29 Jun
2023
29 Jun
'23
9:19 p.m.
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.jarratt(a)ntlworld.com>
Sent: 25 June 2023 18:07
To: 'Tony Duell' <ard.p850ug1(a)gmail.com>om>; rob(a)jarratt.me.uk
Cc: 'General Discussion: On-Topic and Off-Topic Posts'
<cctalk(a)classiccmp.org>rg>; 'Brent Hilpert' <bhilpert(a)shaw.ca>
Subject: RE: [cctalk] Re: Rainbow H7842 PSU Fault
-----Original Message-----
From: Tony Duell <ard.p850ug1(a)gmail.com>
Sent: 25 June 2023 18:00
To: rob(a)jarratt.me.uk
Cc: General Discussion: On-Topic and Off-Topic Posts
<cctalk(a)classiccmp.org>rg>; Brent Hilpert <bhilpert(a)shaw.ca>
Subject: Re: [cctalk] Re: Rainbow H7842 PSU Fault
On Sun, Jun 25, 2023 at 5:52 PM Rob Jarratt
<robert.jarratt(a)ntlworld.com>
wrote:
about the
fan turning.
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
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