2023-01-15

The rack-mounted drive is an NEC FD1035, taking 2W on each of two power rails.

Therefore 12V is 2/12 = 0.167 amps, and 5V is 2/5 = 0.4 amps.

The drive of unknown provenance is a TEAC FD235HF which requires only 5V at 0.8 amps peak, i.e. 4 W total peak power.

I don't know why they are behaving differently, other than maybe one is dead. The FD1035 is single density. So I may simply buy a new FDD that is guaranteed working.

2023-01-16

Made a new 34-way ribbon cable, just to make sure the cable is not the problem.

The FDD that didn't respond did not even light its LED so I guessed it was not seeing its drive select signal. I looked for a link suggesting drive selection. There are no jumpers but there was a surface-mount 0R resistor in a position marked DS1 which it shared with one marked DS0. Moved the resistor to DS0 and the drive responds in the same way as the first FDD. 

Two boards, two drives, four combinations, one disk. I think the problem is the disk. The CP/M manual for this board says the sectors are interleaved in the order 1, 6, 2, 7, 3, 8, 4, 9, 5 but it is failing to read sector 1 so the interleaving is not the issue.

2023-01-19

New FDD arrived today. Familiar problem, needed opening up and a solder-blob link changing to the DS0 position. Familiar result, sectors not reading. This is with the FDD and processor board driven by two different power supplies. Not ideal.

Changed to Steve's board, powered by same crate as the FDD. I did not get an instant sector fail, but did get an error eventually on track 2, which implies track 1 had been read successfully. 

Wondering if the disk is slightly off centre, I eject then reinsert it. This seems to help. After quite a few "Retry? y" cycles, it appears to boot.

Press RETURN

Arcom ATLAS
Serial console running at 9600 baud

Insert system disk in drive A: and press RETURN

CP/M V3.0 Loader
Copyright (C) 1982, Digital Research

BIOS error on A: Track-002, Side-0, Sector-006, Read, Not ready.
Retry (Y/N)? y
BIOS error on A: Track-002, Side-0, Sector-006, Read, Not ready.
Retry (Y/N)? y
BIOS error on A: Track-002, Side-0, Sector-006, Read, Not ready.
Retry (Y/N)? y
BIOS error on A: Track-002, Side-0, Sector-006, Read, Not ready.
Retry (Y/N)? y
BIOS error on A: Track-002, Side-0, Sector-006, Read, Not ready.
Retry (Y/N)? y
 51K TPA

BIOS error on A: Track-003, Side-0, Sector-001, Read, Not ready.
Retry (Y/N)? y
BIOS error on A: Track-003, Side-0, Sector-001, Read, Not ready.
Retry (Y/N)? y
Arcom ATLAS CP/M 3 BIOS V1.5
Copyright (C) 1984, Arcom Control Systems Ltd.

BIOS Error on A: T-00001, S-00000, Read, Not ready, Retry (Y/N)? y
BIOS Error on A: T-00001, S-00000, Read, Not ready, Retry (Y/N)? y
BIOS Error on A: T-00002, S-00000, Read, Not ready, Retry (Y/N)? y
BIOS Error on A: T-00002, S-00000, Read, Not ready, Retry (Y/N)? y
BIOS Error on A: T-00002, S-00000, Read, Not ready, Retry (Y/N)? y
BIOS Error on A: T-00001, S-00000, Read, Not ready, Retry (Y/N)? y
BIOS Error on A: T-00001, S-00000, Read, Not ready, Retry (Y/N)? y
BIOS Error on A: T-00001, S-00000, Read, Not ready, Retry (Y/N)? yA>
A>dir
A: CPM3     SYS : BDOS3    SPR : BNKBDOS3 SPR : RESBDOS3 SPR : BIOS3    SPR 
A: BIOSKRNL ASM : BNKBIOS3 SPR : BOOT     ASM : BOOTB    REL : BOOTN    REL 
A: CHARIO   ASM : CHARIO   REL : COPYSYS  ASM : CPMLDR   REL : DRVTBL   ASM 
A: FDPH     ASM : FLOPPY   REL : GENCPM   DAT : HELP     HLP : MEMORY   REL 
A: SCB      ASM : SCB      REL : TIME     ASM : TIMES    ASM 
SYSTEM FILE(S) EXIST
A>

On the good side, it looks like the sectors are valid and it manages to run the DIR command from the serial line okay.

This success is short-lived. An attempt to PIP BIOSKRNL.ASM creates more errors.

The hardware manual says:

"If your drives are not working reliably (a good test is to format a disc) the most likely cause is not maladjustment but electrical (or more probably magnetic) interference. A typical symptom is an increasing error rate on the inner (higher numbered) tracks when trying to format discs. Check this by moving the drives and the SCPUA board away from all possible sources of interference, including VDTs, monitors, switch-mode power supplies and mains cables. A noisy power supply to the SCPUA will also increase the error rate."

I shall investigate the PSU. After decades, the smoothing caps may have dried out. The meter reads 5V and 12V correctly.

2023-01-21

The original system in the case was a 68020 running OS9/68K from a SCSI disk, and that also failed to boot. Perhaps that was also a power supply problem.

I removed the FDD power lead off the crate and wired it to the same power rail as the board. I then plugged it into a 5V-only FDD. The system power was a modern 5V 3A wall wart, which is more than the 2A expected load. Same failures as before, so I am beginning to think the power supply is not to blame.

Maybe the disk magnetisation signal is borderline?