Servicing the MARK III

The factory manual↑ TOP

The MARK III's factory paper is split machine by machine, and not every machine's is on this site.

III/2 — the 1988 alignment procedures, "MX-5050 BII and MX-5050 MKIII-2 Alignment Procedures", Edition 2, January 1988. Its operation manual is not on this site.
III/4 — instruction and maintenance manual OS3-035 (PDF).
BQ-II — instruction and maintenance manual OS3-031 (digital edition).
III/8 — no factory manual on this site.

BQ-II: OS3-031's Section 7, Performance Testing and Electronic Alignment, with the alignment itself at 7-6.
III/4: OS3-035's Section 7, Performance Testing and Electronic Alignment (p.7-1, PDF p.75); 7-6 Electronic Alignment starts on p.7-12 (PDF p.86) (PDF).
III/2: the 1988 procedures — 2.2 for its speed, 2.3 for its capstan servo offset, 3.2 for access to its amplifier, 3.3 and 3.4 for reproduce and record (digital edition).

The shared method, with modern test gear, is at Calibrating the MX-5050; its pot numbers are the first generation's, not the MARK III's.

III/4 and BQ-II: 15 and 7½. The III/4's speed pushbutton selects 15 ips at HIGH and 7½ at LOW (OS3-035 PDF p.36); the BQ-II runs "7 1/2 and 15 ips" (OS3-031, 1-4). Both manuals specify equalisation "for 7 1/2 and 15 ips" only (OS3-035 p.1-8, PDF p.24; OS3-031 1-4).
NAB or IEC, and a second reference level. Both manuals quote their levels at 250 nWb/m and, for IEC, at 320 nWb/m — "1.2 dB above" (OS3-035 7-1, PDF p.75; OS3-031 7-1). Changing the equaliser has its own procedure (OS3-031 5-3; OS3-035 5-3, PDF p.60).
A III/2 capstan servo offset. The 1988 procedures give the III/2 a capstan servo offset adjustment of its own, section 2.3.
A III/4 speed-adjustment insert. The III/4 manual carries a "TAPE SPEED ADJUSTMENT" sheet that replaces its Section 6 procedure: speed pots on the capstan servo board and a multi-turn pot, VR-1, on the control board (OS3-035 PDF p.17).