d8b Forum

I'm missing tape return channels 3 and 4 of slot 2. I've swapped cables, of course, and also swapped three different AIO-8 cards, all of which pass all eight channels when in other slots) into that backplane slot with the same results. So my conclusion is that the problem is inside the console. First pass was cleaning that slot's backplane connector. No luck there.

With good luck, it'll be a loose or ribbon cable (or one with dirty contacts) between the backplane and the console guts. With bad luck, it could be bad luck.

So, how do you get inside? I have a couple of copies of the service manual, which tells you how to build a console from a stockroom full of parts, but doesn't explain how to disassemble the console for service. Anybody here ever opened one up? Where do you start? And how far is it safe to go? I'm pretty good a working on these things - been doing it for 50 years - but I'm wary of taking out screws without knowing what they hold together.

Does the bottom panel come off? That might be a good place to start. Since this isn't my console (yet) I don't want to dive in without knowing something about how cold the water is.

Hey Mike; c
Yes turn the d8b on it's Face and take off the bottom. It is built in layers, sort of, Just keep the screwa in seperate bottle, labaled, and take it apart until you get as far as you need to with the card cage. The tricky part to remove is a piece of shet aluminum just under the brain card. It is the width of the console and half the depth. You may not have to remove it to get at the connectors on the card cage. I can't remember now.
It would be a good idea to clean as many of the connectors as you can to save you from having to go in again.

Check any IC's to make sure they are seated.

If you need parts I have spares.

Phil has thoughts on the ribbon connectors before you connect them back. Not sure where that is in here but it is in here.

Cheers and good luck.
Bruce

Take the bottom panel off and you should see most everything related to the card cage backplane.

http://www.sonido-7.com/d8b/photos.html#Post3

Hello Mike,

Had a quick look at the Schematics for the backplane and the DSP board. All the digital audio signals for the tape I/O cards are passed to and fro through two ribbon cables (connectors J47 & J48). Two inputs are multiplexed on to one wire, so it's likely that only one connection is causing the two inputs to fail.
Ribbon cables are a favorite, but could also be a dry solder joint either on the backplane or the DSP board. Could possibly be a failed DSP chip on the DSP board (but I'd expect a pair of outputs to also be non-functional in this case..)

Regards

John

Thanks, guys. Upside down it goes.

I cobbled together one other test using a PDI-8 (AES digital) I/O card in the wonky I/O slot. Still wonky, still the same two channels, so I guess I'll start with the ribbon cables. I hope I can leave enough things connected to test it without having to put it all back together.

May the Force be with you!