Otari MX-5050
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First generation›Service

Generation

MultichannelFirst[Mini Pro]Mark IIBB-IIMARK III[BQ-II]B-IIIMARK IV

First generation

OverviewIdentifySpecsHistoryDocumentsService

Machines

2S4SQXF8

Servicing a first-generation MX-5050

The factory manual↑ TOP

The maintenance manual covers the 2S and 4S and their DC-servo 2SD and 4SD versions; the operation manual, OIM-1005E, covers operating the 2S, 4S, QX and F. The QXD and 8SD have two books of their own, shared with the Mark II.

  • The maintenance manual — "Models MX-5050 2S, 4S, 2SD and 4SD" on its cover (digital edition), a supplement to OIM-1005E "intended for use by qualified maintenance or service personnel only" (Chapter 1). Its Chapter 3 is the performance tests and the electronic alignment.
  • The operation manual, OIM-1005E — the operator's book. Its model table lists the 2S, 4S, QX and F, each in a high- and a low-speed form — 2SHT and 2SL, 4SH and 4SL, QXH and QXL, FH and FL (Table I-1). Its Section IV-3 carries a short operator's version of the same trims.
  • For the QXD and 8SD — Otari's instruction manual OIM-1004E and maintenance manual OMM-1002E, which cover them alongside the Mark II's 2SD₂ and ½QXD (OIM-1004E, Table 1-2; OMM-1002E). The Mark II's service notes cover those books.

Alignment: 2S/4S family↑ TOP

For the 2S/4S/2SD/4SD, the factory procedure is their maintenance manual's 3-5 Electronic Alignment and 3-6 Record and Bias System Adjustment, after the performance tests in 3-4. The operator's version is OIM-1005E's IV-3 Electronic Alignment: standard reference level, bias and record equalisation only.

The bench guide using this procedure, with modern test gear, is Calibrating the MX-5050. For the QXD and 8SD, use OMM-1002E's own performance tests and alignment; its step numbers and adjustments must be read from that book.

The 2S/4S bench guide↑ TOP

Calibrating the MX-5050 was written on a 2SHT, so the adjustment points it names — the record EQ pairs R28/R128 and R29/R129 among them — come from the 2S/4S maintenance manual (3-6-(4)). Inside the audio path walks the same machine's record/reproduce electronics from its factory schematics.

Before you open a 2S/4S: the dummy plug↑ TOP

If the transport is completely dead, check the accessory/remote socket before anything else. The transport control circuit runs through that socket and must be closed by a shorting "dummy plug" whenever no remote is connected. A missing plug makes a healthy machine look broken — this site's own deck was sold as faulty for exactly that reason (listed as broken). The pinout, read off the transport schematic, and two ways to build one are in No dummy plug — no problem!.

2S/4S details in the factory books↑ TOP

The bench guide follows the 2S/4S procedure above. Its factory books also record these model details:

  • Two speed pairs. H models run 15 and 7½ ips, L models 7½ and 3¾ (OIM-1005E, Table I-2).
  • A synchronous capstan, or a servo. The transport has "a 2-speed hysteresis-synchronous motor for the capstan" (I-1-(1)); the specifications give "Two speed hysteresis synchronous or DC servo controlled motor" (I-5).
  • Equalisation follows the speed switch. The front-panel speed pushbutton "also switches equalization" (I-1-(1)); the standard is NAB, with EIA, CCIR and IEC "also available" (I-5).
  • The boards come out from below. The three record/reproduce boards are reached by removing the base of the cabinet, four screws (3-5).
  • Record EQ pots depend on the speed pair. For 7½ ips the manual trims R28/R128 on high-speed models and R29/R129 on low-speed models (3-6-(4)).

Sources↑ TOP

Maintenance manual

Instruction manuals

  • Operation manual OIM-1005E — Table I-1 (models), I-1-(1) and Table I-2 (capstan motor, speed pairs, equalisation switching), I-5 (capstan and equalisation specifications), IV-3 (operator's alignment).

  • Instruction manual OIM-1004E — Table 1-2 (the QXD and 8SD models).

From the restoration log