PDP-11/44 problem - RUN stays on

I pulled all boards from the 11/44 backplane and used an eraser to clean all the contact fingers. Then I vacuumed the slots. After wiping the boards clean of any small particles, I reseated the boards ... the system still shows the same problem, the RUN LED stays on and I don't get the >>> prompt. Then I swapped the CTRL (M7095) board. ^P gives me the >>> again. However, "H" (halt) gives the response "?Failed to halt". The "T" (selftest) command seems OK, the LED on the MFM board is briefly ON. As the MFM board was also suggested to be causing problems, I replaced the MFM board. Now the RUN LED stays OFF! However, I get an other problem. The VT100 displays: CONSOLE ?22 CP HUNG I can enter the T and the H command. That works fine. But, for example, an E (examine) command gives the ?22CP HUNG. When I install the original MFM board again, the RUN LED stays ON, but the "E 2" command gives the response " P 00000002 000001" and the H command says "?Failed to halt". According to the documentation you can do EXAMine commands while the system is running, but you can not do a DEPosit. Proof: I entered "D 2 2" and the response is "?Halt CP". So, one MFM board gives "?22 CP HUNG", but the RUN LED is OFF, the other MFM board allows examine, but the RUN LED stays ON, and you can not halt the processor. I am still reading, but give these symptoms perhaps clues? thanks, - Henk. This message and attachment(s) are intended solely for the use of the addressee and may contain information that is privileged, confidential or otherwise exempt from disclosure under applicable law. If you are not the intended recipient or agent thereof responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication is strictly prohibited. If you have received this communication in error, please notify the sender immediately by telephone and with a "reply" message. Thank you for your cooperation.