NeXT Cube powers up, 3 secs later powers down

[daniel.dlds]

I got the attached image from the ATX conversion page :



Which PINS of the left most column should I short ? When doing this, I think that I should put 3V on the pins of the column to the right ?

PS: if image does not appear it is at : https://ibb.co/1QD9Y3b

Thanks for any help,
Regards

[barcher174]

The RTC is next to the battery and a small surface mount crystal. To check the power supply rails you also may need a load across the -12v rail to keep it powered. Otherwise, yes just hook the battery to the marked input.

[daniel.dlds]

The RTC is next to the battery and a small surface mount crystal. To check the power supply rails you also may need a load across the -12v rail to keep it powered. Otherwise, yes just hook the battery to the marked input.

So to power on the power supply I should (in sequence) ? :
- apply a load between a pin on the 12V and GND
- supply the 3V to the input marked -3V momentarily (I suppose this is the signal sent from the battery when the power button in pressed)

Thanks for any help,
Regards

[barcher174]

1) -12v to GND ~330ohm

2) You need to keep the 3V applied I think.

[daniel.dlds]

I made a small diagram of the connector of the Cube's power supply, the resistor acting as the Load and a bench power supply to turn on the NeXT power supply.
it is here : https://ibb.co/8gRjGj5

There is a question mark on the second wire coming from the power supply (GND or negative, I really don't know which). I think I need to make this connection somewhere because if not, no current will flow into the -3V of the PSU.

Am I right ?

[barcher174]

The 330ohm should go from the blue boxed -12v to black boxed GND. The battery should attach from light blue boxed 3v input to black boxed GND.

[daniel.dlds]

Thanks for you reply.
What is the power rating of the 330 Ohm resistor, that I should use ?

Thanks,
Regards

[barcher174]

A big one. Like 5w. Alternatively I use a bulb like this: CBconcept - 10 Bulbs - 12V 5 Watts, AC/DC JC T3 G4 Bi-Pin 5W Halogen Light Bulb, Accent Lighting, Chandelier, Puck Light, Microwave, Range, RV, Landscape Lighting - Designed in CA https://a.co/d/e9Fb0Vd

[daniel.dlds]

I tried to test the power supply in isolation, by connecting the 12V to a light bulb and the battery across the -3V pins. The power supply didn't turn on. I don't know what I did wrong.
Anyway, I re-installed the PSU in the cube, and powered it on. This time it didn't shutdown after a few seconds. I left it running for about half hour and it stayed on.
Problem is that now the computer shows a grey screen with vertical stripes, and does not boot. It even does not do the system test. It just stays on the grey screen. (link to a photo of the screen : photo)

So I am starting to suspect that there was nothing wrong with the power supply, but with the main board.
How can I continue testing ?

Thanks,
Regards

[barcher174]

No easy answers from here. Recap —> RTC chip —> cpu or next asic fault

[Rob Blessin Black Hole]

Hello Daniel: You can also try removing the ram and unplugging the hard drive then powering it on to see if is the main board causing that pattern. I have had that happen with incompatible ram or a bad memory stick or like Brian is saying new caps

[daniel.dlds]

I removed all the RAM disconnected the hard drive (SCSI2SD), but the behaviour is the same.
The board was sold to me recapped. Is it possible that in the space of a year or so a cap may be bad ?

[barcher174]

Can you post some high res pics of both sides? Also some close ups around the new caps.

[daniel.dlds]

Links to the pics :
https://danielsantos.world/IMG_0221.JPG
https://danielsantos.world/IMG_0222.JPG
https://danielsantos.world/IMG_0223.JPG
https://danielsantos.world/IMG_0224.JPG
https://danielsantos.world/IMG_0225.JPG

Best Regards

[barcher174]

There is a cap missing on the left hand side of pic 1 next to the video ram. Some of the ceramic replacements look questionable. I would redo the work.