Energy-Onix SST-30

[TomT]

Given to me as a basket case.

This is actually an RVR exciter, they made various iterations for various companies including Energy-Onix and Bext. This unit has a BCD switch for frequency select on the left, 3 LED's for voltage indication, and a meter for power output/vswr on the right.

Looking at the innards from the front, there is a toroidal power transformer on the right, then, to the left, the power supply board mounted on a long vertical (front to back) heat sink, then the PA, (another long heat sink), then the main board laid out horizontally on stand-offs, which has the audio sections, frequency synthesizer,vco, and mod osc. Everything tied together with ribbon cables.

The fan on this unit died, resulting in the power supply melting down, burning up the power transformer. Replaced the transformer, rebuilt the supply, replaced all the electrolytics, and, of course, the little Papbst fan that caused the problems in the first place.

But apparently still have a problem on the main board. The unit will come up, AFC locks, & I get power out of it (maxes out around 28 watts), but after about 10 seconds, the +12 supply crowbars. As I mentioned, everything is connected by ribbon cables, so popping the cables off the headers isolates this problem to the main board very quickly. Obviously not a heat problem, since the unit doesn't run long enough to get anything hot. I suspect something is oscillating.

Anyone run into this problem before?

I have a manual, couple of them, in fact (--one for this 1992 vintage exciter, one for a newer Energy-Onix, and one for a Bext 30 watt version of this same exciter) but none of them have very good schematics or any in-depth description of the circuits.

 

[vxo]

If this poor thing got hot enough to roast, I would suspect a screw may be loose somewhere in there, breaking a ground connection. This could be the source of oscillating nasties!

Also, are there any tantalum caps? Those are... um... special. They should be replaced if present.

 

[TomT]

My thought, too, on the tantalums--hard to determine values on some since the printing has faded & the schematics are so fuzzy.

May have found the problem, though. Careful examination of the replacement 12 volt regulator indicates that it may be the problem--will find another one from different manufacturer and install it.

 

[TomT]

No, that was the 15 volt regulator--a tab mount device. The 12 volt regulator is in a to-3 (metal case).

Replaced it anyway & problem cured. Why the 12 volt supply died I don't know, unless the front panel silk screening is reversed. Why this particular 7815 was a problem I also don't know--brand new--but it was running hot even with the main board disconnected. Infant mortality I guess.

Next problem proved to be a MJ3001 which controls the power output (a Darlington pair). After one popped I put in an NTE 245 which is listed as a replacement but appears to be more rugged than the MJ3001.

Works fine now with about 30 watts out. Still to do is to replace the broken meter switch on the front panel, and get some super glue to re-mount the meter--the bezel is broken & hard ware missing (but that's the part of the bezel that is broken as well.

Will put this on a translator, freeing up my Continental 802A.

Now a tip for folks that have the various versions of these RVR exciters. Reverse the fan! The fan is installed so as to blow air out of the box; however, the heatsink on the power supply gets pretty hot at full output--even with the cover off. Switching the fan around to blow INTO the exciter makes for a cooler operation.

The cover is vented on top, so you will need to allow some space in the rack for the air to blow out.