Thank you to everyone who helped me with this. The PSU if finally fixed. I have posted about it on my blog: https://robs-old-computers.com/2023/06/29/h7842-finally-fixed/
Regards Rob > -----Original Message----- > From: Rob Jarratt <robert.jarr...@ntlworld.com> > Sent: 25 June 2023 18:07 > To: 'Tony Duell' <ard.p850...@gmail.com>; 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 > > > > > -----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
