[TenTec] Model 963 25A Power Supply 'burning smell' problem

[Dr. Gerald N. Johnson]

On Thu, 2007-11-15 at 10:38 -0800, Jerry Volpe wrote:
> Anyone else experience over-heat damage to the the fuse area on the 
> 963's power supply's circuit board? If so, what did you trace the 
> over-current problem too? In my case it appears that the mini-glass 
> fuses are getting too hot and oozing a reside out one end which seems to 
> be contaminating the physical connection of the fuse at that end and the 
> circuit board clip.... thus inserting some resistance where it shouldn't 
> be. This increase in resistance is creating a current 'hot spot' where 
> the clip is soldered to the circuit board and that area is beginning to 
> literally burn. The power supply is about two years old.

It might be good to check the source of your fuses and to bend the clips
a bit with the fuse out to get a tighter grip on the fuses. Many fuses
made off shore are poor approximations of a proper fuse. I like those
made by the Bussman Company.

In new construction I'm using the small automotive blade fuses. Seems
like there's better contact to the blades than to round fuses, shorter
springs in the connectors and some edge grip to bit through oxidation.
Some in line fuse holders supplied with certain vintage ham rigs seem to
have excess voltage drop from bad connections to the point of melting
the fuse holders and limiting power output. I believe I'm getting better
results with the modern automotive fuses.
> 
> About two months ago I noticed a bad 'burning' smell in the shack for 
> the first time. Took a few moments but the smell was traced to my 963 
> power supply running my Orion 565. Power output voltage was correct, 
> nevertheless I turned it off immediately and did a visual inspection. 
> Inside I found the circuit board had a small chard area on one side of 
> the circuit-board mounted fuse clip (as described above). I also noted a 
> residue around that end of the glass fuse. There were no other signs of 
> overheating on any other components or on any other part of the circuit 
> board.
> 
> I replaced the fuse with a new 10a, 220v fuse and cleaned the fuse 
> holder... checked the solder connections.... reassembled. All was good 
> till this morning. Of course I was getting ready to 'chase' a new one 
> and that familiar smell was in the air. Turned the power supply off and 
> did another internal inspection. Found the new fuse 'leaking' on the 
> same end of the fuse clips and that charred area a bit larger this time. 
> I drilled the back panel and mounted an appropriately sized screw-type 
> fuse holder. I removed the old clips from the board and attached #12 
> stranded/insulated wires between the circuit board and the new fuse 
> holder..... replaced the fuse. At the moment all is well. However, I did 
> purchase an Astron RS-35M to replace the 963 until I can figure this one 
> out.
> 
> Thoughts?
> 
> 73,
> Jerry, KG6TT
> 
73, Jerry, K0CQ