The part number is L 1671 B1 J000 This is an obsolete display and is nearly impossible to find. After a month of research I was able to find a very small number of them. Since they are now very rare the price is much more than it should be but still a lot better than buying a new controller. I have 3 extras that I would be willing to sell. PM me for details.
Where is the pot to turn up the brightness? Mike, thanks for the part number. Mine is also very dim, but still readable. You're right, no one has it. But I did find a cross reference from Oregon State University. http://eecs.oregonstate.edu/ed...ets/lcd_crossref.pdf
I found that the Hantronix version is available at Mouser and on eBay. Ordered one off of eBay for $15.50, shipping included.
Only bad part is that I bet it requires soldering. I suck at that...
Yes, the old display has to be unsoldered and gently pried off. Then the new display needs to be soldered in place. Lots of care is needed to not damage the circuit board when doing this. If you are not experienced in removing a part from a printed circuit and soldering a new one in, it would be worth paying an experienced electronics tech to do this for you. The main circuit board for the IQ-4 is no longer available so if you damage that board, the only option is to upgrade to the IQ-5 which is a very nice, but very expensive upgrade.
I have been doing this type of circuit board work for over 50 years and it was still a difficult procedure. Maybe it was the fear of an $1800 mistake that made it more stressful than usual, but the replacement display works and has restored it to like new brightness. I also replaced the membrane that goes over the buttons and the display as the plastic had yellowed and even with the new display it was difficult to read until I replaced it.
Here's the cross reference chart (in case the link above ever goes away)