDA1060.
A timed burst of drive pulses are then passed to the base of the V1615 driver transistor which follows the LIME GREEN path to the T1603
driver transformer, which then drives the base of the BU208.
If all is well, the terminals 4-3-5 winding of the power transformer supplies voltage pulses to be rectified and filtered by diodes
V1605-1607 to be establishing a constant power supply by using C1623 (gotta be GOOD !).
Then the ORANGE ARROW path carries that voltage down to the apex of the initially used PINK ARROW path that started up the unit.
with the temporary power to pin #1of the TDA1060.
The unit then runs the TDA1060 on this mentioned ORANGE ARROW path supply.

E-caps that could decline in functional capacitance and shut down the unit could also be YELLOW C1611--C1609 and down in the
TDA1060 proximity . . . . C1621--C1622.
Also check R1613 1 meg resistor for high or open.


POWER SUPPLY PRIMARY MARK-UP . . . . . .

73's de Edd . . . . .
. . . . . . . . . . . .

I used to be an airline pilot. . . . .
I got fired because I kept locking the keys in the plane.
That was when security caught me on an 80 foot step ladder with a coat hanger wire.

 

[BEripsta]

Again thanks alot for all the suggestions!

I will be looking further into it when I have the time to do so, unfortunately exams will be coming up so I wont have much spare time. Once I know more, I'll update this post!

 

[BEripsta]

An update on the project:

Yesterday I was checking some values in the power supply, Transistor BU208 seemed to be in good working condition. I measured the resistance between the low power rail and the casing, everything seems to be alright there too. The voltages at the chip TDA1060 were alright as well.

The weird part is that I could not understand what was wrong, so I plugged the cables back in and tried to start the oscilloscope one last time just in case. And by magic it turned on just like nothing happened! I have tried it again today and everything seems to be working fine so I don't really know what was wrong.

Maybe there was a bad connection between the BU208 transistor and the board (I took it out to measure)...

Hopefully it will stay in this working state!