|WikiProject Computing||(Rated Start-class, Mid-importance)|
I quote from the article at http://www.funet.fi/pub/cbm/documents/projects/memory/reu/1764to512kB.html, seventh paragraph, which quotes CBM engineer Fred Bowen:
- There is a 390 Ohm resistor in the 1700 and 1750 REU's that is not present in the 1764. The resistor's position is located in the upper-left corner of the board, and labelled R4 in the 1764. According to Fred Bowen of Commodore, this resistor "tweaks" the signal that is supplied to the C-128 computer. There are C-64 users that have installed unmodified 1750 REU's without reporting problems. In these installations, larger power supplies rated at 2.5 amps DC are used. Also, there are C-128 owners who have used 1764 REU's without difficulty. Therefore, the presence or absence of this resistor seems to be a non-critical factor for most C-64 or C-128 computers, at least when using the REU with GEOS. Numerous Usenet messages on comp.sys.cbm from Fred Bowen and other CBM engineers in the late 1980s on Usenet make mention of R4, viewable by searching groups.google.com with the phrase "1750 1764 R4". The purpose of R4 was to accomodate very slight differences in the expansion port between the 64 and 128. The 128 benefited from R4; the C64 benefited from it not being there.
So the 1750 and 1700 had the resistor at R4. The 1764 did not. I'm re-correcting the entry. --Dave Farquhar 14:55, 1 Oct 2004 (UTC)