13 Jan
2006
13 Jan
'06
12:04 p.m.
On Fri, 13 Jan 2006 09:09:26 -0500, Brad Parker <brad at heeltoe.com>
wrote:
Hi
I've got an old HP 6286a bench supply. It's been sitting for a while
and I turned it on and discovered it seems to have no voltage
regulation
- it gives out about 23VDC not matter what. The current regulation
seems to work however.
Does the voltage drop down from 23VDC when you limit current?
Shorting the output and playing with the current control will
indicate that the current limit is working and that the output
transistors are okay. A better test is to place a low-valued resistor
across the output and limit current while measuring the voltage
across the resistor. This will tell you that the output stage is
working.
Anyone ever look inside of one of these? It looks
like a nice supply
and I hate to toss it.
-brad
The 6286a is a 20V, 10A supply with voltage and current controls.
Great for reforming caps and testing old hardware. I would make an
effort to resurrect the beast.
I have found in a number of supplies the front panel adjustable pots
open up or the wiper go south. This will make the output go to max.
Another problem is small electrolytic caps in the voltage control
circuit going bad. Often, blindly shotgunning all the small caps will
make things work for another 15 years (sorry Tony...).
The Boat Anchor Manual Archive <http://bama.sbc.edu/hp.htm> has a
copy of the 6285A which should be close to what you have.
Good luck.
CRC
16 Jan
16 Jan
3:43 a.m.
At 01:04 PM 1/13/06 -0700, you wrote:
I have found in a number of supplies the front panel adjustable pots
open up or the wiper go south. This will make the output go to max.
Another problem is small electrolytic caps in the voltage control
circuit going bad. Often, blindly shotgunning all the small caps will
make things work for another 15 years (sorry Tony...).
Don't apologize. There's nothing wrong with that approach. If one cap has
failed, it's mostly likely that the other's aren't far behind.
Joe
The Boat Anchor Manual Archive <http://bama.sbc.edu/hp.htm> has a
copy of the 6285A which should be close to what you have.
Good luck.
CRC
4:27 p.m.
At 01:04 PM 1/13/06 -0700, you wrote:
This is a constant flamewar in the UK vintage radio magazines...
I would be careful shotgunning parts. Firstly that you don't introduce
more faults (either by using unsuitable capacitors or mis-connecing
them). Secondly that you don't cause problems by changing a capacitor in
a timing cirucit and having to re-align things).
And of course you do need to be able to trace the fault 'properly' if
changing the capacitors doens't fix it.
My expeireince with old HP instruments (mostly from their decktop
calculators) is that capacitors are not a major source of problems. If I
had this PSU in for repair, I'd trace the fault properly first. If I
found it was due to defective caps, I probably would change the lot. If
it wann't, I might well leave them all alone.
That said, there are capacitors I would always change in old equipment.
Top of the list (and unlikely to apply to this list) is the coupling
capacitor to the grid of an output valve. If that goes leaky, it can mean
a burnt-out output valve, a burnt-out rectifier valve, and a burnt-out
output transformer.
-tony
I have found in a number of supplies the front panel adjustable pots
open up or the wiper go south. This will make the output go to max.
Another problem is small electrolytic caps in the voltage control
circuit going bad. Often, blindly shotgunning all the small caps will
make things work for another 15 years (sorry Tony...).
Don't apologize. There's nothing wrong with that approach. If one cap has
failed, it's mostly likely that the other's aren't far behind.
18 Jan
18 Jan
3:10 a.m.
At 12:27 AM 1/17/06 +0000, you wrote:
I think both of those would apply without having to state the obvious.
At 01:04 PM 1/13/06 -0700, you wrote:
This is a constant flamewar in the UK vintage radio magazines...
I would be careful shotgunning parts. Firstly that you don't introduce
more faults (either by using unsuitable capacitors or mis-connecing
them). Secondly that you don't cause problems by changing a capacitor in
a timing cirucit and having to re-align things).
I have found in a number of supplies the front panel adjustable pots
open up or the wiper go south. This will make the output go to max.
Another problem is small electrolytic caps in the voltage control
circuit going bad. Often, blindly shotgunning all the small caps will
make things work for another 15 years (sorry Tony...).
Don't apologize. There's nothing wrong with that approach. If one cap has
failed, it's mostly likely that the other's aren't far behind.
And of course you do need to be able to trace the fault 'properly' if
changing the capacitors doens't fix it.
My expeireince with old HP instruments (mostly from their decktop
calculators) is that capacitors are not a major source of problems.
That usually true of HP gear but it's a BIG problem in Tektronix and
other brands. I've found that I can't leave a Tektronix scope of the 465
vintage powered off for very long without them developing shorted
capacitors. I had a Tek 465 that I only used occasionally and everytime
that I turned it on (several months apart) it had a new capacitor problem.
That went on for over two years till I finally gave up on it and found a
newer scope (Tek 2445). I suppose the difference is due to the different
type/brand of caps that HP and Tektronix used.
FWIW I like the Tek scopes better than HP scopes but the HPs hold up
better.
Joe
8:30 a.m.
I would be
careful shotgunning parts. Firstly that you don't introduce
more faults (either by using unsuitable capacitors or mis-connecing
them). Secondly that you don't cause problems by changing a capacitor in
a timing cirucit and having to re-align things).
I think both of those would apply without having to state the obvious.
6914
days inactive
6919
days old
4 comments
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