Power Supplies in Imported TV sets

Working on High voltage Power supplies we had a constant problem with 5 watt series resistors getting so hot that they would burn not only the conformal coating off the resistors but also charred the circuit cards. These were used in N.T.D.S. (Naval Tacticle Data Systems) systems for large CRT planning screens. They produced symbols showing and Identifying surface craft and aircraft and incoming missiles.
We modified the circuit by raising the resistors off the board, and repairing the damaged traces & solder holes because of Constant heat expansion and cooling from the hot resistors (18 in series). We would also put a U shape in the leads to help the leads from strain while hot. My method also was insert a tongue depressor under each resistor in turn to have a uniform spacing above the circuit cards while soldering each resistor in turn. We repaired the circuit card charred areas with circuit card fiber glass mixed with epoxy after cleaning out the charred areas. Then of course moving & using the same depressor in turn.



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In the 60's the Japanese imported quite a number of tube type TV sets into the U.S.
Toshiba, Sony, etc.

 These sets generally used 4 diodes in the main B+ supply.

Now some of these looked like a very small coin, maybe 1/2-5/8" diameter, had a DIODE SYMBOL on them. Usually rated about 500-600 ma, and a good old 1N4007 works fine as replacement most of the time. (These are not MOV's or Glo-Bars), and had the leads bent in a "curly cue" before being soldered to the board.

 I stated in another posting that for diodes to have the rated current carrying capacity the diode must have full length leads to fully be able to dissipate the heat.

 So if you have to replace them- remember to replace all 4 of them-, not just the bad one-(If one is bad, the others have been stressed and can fail); leave the leads full length and up off the board if at all possible. If space is an issue, by all means put the "curly cue" bend in them, but try to space them off the board. This is for better air flow and heat dissipation. Those old tube TV's got pretty hot inside!

As a side note, when I used full length leads and put the "curly cue" loop in them, I never had any fail that I installed in hundreds of TV and radio sets. I also do this on small signal or Zener diodes too.

The only thing to be sure is they do not hit against another part, as sometimes metal cans or shields are really close to them and you don't want them shorting out.