HP 6038A - thoughts?

[Harvs]

Hey Guys

I was just browsing the local sales and a HP 6038A has come up locally for $400.  It's specs would make a nice addition to the lab (particularly accuracy and voltage range), is there anything negative I should know about this range of supplies before I part with a reasonable amount of money?

From what I can see that seems to be a reasonable price for one in good clean order? Noting I'm in a region of Oz that doesn't have this sort of thing come up every day, and hence you often have to add at least $100 shipping to non-local items.

Thanks

[free_electron]

These are autoranging SWITCHERS.

The 6038 is a 200 watt model i believe. 0..10 amps and 0.. 50 odd volts..
This means at 20 volts you can indeed pull 10 ampere.. go to 25 volts and you only get up to 8 ampere... go to 50 volts and you only get 4 ampere.
in other words : you can not go 'over' the maximum power draw.

if you want 5 volts you still can only draw 10 ampere. so it is the lowest of the three that is at play.

These are good power supplies , but , they are notoriously difficult to repair. They use a resonant converter technology. the switching transformer in that beast is huge ... If you take a 500 watt computer power supply the transformer is 2 by 2 by 2 inch... the transformer in this thing is more like 4 by 5 by 4 inches... and there is another , equally large common mode transofrmer behind the secondary rectifier.. to keep the output free from switching noise.

There is a truckload of analog electronics in this machine. Very well built. Has great step response and packs some serious 'kick'.
service manual :

http://cp.literature.agilent.com/litweb/pdf/5959-3346.pdf

if you buy it and decide to do a teardown.. do NOT poke your fingers around in this thing until you made sure the mains capacitors are discharged... There's three honking big capacitors charged to 400 volts... I made the mistake once , while troubleshooting one of these, by powering it down and not waiting long enough before i pulled the drive board out.. i grabbed it by the heatsink which was at 400 volts level and had my other hand on the chassis... not a fun day ...

The tank capacitors are so large they would blow the fuses if it were not for the soft start ... they charge these through a resistor and only once a certain level is reached does a relay short the charge resistor. you hear a noticable 'kloink' when you power it up ... followed by a 'click' about 2 seconds later ...

[Harvs]

Thanks for the great info. 

I'm going to go ahead with the purchase.  In this case it's in great condition and tested fully functional with a 30 day return policy.  So hopefully I should get some years of service out of it without having the need to conduct repair (I probably shouldn't say that, murphys law...)

[free_electron]

These are virtually indestructable. The only way to kill them is to drop them so the transformer shears itself clean off the board and the core splits ( seen that.... ) or , muck about with the rear analog programming terminals and inject some craze voltage there ( control voltage is 0.. 5 ) so you fry that thing. 

If you use it as a power supply this thing is bulletproof.

[nctnico]

I used to have one until it got stolen. The only thing I don't like about it is that it doesn't retain the settings when powered off/on.

[free_electron]

Ah yes. None of the older hp supplies do that since they have no storage in them...

[leitol]

Any hints what to do when my 6038A now displays "SEC bAd" efter startup and then hung? Worked fine a moth ago when last used.

Brgds,
SM5VXO, Leif

[Dave]

Service manual, page 34