GW Instek GPD-3303S Fan replacement

[sequoia]

Scored one of these from eBay (apparently liquidated stock from ITT Tech). PSU seems to work fine and calibration seemed to be spot on (have to still verify if the CH3 has that overshoot when turning output on...)

Only problem is than fan bearing is going out and it's making annoying noise.

Quick look inside and fan seems standard 80mm x 80mm x 25mm computer fan (as it has 4 leads), but schematics imply that two pins are for power and the other two control speed as there appears to be two 20K thermistors in parellel connected across the other two pins. So not "standard" PWM fan used on PCs (?)

Service manual lists fan as:

* FAN MGA8024MR-025, DL24V, 80*80*25, MS, P, CE

So it not 12V fan (and not PWM), so simply replacing fan with inexpensive (and quiet) PC fan doesn't seem to be an option...
Is this type fan standard (where fan speed appears to be proportional to resistance over the two control pins/leads)?

Does anyone have ideas where to get suitable replacement fan? 

[nctnico]

Did you try to put the number on the fan (not the one in the service manual) into Google? That usually leads to shops where they sell it.

[sequoia]

Actual fan in my unit was made by Younglin Tech. Model DFB802512H. (DC12V 2.0W)

This fan contains circuitry to control RPMs based on thermistor connected across two control leads. PSU has two 20k thermistors (one under each heat sink) in parellel configuration, and fan seems to expect 10k thermistor across the control leads.


I got an idea to build small adapter that plugs into the fan connector on the main PCB and and has connector for standard (PC) 12V PWM fan.
I had Adafruit Trinket (5V) laying around and it has just enough I/O pins to handle this.

I used pin 0 (digital input) to read the pulses coming from PWM fan speed (tachometer) pin, and pin 2 (analog input) to read the thermistor.
For output I used pin 3 (digital output) as serial (TTL) output to be able to monitor fan speed/temperature for debugging purposes and pin 4 (digital output) to generate 25kHz PWM signal to control the fan speed.


I put in nice (quiet) 80mm PC CPU fan (Noctua NF-A8) and cant believe how quiet this thing is now

I'm running fan at about 600rpm when heatsinks are in room temperature and then linearly adjust fan speed to maximum when heatsink temperature rises....

[Kalcifer]

Strangely enough, I just connected a noctua fan directly to the header and it works. Although it probably is not following any fan curve, just full speed.