NeXT Cube - powers on briefly then off again

[Brian Archer]

Even a 10W resistor will get really hot. I embed two 5W resistors into a
pentium class CPU cooler for a good compromise on space/thermal concerns.
You can see a pic on my site here:
http://asterontech.com/Asterontech/next_adb_conversion.html

Internal to the cube, I've found using a 5W appliance bulb to be the
easiest.

--
Brian Archer


On Sun, Oct 25, 2015 at 7:46 PM, Toby Thain <toby at telegraphics.com.au>
wrote:

> On 2015-10-25 8:56 PM, Toby Thain wrote:
>
>> 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
>>
>>
> I got a really helpful response from Rob Blessin, from whom I bought the
> splitter cable, along the same lines. My supply must be the 152 type that
> requires a load.
>
> Boiling down all the info so far, it seems that a 20 Ohm resistor across
> -12V and GND (maybe 12V and GND would work equally well?) would dissipate
> 7.2W, which seems enough to keep the supply running (that other link talked
> about a 5W load, so this seems a good margin).
>
> Now, 7.2W is more than one resistor in say a DB-19 shell could safely
> dissipate, so I'm maybe looking at some kind of ambiently cooled board. Rob
> provided these links:
>
>
>   Here: http://www.nextcomputers.org/forums/viewtopic.php?t=3736 and
>   version 1.0 megaload here:
> http://www.nextcomputers.org/forums/viewtopic.php?t=3616&highlight=load+board
>
>
> So I'm wondering what kind of thermal design is both easy and safe. A
> single 10W resistor exposed to the air? Or should I spread it over a few
> resistors on a little board that might have a DB-19 male at the Cube end.
>
> Just noob brainstorming here.
>
> --Toby
>
>
>