> -----Original Message-----
> From: Tony Duell <ard.p850...@gmail.com>
> Sent: 25 June 2023 18:00
> To: r...@jarratt.me.uk
> Cc: General Discussion: On-Topic and Off-Topic Posts
> <cctalk@classiccmp.org>; Brent Hilpert <bhilp...@shaw.ca>
> Subject: Re: [cctalk] Re: Rainbow H7842 PSU Fault
>
> On Sun, Jun 25, 2023 at 5:52 PM Rob Jarratt <robert.jarr...@ntlworld.com>
> wrote:
> >
> > Before I confuse matters too much I should point out that I was not using
> the Rainbow power switch unit but one from a DECmate. I had erroneously
> thought there was a fault with the Rainbow one. I think the fan supply may
> be different on the DECmate switch, so ignore the bit about the fan turning.
>
> It appears that there are 2 ways of powering (different types of) fans with
> this
> power supply. Whether one was used in the Rainbow and the other in the
> Decmate I know not. But anyway :
>
> A 12V DC fan running off the DC output of the power supply. This is the one
> shown in my schemtic for the supply. Note the jumper link in the fan power
> plug that means the supply doesn't get mains if you forget to plug the fan in.
That is what I failed to notice and I thought that somehow there was a fault in
the switch unit.
>
> A 115V AC fan connected to the unused pair of pins on the AC input cable to
> the power supply (top right of the 'switch/fan assy' in my schematc. This uses
> the primary winding of the startup transformer as an autotransformer on
> 230V mains.
>
> Note that the latter fan will run if the chopper side of things is dead, the
> former won't.
>
> -tony
