Cheap NE555 Pulse Generator for fan replacement

I was about to order NE555 chips to build Random Parts Man's fan timer pulse generator circuit, when I came across this NE555-based pulse generator on Aliexpress. There is also a smaller version without caps.

Could these be used to generate the correct fan pulse pattern required for VA1 DCs? If so, they could be a clean/cheap drop-in option. They're $0.70/shipped to the US.

 

Ah, it does look like they will work. I found these in another listing:

50Hz-1kHz or 1KHz-10kHz should be able to be tuned to the correct range unless I'm mistaken.

Smaller type:

And a schematic for the smaller type:

 

A simple resistor does the job as well http://assemblergames.com/l/threads/dreamcast-fan-replacement.57405/

I have since learned that the stock fan doesn't even have a tacho output, it's just a fan stop sensor.
Chances are the 10k resistor even without a fan attached would keep it running (since the sensor pin is pulled high), i have not however tested that.

 

Oh, wow. So just a 10k resistor between 5v and the fan stop pin will suffice? I was over-thinking this

Following this route, is there a way to add the 10k resistor to a VA0 controller PCB to make it compatible with a VA1 motherboard?[/s}

 

I don't know who told you that - but it's not true. The output pin on the VA1 DC fan is most certainly a tachometer. If you connect a scope to it you can see a waveform and the frequency decreases if you slow the fan down with a finger.

[GALLERY=media, 809]DC_Tacho by TriMesh posted Apr 29, 2016 at 12:36 PM[/GALLERY]

I can also confirm that either a constant high level or a constant low level on the input pin will result in the console shutting down.

 

Huh, i looked at a spec sheet of a fan used in the console not to long ago, that listed it as having a stop sensor. I'll see if i can find that again.
I'm happy to be corrected on this, without access to a scope i couldn't measure it myself, thanks for doing this!

The solution i made the thread for certainly works, had it running like that for a while but the new fan was even louder than the old.

Edit: Supposedly in late systems they used the Nidec DF310RI05L1C-01 fan, this is listed as having a locked rotor sensor. They're also said to not be as loud.
http://www.nidec.net/designoptions/options.htm looking at this it makes sense.
My stock fan measures 10k across V and sens.

 

Maybe, but I've never seen one like that, and I've always found the fans interchangeable - the fan in the unit in that photo is a Mineba (NMB) 1204KL-01W-B49, and that (as you can see) clearly does have a tacho output. It also obviously has an internal pullup, because even running it off a 5V bench supply I can still see the pulses (Voh is about 3.9V with a 5.0V supply). I'm also not sure how a motor with a locked rotor sensor could be made to work, because on these boards ("IC BD KATANA MAIN VA1 MADE IN JAPAN 837-13778") either a static high or a static low for more than a few seconds will cause the board to shut down.

 

Fair enough, maybe the specs for said fan are wrong or it was only used in VA2 systems. The part number i actually found on a german forum where members bulk ordered these fans as a noise reduction measure, no idea how effective that is.

Just to be sure i've edited my previous post as to not mislead anyone.

 

I've ordered both types and will post a write-up if I manage to get them working.

 

I installed the non-capacitor type pulse generator today and it provides the correct tach signal for VA1. I tested for an hour with a VA0 fan, which means that any 2-pin fan will work.


VA1 mobo, VA1 controller board, VA0 heatsinks & fan. I swapped the pulse generator's connector for a JST-XH type. The tach wire from the fan's male side isn't connected.


I have LEDs installed that screwed up the photo's saturation, but this shows it running.

 

I did something similar with a VA1 board, modded it by adding a VA0 heat sink. For the fan I was able to acquire a three pin Toshiba UDQFFAB03F metal fan as a replacement. Some of the early European VA1 revisions actually came with metal three pin fans before they cut costs and used the more common plastic type...

Ted.

 

I have one of these and they are by far the quietest fan I have come across in a Dreamcast. If you are after a replacement fan and you can find one of these I recommend getting it...

Ted.