Blogs

All members are invited to blog on Applefritter. Weblogs should generally be of a technical nature and should be written in such a way as to still be readable and useful 50 years from now. Please do not embed outside media. Images and videos can be uploaded via the Media Browser. Files should either be attached to the blog post or uploaded to the file libraries.

When you post to your blog it will appear on this index and on your personal blog page. Once you've made a few posts, contact me about having a graphic added on the top of this page.

Getting warm, in more ways than one

Submitted by gareth_IIe on September 1, 2020 - 10:08pm

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

Tags: 
Apple ][e repair HAL PAL GAL 16v8 341-0170-A

Garbled screen, but progress

Submitted by gareth_IIe on August 30, 2020 - 9:33pm
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
Tags: 
Apple ][e repair

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

Submitted by gareth_IIe on August 5, 2020 - 10:15pm
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.
Tags: 
Apple ][e repair

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