Philips PM 3365 Noisy Fan Replacement

Since I got my first Oscilloscope a few weeks ago - a Philips PM3365 - I really love it. Except for the fan which is very loud. After successfully replacing the noisy fan of my Synthex with a silent fan, I decided to do the same on this scope.

When trying to find out the specs it was surprisingly difficult to find technical information about the Papst Typ 814. It's a known and common brand after all. After some research I managed to gather the following data: 60x60x25mm, 12V-24VDC, Airflow: 19-49m³/h, Direction: out.

PM3365 original fan

According to the service manual the fan runs at 12V, blowing the air at 19 m³/h out of the case. As the Noctua fan performs so great in my Synthex I was aiming for that brand again, after checking their site I ordered the NF-A6x25 FLX.

Noctua Fan

NF-A6x25 FLX specs
Noctua confused ULNA with LNA on the package cover.

The airflow value is 29.2 m³/h, and it comes with two resistor cables which allow to have a slower fan speed. I wondered about the resistor values of those cables and measured them:

• LNA: 52Ω, will decrease airflow to 23.5 m³/h
• ULNA: 159Ω, will decrease airflow to 16.7 m³/h

As I only need around 19 m³/h I installed the LNA cable and added the LNA cable I had from the Synthex Noctua fan, which gives a total resistance of around 100Ω.

I don't know about the airflow rate at that speed, but I have taken a few measurements at different spots inside the closed case. The temperature stays within a certain range, so for me the project is completed, case closed and done.

Installed Noctua Fan and Resistor cables

Btw, be careful when removing or putting back the upper cover. Over the years the plastic has gotten brittle and I managed to crack some off when removing the upper cover.