30 Apr
2023
30 Apr
'23
8:34 p.m.
Looks like the one I used is an L7812CV, which has a looser tolerance. I am going to have
to order some tighter tolerance parts.
-----Original Message-----
From: Wayne S <wayne.sudol(a)hotmail.com>
Sent: Sunday, April 30, 2023 7:42 PM
To: Wayne S <wayne.sudol(a)hotmail.com>
Cc: rob(a)jarratt.me.uk; General Discussion: On-Topic and Off-Topic Posts
<cctalk(a)classiccmp.org>rg>; Rob Jarratt <robert.jarratt(a)ntlworld.com>
Subject: Re: [cctalk] Re: Rainbow H7842 PSU Fault
The CT version is 4%, the ACT is 2%.
Sent from my iPhone
On Apr 30, 2023, at 11:37, Wayne S
<wayne.sudol(a)hotmail.com> wrote:
Spec sheet for the 7812 shows 2 versions - 4% and 2% tolerances. So the
voltages
your measuring are within the 4% part. Maybe you do need the 2%
one.
Sent from my iPhone
> On Apr 30, 2023, at 11:26, Rob Jarratt via cctalk <cctalk(a)classiccmp.org>
wrote:
>
> I think I have found a possible cause, but not too sure what to do
> about it if I have.
>
> I had to replace the 7812 regulator that supplies Vstart. The new one
> has an output that seems to vary between 12.2 and 12.4V. The 7812 on
> the good PSU outputs a steady 12.1V. I think that is enough to cause
> the E3d comparator to turn the comparator off and allow its output to
float
high.
>
> I suspect I may have used one with a wide tolerance rather than a
> narrow one, or just have a bad one. It should be a genuine part as it
> came from CPC Farnell. Not quite sure why the output varies on the bad
one
though.
>>
>> Regards
>>
>> Rob
>>
>>
>>