HP dual power supply, tracking and earth? problem? - Page 1
Forum section: electronics / testgear

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2023, 08:56:59 am
content: I noticed when I try to use my HP dual power supply 6227B, if I have it in tracking mode, and connect earth (oscilloscope) it stops output. Even if I put a jumper banana plug from Ground to the joined channels it drops off.is it broke or is this how it works? it means you need everything connected to it to be floating when its in tracking mode.I think I just did a whole bunch of tests that basically provided no power because I set the voltage, then set it to current monitor mode, then connect the scope. Unless it was working and broke. IDK I lost track of what exactly was happening because I am mega pissed off at this PCB.if someone has one, can you just tell me what happens to the meter when you connect ground to the shared 0V terminal from the PSU when its in Tracking mode??

author: alm
author_rank: Super Contributor
timestamp: December 18, 2023, 09:08:12 am
content: What other front panel connections (e.g. negative of left channel to positive of right channel per manual) are you making, and what does the strapping on the rear look like?

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2023, 09:11:42 am
content: idk its default and I mean if its connected in tracking mode, and you touch the negative terminal to earth ground.i.e. connect 2 and 4 (shared 0v) then connect 3 to 2it says your not supposed to use the rear panel for tracking because of sense.never touched the rear panel

author: wn1fju
author_rank: Frequent Contributor
timestamp: December 18, 2023, 02:35:18 pm
content: On my HP 6227B, here's what happens:1) Set to individual mode, voltage shown on both meters is unaffected if either (or both) negative terminals are shorted to ground terminal (as expected)2) Set to tracking mode, voltage shown on master meter is unaffected if the master channel's negative terminal is shorted to its ground terminal3) Set to tracking mode, voltage shown on slave meter is unaffected if the slave channel's negative terminal is shorted to ground AND the master channel is left floating4) Set to tracking mode, voltage shown on slave meter drops to zero if BOTH the master and slave channel's negative terminals are shorted to their respective grounds. Master channel meter remains at original voltage.So I guess case #4 is the "illegal" one. I usually leave all my power supplies floating anyway.

author: alm
author_rank: Super Contributor
timestamp: December 18, 2023, 02:44:28 pm
content: Quote from: wn1fju on December 18, 2023, 02:35:18 pmRead the manual about tracking operation. I'm pretty sure it says in tracking mode, to always connect the left (master) negative terminal to the right (slave) positive terminal. Which to me implies there is an internal connection, but it may not be capable of carrying all the current. So in that case connecting the master and slave negative terminals together (through earth or not) would short the slave.

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2023, 10:03:00 pm
content: well the problem is I can't connect an osiclloscope to it. Because the oscilloscope is earth ground. So when I clip the probe ground to the PCB it drops to 0.Connecting the clip to ground plane makes the supply tank on both channels.I thought maybe a RF filter element connected to earth had gone resistive or something?Usually floating means you can have whatever be ground. But if you need a floating scope........The only time I ever see ground doing anything to a PSU is when the positive side was grounded by a stray screw so it made a random short.I thought it must be a failure because to require a floating scope just to track channels seems like a terrible trade off.

author: alm
author_rank: Super Contributor
timestamp: December 18, 2023, 10:12:27 pm
content: If you make no connections between any of the front panel binding posts, and connect one (and just one) of the binding posts to earth, does the voltage still go to zero? If not, then I think you need to re-read the section of the manual about tracking mode. Connecting two negative or two positive terminals together is not a supported configuration.

author: coppercone2
author_rank: Super Contributor
timestamp: December 18, 2023, 10:36:26 pm
content: im not running it in parallel I said its wired 2 to 4 that is + (- +) -it has a line drawn on the chassis for where you connect it to tracking operation. IDK where the confusion is here.i put parhethesis around what is wired togheter+ (-) EARTH (+) - EARTHthe line is drawn between channel 1 minus and channel 2 plus.1 = pos12 = neg13 = earth4 = pos25 = neg26 = earthI have neg1 and pos2 connected with a jumper. that is where they draw the line on the front panel

author: coppercone2
author_rank: Super Contributor
timestamp: December 19, 2023, 05:39:48 am
content: hmm I started to poke around. looks like 13.8 ohms to ground on the negative rail near the TO220 transistors. Maybe a sleeve slipped out or something. for channel 1kinda a big job will investigate later.I think this happened to one of the harrisons I was repairing too. SOme have sleeves that stay in to hide from you but fall out at the first oppertunity.I measured earth to ground. I noticed channel 2 reads some Kohm when switch is set to track, but open when set to independant. channel 1 says some kohm all the time. Then i started to probe everything and I think the 13.7 ohms to earth on the To base or whatever is suspectthe cans are isolated pretty good, just one of the base leads. I think it must be bent or something..ugh, open equipment count : 6.I need to start squashing these issues!

author: coppercone2
author_rank: Super Contributor
timestamp: December 22, 2023, 02:54:48 am
content: ok, there was some loose metal shit packed into the hole with the transistor. Like solder scraps or something. IDK how that happened. I like cleaned the fuck out of this board. Made a 15 ohm short to the chassis.also some how destroyed two caps I replaced? I think I kicked it at night because i left it under the table because there is too much open bull shit on my table.

author: coppercone2
author_rank: Super Contributor
timestamp: January 12, 2024, 01:47:25 am
content: Ok, I fixed it and replaced the transistor backwards, then rotated it, works fine now.Good thing that survivedI don't know how I managed to get it in there backwards. But now I can ground it with tracking and there is no problems. The impedance is in the high mega ohms when measured to chassis from each channel.