On 05/01/2013 03:15 PM, Bil Herd wrote: > I am (pleasantly) surprised that _any_ of the units really work after 30 > years given the history we had with some of the IC production (passivation, > ion implanter) and I donít remember where the 7500 fell in whether it was a > finished design rule set or whether all long-term bets are off unless > you're on the 8500. Well, the 8501R1 ist also not known for a long life. Back when I had my first C16, I removed the 7805 from the case (put it outside with a larger heatsink) and put heatsinks on CPU and TED. Never had any trouble. MOS did make a 8501R4 in 1986 and there are even 8501 with a 1990 datecode. Those are rumored to last a lot longer. > The TED system lives with a certain amount of contention, I mentally rated > it at the time at about 20% contention at the time as tristate buffers of > the day turned off much slower than they turned on so some portion of > current was likely to occur during the bus switchover. We used to refer to > it as the bus heater effect meaning that we exchanged the die temperature > (and lifetime) for time to market and unit cost. I still have a working 7501R1 and, surprisingly, it needs about 20mA _less_ power than the 8501R1 and R4. > I remember something being said by management to make sure that the smaller > machines werenít easily upgradable but at the engineer level we didn't hold > too much regard as we had all heard the stories of the alienation that > drilling out the PET PCB's had done. I donít think we could have gotten away > with anything where all you had to do was swap DRAM's, though 16Kx4's were > brand new at the time and 256k DRAMSs didnít yet exist that I remember. You could have put a RAM_enable signal on the expansion port without needing extra gates though. Both C16/116 and Plus/4 have some spare gates that could have been used to gate _CAS so that a module on the expansion port could have disabled the internal RAM. But someone in Management might have noticed... As for keeping the systems operational, what I usually do besides memory expansion: - Replace 7805 with switching regulator (RECOM 5V/1.5A type) - Remove R10 (the large ceramic resistor) - Add heatsinks to CPU, TED and PLA - Replace the ROMs with properly programmed 27C128 or 27C256. (saves about 50mA per ROM replaced) That makes the system run a lot cooler in general, also meaning cooler dies for TED and CPU and hopefully some more years. Gerrit Message was sent through the cbm-hackers mailing listReceived on 2013-05-01 17:00:04
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