Purchased a 1998 John Deere 690 E LC with a Waratah HTH20 (an older style 622b with the smaller feed rollers) 3 weeks ago. 17k hours on the machine, engine and hydraulics all redone 3k hours ago. So far I've worked on it for 50 hours and ran it maybe 10, frustration is beginning to mount ever so slightly. After fixing several major hydraulic leaks, a couple electrical issues, and a fair bit of grease, I had it going fairly good for about 3 hours. Everything was functioning great, hydraulics at all points were strong and tight. Then after it warmed up fully, the main saw cylinder started to get lazy (wouldn't return home). That in particular looks like just a bad cylinder due to a fairly leaky main seal. The next day i just ran it as a limber to at least get some tree length stuff processed that was on the ground already. The main grapple, feed roller grabbers, and the rollers themselves worked fine for probably another 3 hours. Again, once it was fully ro temp, the feed rollers started to get weak. At first I just had to swing the head and roll at the same time to get them to feed through, then they wouldn't move the wood at all. Keep in mind this is all dead, dry, 10-18" dbh pine so it's not particularly heavy. Without wood in the head they seem to respond just fine, all three wheels roll at the same rate, start and stop at the same time, and don't have any leaks.
Contact Wayne at Axis Forestry in Kamloops Canada, Waratah wizard. We use them for all of our processor parts and support. Otherwise can call Waratah factory support as well. Can try Blackhills in SD as well, but they're hard to get sometimes.
Almost sounds like the drive motors for the rollers are worn out. Some pressure and flow checks are in order I would say.
I’m Putting my money on excessive case drain pressure from the feed roll motors.
Usually a tired drive motor will stall and the others will spin out, usually if you grab the feed roller and try and roll it back and forth and has a lot of play that will be another sign things are not ideal. Could also be a spool or coil on the head not working well when it gets hot which is quite common, think you can swap coils around on the head and test them out that way. The spools should also allow for manual actuation.
So far I've worked on it for 50 hours and ran it maybe 10, frustration is beginning to mount Are you sure you didn't buy a boat? Joe H