----- Original Message ----- From: "Damien Mannix" <damienman...@hotmail.com>
To: <drakelist@zerobeat.net> Sent: Saturday, August 25, 2012 8:36 AM Subject: [Drakelist] Exploding Cap' ???
Hello all, I am embarrassed but most grateful for all the kindness and helpful advice given to me. Too many to thank individually but many many thanks to all. The safety advice is taken very seriously and I will be ultra cautious bearing in mind my inexperience. Already I am puzzled. Astonished in fact. A most careful examination of every component in the AC4 and then the TR4, magnifying glass and high power flashlight and what a lot under the TR4, shows no sign of distress to any component!! Clearly the bang came from somewhere, I was not dreaming, so I guess it is time to carefully take some voltage measurements from the AC4 as a first step. DamienG3XER Electrolytic caps usually smell pretty strongly when they explode. Actually, these caps usually have a vent to prevent an actual explosion if they develop an internal short but they still smell when they go. Film caps do not often explode and seldom short. A resistor also smells when it heats enough to explode but the odor depends on the type. Carbon composition resistors usually have the typical carbolic acid odor of burning phenolic but film caps may not have an odor.
Its possible this was an arc-over. That may be hard to find. I would certainly inspect the switch decks, especially in the RF section, very carefully. Also inspect the variable capacitors in the RF section for any sign of arcing on the plates. An arc will usually leave some sort of trace, sometimes a dark track and sometimes a small area where its melted the metal at the surface. Its possible for dirt to cause an arc and be burned away. Its also possible for moisture to cause an arc.
You can check the power supply with it disconnected from the transmitter by shorting the AC switch pins on the connector. Unloaded voltages will be higher than indicated on the schematic. I variable transformer is useful here.
-- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com _______________________________________________ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
