I have two basically identical 600XLs. Both Rev A, both have the 3-wire 64K memory upgrade and both have UAV Rev D. Oh, they both have Hias' 1.30 high speed ROM too. (The perfect compact combination for anyone that isn't into demos or actually doing a bunch of typing, IMO)
One suddenly has a black screen on boot. Power LED lights and the TV goes from blue (unconnected default) to black. I never hear the "data sound" of basic loading.
Since I have another (and happily the RAM upgrade I did doesn't require soldering to the MB) I have been able to swap all chips between the two units, 3 or 4 at a time. The bad unit remains bad and the good unit remains good.
There is no apparent damage to the MB and the contacts all look good - nothing bent, apparent corrosion, etc. I did reseat each chip a couple of times. No joy.
Any ideas on what it could possibly be? I do have reasonably good electronic troubleshooting skills and tools (including an o'scope), but I don't know enough details about the circuits to know where to start or what to look for. Does the black screen point to any particular circuit?
Any help would be much appreciated.