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Technical Service Bulletin SN2-001

Cassette Load Programs

August 10, 1982

Most technicians know that the red lead of some ohmmeters is negative while on other ohmmeters it is positive, thus it is important to establish the correct polarity versus color prior to checking diodes or other devices. The polarity depends on the internal circuitry and battery placement.

This non-standardized practice within our industry was emphasized recently when a service center technician related an experience he had using a cassette recorder connected to a Chroma. The Chroma would not sense the motor controls properly. During troubleshooting the technician found that the motor leads brought out to the remote switching jack were of reversed polarity compared to those used in the recommended cassette recorder. The cassette player we recommend is the Radio Shack CTR-80A, Catalog Number 26-1206. The cassette player with the reversed motor lead polarity is the Radio Shack Model CTR-41, Catalog Number 14-841 having the additional disadvantage of auto-level instead of a completely adjustable record/playback level. The recommended Model CTR-80A is manually adjustable in level allowing the operator to set levels for the best load/save functions.

So--If you are using a cassette recorder and the Chroma fails to control the motor, check the polarity of the motor leads. The proper polarity results in a positive level at J18-4 and a negative level at J18-5 on the I/O Board or motor + on the tip and motor - on the sleeve of the remote plug.

Bill Thomas
Rhodes Chroma National Service Manager