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Technical Tips from Mark W. Persons
Rectifier Module for a
Harris Z10 FM Transmitter

Monday, July 16, 2013:  Another rectifier module from a Harris Z10 (10 KW FM Transmitter)

A station on St. Thomas in the Virgin Islands owns it. 

This particular rectifier handles three-phase power.

If you look closely, a fuse near the center on the circuit card on this side is missing.

Let's find out why.      

(left photo) The fuse in a hand is one that was in the fuse socket on the other side of the module.  Yes, a fuse has failed on this side too. 

The fuses did not open because of a failed component in the circuit.  Rather, the fuse overheated because of a poor electrical connection to a fuse clip.  Sometimes the metal cap on the fuse turns a blue color when when running hot.  Any fuse like that should be discarded because it is bound to fail soon anyway.

These are 30 ampere fuses.  Lots of current and a high chance of failure when the parts do not fit together tight.

Best not to reuse one that had overheated.  Instead use new clips for a repair, as shown above.

Replacing a fuse clip often times requires removing an entire circuit card with its 19 screws.  A somewhat time consuming task.

Three of the semi-conductor devices on this side needed to be kept insulated from the heat sink.  Most of the devices are SCR's (Silicon Controlled Rectifiers).

Above is a close-up of where a new fuse clip was soldered in.  Heat from the original failure caused the green mask paint to flake off exposing the copper trace.

Think through a technique for testing the SCR's without having to pull them out or put the rectifier assembly back in the transmitter.  Installing a module in a transmitter can be a 45 minute job.  Harris does not repair these, but charges about $2000 for new modules. 

The stories go on and on.  Stop in again sometime.  I'll leave the soldering iron on for you. 
Mark W. Persons   ham W0MH      

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