Thank you for contacting  Ask Extension  about your raspberry plants. There are a few possibilities for what is happening to your plants.
1. You mentioned that your plants are now 25 years old while the normal lifespan of red raspberry plant is closer to 20 years so perhaps they have reached the end of their lifespan. There are many new exciting varietals out there to replace them. If you do replace them, it's best to plant in a new location in your garden.
2. Raspberries grow best in well drained soil that has a pH between 5.5 and 6.5, if you bring a sample to the OSU extension office we can test the pH level for you for free. 
3. Although I didn't see any obvious signs of insect damage from your photos, have you seen any insects on your plants or eggs on the underside of the leaves? Cut into a dead cane and look for signs of a crown borer. 
4. Phytophthora root rot is also a possibility. This soil borne fungus is a common cause of wilting in red raspberries and can spread by water or root to root between plants. The canes wilt and turn brown resulting in a chocolate brown discoloration of the roots. On the dead canes, dig up some of the roots and examine them by scraping off the outer surface, uninfected roots are white while infected plants will be brick red to dark brown. Unfortunately, if this is the case, there is no cure. The best solution is to get rid of all the plants and start over with new ones in a different area. Note: One major difference in distinguishing between root rot and winter damage is that infected plants will continue to decline as time goes on while winter injured plants will send up healthy canes next spring.
5. Although difficult to diagnose, another possibility is herbicidal "drift". This occurs when a herbicide is sprayed nearby and the wind carries it to any site other than intended.
This is a link to a great OSU publication that you may find useful "Growing Raspberries in Your Home Garden": https://extension.oregonstate.edu/catalog/pub/ec-1306-growing-raspberries-your-home-garden
I hope you find this information useful.
Happy Gardening
Laurie W

Thank you Laurie. I appreciate all of this very good information. Thanks for taking the time to write it all up. We will investigate! We appreciate you and the work you do!
Sent from my iPhone



You're very welcome!