tgoodhew wrote on 2024-09-15, 22:00:

Hey All, […]
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Hey All,

Previous visitor, first-time poster, so please point me in the right direction if this isn't the correct forum.

I've had a Dolch Pac 65 for some time (I use it to run old HPIB software & a HP 82324B 'Hyper-Viper' card) and recently the CI6BM motherboard died. I stripped it down, extracted the SBC motherboard and proceeded to acquire a replacement board.

During the time it took to get a "working" board, I removed the LCD to confirm that it was powered and that the keyboard socket wasn't shorted (two of the 'replacement' boards I received had issues, one a dead Trident video IC, the other a dead PS/2 keyboard processor). I finally received what I think is a working board but now I'm running into an issue that I didn't have originally.

When I access the IDE controller, either primary to the CF IDE Adapter/actual IDE Hard Drive or secondary to the CDROM drive, I get heavy interference on the LCD and Trident outputs - If I put an PCI video card in the machine then I see no interference.

So I'm left to wonder what the cause is?

I wouldn't be surprised if I forgot to return a screw that is critical for grounding or did something like that but for the life of me I can't find anything - I wondering if anyone else has ever seen this and if so, what the solution to it was? I could probably pull the unit all apart and wrap the LCD cable in some type of "foil" sheeting to insulate it from the noise but this seems a bit of a magic fix (assuming it worked) as apart from the new CI6BM everything else is the same in the system.

Checking the power rails didn't show any way out there noise (I'd have to go back and look again as I didn't save the scope pictures or write it down but they didn't seem unreasonable for a no-name PSU).

Look forward to hearing any thoughts anyone might have?

TonyG

PS. I know I could dump the Dolch Pac and just use an old machine, I have a Dimension V400C that would work, but I like not needing to either setup a desktop or dedicate the bench space to it and the pluggable gives time a simple way to take ti off the shelf and use it.

Hmm, I would've suggested it could be interference and grounding the LCD cable or shielding it would help, but it's affecting both the VGA output and the LCD output? That means it's something more fundamental than EMI...

Could you take a picture or video of the interference?

Are the jumpers set up exactly the same on both the old and the new board?

The jumpers are set identically - The way the Dolch Pac 65 is put together has a short riser cable from the VGA connector on the CI6BM to where the expansion slots are. This is simply a bunch of wires connecting a VGA plug to a VGA socket in the whatever the metal brackets are that go into the open slot to seal it up around the back of the expansion card - They aren't shielded at all.

It's a tad hard to capture the effect so here is a image:

You can see it better in this video (sorry don't know how to embed videos here):

https://1drv.ms/v/s!Amqar8_XQ9Uzk9hNU0hvVU9kcxruPg?e=xsS3fM

TonyG

Quick follow-up to explain what I meant about the VGA riser - In this image you can see that it's just a bunch of wires going to the socket in the expansion slot - The VGA output on the CI6BM is under the PSU in the upper right corner so it isn't visible

TonyG

Are you sure LCD/VGA cables werent wrapped in alu foil before?

Yes - They're exactly how they were - The cables stayed with the machine, only the motherboard was replaced.

TonyG