> -----Original Message-----
> From: Dave Dunfield via cctalk <cctalk@classiccmp.org>
> Sent: 25 November 2023 14:06
> To: cctalk@classiccmp.org
> Cc: Dave Dunfield <1297.dunfi...@gmail.com>
> Subject: [cctalk] Re: VT100 Monitor Board
>
> > Rob Jarratt 25 Nov 2023 8:47 a.m.
> > Of course the worry is, why? There could be a fault on the board.
> > I am hesitant just to replace the fuse and try it...
>
> An older CRT terminal is probably a bit too much current draw for this, but
> you can prob use it in a setup to test parts...
>
> A very handy gadget you can make very easily, which I use all the time when
> testing small devices in "unknown operational state" is a simple current
> limiter. (following discussion based on North America power, numbers may
> be different if you are in a different part of the world).
>
> The "smallest" typical line circuit is 15A which is more than enough to cause
> damage to small devices experiencing excessive power draw through a fault
> (often indicated by a blown fuse).
>
> The "limiter" relies on the fact that an incandescent light bulb will
> draw/pass a
> fair bit of current when it is cold, and much less when it's warm. (this is
> because they are designed to "turn on" fast)
Thanks. I am familiar with the light bulb current limiter, although I must say
I hadn't thought of using it in this case. I have used it when testing PSUs,
but as this is downstream of the PSU I wonder if it would help? My bench PSU
has current limiting abilities though, so I can provide current limited
voltages within the range of the PSU. It is actually a twin PSU each with a
0-30V range, so I probably could drive the board that way.
Thanks
Rob
>
> In my case, I have three light sockets wired in parallel, all in series with
> the hot
> side of a receptacle. This lets me change from a single 25w bulb (very little
> current possible) up to 3 100w bulbs (a good part of amp before it seriously
> limits). For example, 100w bulbs draw .833ish (100/120) when operating fully
> lit - x3 = 2.5A max current - this would only happen if the device under test
> was "shorted", presenting 0 series resistance and would therefore effectively
> have 0 volts across it.
>
> In practice, you could prob. draw 1/2 amp (160ish ma per bulb) without
> warming them "too much" to seriously drop a lot of voltage. Much more than
> that and the bulbs will light up rather than hearing "popping" sounds from
> the device under test :-)
>
>
> -- Btw, I've given most of my CRT terminals away - For VT100's I use my
> "PC100"
> program - It provides very good VT100 emulation using an old DOS (or
> DosBox) PC - it remains "text" mode, so it turns "smooth scroll" into "slow
> scroll"
> and
> large fonts into "double spaced" fonts - but in all other respects nothing
> I've
> used it on has been able to tell it's not an actual VT100!
> (I'm sure there are better/graphical VT100 emulations "out there")
>
> Dave
>
> --
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