exxos blog - random goings on

[exxos]

This morning I turned it on and..

:pullhair:

Could you scope D11,D13,D15 on your falcon ST-RAM @Badwolf . Also what RAM do you have in there (part number of DRAM IC) ?

[Badwolf]

Could you scope D11,D13,D15 on your falcon ST-RAM @Badwolf . Also what RAM do you have in there (part number of DRAM IC) ?

Not trivially, I'm afraid. Mine's a 72-pin SIMM mounted on the bottom of the board.

I can see if I can find an old 4MB module I was sent years ago. It has failed chips on it, but for the purposes of scoping, it may be better?

BW

[exxos]

I can see if I can find an old 4MB module I was sent years ago. It has failed chips on it, but for the purposes of scoping, it may be better?

If you have a board which has failed chips then that would be perfect. I'm more just interested in the numbers on the chips which are failing.

[Badwolf]

I can see if I can find an old 4MB module I was sent years ago. It has failed chips on it, but for the purposes of scoping, it may be better?

If you have a board which has failed chips then that would be perfect. I'm more just interested in the numbers on the chips which are failing.

Righto.

Can't tell you the history of it, I was sent it as a bonus by a chap I bought something else off (I forget now!). I tried it for a bit, found it failing, so thought nothing more of it. I'll see if I can locate it.

BW

[exxos]

Can't tell you the history of it, I was sent it as a bonus by a chap I bought something else off (I forget now!). I tried it for a bit, found it failing, so thought nothing more of it. I'll see if I can locate it.

Always possible people are blowing them up with bad power supplies or something. Unfortunately it be a total unknown in that respect.

How things are looking, -2.5v is pretty bad. Some datasheets specify only the negative spikes for as little as 15ns and even that's down to -1v.

Indeed if anyone reading this as a faulty Falcon memory board and please post the numbers off the chips.

[exxos]

Dug out my original Falcon 1MB / 4MB board. That was in daily use for some years and never failed.

TC514256.PNG

Vs the chips spec I am using.

HYB5117405.PNG

So -1.0v on the original vs -0.5v on mine, and VCC +0.5 = 5.5V vs 6.5V on the original . Feking Atari computers :roll:

EDIT:

This is the chip @Badwolf has in the below post.

HY514400J.PNG

Again -1.0v, but VCC +1V, so 6V. So maybe not quite as good as the above chips.

[Badwolf]

OK, so I have to hold my hand up that this grounding is fairly pisspoor. I can't find my little ground springs so this is with the normal croc-flyleaf to the negative leg of the big axial cap.

First up is probing with permanent persistence from the top of the connector pin (I know it's not the chip, but not sure which line goes to which chip, and this is a baseline):

D15:

IMG_5966.jpeg

D13:

IMG_5967.jpeg

D11:

IMG_5968.jpeg

The latter with the manual cursor to get the proper extremes.


Then probing pin 1 of chip U2 as the data lines seemed to go in that direction:

IMG_5970.jpeg

Not enough hands to capture it, but when holding the croc clip on a more local ground, the excursions seemed less severe. Probably because ground itself seems to have a 250mV p-p bounce.


This is the board under test (original Atari, by the look of it -- can't make it fail now, interestingly):

IMG_5962.jpeg

This is my normal SIMM board (got it with the machine from Silica, to my surprise) and it's current incumbent SIMM. Not the device under test here.

IMG_5961.jpeg

BW

[exxos]

Thanks @Badwolf . Looks like yours isn't "as bad" as mine in some respects. But still not great.

Not enough hands to capture it, but when holding the croc clip on a more local ground, the excursions seemed less severe. Probably because ground itself seems to have a 250mV p-p bounce.

Yeah, I tried clipping on the corner of the RAM boards ground, but wasn't any difference to the big MB cap ground, or the outer MB ground. Granted there is a margin of errors in results but good enough to get a idea whats going on anyway.

This is the board under test (original Atari, by the look of it -- can't make it fail now, interestingly):

To clarify, this was the board you mentioned before which "died" ?

[Badwolf]

Thanks @Badwolf . Looks like yours isn't "as bad" as mine in some respects. But still not great.

Down to -1.2V in places!

This is the board under test (original Atari, by the look of it -- can't make it fail now, interestingly):

To clarify, this was the board you mentioned before which "died" ?

Yes, it came to me as a gift and I categorised it as dead on arrival as it failed tests I ran on it during the first week. Perhaps I had a bad seating?

...Or perhaps several years being stored in the shed has magically restored its powers!

Open mind. ;)

BW

[exxos]

Down to -1.2V in places!

Still about half what I see at times though.

Yes, it came to me as a gift and I categorised it as dead on arrival as it failed tests I ran on it during the first week. Perhaps I had a bad seating?

Could have been bad connection. Maybe slightly corroded connector or something :shrug:

...Or perhaps several years being stored in the shed has magically restored its powers!

Open mind. ;)

Certainly possible. I already concluded these machines either work or not work depending on the alignment of the planets!