NeXT Cube - powers on briefly then off again

[Toby Thain]

On 2015-10-25 8:42 PM, Ian Finder wrote:
> No- if it works with the standard display, the supply is fine.
>
> Now that that's clear, I recall some cube supplies would do this without a load for a display- I used to test them by triggering the power-on pin, and seem to remember this behavior occurring if I didn't have a big-ass resistor attached across the pins that normally supplied power to the CRT.
>
> Try getting a dummy load on there, the circuitry you have may not be putting enough load on the lines that usually run the CRT to keep the supply in a steady state.
>


Even though I'm an electronics noob, that seems pretty logical. Can you 
spell out what kind of resistor I'd need?

Is it the 20 Ohm 20W between pin 12 (-12V) and GND that is mentioned here:

http://www.nextcomputers.org/forums/viewtopic.php?t=1374&sid=80e5f0626eeb6a10eed066e21b61808d

Is 20W the right rating?

Thanks!
--Toby

> Cheers,
>
> - Ian
>
> Sent from my iPhone
>
>> On Oct 25, 2015, at 16:37, Toby Thain <toby at telegraphics.com.au> wrote:
>>
>>> On 2015-10-25 7:21 PM, Ian Finder wrote:
>>> I would replace the electrolytic capacitors in the power supply before going further.
>>
>> Well, the problem disappears with the standard setup. You still think caps could be at issue with the splitter setup? What's your detailed thinking?
>>
>> --Toby
>>
>>> Sent from my iPhone
>>>
>>>>> On Oct 25, 2015, at 15:38, Toby Thain <toby at telegraphics.com.au> wrote:
>>>>>
>>>>> On 2015-10-25 5:28 PM, Toby Thain wrote:
>>>>> Hi,
>>>>>
>>>>> After a few years I wanted to try my Cube with the soundbox/VGA splitter
>>>>> configuration for the first time. (I have the fading phosphor N4000A so
>>>>> have been keen to have an alternate video solution.)
>>>>>
>>>>> However, all is not well. Using the keyboard power button, the machine
>>>>> powers on for a couple of seconds, just long enough to see a NeXT logo
>>>>> and grey desktop on the VGA (yay!) but then powers itself off again.
>>>>
>>>>
>>>> I did the obvious thing and tested it with a standard monitor and cable and everything is okay. So the problem must exist with the splitter/soundbox setup. Soft power signals?
>>>>
>>>> Any suggestions welcome.
>>>>
>>>> --Toby
>>>>
>>>>> Any clues?
>>>>>
>>>>> Thanks in advance
>>>>>
>>>>> --Toby
>>>>> (not having a good classic computing week)
>>
>