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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) came in to the shop for repair. 

A station on St. Thomas in the Virgin Islands sent it to us. 

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 my 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.

Fortunately we had some new clips on hand for the 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.

The repair went well.  I developed 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.  The repair, with testing, came to about $250.  Harris does not repair these, but charges about $1400 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 WMH      

Questions?  Email Mark Persons:  teki@mwpersons.com         

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page last edited 02/24/2016