Servicing the MARK IV

The factory manual↑ TOP

The operation and maintenance manual OS3-298 (PDF) covers the MKIV-2 and MKIV-2E, in one book with the upright B-III. It lists the half-inch MKIV-4 and MKIV-8 in its family table but does not describe them — "This manual describes the MX-5050 MKIV-2, 2E, BIII-F, BIII-2 and BIII-2E models" (PDF p.15). No factory manual for the MKIV-4 or MKIV-8 is on this site.

Alignment↑ TOP

OS3-298's Section 7, Audio Alignment (p.7-1, PDF p.78), from the tools and alignment tapes in 7.1 through reproduce (7.3) and record (7.4) adjustments. The shared method, with modern test gear, is at Calibrating the MX-5050; its pot numbers are the first generation's, not the MARK IV's.

How it differs from the shared method↑ TOP

Otari's paper disagrees about the MKIV-2's speeds. OS3-298 says "The MX-5050 MKIV-2 cannot be changed to Low Speed" (section 2.7, PDF p.32; again at PDF p.23), while the 1991 data sheet says "B-III & MARK IV-2 models offer 3 speeds", switch-selectable between 15/7½ and 7½/3¾ ips, with the 7½/3¾ pair optional on the MARK IV-4 and 8 (OA-321C, p.4, note 1). Check which pair your machine runs before choosing alignment tapes.
NAB or IEC from a rear-panel switch. The equalisation is set to the customer's order at the factory and changed by sliding the EQUALIZER switch on the rear panel; after a change, the adjustments in 7.3.3 and 7.4.5 must be made (section 2.8, PDF p.32).
Alignment tapes for three speeds. Table 7-1 lists MRL tapes at 15 and 7½ ips — 250 nWb/m for NAB, 320 nWb/m for IEC — and at 3¾ ips, 200 nWb/m (PDF p.79).
A brushless direct-drive capstan. "Capstan x 1 (DC brushless PLL servo motor)" (PDF p.91); the capstan shaft "is directly driven by a DC servo motor" (PDF p.35).

Sources↑ TOP

MX-5050 MKIV-2, BIII-2 operation and maintenance manual, OS3-298 — PDF p.15 (models covered), p.23 and p.32 (the MKIV-2's fixed speed pair; section 2.8), p.35 (capstan drive), p.78 (Section 7 contents), p.79 (Table 7-1), p.91 (capstan motor).