gareth_IIe's blog

Getting warm, in more ways than one

So in my last entry I mentioned that the ICs LS245, 341-0170-A, 74166, 6502 and 341-0150 were getting warm.  This wasnt the full list, the MMU, IOU and ROMs were also feeling a bit above room temperature, but it was subtle.  After looking at the schematic however, I think I now have a pretty good idea of what's going on.  The LS 245 is getting very hot.  It is an octal bus trancever that connects 74166 to the databus, based on it's inputs from the HAL and the MMU.  The 74166 is also getting very hot and it is controlled by the MMU and the IOU.  The ROMs and the CPU are getting hot because t

Garbled screen, but progress

So the first thing I tried was swapping the RAM out and that had no effect.  I then had a look at the EF ROM.  Testing it wasn't too difficvult, and with the air of an Arduino and breadboard I descovered that blocks of the rom appeared blank.  I read the rom a few times and the blank areas moved about.  I put a PCB together with a ZIF socket and soldered the connections to make certain the blank areas weren't a loose connection.  I then downloaded the rom, bought an EPROM and turned my reader into a programmer.  However with the faulty rom replaced very little changed, how

First sign of life in over 25 years from my Apple ][e

So the replacement caps arrived today.  It turned out that while one of the tantalum capacitors on the main board had failed short, some actually seemed ok.  However I replaced the lot as a couple more had odd readings and there are only 9 of them anyway.  Powering the board up I actually got some output, though it's garbage with a flashing cursor a 3rd of the way down the screen.  Still, not at all bad for a computer that has sat idle for 25 years.  I'm thinking a short on the data or address bus, or maybe a faulty ram chip.

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