Osage,
The 1600+ has a default Multiplier = 10.5X which has the .5X, 1X, 2X and 4X Bit Values Set HI by the L3/L4 bridges and the 8X Bit Value is set LO by the L10 bridges. So if the .5X L1 bridge was "open" you'd get all the n.5X Multipliers cause the .5X Bit Value is set HI by default, but mobo/bios would be unable to reset that .5X Bit Value LO thru an open L1 bridge to get the n.0X Multipliers.
But that's not what you get, you get the n.0X multipliers, but not the n.5X Multipliers, which means that the .5X Bit Value has been reset LO with a "hard/direct ground" which cannot be reset HI by the mobo/bios. You have apparently cleared the grounded 2X Bit Value, but now have a similar problem with the leftmost .5X one.
The ground does not have to be just in the leftmost .5X BV L1 bridge cavity. It can be grounded on the surface as well, since the triangle icon to the left of that bridge and all the labels on the surface are reported to be at electrical ground voltage level. Also the 2 leftmost L3 bridges connect to the .5X BV signal bus. So we'd inspect the surface first to see if some of the bridge closing material applied to the L1 and the leftmost 2 L3 bridges has spilled over and is contacting any of the surface "ccopper" grounds mentioned above. If not then might be the .5X BV L1 bridge cavity this time, assuming that it was the cavity in the 2X BV problem which seems to have been fixed.
John C.
Edit:- do not mess with the L3/L4/L10 unless you've read the Palomino bridges Decoding article and understand it thoroughly. For example to change a particular Bit Value you reverse the open/closed status of that particular "bridge pair"...and there are 5 bridge pairs in the 10 L3/L4/L10 bridges. Further, suppose you did not like the new setting, or it didn't post...then you'd have to redo the mod over again...and for some setting changes 2 or 3 bridge pairs might be necessary.