The Bernina Doctor Technical Advice Note Title: Bernina Electric Sewing Machine Suppressor Network Replacement 1.
Applicability
Bernina Record Models 730-to-732, 830-to-832 Bernina Sport Models 801-to-803 Bernina Minimatic Models 707-to-710, 717-to-719, 807-to-812, 817-to-819
2.
Overview
This advice only applies to sewing machines that have a separate motor box on the rear of the machine.
The type a707 motor used in these boxes is provided with a suppressor network to prevent interference to radio and television and to reduce arcing on the commutator contacts that leads to fouling of the contact blocks. Failure of these suppressors is now common due to age-related degradation of the product, this often being accompanied by a loud ‘pop’ and sometimes acrid-smelling smoke. In some cases, the machine may start running, uncontrolled, with potential safety implications so the machine should not be used until it is replaced. Some technicians simply remove failed suppressors without replacing them; this is very bad practice and is not recommended. Models of sewing machines covered include variants that are insulated to Class1 (earthed) or Class2 (double insulated) standards and it is important to take account of this when undertaking suppressor replacement to ensure that the relevant electrical safety is not compromised. All models and variants use a 4-pole connector on the motor box for the mains/foot-controller cable. Despite this there are variants that have different numbers of internal terminals, dependent upon whether a motor speed switch is incorporated into the box or the switch is external to it. Additionally, Class2 double-insulated variants have one pin/terminal missing to prevent connection of the mains earth to the machine’s chassis and later models using a type 232 or 239 electronic foot controller have a different shape connector. Iss3 May 2015
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