ST-RAM card: White picture with red border

[frank.lukas]

At the Diag Menu it display 4MB ST Ram when the card is working. There is no extra menu for the card. The ST Ram is 64bit organized and when the Diag cart display only 2MB ST Ram in total the whole Datalines are missing I think?

May be you can measure from a Dram Chip Mdata at the extra 2MB card to a correspondence/equivalent chip on the Mainboard. It should be 0 Ohm. See the schematics ...

... the second mcu of the extra 2MB ST Ram card is basically/practical parallel to the onboard mcu

[wolfman]

At the Diag Menu it display 4MB ST Ram when the card is working. There is no extra menu for the card. The ST Ram is 64bit organized and when the Diag cart display only 2MB ST Ram in total the whole Datalines are missing I think?

May be you can measure from a Dram Chip Mdata at the extra 2MB card to a correspondence/equivalent chip on the Mainboard. It should be 0 Ohm. See the schematics ...

... the second mcu of the extra 2MB ST Ram card is basically/practical parallel to the onboard mcu

Sure - I saw "2 MByte STRAM" in the diag menu, so it was clear that the additional card wasn't detected.
I checked all addresslines for continuity of both MCUs (U12 "RAM card" and U206 "onboard") and they are all connected -> connectors seem to have contact (at least for the addresslines).
I checked (so far) all D0-pins from all RAM chips (RAM card) for continuity to the solderside on the mainboard (corresponding connector to J1 on the RAM card) -> D0 of all RAM chips are connected to the mainboard.

[Icky]

Do you have any pictures of the RAM board. May help the forum members spot anything out of the norm.

[frank.lukas]

I checked (so far) all D0-pins from all RAM chips (RAM card) for continuity to the solderside on the mainboard (corresponding connector to J1 on the RAM card) -> D0 of all RAM chips are connected to the mainboard.

You mean Mdata 0 to 63 ...

[wolfman]

Do you have any pictures of the RAM board. May help the forum members spot anything out of the norm.

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IMG_20230318_142329.jpg (327 KiB) Viewed 1570 times

... I can't find anything out of the ordinary ...

[wolfman]

I checked (so far) all D0-pins from all RAM chips (RAM card) for continuity to the solderside on the mainboard (corresponding connector to J1 on the RAM card) -> D0 of all RAM chips are connected to the mainboard.

You mean Mdata 0 to 63 ...

Yes, but D0 only: D1-D3 is unchecked at this point.

[wolfman]

All datalines (MDATA 0-63) checked for coninuity to the solderside of the mainboard -> all connected.
Measured from the pins of the chips down to the solderjoints on solderside of the mainboard.

[frank.lukas]

... my guess is that the mcu is fine.

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Check the (all) control signals from Mainboard (mcu) to the daughterboard ST Ram mcu ...

[wolfman]

Work kept me busy lately - so today I had some time to come back to this faulty card.

As suggested I checked connectivity to/from the MCUs and I might found the issue:
C2 seems to be the smoking gun: it spilled out its guts to the PCB:

leaky cap

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before cleanup

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traces eaten away

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I didn't see that initially because the cap was flush to the board. Checking continuity pointed me to the underside of the cap.

Now I have to recreate 3-5 traces and source 3x 47µF, 16V axial caps

[stephen_usher]

It’s very unusual o see leaking axial caps as they’re usually better sealed.