More RLV12/RL02 problems (faults on Write)

Re: my PDP-11 (KDF11-BA QBus CPU) with RL02 and RLV12 controller: Although I can read from my RL02 fine, and run the various XXDP diagnostics, any attempt to *write* to the disk instantly causes the heads to retract, the LOAD light to go out, and the FAULT lamp to stay on. The write protect lamp works with the button and was not on. Running the diagnostics VRLB?? (Diskless Controller Test) & ZRLG?? (Controller Test 1) pass with no errors. However, ZRLH?? (Controller Test 2, the first test that writes to the disk) fails as follows: CZRLH DVC FTL ERR 00300 ON UNIT 00 TST 002 SUB 000 PC:015044 RLCS HAD FOLLOWING ERR(S): COMP DRV WRT OP-INTR MODE BEFORE COMMAND CS: 000313 BA: 003426 DA: 000000 MP: 000000 TIME OF ERROR: CS: 140312 BA: 004026 DA: 000001 MP: 000667 003400 174000 followed immediately by another fatal error "COMP OPI RD HDR OPR'TN-FLAG MODE". While the RL02 was still in Fault mode, I also entered the "Toggle-In Program" from the RL02 Disk Subsystem User's Guide, Appendix C and it returned 102210 which is WGE (Write Gate Error) i.e. either Write Protect was set, or a sector pulse occurred during the write operation. I think I should be looking inside the RL02 on the logic board but can someone with more diagnostic-pack experience tell me if this is actually a controller problem? thanks Charles