How do I open an A400 PSU?

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IanJeffray
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How do I open an A400 PSU?

Post by IanJeffray » Mon Sep 07, 2020 11:35 am

Apparently this "Blew smoke". I've not even switched it on - want to do visual inspection first, but can't figure a decent way of getting in to the darn thing. It looks like the metalwork is folded around after assembly of innards? Before I get medieval with the thing, has anyone advice on opening such a power supply? I've removed all the obvious screws and covers - now I'm stuck.
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IanJeffray
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Re: How do I open an A400 PSU?

Post by IanJeffray » Mon Sep 07, 2020 12:34 pm

As ever, serious impatience on my part sees me bending the two mounting feet out of the way, then removing the cable gland, the wires can be pushed further inside and the board wiggles its way out.

No obvious source of reported smoke. Time to to attack with the multimeter.
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IanS
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Re: How do I open an A400 PSU?

Post by IanS » Mon Sep 07, 2020 1:16 pm

There must be a way of getting it out without bending the tabs, but it looks like you aren't the first to give up and bend thr tabs.
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Re: How do I open an A400 PSU?

Post by IanJeffray » Mon Sep 07, 2020 2:10 pm

Didn't think I'd be the first to try to open this, but failed to find previous postings. I can't imagine they really welded up the case after inserting the board, but ... legs bent out and bent back easily enough, so that'll do for me.

PSU checks out fine... 12V is down at 11.7 but not concerned about that. Machine rebuilt and now getting more POST codes than I've ever seen before on a single machine. &D109 : Sirq & Virq timing filed, IOC register test failed (NEVER seen this one), plus the usual CMOS etc. This is going to be fun to diagnose. Anyway, that would be a new topic :)

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Re: How do I open an A400 PSU?

Post by steve3000 » Mon Sep 07, 2020 6:45 pm

IanJeffray wrote:
Mon Sep 07, 2020 2:10 pm
IOC register test failed (NEVER seen this one)
My A4 had this, solved by replacing the IOC in that case... will be a lot easier to test this on an A4x0!

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Re: How do I open an A400 PSU?

Post by philpem » Tue Sep 08, 2020 1:30 pm

Given that IOC and VIDC errors are appearing together, I'd bet on a data or address bus issue. Probably a failed 74LS/74HC buffer somewhere, or a stuffed RAM chip pulling the bus down.

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Re: How do I open an A400 PSU?

Post by IanJeffray » Tue Oct 13, 2020 7:17 pm

philpem wrote:
Tue Sep 08, 2020 1:30 pm
Given that IOC and VIDC errors are appearing together, I'd bet on a data or address bus issue. Probably a failed 74LS/74HC buffer somewhere, or a stuffed RAM chip pulling the bus down.
Back to this machine, and I took a punt on it being IC13, the 74HCT573 that buffers data out of IOC - swap out a 20p component and bingo, quick and easy win - A420/1 back to life, no POST issues at all, 4MB RAM, all seems good. \:D/ Spot on with the diagnosis, Phil.

Whilst I'm here, I'm tempted to swap out IC20, the other 74HCT573 on the bus.

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