TT - AT PSU mods

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damosan
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TT - AT PSU mods

Post by damosan »

I'm working on fixing up TT (daughterboard version). I've read a few threads across the net that says "do this and do that" but does anyone have a step by step guide on getting a AT PSU working with a TT? Something has to happen with the "power good" line but I'm not quite sure what.

Thanks for any help you can provide.
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Arne
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Re: TT - AT PSU mods

Post by Arne »

What are you talking about?
AT PSU have PG on Pin1 and MSTE/TT PSU have PG on Pin 1, too!
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damosan
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Re: TT - AT PSU mods

Post by damosan »

Arne wrote: Mon Nov 22, 2021 11:21 pm What are you talking about?
Let me try again.

This is a modern 150w AT PSU. It powers up a drive just fine. When I connect it to the TT and hit power the PSU causes one of the motherboard fans to wiggle a bit and then the PSU shuts down.
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Arne
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Re: TT - AT PSU mods

Post by Arne »

damosan wrote: Mon Nov 22, 2021 11:42 pm This is a modern 150w AT PSU.
Why don't you say that upfront?
damosan wrote: Mon Nov 22, 2021 11:42 pm (..) one of the motherboard fans to wiggle a bit and then the PSU shuts down.
What "motherboard fan"? None of my TTs has a "motherboard fan".

I connect the original TT PSU to the TT. Powers up as it should. I remove the PG line from the connector. Still boots up as expected.
Did you have a look at the schematics what parts really ARE connected to PG?
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Arne
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Re: TT - AT PSU mods

Post by Arne »

BTW: does the AT PSU come with a green cable on its connector?
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Re: TT - AT PSU mods

Post by joska »

The TT has two fans. One in the PSU and one powered by 12V from the motherboard. Does the PSU fan run? Because it sounds like the PSU does not power up. This would normally not be a "Power good" issue with an AT PSU, because this is a PSU->motherboard signal that is used by a circuit on the motherboard to trigger the motherboard power-up when the PSU has powered up and the voltages are stable. It sounds more like a short that overloads the PSU and prevents it from powering up.

Why are you replacing the PSU? Did the TT work before you did that? What happens if you disconnect all perhipherals (floppy, disk, external drives, TT-RAM etc)?
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Re: TT - AT PSU mods

Post by susher »

Actually, only the very earliest TTs had a case fan on the right-hand side behind the ST-RAM board.
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