HV Power Supply - Test For Ripple

Scope it under load.

Transmit, receive or both? You can't rule out the PS entirely if its only on transmit but you have the added possibility of rf getting in via the mic, etc.

Yep, scope it under load. You can even use a DMM or VTVM set to AC. Of course you need to know the original specs or a ballpark idea how much ripple (%-wise) is to be anticipated in order for the readings to be meaningful.

GL, Bill

** Posted from **

Thanks Bill. I wanted to use my DVM (Fluke 87), but don't know the original specs on the power supply. I have been trying to find them on the Internet.

Dick

** Posted from **

Dick wrote in news:1e9nv3h6uskeei64q8i1j94elo7dhijpsl@

4ax.com:

If you don't have a scope, look at the AC voltage on the DC lines. Transmit into a dummy load and see if you get AC on the DC line as you modulate the rig.

You need to have some idea HOW MUCH ac is allowable. Perhaps the specs of the rig will help. In any case, the AC should be MUCH less than the DC voltage.

--
bz    	73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an 
infinite set.

bz+ser@ch100-5.chem.lsu.edu   remove ch100-5 to avoid spam trap

Dick wrote in news: snipped-for-privacy@4ax.com:

The DC blocking cap on your DMM better be good enough for the AC voltages you're measuring....

a TEK P6015A HV probe and a scope would measure your HV supply ripple. Safer,too.

--
Jim Yanik
jyanik
at
kua.net

With a suitable highvoltage probe.

Take a capacitor rated for the voltage in question. Place this cap in series with your AC volt meter to block the DC component. Measure the AC component and that gives you the ripple voltage. A bit of math will give percentages, and all else you need to know.

AC coupled. :)

--- sam | Sci.Electronics.Repair FAQ:

Repair | Main Table of Contents:

+Lasers | Sam's Laser FAQ: | Mirror Sites:

Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.

Here's the schematic in case you don't have it.

If it is hum distortion on receive as well the +275 line and the -110 line would be most suspect. I rebuilt a couple of Galaxy supplies similar to this one and if you start finding bad filter caps it makes sense to just do a clean sweep of all of them.

I don't know your meter but indeed check to make sure it can handle the range for AC+DC!

Good luck, Bill

** Posted from **

Well that's a given. He didn't specify how high the "high voltage" is, if it's only a few hundred volts, a normal 10x probe should be fine. Up to a couple thousand, a simple resistor divider will work ok.

The high voltage is a little over 900V. The medium voltage is 300V. Those are the two lines I shorted together momentarily by accident. That's when the receiver became highly distorted. Don't know the effect on transmit yet, but expect similar problems. The HV line is fused. The 300V line is not. The fuse blew instantly. I suspect the damage, if any, is in the 300V section. The Swan supply was completely rebuilt with an upgrade board. The only old components remaining are the power transformer and the choke. Everything else is new. Everything was working great until I got clumsy with a probe.

The Fluke 87 is a true RMS DVM with a max input for AC and DC of 1000 volts. I have a Tektronix 475 scope. It has a max input of DC coupled: 250 V (DC + peak AC) or 500 V P-P AC at 1 kHz or less. AC coupled: 500 V (DC + peak AC) or 500 V P-P AC at 1 kHz or less.

I don't know much about the use of oscilloscopes. Just enough to be dangerous. I'm assuming I need some type of probe that will let me test the 900V line in the supply without damaging the scope. I can see A/C ripple on the 300V line, but I don't know how much is too much.

Dick

** Posted from **

I'd never assume that!

He said a Swan which is probably an old(er) tube HF rig. I'd guess as much as a kvolt on the finals.

Yes, I though about a resistor divider too. I hope the OP doesn't kill himself!

>

use a resistor divider network, and a blocking capacitor rated for the full voltage.

I'd not use a standard probe even on the 300 volt line. Use a high voltage probe if you want to use the scope.

What, and miss all the fun?

Sometimes there's a bleeder resistor on the output of the supply. Often, it's made up of several series resistors. Sometimes you can measure the ripple across the bottom resistor and do the math. Or just install another resistor in the bottom of the bleeder chain.

Or just unhook the cap, drive it with a pulse generator and look at it on the scope. The shape of the waveform will tell you the capacitance and ESR of the cap. If the cap is good and the diodes are good, there ain't much else to look for. mike

--
Return address is VALID!

There are two series bleeder resistors (120K 3W) on the output of the HV supply, with an electrolytic across each one. If you ground the bottom of that chain, you get 600V output. The 275V supply is placed in series with the HV supply for 900V output by moving the fuse from one location to another. I could send you a PDF of the schematic if you would like.

Dick

** Posted from **