I just had this problem fixed on my 65hm167. Fortunately, it was under an extended warranty, so cost was zero to me.
The repair people admitted that it was the DMD chip that was going bad, but that they only replace the entire light engine on these sets. The reason given was that the chip needed alighment after replacement, and that took hours of effort. When the light engine is replaced, it is already aligned and it is about a 30 minute process to repair.
I think the repair people were giving me a story that led to the least effort and most profit for them. Many people have replaced just the chip themselves and had the problem fixed entirely at a much lower cost.
There is a thread on this board that gives part number details and pretty much step by step instructions on how to get the chip replaced. So a search of the model number and you'll find it. Most of the chip replacement discussions are in the last few pages of the thread.
The only issue with my repair was getting a light engine. The repair guys only wanted to install a brand new unit from Toshiba. They told me that other sources sell rebuilt units that have a higher failure rate, and there is a chance that the DMD chip on the new light engine was not one of the parts that was replaced during the rebuild.
Toshiba had these on endless backorder, with no real estimated time of arrival. I ended up waiting over 2 months for one. When the repair guy would check with Toshiba, the expected arrival date was always the 1st of the next month. I'd guess that if they have something backordered their system just bumps the date up a month automatically.
Once the new light engine came in (it was from Toshiba as it was marked on the box) the replacement was quick and looked easy. Most of the work seemed to be taking the screws out of the cabnet. Once that was done, it looked like a couple of screws held the light engine in place and a few cables needed to be unhooked. New on slipped in and we powered up the set with no problems - especially white dots.
If I had not had the extended warranty covering this repair, I would have tried the chip replacement. It looks like it can be done without fully removing the light engine from the set and does not involve any soldering or other work that doesn't just involve a screwdriver and a bit of time.
The chip that is going bad is the same one Samsung replaced under warranty. Mitsubishi DLP sets used this same chip in some of their models. It can be found on E-bay, ShopJimmy, and Samsung parts.
The part itself was made by Samsung.
Good luck to those developing this problem. It only gets worse over time. I got a new white dot about once a week and they never cured themselves.
My set looks like it did when it was brand new. All my settings were retained and I'm hoping to get another few years of use out of the set.