Hello all,
My name is Steven and I've recently acquired three of these machines in non-working condition. I received one first, and got to work attempting to diagnose and get it booting. It initially only showed a black screen. A lot of trial and error was involved, but I actually, at one point, got all the way through to BASIC and TEX. Unfortunately, BASIC was a scrambled screen and I really didn't know what to do in TEX. Since then though, the machine is back to the basic black fill. The speaker ticks once when the power switch is thrown. I've recently acquired an oscilloscope and am trying to follow the service manual, but am quite unsure as to what to expect. First questions: - I've replaced all of the 603 transistors with BC547s. Was this a smart move? I had to re-align the legs to get them in, but I actually had the machine booting at one point. - I've started replacing all the ICs on the mainboard with 74HC equivalents. This doesn't seem to be helping at all. - I can't seem to get 7.5v on pin 16. The service manual indicates that there's a bunch of components that need replacing. I did so, but used a 1N914 for the signal diode and BC547 for the 603. I also socketed the 4013. Unfortunately, it's still only producing ~6.8v - One of the machine clicks the relay on the board, along with the speaker, when it powers up. It also shows a black screen. Should the relay fire when the machine starts? Is there any 'start up process' that I should be looking for when the machine starts booting? i.e. certain voltages in certain locations. Pins in states, etc... so I can tell what part of the boot I am locked up in? Could all the ROMs be damaged? Of the 3, I swapped the ROMs between the machine that I had booting once... but still no avail. Can't get it past the black screen at all. Am starting to think there is something fundamental that I'm missing and I'd love to know if there are any pointers. The current story is documented here: http://modelrail.otenko.com/retro/nec-8201a-portable-computer-black-screen Thanks in advance, Steven.
