Circuit diagram errata...
Posted: Tue Feb 26, 2019 7:16 pm
I spotted a little mistake in the QL schematic from the service manual. It's not an easy mistake to make, but if you follow the schematic, Very Bad Things could happen.
IC35 is the 5V regulator. IC36 is -12V (7912) and IC37 is +12V (7812). Note that the two ground pins of the 7812 and 7912 meet, and logically, this is ground, with zero potential. 0 volts.
If you follow that 0 volt line to the right and down, notice it's connected to the DC input voltage, which is 9V. It should not connect there, but continue down to GND.
IC21 is listed as a 74LC257, but is 74LS245
On the Issue 6 schematic, IC23, the 8302, is shown connecting to DB[0..7], but it connects to D[0..7] - this changed for Issue 6. (This is quite clever.)
What other errors do people see?
I'll collect them and do a fresh drawing in the coming weeks, while I have some extra free time. When it's done I'll post it here for checking, then send it to Dilwyn for publication.
IC35 is the 5V regulator. IC36 is -12V (7912) and IC37 is +12V (7812). Note that the two ground pins of the 7812 and 7912 meet, and logically, this is ground, with zero potential. 0 volts.
If you follow that 0 volt line to the right and down, notice it's connected to the DC input voltage, which is 9V. It should not connect there, but continue down to GND.
IC21 is listed as a 74LC257, but is 74LS245
On the Issue 6 schematic, IC23, the 8302, is shown connecting to DB[0..7], but it connects to D[0..7] - this changed for Issue 6. (This is quite clever.)
What other errors do people see?
I'll collect them and do a fresh drawing in the coming weeks, while I have some extra free time. When it's done I'll post it here for checking, then send it to Dilwyn for publication.