Originally Posted by plow_dog
Glad this is still an active thread.
I have what I'd call an older 3500STBII - without the 3-4 switch.
It has been in a room where it has not been used much - maybe 100 hours.
I noticed a few days ago that the display was off and would not come on.
Unplugging it from the 120 volt AC, removing the cover, plugging it back in, and checking the output of the power supply board showed 12 volts on the 12 volt wire, but only 2 volts on the 5 volt wire.
Not being very knowledgeable about this stuff, I rather assumed that a transformer was bad.
But, after reading your comments, I looked at the capacitors on the board.
All but one have a flat surface on the end.
The capacitor located at C6 on the board is not flat, and looks to be swelled up - or convex instead of flat.
The writing on the plastic wrap of the capacitor has 1000uF 10 V.
Might this be the same capacitor that you replaced?
If so, maybe I could save this unit from the electrical trash heap by finding, and soldering in, a new cap, or, if available, maybe replace the entire power supply board/assembly.
Also, if so, any idea how/where I might acquire the cap or the board?
Thanks in advance,
The power supplies are "Switchers" which rectify "line-voltage" on the input side; follow it up with a high-frequency switching regulator; and rectify and filter the output on the low-voltage side. It's more economical than a lotta iron and copper of traditional power supplies.
My power supply failures were with first-generation 3500's.
The particular capacitor that failed was the tall, fat 1000µF 10V Electrolytic with radial leads.
In my cases, the capacitor didn't show outward signs of failure. No bulging or leaking. The capacitance had dropped to 30µF or less when I measured it.
If you have a Gen 2 or Gen 3 unit, it appears they didn't change their procurement, and that the selection is ill-advised. It's not robust enough.
When you're shopping for a replacement, pick one with the right pin-spacing, and diameter, AND with the highest reliability or longest projected lifetime you can find. Pick parts with the same or greater capacitance, and the same or greater voltage rating. Be willing to spend 10% or 20% extra for better quality parts. Look at vendors like Digi-Key or Arrow or Mouser. (You can take your chances with Amazon too, or ebay) I kinda like the low ESR organic electrolytics like the Os-con. When I was working on a high reliability project before retiring, our reliability engineer steered us to products manufactured on the same production lines used to produce the MIL-SPEC parts. It paid off in low failure rates in the experiment hardware that got installed in the ice at the south pole.
If you have a capacitance meter (some good modern digital voltmeters have the feature), you might consider checking the other electrolytics too. It might save you a second assault on the PCB. Unfortunately you have to remove the parts from the board to reliably test them.
Good luck. Be careful.
Unplug for long enough before working on the board.
Don't burn your fingers. Don't lift PCB traces. Don't short traces when soldering.
Picture before beginning work are helpful. Just a lotta common sense stuff.