My experience (and I believe this is shared with others on this list) is that the ROS (read-only storage, i.e. ROM) chips tend to go bad; I?ve had a couple of 5120s go through my hands with failed ROS boards. If you?re just getting garbage on the screen, though, it could be indicative of something else having failed. I do have a spare set of boards (with only one bad ROS board :)) if you need some spares? - Josh On Nov 10, 2013, at 7:46 PM, Ellis Holman <buddy.holman at gmail.com> wrote:

On Sun, 10 Nov 2013, Ellis Holman wrote: Square blocks or rectangular blocks? I suppose the latter. That would mean that everything read from memory is X'FF. Another possibility would be a screen full with the double-zero character (X'00). This is not good, but would probably mean that either the first memory bank is malfunctioning, or the graphics adapter (which does cycle stealing). What do you see if you switch from normal to register display? Here's a checklist for troubleshooting: - open the case - put the internal switch right to the monitor from RUN to HALT - power-on the machine - check the display You should see the first 1024 bytes (64x16) from the Executable ROS (in normal display mode) or the first 512 bytes as hex values in register mode. Until now, the processor hasn't executed a single instruction. The registers are memory-mapped but on the processor board instead of being located in RWS. So even if the memory (RWS or ROS) is faulty or missing (X'FF would be such an indication) the registers should be displayed (register mode). They are located from 0000-001F for level 0, 0020-003F for level 1, 0040-005F for level 2 and 0060-007F for level 3. Oh, BTW, are you sure that you have all cards and that they are in the correct slots? For reference, here's the disassembly of the beginning of the Executable ROS; you should see the hex dump on the screen after the procedure above (start address is 000A!) ; ********************************************************************** ; *** BEGIN OF ROS PART 1 ; ********************************************************************** 0000 000A DW $000A ; R0L0 0002 0000 DW $0000 ; R1L0 ; ---------------------------------------------------------------------- 0004 2868 MOVE R8, $D0 0006 12BF CTRL $2, #$BF ; switch to meta-interpreter 0008 2056 JMP ($00AC) ; ---------------------------------------------------------------------- ; Clear all memory ; (Memory parity check seems to be disabled) ; This will also clear all registers from R4L0 ; to R15L3! 000A 1FFF CTRL $F, #$FF ; Reset all devices 000C 0204 MOVE R2, R0 000E 8208 LBI R2, #$08 ; R2 <- $0008 0010 0324 MOVE R3, R2 0012 8300 LBI R3, #$00 ; R3 <- $0000 0014 5321 MOVE (R2)+, R3 0016 012C MHL R1, R2 0018 0126 OR R1, R2 001A C103 SZ R1 001C F009 BRA $0014 ; Loop ; Size installed memory in increments of 8 kbytes 001E 8F1F LBI R15, #$1F 0020 0FFD MLH R15, R15 0022 8FFF LBI R15, #$FF ; start with last address $1FFF ; If there is no memory at the location pointed ; to by R15, a read will return $FF instead of $00 0024 61F8 MOVB R1, (R15) 0026 C10C SNS R1 0028 A00D BRA $0038 ; no memory here ; Next memory location (increment by $2000) 002A 05F4 MOVE R5, R15 002C 01FC MHL R1, R15 002E A11F ADD R1, #$20 0030 0F1D MLH R15, R1 0032 81FF LBI R1, #$FF 0034 C517 SBSH R5, R1 ; done 0036 F013 BRA $0024 ; Loop 0038 10FB CTRL $0, #$FB ; Toggle level 0 003A 1FFF CTRL $F, #$FF ; Reset all devices ; Put $FFFF (halt code) in R7L0 ; R7 remains unaltered during bring up diagnostic 003C 0771 DEC R7, R7 ; R7 <- $FFFF ; Test RWS locations $0020-$05FF 003E 8420 LBI R4, #$20 ; R4 <- $0020 (start address) 0040 8606 LBI R6, #$06 ; R6 <- $0006 (high end address) 0042 8104 LBI R1, #$04 0044 011D MLH R1, R1 0046 81C4 LBI R1, #$C4 0048 0203 INC2 R2, R0 004A 0014 RET R1 ; test memory (call $04C4) Christian

On Mon, 11 Nov 2013, Ellis Holman wrote: Well yes, I also guess that the graphics adapter is functional. But what characters do you see in register display mode? That's obvious. See the MIM[1] section 209 (A1 board). And BTW, please also check the voltages and check if all connectors are properly seated (especially those around the side of the backplane). For example, the storage needs +8.5V and -5V. Those details are described in the MIM. See also the bring up chart on page 4-7 of the MIM. Christian [1] IBM 5110 Computer Maintenance Information Manual