Philips PM3215 Scope Tantalum Capacitor Upgrade

[Mooly]

Originally Posted by techbiker

Mooly, what should I be looking for if I measure the scope with its own probe? I've never checked rails for ripple.

Also, I double checked and the 4700uf 40v capacitor is listed as an electrolytic tantalum in the service manual. These do exist, but they are very expensive.

Any regulated (stabilised) rails should be virtually pure DC.

So with the scope AC coupled and the probe on the appropriate rail you should see only a minimal AC component present. Perhaps as low as a couple of millivolts. Somrthing like the 4700uF cap (and I'm guessing without seeing the circuit) sounds like a main reservoir cap before any regulators and so a couple of volts of ripple may be present here.

All test like this assume that the negative end of the cap is at ground potential (or positive end of cap in the case of negative rails).

Don't connect the ground of the probe to any point internally in the scope. If a cap seems to have a large ripple component then measure on the other end as well. It may not be at ground potential.

I think tbh the scope will be performing to spec... so don't break it

[techbiker]

Thanks for the recommendations. I will test the scope and see if I could benefit from new capacitors.

The build quality on this scope is actually pretty good. It's amazing that working test equipment from the 60's-80's is still floating around!

I called up Philips and they had no idea what the "Scientific and Industrial" division was lol. I then called up Fluke and the VERY helpful guy on the phone flat-out refused to support their older equipment.

It's a good thing this forum exists, that's for sure!