Vectorlist Archives: RE: Safe to run XY PCB w/ monitor disconnec

From: James Nelson <nelsonjjjj_at_didactics.com>
Date: Fri Apr 20 2001 - 16:26:20 EDT

Ok, If the input could be loaded down, current can flow reverse through the
device, and if it exceeds 1.0 Amps, there is a chance the device will blow
internally At 2.5 Amps, Blowout is certain. The reverse diode is an
excellent idea in this situation.

Have a great weekend everyone
James

-----Original Message-----
From: owner-vectorlist@synthcom.com
[mailto:owner-vectorlist@synthcom.com]On Behalf Of Rodger Boots
Sent: Friday, April 20, 2001 2:19 PM
To: vectorlist@synthcom.com
Subject: Re: VECTOR: Safe to run XY PCB w/ monitor disconnected?

Backfeeding is NOT acceptable. If there is a possibility of backfeeding a
diode
should be connected from input to output. Any data book should tell you
that.

James Nelson wrote:

> I still don't get that. First of all, undervoltage on those regulators
just
> causes them to go to minimum voltage drop and they run cold as ice.
Second,
> if any thermal condition existed, they are protected against that. They
are
> also protected against shorts. Backfeeding the output is also acceptable
> practice.
>
> FORGET ABOUT IT.
>
> By the way, they only cost about $0.25 and are plentiful.
>
> -----Original Message-----
> From: owner-vectorlist@synthcom.com
> [mailto:owner-vectorlist@synthcom.com]On Behalf Of John Robertson
> Sent: Friday, April 20, 2001 12:25 AM
> To: vectorlist@synthcom.com
> Subject: Re: VECTOR: Safe to run XY PCB w/ monitor disconnected?
>
> Ah, now I understand!
>
> You MUST raise the outputs of the regulators IF you are feeding voltage
> AFTER THEM. In other words, the author is not providing the +/-25VDC or so
> that the regulators normally get on their inputs, rather he is providing
> somewhat lower voltages (+/-12VDC) than the regulators produce (+15,
> -15VDC) and this WILL destroy the regulators if they are left in circuit.
>
> Thus, IF you are providing the +12,-12VDC etc. substitute voltages, then
> you MUST disconnect the outputs of the regulators.
>
> John :-#)#
>
> At 08:40 PM 4/19/2001, you wrote:
> >Ok I Have a question now On the page
> >http://www.geocities.com/SiliconValley/Horizon/2253/vectors.html
> >It states
> > >>The first thing you MUST do is to desolder/clip the outputs (pin 3) of
> > the 7815
> >(VR3) and >>7915 (VR1) regulators away from the PCB. If you do not, they
> >will get
> >HOT and be >>destroyed!
> > This is just because the page author was feeding the board 12 volts
> > rather then
> >10, Right? or Am I missing something? Why would anyone really need to do
> >all that
> >hacking to put a display up on a scope?
> >
> >-=Mark=-
> >
> >
> >Rod Spade wrote:
> >
> > > Bret Pehrson wrote:
> > > >
> > > > Specifically with Atari -- Star Wars and Major Havoc, is it safe to
> > run the
> > > > PCB with the monitor completely disconnected or can it cause
problems?
> > > >
> > > > I'd like to work on the games using a scope for the output, and
> > disconnect
> > > > the monitor (at least the power) until I get the boards working
> > correctly.
> > > >
> > > > The reason I ask:
> > > >
> > > > http://www.geocities.com/SiliconValley/Horizon/2253/vectors.html
> > > >
> > > > indicates that the regs output needs to be clipped.
> > >
> > > I think he just did that so he could use an alternate power supply for
> > > the board - but I'm certainly not an expert.
> >
>
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> >
> >
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RE: Safe to run XY PCB w/ monitor disconnected?