Restoring / Repairing a 004A 005A A11 Static Exciter & Voltage Regulator

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Every now and then, Owners of 004A’s and 005A’s post questions on how to fix their A11’s because they have no more Power / Voltage available at the output terminals

I will brake this information down into multiple posts because of the amount of pictures

First, the internal A11 failures:

1. a visibly burnt T2 transformer





This is the most visible damage to A11’s when the cover is removed.

However, the burning out of the T2 Transformer has other causes which will be shown and discussed in the next Post #2 below this post

 

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2. Causes for the failure of T2

the A11 has 6 Diodes installed on the Heatsink. They usually look like this after decades of Genset being stored in the elements



These diodes have to be tested according to the TM -34

Further issues are defective parts on the voltage regulator board:






then the canon / Amphenol connector on voltage regulator assembly


Continued on next post

 

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Continuation of post #2

the SCR’s mounted on PCB heatsink

the heat sinks are visible below canon / Amphenol connector

the PCB contains several semiconductors, resistors and capacitors which all have to be evaluated / tested after the conformal coating has been stripped and replaced
Continued in post #4

 

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Continuation of post #3

further C2 has now reached an age where they are dried out even though they show correct capacitance when tested, but because they are bone dry, can no longer maintain this capacitance at or near their rated AC / DC working Voltage

these are Motor start capacitors, or at least very similar to those.





this capacitor here as example, was manufactured in week 08 in 1976

continued in post #5

 

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Continuation of post #4

we have rebuilt several of these A11’s over the years and found a replacement T2 transformer because the original T2 was no longer available for quite a few years. Some NOS T2 have now surfaced on eBay

I would say it’s a matter of choice which one to use / buy - both work equally well

this is a completed A11 which has been fully tested as per TM -34






In this repaired A11 we used the substitute T2 (Hammond Transformer) and we left the Original C2 capacitor in place at the sole risk of the customer who did not want to spend the additional money on a new C2 capacitor and did not want the new cheaper Chinese capacitor as substitute either.

The successful repair / overhaul requires a experienced Electronics Technician with specialized bench test equipment
Most ET’s who can fix TV’s / VCR’s can successfully repair those A11’s

This is not a weekend project for a beginner in Electronics

We do normally not repair any electronics as we are a original electronics / equipment manufacturer short OEM and not a repair shop, but as you can see, have made exceptions