I just bought an old miller dialarc HF "whiteface" vintage. while
getting ready to test it, and cleaning it out, I noticed some of the
leads on the tiny capacitors in the main rectifier bridge are loose,
kind of like how quarter-inch round rod would rattle around inside a
piece of half-inch water pipe. they're "probably" bad, because of that
alone, I'd guess, but, umm, what exactly is the electrical function of
those four tiny things supposed to BE? like "what're they doing for me?"

here'a an extreme closeup of one of the 'loose leads' capacitors, next
to one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/53...or_closeup.jpg

here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg

and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/53...0schematic.jpg

electrically, I'm a "real slow learner", so, thanks for your help, guys :-)

toolie

I think that their purpose is suppressing high voltage from HF arc
starting subsystem, so that it would not damage the rectifiers.

i

On 2008-08-13, dave wrote:
I just bought an old miller dialarc HF "whiteface" vintage. while
getting ready to test it, and cleaning it out, I noticed some of the
leads on the tiny capacitors in the main rectifier bridge are loose,
kind of like how quarter-inch round rod would rattle around inside a
piece of half-inch water pipe. they're "probably" bad, because of that
alone, I'd guess, but, umm, what exactly is the electrical function of
those four tiny things supposed to BE? like "what're they doing for me?"

here'a an extreme closeup of one of the 'loose leads' capacitors, next
to one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/53...or_closeup.jpg

here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg

and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/53...0schematic.jpg

electrically, I'm a "real slow learner", so, thanks for your help, guys :-)

toolie

dave wrote:
I just bought an old miller dialarc HF "whiteface" vintage. while
getting ready to test it, and cleaning it out, I noticed some of the
leads on the tiny capacitors in the main rectifier bridge are loose,
kind of like how quarter-inch round rod would rattle around inside a
piece of half-inch water pipe. they're "probably" bad, because of that
alone, I'd guess, but, umm, what exactly is the electrical function of
those four tiny things supposed to BE? like "what're they doing for me?"

here'a an extreme closeup of one of the 'loose leads' capacitors, next
to one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/53...or_closeup.jpg

here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg

and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/53...0schematic.jpg

electrically, I'm a "real slow learner", so, thanks for your help, guys :-)

toolie

they're probably to provide a DC path to ground for AC spikes.

Jim

The "water pipe" as you describe it, is insulation, either polyester coated
fabric or shrink tube. If the cap leads are intact on both ends, I'll bet
they're ok.

"dave" wrote in message
...
I just bought an old miller dialarc HF "whiteface" vintage. while getting
ready to test it, and cleaning it out, I noticed some of the leads on the
tiny capacitors in the main rectifier bridge are loose, kind of like how
quarter-inch round rod would rattle around inside a piece of half-inch
water pipe. they're "probably" bad, because of that alone, I'd guess, but,
umm, what exactly is the electrical function of those four tiny things
supposed to BE? like "what're they doing for me?"

here'a an extreme closeup of one of the 'loose leads' capacitors, next to
one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/53...or_closeup.jpg

here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg

and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/53...0schematic.jpg

electrically, I'm a "real slow learner", so, thanks for your help, guys
:-)

toolie

dave wrote:
I just bought an old miller dialarc HF "whiteface" vintage. while
getting ready to test it, and cleaning it out, I noticed some of the
leads on the tiny capacitors in the main rectifier bridge are loose,
kind of like how quarter-inch round rod would rattle around inside a
piece of half-inch water pipe. they're "probably" bad, because of that
alone, I'd guess, but, umm, what exactly is the electrical function of
those four tiny things supposed to BE? like "what're they doing for me?"

here'a an extreme closeup of one of the 'loose leads' capacitors, next
to one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/53...or_closeup.jpg

here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg

and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/53...0schematic.jpg

electrically, I'm a "real slow learner", so, thanks for your help, guys :-)

toolie

Those are standard ceramic caps. They have bare wire leads run inside
insulating sleeves. As long as the wire leads are still attached to the
caps they should be OK. Now if the wires pull out easy then they are bad.

From the schematic, they look like they are simple filter caps.

--
Steve W.
Near Cooperstown, New York

dave wrote:
I just bought an old miller dialarc HF "whiteface" vintage. while
getting ready to test it, and cleaning it out, I noticed some of the
leads on the tiny capacitors in the main rectifier bridge are loose,
kind of like how quarter-inch round rod would rattle around inside a
piece of half-inch water pipe. they're "probably" bad, because of that
alone, I'd guess, but, umm, what exactly is the electrical function of
those four tiny things supposed to BE? like "what're they doing for me?"

here'a an extreme closeup of one of the 'loose leads' capacitors, next
to one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/53...or_closeup.jpg

here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg

and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/53...0schematic.jpg

electrically, I'm a "real slow learner", so, thanks for your help, guys :-)

toolie
They probably do a couple of things. As Iggy mentioned, they will help
keep the HF out of the diodes. The other thing is that when diodes start
and stop conducting in a rectifier, they do so very abruptly, which
creates high frequency noise. This noise can cause interference problems
with nearby radio and TV sets (though nothing like the HF will) and it
can also shorten the life of the diodes. These caps will short that
noise to ground.

By the way, the Dialarc HF is a nice machine! I had one for many years.
It only got replaced when I started doing more aluminum and small stuff.
Be sure to follow the directions for cleaning and setting the spark gap
points. Ernie L says that the caps in the HF circuit need replacing
occassionally also.

BobH

On 2008-08-13, BobH wrote:
dave wrote:
I just bought an old miller dialarc HF "whiteface" vintage. while
getting ready to test it, and cleaning it out, I noticed some of the
leads on the tiny capacitors in the main rectifier bridge are loose,
kind of like how quarter-inch round rod would rattle around inside a
piece of half-inch water pipe. they're "probably" bad, because of that
alone, I'd guess, but, umm, what exactly is the electrical function of
those four tiny things supposed to BE? like "what're they doing for me?"

here'a an extreme closeup of one of the 'loose leads' capacitors, next
to one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/53...or_closeup.jpg

here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg

and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/53...0schematic.jpg

electrically, I'm a "real slow learner", so, thanks for your help, guys :-)

toolie
They probably do a couple of things. As Iggy mentioned, they will help
keep the HF out of the diodes. The other thing is that when diodes start
and stop conducting in a rectifier, they do so very abruptly, which
creates high frequency noise. This noise can cause interference problems
with nearby radio and TV sets (though nothing like the HF will) and it
can also shorten the life of the diodes. These caps will short that
noise to ground.

Bob, these are SCRs, for sure they stop conducting at zero crossing
only. As far as starting to conduct, are you positive that they do it
very abruptly? I thought that it was not the case, but maybe I am
wrong.

By the way, the Dialarc HF is a nice machine! I had one for many years.
It only got replaced when I started doing more aluminum and small stuff.
Be sure to follow the directions for cleaning and setting the spark gap
points. Ernie L says that the caps in the HF circuit need replacing
occassionally also.

These are great, indestructible welders...

i

"Ignoramus6985" wrote in message
...
On 2008-08-13, BobH wrote:
dave wrote:
I just bought an old miller dialarc HF "whiteface" vintage. while
getting ready to test it, and cleaning it out, I noticed some of the
leads on the tiny capacitors in the main rectifier bridge are loose,
kind of like how quarter-inch round rod would rattle around inside a
piece of half-inch water pipe. they're "probably" bad, because of that
alone, I'd guess, but, umm, what exactly is the electrical function of
those four tiny things supposed to BE? like "what're they doing for me?"

here'a an extreme closeup of one of the 'loose leads' capacitors, next
to one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/53...or_closeup.jpg

here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg

and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/53...0schematic.jpg

electrically, I'm a "real slow learner", so, thanks for your help, guys
:-)

toolie
They probably do a couple of things. As Iggy mentioned, they will help
keep the HF out of the diodes. The other thing is that when diodes start
and stop conducting in a rectifier, they do so very abruptly, which
creates high frequency noise. This noise can cause interference problems
with nearby radio and TV sets (though nothing like the HF will) and it
can also shorten the life of the diodes. These caps will short that
noise to ground.

Bob, these are SCRs, for sure they stop conducting at zero crossing
only. As far as starting to conduct, are you positive that they do it
very abruptly? I thought that it was not the case, but maybe I am
wrong.

By the way, the Dialarc HF is a nice machine! I had one for many years.
It only got replaced when I started doing more aluminum and small stuff.
Be sure to follow the directions for cleaning and setting the spark gap
points. Ernie L says that the caps in the HF circuit need replacing
occassionally also.

These are great, indestructible welders...

i

those DIODES are DIODES, not SCRs.
SCRs have 3 leads, Anode, Cathode & Gate.

john G.

Dave wrote:
Bob, these are SCRs, for sure they stop conducting at zero crossing
only. As far as starting to conduct, are you positive that they do it
very abruptly? I thought that it was not the case, but maybe I am
wrong.


If they're conventional SCRs, yes. If they're GTO (gate turn-off) SCRs,
they can be squinched off while conducting.

LLoyd

In article ,
Ignoramus6985 wrote:

On 2008-08-13, BobH wrote:
dave wrote:
I just bought an old miller dialarc HF "whiteface" vintage. while
getting ready to test it, and cleaning it out, I noticed some of the
leads on the tiny capacitors in the main rectifier bridge are loose,
kind of like how quarter-inch round rod would rattle around inside a
piece of half-inch water pipe. they're "probably" bad, because of that
alone, I'd guess, but, umm, what exactly is the electrical function of
those four tiny things supposed to BE? like "what're they doing for me?"

here'a an extreme closeup of one of the 'loose leads' capacitors, next
to one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/53...or_closeup.jpg

here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg

and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/53...0schematic.jpg

electrically, I'm a "real slow learner", so, thanks for your help, guys :-)

toolie
They probably do a couple of things. As Iggy mentioned, they will help
keep the HF out of the diodes. The other thing is that when diodes start
and stop conducting in a rectifier, they do so very abruptly, which
creates high frequency noise. This noise can cause interference problems
with nearby radio and TV sets (though nothing like the HF will) and it
can also shorten the life of the diodes. These caps will short that
noise to ground.

Bob, these are SCRs, for sure they stop conducting at zero crossing
only. As far as starting to conduct, are you positive that they do it
very abruptly? I thought that it was not the case, but maybe I am
wrong.

SCRs are like switches, and conduction starts abruptly upon triggering,
with a risetime in the microseconds. This abrupt rise can and does
cause interference to nearby radio receivers.

War story from the late 1960s, when I was in school: In the Geophysics
Department there were a number of furnaces used to heat samples of
powdered rock in platinum capsules. Accurate temperature control was
needed, and so one of the professors built SCR temperature controllers
for the furnaces. (SCRs were new then.) It was soon discovered that
all the furnaces were varying together, without regard for the
temperatures of the furnaces in question. Huh? What was happening was
that the RF noise pulse from the first SCR to fire was travelling over
the AC power lines to all the other SCRs and firing them prematurely.
The solution was to add a simple LC filter at the input of each
controller.

Joe Gwinn

http://www.datasheetarchive.com/pdf-...DSA-369352.pdf

My guess is that the part above might be similar to what is in the
welder. I like the explanations of the caps used for filtering
(especially seeing the choke in the circuit). Another way of
explanation might be that the caps help keep a small forward voltage
across the rectifier to keep it from cutting out. (See voltage vs.
amp curve) The welder might work without the caps, but it could have
a noisy erratic arc and you might have more problems with sticking
electrodes when you got too close using SMAW.

Now I’ll return to my seat in the peanut gallery!

Ignoramus6985 wrote:
On 2008-08-13, BobH wrote:
They probably do a couple of things. As Iggy mentioned, they will help
keep the HF out of the diodes. The other thing is that when diodes start
and stop conducting in a rectifier, they do so very abruptly, which
creates high frequency noise. This noise can cause interference problems
with nearby radio and TV sets (though nothing like the HF will) and it
can also shorten the life of the diodes. These caps will short that
noise to ground.

Bob, these are SCRs, for sure they stop conducting at zero crossing
only. As far as starting to conduct, are you positive that they do it
very abruptly? I thought that it was not the case, but maybe I am
wrong.

They are diodes. The Dialarc used a magamp for current control, no fancy
electronics.

After thinking about the circuit operation more, I don't think that
there is a large snap on or off of those diodes since they will only
switch around the AC line zero crossing. The voltage will only be a
couple of diode drops away from ground when they switch, so their abrupt
turn on is a pretty low amplitude event. It will still be fast but only
a couple of volts.

Bob

On 2008-08-13, Ignoramus6985 wrote:
On 2008-08-13, BobH wrote:
dave wrote:

They probably do a couple of things. As Iggy mentioned, they will help
keep the HF out of the diodes. The other thing is that when diodes start
and stop conducting in a rectifier, they do so very abruptly, which
creates high frequency noise. This noise can cause interference problems
with nearby radio and TV sets (though nothing like the HF will) and it
can also shorten the life of the diodes. These caps will short that
noise to ground.

Bob, these are SCRs, for sure they stop conducting at zero crossing
only. As far as starting to conduct, are you positive that they do it
very abruptly? I thought that it was not the case, but maybe I am
wrong.

Nope -- they are *not* SCRs -- just plain rectifiers. No third
terminal for the gate input of an SCR -- and just the schematic symbol
for a plain (if heavy) diode.

Enjoy,
DoN.


--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

I was in RF before retiring.

1. Notice the #10 or such wire that the cap is attached.

The large diameter has lower inductance and higher DC and AC current.
2. Since the cap is in series (and yes legs wiggle mean it is dead) Only AC
current flows. The value of the cap and the inductance of the total
lead set determines what frequency it is shunting. The inductor Z
when it turns on and turns off produces spikes. Switching hot does as well.
3. Notice the ones in parallel to the rectifiers (diodes). They keep RF
current from inside the diode which might arc on the internal die and kill
the unit. Down in the bottom right is a RF high voltage arc with a set
of arc points that are used to limit the output RF arc. If these eat back
then the voltage increases and can cause more problems. But normally,
this is a source of RF noise that can harm transistors and diodes.
4. The module below the bridge is a filter. Likely an RC but with the
'V51' that tends to indicate an AC item. So resistor for better control.
5. The resistor R2 is a minimum load.

Replace the caps - keep their leads short. Higher voltage is just fine.
Get the same value as in the spec - that is the 'frequency' it shorts...


Hope that helps.

Martin


Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Jim Chandler wrote:
dave wrote:
I just bought an old miller dialarc HF "whiteface" vintage. while
getting ready to test it, and cleaning it out, I noticed some of the
leads on the tiny capacitors in the main rectifier bridge are loose,
kind of like how quarter-inch round rod would rattle around inside a
piece of half-inch water pipe. they're "probably" bad, because of that
alone, I'd guess, but, umm, what exactly is the electrical function of
those four tiny things supposed to BE? like "what're they doing for me?"

here'a an extreme closeup of one of the 'loose leads' capacitors, next
to one of the four "big honkin" diodes in the bridge.
http://www.image-upload.net/files/53...or_closeup.jpg

here's a page from the owners manual, where they're descibed...
http://www.image-upload.net/files/5385/parts_blowup.jpg

and here's the parts schematic, for the same machine.
http://www.image-upload.net/files/53...0schematic.jpg

electrically, I'm a "real slow learner", so, thanks for your help,
guys :-)

toolie

they're probably to provide a DC path to ground for AC spikes.

Jim


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On 2008-08-14, Martin H. Eastburn wrote:
I was in RF before retiring.

1. Notice the #10 or such wire that the cap is attached.

Hmm ... that looks to me (I still have the image saved locally)
like about 22 ga wire, with insulating sleeves slipped on over it.
Looks like the silicone rubber in fabric type of insulating sleeve --
something which is unlikely to go brittle over years of exposure to UV
and weather.

And if that is the case, then wiggle is perfectly normal.

The large diameter has lower inductance and higher DC and AC current.

Yes -- it would, *if* the wire actually had a larger diameter.
I don't think that it does. It should be possible to slide the end of
the sleeve down a little away from the capacitor body to verify this.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---