power supply trouble!

[packrat]

I have an FT757HP power supply that I use on my rigs, and it has worked fine til now. I hooked up my 7800r to it and it wouldnt come on or if it did it went right out, so I thought I had a connection problem. I got my VOM and started looking for the problem. What I found was that the supply was putting out 16-17 volts. The 7800 saw an overvoltage and went into protection mode.

I hooked the 7800 to another supply and it is fine. I have pulled the Yaesu supply out of line now, and replaced it with my pyramid supply. I wondered if anyone can help me diagnose it? I dont have a schematic, but I dont see any voltage adjustments.

Any Ideas??

PR

 

[Sonwatcher]

Wow ! I traveled down that road. My 757hd quit one day. I never could find the problem for certain . I also replaced it with an old Pyramid which just recently quit. Hope you find the problem. Someone had me check several things and concluded that the transformer winding went bad.

 

[packrat]

Ya know, the scary part is that I have been running my 570 on the power supply for the last 6 or 7 months, luckily, without problem.

PR

 

[295]

Wow ! I traveled down that road. My 757hd quit one day. I never could find the problem for certain . I also replaced it with an old Pyramid which just recently quit. Hope you find the problem. Someone had me check several things and concluded that the transformer winding went bad.

Wow, transformer windings going bad is really rare. If I can find a schematic online I will take a look, linear power supplies are fairly simple to diagnose and fix. Could be something simple like the varible resisitor which controls voltage level has changed in value due to dirt, humidity, age, etc, or could be something in the regulator circuit like a zener diode or the regulator chip itself. If I can find a schematic, I will post back.

73

 

[Sonwatcher]

Wow, transformer windings going bad is really rare. If I can find a schematic online I will take a look, linear power supplies are fairly simple to diagnose and fix. Could be something simple like the varible resisitor which controls voltage level has changed in value due to dirt, humidity, age, etc, or could be something in the regulator circuit like a zener diode or the regulator chip itself. If I can find a schematic, I will post back.

73

It's been a couple years but if I remember correctly there was input voltage to the transformer but nothing out of the output taps off the windings.

Anyway, I don't want to highjack the thread as that supply is long gone. Back to helping Packrat

 

[packrat]

Appreciate all the input. I was hoping that there was a variable in the output circuit, that would be great. I dont have the schematic, and I havent opened her up yet. I am just grateful that I didnt damage my rigs. I checked the specs on the 570, and it showed 13 volt input, + or _ 10%. 17Volts is a bit high, high enough that the 7800 shut off immediately.

PR