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| IIsi fault ... |
Posted by: franklyn on 2024-04-21 10:16:27
... nevertheless trouble with the RAM, more precisely with the ALS245 chips.
UF5 Pin18 (D8) has no contact with the Simm socket pin3
UG5 Pin13 (D21) has no contact with the SIMM socket pin20
Unfortunately the VIA from D8 was under the ALS245 and had to put a wire around the board. On D21 I was able to patch the spot with solder.
The Macintosh IIsi board doesn't seem to be of such good quality!?! The schematics are terrible too ...
I'm glad it's working again |
Posted by: alectrona6400 on 2024-04-21 10:32:07
the macintosh IIsi was a cheaper, low cost alternative to the IIci... so its a bit haphazard in terms of internal design. it's an okay machine and it works for what it is. |
Posted by: franklyn on 2025-07-28 08:50:42
The computer has been stored away for a few months. Now it's making a chime of death. I've checked all the connections from the ALS245 to the four RAM sockets and on the other side to the onboard 1MB of RAM, and everything is fine there. All ALS245 are new ones.
74ALS245 all Pins1 -> (R/W) CPU Pin117 (R156) -> UA3 Pin77
74ALS245 all Pins19 -> UI4 MDU Pin128
... all fine
What else could the problem be ...? |
Posted by: franklyn on 2025-07-29 10:27:34
I check as good ...
- all Data and Control connections to and from the four 74ALS245
- all RAS, CAS and WE connection from the VGT8002-6215 to the 1MB Ram Bank
- all Data connection from the 74ALS245 to the CPU
- all Address lines connection from the VGT8002-6215 to the Ram chips
I couldn't find any fault and I'm at a loss as to what was wrong. The computer is working again now. An error like this is really bad; I would have preferred to have found something and fixed it. |
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