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Machines and Accessories Report No. 98-08

Date: November 6, 1998

Subject: C-1 Amplifier Board Tester

With a few minor, reversible modifications to an up-to-spec
C-1, a repair person can build a very effective and
easy-to-use C-1 amplifier board tester.  This device
positively identifies amp boards that are operating up to
spec and defective ones, saving valuable technician time by
quickly resolving a suspected failure and saves significant
repair-part dollars by positively identifying for repair
only those boards that have actually failed while assuring
that good boards remain in service.

The basic idea of the board tester is to modify a C-1 so
that you can easily plug a board into the C-1 circuit from
the exterior of the machine without having to open the case.
A requirement for success is that the modified C-1 act as a
test standard and be kept up to specifications at all times.

To perform the modification, you can use any C-1 as is, or
you may prefer to use the top case from a machine slated for
disposal.  That way changes can be made without concern for
returning the unit to service at some future time.  The same
unit slated for disposal can also serve as a source for a
cable extender.

Build the tester as follows:

 -- Identify and mark test tapes that will be used
exclusively with the tester.  This ensures accuracy and
consistency.

 -- Bring the unit up to specifications and remove the amp
board.

 -- Remove the metal plate that identifies the machine's
controls to prevent short circuits when the board under test
is set on this surface.

 -- Extend the cable that connects the amp board to the rest
of the unit, and bring the cable up through the opening
previously occupied by the speed or side switch.  You can
use a wiring harness from a machine slated for disposal.
When extending the cable, be sure to keep the head shield
lead intact.

 -- Put Lubriplate on the contacts in the extended cable to
facilitate board connect and disconnect.

To test an amp board of unknown quality, simply plug it into
the arrangement described above and verify that the tester
plays at specifications, particularly the frequency response
specification.  Also check operation of the tone, volume,
side, and speed controls.  If operation is up to
specifications, then the amp board is operating properly.
If not, tag the defective board with a description of the
failure, and send it to a repair facility.

Thanks to J.C. Powell of North Miami, Florida, for this
valuable suggestion.

For further information contact:

Kevin Watson
Assistant Equipment and Materials
Maintenance Coordinator