NeXT Cube - powers on briefly then off again

[Ian Finder]

I should make clear that for what I'm saying below, I was NOT testing supplies on their own, but was indeed testing a complete cube with the logic and hard drives hooked up- just with no MegaPixel display attached.

And the point stands- Without a reasonable dummy load for the display itself, some cubes wouldn't stay on.

This was about 12 years ago and I was in middle school so I didn't take notes like I do now. Ergo I don't recall more specifics. 

Just that I used two sizable ceramic resistors that hung off the display connector to mitigate this behavior.

Sent from my iPhone

> On Oct 25, 2015, at 17:42, Ian Finder <ian.finder at gmail.com> 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.
> 
> 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)
>>