Hello,
I've got a Philips PM3305 oscilloscope. This is an analog oscilloscope with digital memory mode. It presents a problem whether I select a microseconds time-base and the MEMORY ON button is pressed. If the time-base is higher than microseconds (ms, s), the waveform is correct:
If the time-base is set in microseconds, the waveform changes:
As you can see, there's like an electrical noise over the entire waveform.
This "noise" remains even though the channel is zeroed:
Since the service manual of this oscilloscope doesn't provide any schematics of the unit, I opened the oscilloscope and I looked for missing/broken components. I found out two leads connecting nothing on the side board (the logic unit):
By surfing the net I found
this thread with all the photos of the boards. By comparing them with mine I found out the component was a capacitor:
Anyway I don't know neither value nor the kind of the capacitor. It probably is a 6.8uF 16V Philips tantalum capacitor since they are all over the logic board. It connects pin 17 (Vref) of AD7541JN (digital-to-analog converter) to ground.
I tried to replace it with another 6.8uF 16V capacitor. Now when the oscilloscope is switched on memory mode with microseconds as time-base, the signal is always at 0V.
I hope someone who has this oscilloscope can help me.
Thanks in advance