H720 PSU?

Tony Duell ard at p850ug1.demon.co.uk
Thu Apr 16 13:14:05 CDT 2009

> > It's the 11/44 (a much later machine) that has odd fans -- 35V 70Hz or
> > something. They run off a transistorised full-H driver circuit in the
> > PSU, so they can be run off the backup battery.
> That's the one.  I guess I should have paid more attention - I have an
> 11/44, but I've never fiddled with the fans.  I think I'll put "check
> and clean 11/44 fans" on the list of summer classiccmp tasks.

The fan assembly slides out of the side of the machine, I think there's a 
connector to unplug once you've got it out about 1" or so. The fans are 
conventionally made, you can remove circlips and washers from the centre 
of each one to extract the rotor/blades and thus clean/lubricate the 

Do not short either fan lead to the chassis when the machine is powered 
up. If you do, you blow at least one of the driver transistors. Please 
don't ask how I found that out.

> OK.  So... that makes finding at least one H720 more important.

I have at least 2 of them, but neither are spare (not to mention the fact 
that (a) they're the 230V version and (b) shipping would be expensive). 
One runs the RK11C on my 11/45 system. The other is part of a DX11 which 
I really must get round to investigating.


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