A5000 IDE interface just died... what to try next?

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steve3000
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A5000 IDE interface just died... what to try next?

Postby steve3000 » Mon Sep 25, 2017 10:30 pm

Well there I was minding my own business playing a quick game of Arc Elite on my A5000, popped back to the desktop to save my position and was greeted by a "Broken directory" error, followed by "Disc not understood, has it been formatted?" when I clicked on the hard disc icon. :shock:

Resetting the computer gave an unusually long-reboot time, typical of a failure to identify the HDD, and sure enough when the desktop appeared the hard disc icon just said "4" instead of the drive name. Clicking on the icon gave the same "Disc not understood, has it been formatted?" error. :(

The "hard disc" itself is actually a SD card fitted to a SD to IDE adaptor, so of course this was the first suspect, but upon testing in my A4000 the adaptor and card were fine - loading up perfectly.

Next I tried swapping the IDE data cable (it was fine), and then tested the continuity of all the 40 pins of the IDE plug on the A5000, but all were fine to their respective destination ICs...

I then popped the SD to IDE adaptor back in the A5000 and interrogated it using !HForm. This gave very interesting results, in particular see the "Description" field in the pic below:
A5k failed IDE.png

When the same adaptor is plugged into the A4000, the "Description" reads correctly:
A4k working IDE.png

Any thoughts as to what could be wrong here and where to check next?

*Ignore the different number of cylinders in the two pics, I was experimenting with different SD cards to ensure the cards were not the problem.

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DutchAcorn
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Re: A5000 IDE interface just died... what to try next?

Postby DutchAcorn » Tue Sep 26, 2017 5:52 am

I've had issues with A5000 IDE data corruption that were caused by a faulty buffer chip: IC49. You could check out IC37 and IC49.
Paul

RobC
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Re: A5000 IDE interface just died... what to try next?

Postby RobC » Tue Sep 26, 2017 7:43 am

That looks like D4 is getting stuck high on every other byte (e.g. 'e' -> 'u' but 'm' -> 'm' in "Mem").

I'd look at the schematic and look for the buffering on the data lines from the IDE interface.

EDIT: It's a 16-bit interface so it'll be D4 or D12 causing the problem. Looking at the schematic, IC49 buffers D0-D6 (not a typo) and IC37 buffers D8-D15. If the IDE socket's connections to them are good, I'd look at scoping their inputs and outputs.

steve3000
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Re: A5000 IDE interface just died... what to try next?

Postby steve3000 » Tue Sep 26, 2017 10:26 pm

Thanks for the replies!
DutchAcorn wrote:I've had issues with A5000 IDE data corruption that were caused by a faulty buffer chip: IC49. You could check out IC37 and IC49.

Ahh, yes, that could be it - I had also noticed a couple of seemingly random write errors occurring recently when using the SD to IDE adaptor, but again I suspected the adaptor since the errors seemed random and I couldn't get them to appear when using a real hard disc. (...although thinking about it, the lower write speed of a real HDD might have avoided a slightly slow/sticky bit on the buffer IC?)
RobC wrote:That looks like D4 is getting stuck high on every other byte (e.g. 'e' -> 'u' but 'm' -> 'm' in "Mem").

I'd look at the schematic and look for the buffering on the data lines from the IDE interface.

EDIT: It's a 16-bit interface so it'll be D4 or D12 causing the problem. Looking at the schematic, IC49 buffers D0-D6 (not a typo) and IC37 buffers D8-D15. If the IDE socket's connections to them are good, I'd look at scoping their inputs and outputs.

Bingo!

I had just been thinking this - after looking at the "0 0 0 0 "s at the end of the description - these should all be spaces (ascii 32) but the "0" every other letter is ascii 48, showing bit 4 is set (or bit 12 of 16bit, as you say).

I don't have a scope and can't think of a sensible way to test these using just a logic probe on the live system. So I've gone ahead and ordered a couple of replacement buffer ICs.

I'd guess IC37 is suspect, assuming the start of the description text is the low byte of the 16 bit data transfer... (unless it is reversed?). Looking at the schematic now, I see what you say about bit 7 - this goes via a different route...which is odd? But this leaves a spare gate on IC49. If I get a free few minutes tomorrow I might just patch the suspect bit 12 from IC37 over to this spare gate on IC49 and see if that solves things.

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jgharston
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Re: A5000 IDE interface just died... what to try next?

Postby jgharston » Thu Sep 28, 2017 3:24 am

Similar thing happened to my A5000 a few weeks ago, the battery had eaten through the tracks.

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

steve3000
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Re: A5000 IDE interface just died... what to try next?

Postby steve3000 » Thu Sep 28, 2017 11:10 pm

steve3000 wrote:If I get a free few minutes tomorrow I might just patch the suspect bit 12 from IC37 over to this spare gate on IC49 and see if that solves things.

Patching bit12 from IC37 over to the spare gate on IC49 didn't solve the problem... :(
tn_DSC_4601x.JPG

However, patching bit4 on IC49 to the spare gate did fix the problem! :D :D
tn_DSC_4603x.JPG

So this means that for every 2 bytes in the description text, the first is transferred in the upper bits (8-15) and the second byte in the lower bits (0-7) of the 16-bit interface.

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DutchAcorn
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Re: A5000 IDE interface just died... what to try next?

Postby DutchAcorn » Fri Sep 29, 2017 5:56 am

Nice fix! Looks like a belated battery leak damage. It is very possible that other gates will fail in the near future, but at least you'll know the most likely culprit then :D
Paul

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flaxcottage
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Re: A5000 IDE interface just died... what to try next?

Postby flaxcottage » Fri Sep 29, 2017 10:23 am

Nice job of soldering. :D =D>
- John

Currently running Level 4 Econet with BBC B, BBC B+ 128K, Master 128K, 4Mb A3000, 4Mb A3020, 4Mb A4000, 4Mb A5000 dual FDD; UK101; HP41CX setup; Psion 3a, 3mx and 5mx; Z88; TI-58c, TI-59 and printer

RobC
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Re: A5000 IDE interface just died... what to try next?

Postby RobC » Fri Sep 29, 2017 10:43 am

Good job - glad you got this sorted and useful to know for future reference.

steve3000
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Re: A5000 IDE interface just died... what to try next?

Postby steve3000 » Fri Sep 29, 2017 8:56 pm

Yes - most likely battery damage related, there was quite a lot of corrosion to clean up, but it's been running fine for a long time.

Two new buffer chips arrived this morning, so when I get a chance these will go in, but am very happy with the temporary fix for the moment.

Soldering is always 'fun' with these SMDs, especially lifting two of the pins from midway along the chip, but in this case the solder hadn't been badly degraded by the battery damage, so they pins lifted much more easily than I expected :)


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