Does anyone have any information about the Lincoln Pro-Cut 25?
(other than the Owners Manual and the Online Service Manual - I already
have those). Specifically I am looking for another person whom
may have a single sheet full schematic. Recently I had the pleasure
to repair a failed unit; during that endeavor I made a single sheet,
full schematic and would like to compare notes....

Thanks,
MK

Here is the schematic/electronics depicted for the unit
which I repaired. The only block for which I have no information
is the gate driver daughter board on the inverter board. For
some reason it is painted black so that the parts cannot be
identified by part number. The other block is the TDA1060 chip
which is the pwm chip. I chose not to include the chip's block diagram
so as to reduce the complexity of that section of the schematic.
Datasheet is available online. Guess I need to include the usual
disclaimers here: The information provided on the attached schematic
is provided as is with no warranty or guarantee in any respect. I have
found it to be accurate. If you use this information you do so at
your own risk. By using the information on the attached schematic
you agree to use it responsibly and safely and to hold the me harmless
in all respects.
It has taken me many hours to produce this diagram and I post it
with the intent to provide an insight into the inner workings of the
Lincoln Pro Cut 25 for educational purposes only.
enjoy.
mk

Hello Guys,
I have been fault finding a Procut 25 and came across your forum.
The unit is establishing an arc erractically but not comming up to full cutting current. I have checked all connection and DC voltage at the inverter board is around 320.

Any help on this one would be appreciated.

cheers Tone

Hello Guys,
I have been fault finding a Procut 25 and came across your forum.
The unit is establishing an arc erractically but not comming up to full cutting current. I have checked all connection and DC voltage at the inverter board is around 320.

Any help on this one would be appreciated.

cheers Tone

There are several scenario's that might cause the
symptoms you describe. The easiest one is a fault with
the trigger switch (assuming new consumables and a
dry air source); but, in order to adequately address
your concern I need to know your level of electronics
knowledge and background.
If you don't feel comfortable posting that information for
all to see then please pm me.
mk77

Thanks for the reply MK,
I did electronics many years ago in my electrical apprenticeship. I am a qualified electrician. I am definately rusty!!!! but I will give it a go!
I have checked the trigger circuit and it operates correctly. Actually gone through most of the checks in the service manual. New nozzle and electrode.
I think the problem is on the inverter board?
Thanks again Tone

By the way, what was the fault with your machine?

The machine I repaired had multiple problems - but the main malfunction
was an inoperative trigger due to a shorted component on the
control board.
on to your machine...
"electrician", ok I now feel you understand about bonding.
I need some background on how you run
your machine i.e. what input power do you use? (i.e. 120 or 220 and
what sources this power?).
What current setting is used? Do you get the same indications
with a 'high' current setting as well as a 'low' current setting?
When was the last time or have you ever disassembled and cleaned
the work piece clamp wire connections? (yes, the clamp does come apart)
Do you have soldering skills? or would you feel comfortable
performing soldering on a circuit board?
mk77

Thanks MK,
The machine is running on 230Volt AC. Australian model, it does not appear to have the 115volt change-over circuit on the supply board. They possibly made a 230volt only version for Australia?
Good supply as I have 3 phase in the shed.
Changing the current setting seems to make no difference.
Set at 65 PSI and I have had the torch apart and checked all.
I did find one of the clamps on the solenoid hoses broken but it has been fixed.
This did not change the problem. Solenoid operates OK.
It appears to arc from the nozzle to the work and leave burn / pitting marks... but not all of the time.
I did check the resistance from the clamp to the crimp... came up ok, but I will give it a good clean tomorrow!
I am ok with soldering.

Thanks again for your time!

Set at 65 PSI and I have had the torch apart and checked all.


The condition of the rubber seal rings is critical to proper
operation of the mechanism by which plasma is generated
and the jet maintained. The piston may travel when pushed
on by hand but it must move freely when the head
is assembled and pressurized air is present. If the piston
does not move with air pressure then the electrode will
not "disengage" from the nozzle. The unit will not
generate the plasma jet and will tend to arc from the
nozzle to the work piece. The unit I worked on did
this also, but in your case it seems to do this
intermittently, if I understand you correctly.
I found that by very lightly lubricating the V seal
helped tremendously. It would be a good idea to check
and lube the isolator O rings since you will have the
head apart. Just a very light coat of silicon grease
to 'recondition' the seal material and allow it to
move freely will do. In the unit I worked on, one
of the isolator O rings was damaged and did not
provide a seal - had to replace it.
If you need isolator rings I have some extra, they are
hard to come by (no longer made) ... but I don't have the V ring.


It appears to arc from the nozzle to the work and leave
burn / pitting marks... but not all of the time.


This is indicative of, among other things (but first things first), the
electrode coming in contact with the nozzle. The air pressure in
the head is not strong enough to move the piston against the
spring if the V ring is dry/sticky (away from the nozzle) OR if
the piston slips back toward the nozzle for what ever reason
(kinked/crimped/obstructed air line, flaky air valve, incorrect overly
strong spring, or if the unit randomly changes between modes
due to other reasons, but like I said first things first).
I need to ensure the head is functioning properly before proceeding.


I did check the resistance from the clamp to the crimp... came up ok,
but I will give it a good clean tomorrow!

Good show!

Thanks MK,
I may not get to it today.... I have a few jobs and some study to do for a solar course I am on for the next 3 days. Soon as I can I will get back to you with the results.

cheers

Hello MK,
I finally got to do all the fault finding you recommended.
The clamp is clean and the wire connected under screw was soldered.
I had the torch apart again. I cleaned it & checked all of the o rings.
They all appear to be doing their job.

Tried the torch again after assembly.
It appeared to get a few good plasma arcs out of about 30 attempts.
When it did arc, the metal would only just start to melt (on full current setting).
So now I am not sure which way to go? My gut feeling is an component problem?

Over to you for some more deductions.
Thanks tone

Well, will try to help you out here... but there is only so much I can
do from a distance. Before we delve into the circuit board please check
the input wires and connections again - mainly on the main power switch
and see that it has a good continuity thru the switch - possible bad contacts
inside the switch or loose connection.
How is the overall cleanliness of the inside of the cabinet? Is there much
corrosion on the supporting circuit board mounting screws/posts?
I forgot to ask about the front panel indications when you run the
machine - do any of the fault lights illuminate when you experience the
erratic operation? Even momentarily?
- once verified....

...the next step is to reflow the solder connections
in the high current path on the inverter board. To do this follow the
service manual to discharge the capacitors.... i.e. unplug unit, remove
covers, let unit stand for about 15 minutes or more etc..

Once your are absolutely sure the caps are discharged then proceed.

The inverter board has a thick layer of conformal coating (at least the one
I worked on did) and you will need to carefully remove this
from the solder pads of interest in order to get the connection resoldered.
Dental tools work great for this kind of work but a razor blade will also
do the trick. I have attached a portion of the schematic "reflow_1" from
the service manual with the area's to be reflowed circled in red - this is
just to give you an idea for the portion of the circuit in which the
resoldering needs to be performed. The idea here is to get fresh solder
into the connections and "renew" the bond between the components and
the circuit card traces. Attached file "reflow_2" is a parts placement diagram
which indicates those components which need to have their connections
resoldered. I know this is a tedious and time consuming process but the
better these connections mechanical and electrical integrity the better
the circuit will perform. Be careful not to put too much solder as it will
drip out the other side of the board and this has the potential to cause
more problems. Also the shunt and the lugs (for the head connections)
have a tendency to move when the solder gets to temperature so some method to prevent them from moving is a good idea. I should also
mention that while this is a high power circuit overall the potential to
do harm from static electricity still exists. Please follow good ESD
practices when working on the board.
I am anxious to hear how you fare with this... look forward to hearing from
you. Good Luck.
mk

a side note: when performing the soldering on some
of the larger pads/connections I found a larger iron to
be more efficient. A 40 watt soldering iron is just too
small for some of the larger connections. An 80 watt
iron with a large tip seems to do better. Try not to linger
too long on the pad when heating it up so as not to
overheat the board and damage it.
Also once you have completed the reflow project, and
before you power up the unit again, some sort of sealant
is needed to replace the conformal coating which was removed.
Before you apply the sealant all of the flux residue must
be removed (cotton swabs with alcohol). If you don't
remove it, over time it will cause more problems. A solvent
such as 99% rubbing alcohol will work. Once the flux
residue is removed the sealant may be applied. Which
you use is largely up to you. I used an acrylic based
liquid with a small built-in brush on the cap. Your wife/grlfrnd
will usually have an ample supply of this stuff....and
if you can wrangle it away from her is a quick and easy
solution. :D To be on the safe side though a high temperature
coating such a Fine-L-Kote H T tech spray works well.
A couple of coats and allow ample drying time...

mk