>
> A line of thought for consideration, with the usual disclaimer: I've seen
> these (VT100) supplies before but I haven't had to repair one,
> the following is based only on a cursory purview of the schematic.
>
> Let's look at some of the design nature of the supply.
>
> All the outputs extract
On 2016-Aug-17, at 1:48 AM, Mattis Lind wrote:
> Normally I manage to repair the SMPSU that I dive into. But this time I
> must admit that I am defeated.
>
> It is a VT100 PSU (H7831). I tested it with dummy loads and it worked fine.
> But when used in the terminal with the Basic Video board and m
On 8/17/2016 1:19 PM, tony duell wrote:
More load _reduces_ the ripple? That's very unusual.
Perhaps a parasitic oscillation that's defeated by more load
because now the loop gain is below 1?
But loading the +5V output also reduces the ripple on the +12V
output. Loading the +5V output would,
>
> > More load _reduces_ the ripple? That's very unusual.
>
> Perhaps a parasitic oscillation that's defeated by more load
> because now the loop gain is below 1?
But loading the +5V output also reduces the ripple on the +12V
output. Loading the +5V output would, I think, vary the mark-space
rat
> On Aug 17, 2016, at 2:07 PM, tony duell wrote:
>
>
>> When I used a variable load on the 12V both the amplitude and the period
>> varied. More load less amplitude.
>
> More load _reduces_ the ripple? That's very unusual.
Perhaps a parasitic oscillation that's defeated by more load because n
> When I used a variable load on the 12V both the amplitude and the period
> varied. More load less amplitude.
More load _reduces_ the ripple? That's very unusual.
> Added the AVO option. Then I have perfect picture. So the extra loading
> makes a difference.
But that mostly loads the +5V line.
> It's certainly an odd one...
>
> There are several things that are curious. The first is the frequency
> of the waveform. 329Hz or so according to your 'scope (assuming
> I am reading it right). That is far too high to be mains ripple. It is too
> low to be the oscillator in the SMPSU. So where i
> Normally I manage to repair the SMPSU that I dive into. But this time I
> must admit that I am defeated.
>
> It is a VT100 PSU (H7831). I tested it with dummy loads and it worked fine.
> But when used in the terminal with the Basic Video board and monitor board
> it gives a jumpy picture. Both
2016-08-17 11:14 GMT+02:00 Peter Coghlan :
> >
> > It is a VT100 PSU (H7831). I tested it with dummy loads and it worked
> fine.
> > But when used in the terminal with the Basic Video board and monitor
> board
> > it gives a jumpy picture. Both horizontally and vertically. First I
> thought
> > th
>
> It is a VT100 PSU (H7831). I tested it with dummy loads and it worked fine.
> But when used in the terminal with the Basic Video board and monitor board
> it gives a jumpy picture. Both horizontally and vertically. First I thought
> that it was related to the monitor board but soon recognised t
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