This maintenance manual describes how to maintain the printer in the field. This manual is for customer engineers. For further information, refer to the Users Download OKI ML420 ML421 FIRMWARE UPGRADE PROCEDURE service manual & repair info for electronics experts. OKI and MICROLINE are registered 4 Microline 420/421 User's Guide document, don't try to service the printer yourself. Opening. 2 ml 420/421 user's guide p/n 59348301, revision 1.2 february, 2006 every effort has been made to ensure that the information in this document is complete,Oki Data CONFIDENTIAL. PREFACE This maintenance manual describes how to maintain the ML420/421 printer in the field. This manual is for customer engineers. For PDF manuals: You need Adobe Reader installed on your computer/device. To install Adobe Reader, read download section in the Terms of use page. Oki Data CONFIDENTIAL. PREFACE. This maintenance manual describes how to maintain the printer in the field. This manual is for customer engineers. If that doesn't help, the printhead may be damaged; call for service. The ALARM light is flashing. Try turning the printer off and then back on again. Page 3 Oki Data CONFIDENTIAL PREFACE This maintenance manual describes how to maintain the ML420/421 printer in the field. This manual is for customer OKI MICROLINE ML3410. MAINTENANCE MANUAL. PREFACE. This maintenance manual describes how to maintain the Microline 3410 printer in the field. This manual is