840av machines are prized among 68k Macintosh collectors. It is not going to be easy getting a logic board, because those who have them tend to hold onto them.
The question is, therefore, what is wrong with the logic board that you already have? The chances are high that the trouble is leaking capacitors, leaving electrolytic goo on the surface of the board, and wreaking havoc with the intended function of the chips. It could also, in theory, be any number of minor problems, such as RAM needing re- seated. The Power Supply could also be the source of the trouble, but I would bet in the first instance on capacitor goo. Before launching on a (probably futile) attempt to find another logic board, which is likely to have capacitor failure also, take your machine apart, remove all ram etc., and inspect CLOSELY in the area surrounding those small aluminum tank-like objects that pepper the board. You will most likely see capacitor residue, which looks a little like, say, a child spilled a few drops of juice there some years back. Especially if you find some, but even if you don't (as it almost certainly WILL be there, whether you can find ti or not), give the logic board a wash. A good long cycle in an empty dishwasher (no soap needed) works well. Don't be frightened, as the thing was washed in such a way when it was manufactured, and the water can't hurt the thing as long as you don't apply power to it immediately. A thorough drying for several days then follows, before reassembly. Google the subject and it will come: washing your logic board can works wonders. My 840av is working now only because I washed it. However, the fix may only be temporary, and for a permanent solution, you will need to replace those ancient capacitors, or else have them replaced by an electronics repair shop that does component level repair. On Jun 7, 5:59 am, "Magnetic Control Industry" <[email protected]> wrote: > I still don't understand why nobody has a Quadra 840av motherboard for sale. > This stupid machine is just sitting here with a toasted motherboard. How in > the hell will I digitize videos with my RadiusVideoVision Studio Nubus Card? > I am locked into this machine as it's the only Macintosh to feature 256 > levels of shading with live video to output... > > Thanks! > > -Shaun --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs?hl=en Low End Mac RSS feed at feed://lowendmac.com/feed.xml -~----------~----~----~----~------~----~------~--~---
